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HUD Code The Manufactured Housing Institute, on its website, discusses the HUD Code and makes interesting comparisons to other building codes. It says: Every HUD Code manufactured home is built in a factory, under controlled conditions, and has a special label affixed on the exterior of the home indicating that the home has been designed, constructed, tested and inspected to comply with the stringent federal standards set forth in the code. No manufactured home may be shipped from the factory unless it complies with the HUD Code and is released for shipment by an independent third party inspector certified by HUD. The HUD Code is unique since it is specifically designed for compatibility with the factory production process. Performance standards for heating, plumbing, air conditioning, thermal and electrical systems are set in the code. In addition, performance requirements are established for structural design, construction, fire safety, energy efficiency, and transportation from the factory to the customer's home site. Manufactured homes are constructed with virtually the same materials used in site-built homes. However, in contrast to traditional site-building techniques, manufactured homes have the advantage of using engineered design applications and the most cost-efficient assembly-line techniques to produce a quality home at a much lower cost per square foot. To ensure quality, the design and construction of the home is monitored by both HUD and its monitoring contractor. The familiar red seal (the certification label) attached to the exterior of a manufactured home indicates that it has undergone and passed perhaps the most thorough inspection process in the home building industry.
Identifying Manufactured Homes How do we know if it is a manufactured home? There are some specific characteristics besides the permanent steel chassis. Each HUD Code Manufactured home has a label that is affixed before it leaves the factory: Located at the tail light end of each unit; if multi-section, there must be a label on each section Placed one foot from the floor and one foot in from the road side Contains a three letter designation plus a six digit number Each HUD code manufactured home also has a serial number that is stamped into the foremost cross member of the frame. A data plate is also installed inside each manufactured home with the name and address of the manufacturing plant in which the home was manufactured; the serial numbers and model designation; the date the unit was manufactured; a statement which references that the home was built in accordance with the Manufactured Home Construction and Safety Standards (MHCSS); a list of the certification label number(s); a list of factory-installed equipment, including the manufacturer's name and the model designation of each appliance; a reference to the Roof Load Zone and Wind Zone to which the home was designed; and the name of the agency that approved the design. The data plate is a sheet of paper that may be located in a kitchen cabinet, inside an electrical service panel door, in a utilities closet, or near the furnace. It originally was attached with staples or tape. Unfortunately, when you do your inspection, it may be long gone. End of Page
Insulating Concrete Form (ICF) ICFs are a recent innovation in foundation walls. They consist of an insulated form that is then poured full of concrete. Here is a description from toolbase.org. "Insulating concrete forms (ICFs) are rigid plastic foam forms that hold concrete in place during curing and remain in place afterwards to serve as thermal insulation for concrete walls. The foam sections are lightweight and result in energy-efficient, durable construction. Insulation values of ICF walls vary depending on the material and its thickness. Typical insulation values range from R-17 to R-26, compared to between R-13 and R-19 for most wood-framed walls. The strength of ICF structures relative to lumber depends on configuration, thickness, and reinforcement. However, ICF walls are designed as reinforced concrete, having high wind and seismic resistance." According to that same website: "ICF material cost ranges from about $1.75 per square foot to about $3.50 per square foot. Cost of installation labor, reinforcement, bracing, and concrete placement will be additional. On average, ICF homes cost about two to five percent more than wood-framed construction. However, contractors installing ICFs for the first time, because of training required and a learning curve, may find that total installed cost is from five to seven percent. ICFs allow trade contractors to construct concrete walls without a significant investment in reusable wood and metal forms. Because they use non-biodegradable materials, they are not subject to rot. They can increase the temperature range for pouring concrete to below freezing by insulating the concrete until fully cured. Foundation walls built with ICFs are easier and faster to construct than either concrete masonry unit (CMU) or cast-in-place (CIP) concrete foundations depending on total area and house plan. Insulating forms protect the concrete from freezing and rapid drying. Concrete can be poured in ICFs when ambient temperature is as low as 10°F, requiring only the top of the form to be protected with insulating blankets. In extremely hot weather, in which evaporation is a concern, the top of the form need only be covered with plastic sheeting. The walls of a properly-constructed ICF home are resistant to loads imposed by high winds, and can be designed for all seismic zones. With regard to durability, foam and concrete hold the potential for improved building durability over wood construction because they are more resistant to moisture and less attractive to termites and other pests. ICF walls are more rot-resistant and durable than wood-framed walls." A check of your understanding is next, and then we will cover how the framing members of the house are attached to the foundation.
J Bolts In any of these foundation wall types, "J" shaped anchor bolts are installed when the wall is completed. This will be the method to attach the masonry to the first piece of the wooden structure, the sill plates.
Stone Structural stone houses were among the earliest in the country. The early settlers picked up field stones and used them for the walls. Here is a house in the Hudson Valley, in New York, that was built in the late 1700s by Dutch settlers. Of course many frame houses have been built, and are being built, with a stone veneer over the wood framing; or with decorative stone trim.
ICF Construction Insulating concrete forms (ICF) are being used for exterior walls and structural members. They're not just for foundation walls anymore. Click here to visit a website that has good information and several videos on ICF.
Joist Hangers Sometimes the joists are installed on the side of the girder so that the top of the joist is at the same height as the girder. The joists are attached to the side of the girder using steel joist hangers.
Bridging Bridging is inserted between the joists, in an "X" pattern to stiffen the floor structure and resist twisting of the joists. It used to consist of wooden 1 x 3s cut and fit at the site. Today, bridging is primarily factory-fabricated metal strips.
Clay Tile Roofs Early clay tiles were made by forming clay around a curved surface, sometimes a log, and then fired in a kiln or oven. Fired roof tiles date back to ancient Greece. They were commonly used in the early Spanish missions found in the Southwest and what was to become California. Today, they are still popular in Adobe or Mission style dwellings in the Southwest and Western U.S.; usually combined with stucco walls. Modern clay tiles are still produced by baking molded clay in a factory. The tiles may be glazed or have textures added. Concrete tiles are also produced, which are extruded on molds, under pressure. They can be similar in appearance to clay tiles. These tiles are heavy and should be applied over at least a 5/8 inch thick plywood deck. According to the National Roofing Contractors Association website, care should be taken when choosing an underlayment. They say: "Underlayment (or 'felt paper' as it is frequently called) is installed over the roof deck before the application of tile. An underlayment performs two primary functions: it provides temporary weather protection until the tile is installed, and it provides a secondary weatherproofing barrier if moisture infiltrates the tile roof covering. Many tile roofs have outlived the underlayment felts over which they were installed. Therefore, an underlayment's service life should be comparable to the design service life of the tile roof covering. Asphalt saturated, nonperforated organic felts are among the most common underlayments; they commonly are designated as Type 15 and Type 30 or referred to as No. 15 and No. 30, which are reflective of a once used pound per square weight designation. The terms Type I and Type II now are used within the industry in lieu of No. 15 or No. 30, respectively. Another type of underlayment is a synthetic underlayment. It is characterized as being lightweight, water-resistant and less likely to wrinkle; having high tear strength; and being easy to walk on—even when wet. Theoretically, the product may be left exposed to the elements for extended periods of time. Although synthetic underlayments and their purported attributes seem appealing, there are significant issues to consider before using them. To date, there are no applicable ASTM standards for these products. Many synthetic underlayments do not meet current building code requirements, so manufacturers need to obtain a code evaluation report for code compliance." End of Page
Clay Tile Roofs (cont.) Clay roof tiles can be attached in different ways. According to the same website: "Many different types and combinations of securement methods are used for the various types of roof tile. To select a method of securement, many conditions need to be considered: wind, deck type, seismic considerations, slope, building codes, local practices and manufacturer recommendations. Fasteners should be made of noncorrosive materials that will remain serviceable in the intended environment for the roof's design life. Nails—Nailing is the most common method. NRCA recommends that roofing nails be 11- gauge or 12-gauge galvanized steel or the equivalent corrosion-resistant roofing nails. Nail heads should be low-profile, smooth and flat. Shanks should be barbed or otherwise deformed for added pull-out strength. Nails should be long enough to penetrate through all layers of roofing materials and extend through the underside of the roof deck or penetrate at least 3/4 inch into wood plank or board decks. Wire tie and strapping systems—Hanging tile with wire is used on non-nailable decks, insulated decks or where fastening through metal flashings needs to be avoided. Clips—Nose or butt clips sometimes are used in conjunction with other attachment methods in high-wind or seismic areas. Lug-hung-tile—Many types of tile have formed undersides near their heads that may be hung over a batten. Lug hanging tile usually is used in combination with other securement methods. Bedding Tile—Laying tile in a bed of mortar of foam adhesive is common in some areas of North America where freeze/thaw conditions are not encountered. Bedding often is used in combination with other securement methods." Now, we even have fiberglass tiles which are similar in appearance to clay tiles and are lighter weight. We'll address two newer roofing products on the next two pages.
Precast Concrete Foundation and Wall Panels Precast concrete panels are seeing increasing usage. Here is a description of them from toolbase.org: "Precast concrete foundation and wall panels can take many forms. Some consist of steel-reinforced concrete ribs that run vertically and horizontally in the panels. Others are solid precast concrete panels. Panels are precast and cured in a controlled factory environment so weather delays can be avoided. A typical panelized foundation can be erected in four to five hours, without the need to place concrete on site for the foundation. The result is a foundation that can be installed in any climate zone in one sixth of the time needed for a formed concrete wall. Some manufacturers cast the concrete against foam insulation that provides the form during manufacture and added R-value in the wall. Panels range in size from 2'-12' in width by 8' - 12' in height and are typically installed with a crane on top of 4" to 6" of compacted stone. The stone facilitates sub-slab drainage and adequately carries and transfers the load from the foundation wall. Panel connections consist of bolts and sealant. The foundation can be backfilled as soon as it is braced per manufacturer's specifications. The controlled temperature of the processing plant allows the manufacturer to work with concrete admixtures that focus on ultimate strength rather than cure time and temperature. Manufacturers are able to produce mixes that harden to 5,000 psi, which is stronger than concrete block or concrete walls formed and cast in the field. Better control of the concrete mixture and curing environment allows the use of low water/cement ratios that results in a dense material that prevents water penetration."
Concrete Blocks When completed, block walls are not as strong or waterproof as poured walls, but cost less. Two coats of parging, consisting of troweled-on Portland cement, are applied to the exterior of the wall for moisture control. Then, there should be an additional layer of tar or other waterproofing material. Reinforcing mesh is laid between the courses and rebar may be applied vertically, through the holes in the blocks. Sometimes the holes are poured full of concrete. Long walls may need additional support from pilasters. Pilasters are additional courses of block laid up to form a column for additional support. In addition, insulating material, such as Vermiculite, may be poured into the blocks. Some recent blocks are constructed of lighter-weight concrete and some have particles of insulating material, such as Styrofoam, built in.
EIFS Exterior Insulation and Finish Systems (EIFS) are sometimes known as synthetic stucco. They combine the insulation and exterior finish in one process. The exterior surface is quite water resistant but there have been many problems with water infiltration where they meet other components such as windows, doors, roofs and chimneys. They have been used in recent years, primarily in the South, and have gotten a bad reputation for leaking. It turns out, though, that most leaking problems stemmed from improper installations. The system is composed of 5 layers: Substrate Adhesive Insulation board Base coat with imbedded fiberglass mesh Finish coat in desired color
Drainable Systems Here is a good solution - from toolbase.org. "Exterior Insulation and Finish Systems (EIFS), also called synthetic stucco, are available in drainable or barrier systems that resemble traditional masonry stucco finishes. EIF systems are aesthetically attractive to many people due to the variety of colors and textures available, and special architectural features that are easily created. While among the more expensive finishing systems available, drainable EIFS, if properly applied, may benefit the homeowner by providing an insulating exterior finish without the worries about water damage associated with barrier EIFS. Drainable systems may prevent water accumulation problems that sometimes occur with barrier or face-sealed EIF systems. A barrier EIFS resists water penetration at its outer surface but does not allow water that gets behind the exterior surface to drain out of the wall system. Drainable EIF systems consist of an extruded (XPS) or expanded polystyrene (EPS) or a polyisocyanurate foam glass fiberboard. An installer applies them with special mechanical fasteners or adhesives to a metal, plastic, or glass fiber mesh, creating a drainage plane. Alternatively, a grooved foam board can allow drainage. The mesh covers a weather-resistive barrier such as building paper or housewrap, which in turn covers the sheathing or substrate. OSB, plywood, and exterior-grade gypsum sheathing are the most common substrates. A base coat of a cement/polymer mixture covers the insulation board and provides a base for embedding a fiberglass mesh. A flexible, acrylic-modified finish coat in the desired color and texture is applied over the base coat. Application of a special sealant and flashing are also required to provide water-tight seals and to divert water from critical junctions between EIFS and building components."
Platform or Western Framing (cont.) With platform framing, the studs are mounted vertically and have a sole plate nailed across the bottom. If the studs are 2 x 4s, they are installed 16 inches on center. If 2 x 6s are used, they are put 24 inches on center. With 2 x 6s, there is a bigger wall cavity, so more insulation can be inserted. At the top of the studs is a double top plate. There is additional support needed over and around openings in the wall such as doors and windows. Headers are built over the openings to spread the load out to the sides and prevent the windows and doors from getting crushed or sticking.
Engineered Wood Wall Framing More information from toolbase.org: "The decreasing supply of large diameter, old-growth trees resulted in the increased popularity of engineered wood products -- those made from young, small diameter trees and scrap wood that is reassembled into I-joists, boards and beams. But did you know that the engineered wood that is well-recognized in residential construction as header and girder material and I-joist chords, can also be used for wall framing with similar effective results? Engineered wood is made from quick growing, abundant species such as aspen, fir, pine and poplar that are processed into wood veneers or strands, coated with adhesive, compressed into large billets, dried, then sawn into standard lumber dimensions. Often, the process of engineering the performance characteristics of the wood includes orienting the veneers or strands to maximize the member's strength. Laminated veneer lumber (LVL), laminated strand lumber (LSL) and parallel strand lumber (PSL), are some of the types of engineered wood products. In walls, engineered wood can be used as a replacement for 2 x 4 and 2 x 6 dimensional lumber, installed with the same process, tools, and fasteners. Because engineered wood products are superior in strength, stability, and uniformity to standard lumber species of the U. S., headers and girders can be engineered for greater clear spans or to carry greater loads. This means that taller walls can be designed for greater environmental conditions (like high wind speed or seismic activity) at greater spacing (for windows and doors). This greater design flexibility, reduced waste (no culling), and the material's dimensional stability drive the value decision."
Structural Insulated Panels (SIP) The Structural Insulated Panels Association, on its website, defines a SIP this way: "Structural insulated panels (SIPs) are high performance building panels used in floors, walls, and roofs for residential and light commercial buildings. The panels are typically made by sandwiching a core of rigid foam plastic insulation between two structural skins of oriented strand board (OSB). Other skin material can be used for specific purposes. SIPs are manufactured under factory-controlled conditions and can be custom designed for each home. The result is a building system that is extremely strong, energy efficient, and cost effective. Building with SIPs will save you time, money, and labor." End of Page
FAQs Here is an FAQ from their website: What is the R-value of structural insulated panels? R-values for SIPs depend on the thickness of the SIP and the type of core material that is used. (See SIPA's R-value chart for the minimum R-values of commonly available SIPs.) Static R-values, like those included in the chart, rate the effectiveness of insulating material. However, they do not accurately describe how products perform in a real world setting. When fiberglass or other types of insulation are installed, they are installed around structural members made of wood or metal which have a very poor insulating value. Field-installed insulation materials are also prone to installation imperfections. The Department of Energy's Oak Ridge National Laboratory has studied and tested the performance of entire wall assemblies in large sections. The resulting whole-wall R-value data reveals that a 4.5" SIP wall rated at R-14 outperformed a 2"x6" wall with R-19 fiberglass insulation. Here is another FAQ that answers a lot of questions: How much faster can I build with structural insulated panels? SIP homes go up faster than traditionally framed buildings. A properly trained SIP installation crew can reduce labor costs by more than 50 percent compared to traditional stick framing, according to a third party study conducted by the R.S. Means unit of Reed Construction Data. Panels can be manufactured as big as 8 X 24 ft., so entire walls can be put up quickly. SIPs can be supplied as ready-to-install building components when they arrive at the jobsite, eliminating the time needed to perform individual jobsite operations of framing, insulating, and sheathing stick-framed walls. Window openings may be precut in the panels, and depending on the size, a separate header may not need to be installed. Electrical chases are typically provided in the core of panels, so there is no need to drill through studs for wiring." For additional info, go to www.sips.org
Sills The sills are usually 2 x 6 or 2 x 8 wooden boards, depending on the thickness of the foundation wall. They are the first piece of wood that attaches to the masonry foundation and should be treated wood. This helps prevent moisture and insect damage. Before they go down on top of the foundation wall, there should be an insulation strip or sill sealer. Many such sealers are fiberglass, which gets compressed when the nuts on the anchor bolts are tightened down. This provides a good barrier against insect, dust, and air infiltration. In areas where termites are a problem, a metal termite shield can be installed between the foundation and the sill. It will prevent termites from crawling up the side of the house and getting into the wood. Termites live in the ground and just come into the house to dine. Termite shields are very low-tech, but they work. Obviously, they cannot be retrofitted. You only have one chance to do it right.
Floor Framing Girders are the main support beams and are set in pockets that were formed in the top of the end walls of the foundation. Steel girders may be used and are very strong. Wooden girders may be fabricated by nailing together three or more wooden planks. Usually these members have plywood spacers for additional strength and are glued as well as nailed. There are also modern "engineered" wood girders, including brand names such as "Glulam" and "Microllam". The size of the girders can be calculated from beam formulas, span tables, or local codes.
Subflooring (cont.) Plywood is constructed of several thin layers of wood that are glued together. Each layer is arranged with the grain of the wood running in the opposite direction to the layer below (cross-oriented). This results in greater strength. Nevertheless, plywood will warp, especially if exposed to moisture. This type of wood should not be used for exterior applications that are exposed to weather. A common trend in subflooring today is the use of oriented-strand board (OSB). OSB is an engineered wood product that is similar in appearance to plywood, however it is constructed of small chips or strands of wood, which are combined with glue and wax and pressed together under heat, to form a sheet (usually 4' x 8'). OSB is more resistant to warping than plywood, however like plywood it will deteriorate when exposed to moisture, and should not be exposed to weather.
Framing Systems Framing systems have to endure tremendous stresses and must be engineered to handle them. The entire weight of the roof presses down on the walls and tries to spread the walls outward. The walls carry the weight of the entire structure down to the foundation and ultimately the footings. From there, the forces are dispersed to the surrounding earth.
Girder Support Because girders cross long spans, they need support from underneath. In the old days, this support was provided by wooden posts. In Colonial times, beams were hewn, or in some instances, tree trunks were utilized. These were set on flat rocks on the dirt floor of the basement. By the mid-1900s, we saw the advent of steel posts, or lally columns. Most were adjustable with an internal screw mechanism, so that if the girders sagged over time, they could be jacked up to level again. These supporting posts should rest on reinforced footing pads. Remember, in the last chapter, we saw a photo of footings being installed around the perimeter of the foundation. In addition, there were small, rectangular footing pads poured where each support post would go. Precast concrete posts are commonly used to support girders in crawl spaces.
Joists Joists are horizontal structural members, placed on edge, which carry the house loads to girders and sills. The thickness, width, and spacing are determined by the live loads placed on them. They commonly are 2 x 10s or 2 x 12s. The joists are laid perpendicular to the girder. They generally rest on top of the girder. The outside ends of the joist rest on top of the foundation wall and are butted into the header joist. Engineered joists deliver better dimensional stability and strength. They resist twisting and shrinking which provides quitter floors with less shrinks. Some engineered joists also have a fire protection coating applied.
Factory Built Housing We will briefly discuss the different types of factory-built housing here. We covered this material in more depth in a previous chapter (Chapter 4) but a brief refresher is a good idea at this point. Freddie Mac, in their Glossary of Finance and Economic Terms, defines factory-built housing as Generic term for the type of housing constructed in a factory and transported to a residential site as opposed to assembled piece by piece at the construction site. Examples of factory-built housing include manufactured, modular and panelized housing. Factory-built homes are constructed in a more efficient way because they're built in a centralized, controlled indoor environment. They are not subject to weather delays and cost overruns dictated by having to build in the rain, snow, or wind. On-site contractors do not have the availability of sophisticated production tools. They are more subject to subcontractor delays, weather damage to building products, theft of materials, vandalism, and delivery problems. Industry data shows that the labor cost component of a modular or manufactured home is typically 8 to 12 percent of the total house construction cost, while the labor cost of a site-built home is upwards of 40 to 60 percent of the total cost. Factory-built housing represents about 21% of U.S. homebuilding. End of Page
Manufactured Homes There are multiple definitions of manufactured housing. In a Frequently Asked Question, HUD defines manufactured housing this way: A manufactured home (formerly known as a mobile home) is built to the Manufactured Home Construction and Safety Standards (HUD Code) and displays a red certification label on the exterior of each transportable section. The Manufactured Housing Institute says: A manufactured home is a single-family house constructed entirely in a controlled factory environment, built to the federal Manufactured Home Construction and Safety Standards (better known as the HUD Code). Fannie Mae, in its Selling Guide, defines a manufactured home this way: Fannie Mae defines a "manufactured home" as any dwelling unit built on a permanent chassis that is attached to a permanent foundation system and evidenced by a HUD Data Plate and HUD Certification label. Freddie Mac has this to say in its Single-Family Seller/Servicer Guide: The Manufactured Home must be built on a permanent chassis in compliance with the applicable HUD Codes for Manufactured Homes (HUD Codes) in effect as of the date the Manufactured Home was constructed. The definitions all have similar characteristics. For example, they all mention the HUD Code. End of Page
Structural Insulating Sheathing Here's another new product, as detailed at toolbase.org. "Exterior walls must provide multiple functions including weather and air resistance, energy efficiency, and structure. Most commonly, these functions are met with a combination of materials that are typically individually installed. Structural insulating sheathing provides a multi-function exterior wall sheathing product that is applied in a single layer and provides additional continuous insulation, a weather- and air infiltration-resistant barrier, and structural wall bracing. The product is a marriage of two proven sheathing materials—foam sheathing (polyisocyanurate) and structural laminated fibrous board with a thermal resistance of R-3 for ½-inch thickness. Structural insulating sheathing provides a structural method of design for braced wall panel construction, and many additional benefits. Using a single product simplifies wall construction and allows labor savings. It can be installed using common construction tools and skills, and time is saved since it eliminates the installation of a separate layer of building wrap or felt paper for the weather-resistant barrier (WRB). Further, it reduces handling and improves worker safety by replacing two installations with one of a lighter panel weight. The material fits together with standard components - window and door jambs do not require extension with ½-inch-thick sheathing material. It is more rigid and impact resistant than traditional foam sheathing, and improves energy performance of exterior wall assemblies. Additionally, one manufacturer's product contains 80 percent post-consumer recycled material."
Masonry Construction Masonry construction is also popular, in many varieties: Brick Stone Concrete block Poured concrete It is sturdy, durable and low maintenance, but generally costs more than frame construction. Masonry construction has been around longer than frame construction.
Number of Manufactured Homes Here is a comparison of the number of manufactured houses built versus the number of site-built homes in recent years. Source: Manufactured Housing Institute You can see that the percentage of new construction of manufactured housing stayed pretty steady in the 1980s and 1990s, at around 20%. It declined sharply from 2000 to 2003; dropping from 17% to 8% and then slowly regained ground to stay between about 12% and 14% in recent years. End of Page
Modular Homes A modular home is defined by the National Modular Housing Council this way: Modular means a method of construction that utilizes pre-engineered, factory-fabricated structures in three dimensional sections that are transported to a job site, assembled and finished. Modular homes are built in self-supporting modules or "boxes." They are transported to the site on flatbed trucks and then either rolled onto a foundation or set in place with cranes. The modules are shipped at least 70 to 85 percent complete. In many cases they are 90% or more complete. The modules are joined together at the site and finishing touches are done. This usually includes taping and painting where they join together, finishing of the electrical, plumbing, and heating connections. The early modular homes consisted of just two sections and looked a lot like manufactured homes. They had low pitched gable roofs and modest exterior finishes. Today, good quality modular homes are virtually indistinguishable from conventionally built homes. They may be two or more stories high, have irregular shapes, and can be created from joining 6 or 8, or more, modules together. Hinged rafters enable steeper roofs to be transported on the highway and then extended up into place at the site. Because they have to travel down the road, they are built stronger. There is typically 20% to 30% more lumber used in the framing and most factories glue, as well as nail and screw, the various components together. Modular homes account for approximately 2% of new construction.
Brick Brick construction may be solid brick, where the wall is laid up in two layers with interlocking bricks. The brick themselves can be laid in different patterns and come in many colors. A cheaper alternative is to apply a brick veneer, a layer of brick over a frame wall. It may be applied to all four walls or maybe just the front façade. A recent product is called thin bricks. It consists of brick material that is only about an inch thick and is applied over a frame wall. Here is an early Georgian brick house (late 1700s) in Vermont.
Mortarless Brick Veneer Here is another newer product, as reported by toolbase.org. "Skilled masonry work is a major cost factor for veneer brick walls. A new exterior wall system uses concrete bricks cast in special shapes which require no mortar and can be installed by anyone with basic carpentry skills. In most applications, the existing wall framing structure supports the weight of the bricks, so foundation ledges are not required, and the system is suitable for retrofitting existing walls. The manufacturer states that the system provides homeowners with the luxury look of real brick exteriors at a more affordable cost. The dimensions and appearance of the brick faces are similar to traditional split-faced bricks, and like bricks used for conventional veneer walls, they are installed in staggered rows. Hidden from view is the unusual shape of the cast block, which allows shingle-like overlapping. Because the system does not require footings or mortar, it can be used on new or existing buildings. Installers stack the blocks in rows and screw them to vertical furring strips attached to the wall sheathing. The furring strips provide a positive connection and create an air space, allowing the veneer surface to breathe and providing drainage for any moisture that may penetrate. Thermal insulation characteristics are about the same as common face brick (R-0.11) and each unit weighs just over 4 lbs. Because of the interlocking shape of the materials, the system requires no mortar and can be installed by a contractor, handyman, or homeowner with basic woodworking and layout skills."
Identifying Modular Homes Sometimes it is hard to tell if a house is a modular or if it has been stick built. If the modular home is existing, here are some clues as to its origin. The "boxes" are self-supporting and self-contained with sidewalls, floor and roof. When they are joined together, the resulting marriage wall is twice as thick as normal interior walls. If the interior walls were framed with 2 x 4's, there would be a wall down the center of the length of the house approximately 8 inches thick. All the other interior walls would be 4 inches thick. If you can examine the basement or the crawl space of a modular home it is obvious there too, that two sections were joined together. The center girder will be composed of 4 or 6 parallel beams instead of the usual 2 or 3. A modular home will usually not have a steel undercarriage. It will have a wooden floor structure, as pictured below. However, be aware of some recent trends that have muddied the waters and made it harder to distinguish. A recent addition to the factory-built housing market is the on-frame modular which is built on a permanent steel chassis, transported to the site on attached wheels and placed on a permanent foundation.
Panelized Homes Panelized homes are factory built homes in which large panels (a whole section of wall with windows, doors, wiring, and siding) are transported to the site and assembled there. They must meet state and local codes for that location. When finished, they are indistinguishable from site built homes and are appraised the same way. The wall panels may be constructed of traditional lumber or metal studs. Panels generally provide more chance to customize a home than with modular construction. Some panelized wall are now being built using structural insulated panels (SIP's). A study by the Building Systems Council found that construction of a 2,600 square foot home with trusses and panels used 26% less lumber, generated 76% less waste and was constructed in only about 37% of the man-hours needed to build a similar stick-built home. A big advantage is that the house can be enclosed and made weatherproof and secure within a day or two. Here are pictures from the NAHB website.
Balloon Framing Balloon framing employs studs that run continuously from the sill to the rafter plate. The second story floor joists are hung and attached to the studs. This was introduced around 1850 after steam powered saw mills became common and long timbers could be easily milled. Balloon framing gave good structural rigidity and was well suited for the plaster interior finishes of the day. The disadvantages were that the two-story cavities between studs were dangerous in the event of a fire. This could be ameliorated by installing horizontal "fire stops" made of 2 x 4s, but by the 1930s and 1940s, balloon framing was outlawed in many municipalities. If you find a house that was built in the late 1800s or early 1900s, it almost certainly will have balloon framing.
Platform or Western Framing Due to the fire hazard and the difficulty of getting good lumber 20 feet long, balloon framing is rarely used today. It has been replaced by platform framing, since the 1930s. With platform framing, the studs run one-story high. The wall sections are framed on the convenient "platform" consisting of the floor joists and sub-floor. If there is a second floor, a whole new platform is erected on top of the walls. Then a second story is framed up with one-story studs. That also makes it more efficient to build as the second floor platform makes a perfect staging area to layout and frame the second-story walls before they are erected.
Post and Beam For over a thousand years, the framing system utilized was the post and beam system. This consists of large vertical posts that support horizontal beams. The posts and beams were joined together by various interlocking joints, such as mortise and tenon, and then secured by wooden pegs.
Post and Beam (cont.) Post and beam construction is quite strong and has many supporters in the building industry. It is not used much today because of the cost of getting and milling large, mature timbers. Also, it takes more skill to design and erect the timbers. This type of construction is now often referred to as timber frame. It is most often found in high-end homes or vacation homes. In many cases, all or part of the framing structure is left exposed for decorative purposes.
Foundation Walls The earliest foundations were made of stone (loose or mortared) and brick. Today, most foundations are constructed of poured concrete or concrete block. Wood foundations have been used successfully in Canada for more than 40 years but have received a lukewarm reception here in the U.S. They have proven to be durable, easy to erect, and come in panels that are insulated and easy to finish on the inside. They are constructed of pressure-treated wood. They probably will never see wide-scale usage until they experience better press and more general public and lender acceptance. Here is a diagram of a wood foundation from the website of the National Association of Certified Home Inspectors.
Poured Concrete The earliest concrete walls and foundations appeared in the early 1900s. With poured concrete walls, forms are erected which usually were steel-braced sheets of plywood. Steel reinforcing rods, called rebar, are inserted into the openings and then the forms are filled to the top with concrete. Anchor bolts are set into the top of the wall, to later fasten down the sill plate. In some cases, when poured, the concrete on the bottom of the wall flows down into a keyway - a slot that was created in the top of the footing when it was poured. In most cases today, rebar is inserted into the footings before the walls are poured to secure the walls to the floor. Today most of the forms are made of steel sections which are bolted together. Then the concrete truck backs up and fills the forms. The inside of the forms is treated with some sort of coating, ranging from engine oil to plastic, to special form-release coatings that may be sprayed on. This facilitates stripping the forms off without damaging the walls. The concrete should be left to harden for at least two (2) days before the forms are removed. Then, ideally, the wall should be left to cure for another week or so. Unfortunately, this step is ignored by many builders in a hurry and that failure to let it cure sufficiently can lead to future cracks. Poured concrete is done in a continuous pour, so the finished walls are seamless. They are strong and good are at repelling water. However, they cost more than concrete block walls.
Synthetic Roof Underlayment Here is another newer product explained by toolbase.org. "Until the twenty-first century, most residential sloped roofs received a layer of asphalt-saturated felt building paper underneath the roofing material. Mimicking the attributes of housewraps, synthetic roof underlayments are now available to serve the same function as a secondary weather barrier with better resistance to tearing, moisture, and ultraviolet rays than traditional roofing felt. Synthetic underlayments are typically made from polypropylene, polyester, or fiberglass fabric which weighs less than felt building paper, can be manufactured with an anti-slip surface, and can withstand exposure to the elements for six months. Recent natural disasters and subsequent rebuilding efforts highlighted the versatility of synthetics as roof underlayment by providing a real-life test environment. After several hurricanes ravaged southern coastal areas of the United States, many people were forced out of their damaged homes. At the same time, large numbers of homes required quick roof repair and 'drying in' to minimize further damage due to water intrusion. With limited resources, contractors triaged homes, repairing the critical components and installing synthetic underlayments as temporary roofing. The underlayments performed better than FEMA's blue tarps and didn't require removal and discard when a roofing crew eventually arrived to install shingles. One manufacturer offers a Class I fire-rated synthetic underlayment for roofs that require resistance to fire, as well as, the durable attributes of synthetic fabrics while the building is under construction." Get ready for another check of your understanding.
Radiant Roof Barriers Here is an explanation of radiant roof barriers from the U.S. Department of Energy. "Radiant barriers are installed in homes - usually in attics - primarily to reduce summer heat gain, which helps lower cooling costs. The barriers consist of a highly reflective material that reflects (or more specifically, re-emits) radiant heat rather than absorbing it. They don't, however, reduce heat conduction like thermal insulation materials. Heat travels from a warm area to a cool area by a combination of conduction, convection, and radiation. Heat flows by conduction from a hotter location within a material or assembly to a colder location. Heat transfer by convection occurs when a liquid or gas is heated by a surface, becomes less dense, and rises (natural convection), or when a moving stream of air absorbs heat from a warmer surface (forced convection). Radiant heat travels in a straight line away from any surface and heats anything solid that absorbs the incident energy. Radiant heat transfer occurs because warmer surfaces emit more radiation than cooler surfaces. When the sun heats a roof, it's primarily the sun's radiant energy that makes the roof hot. A large portion of this heat travels by conduction through the roofing materials to the attic side of the roof. The hot roof material then radiates its gained heat energy onto the cooler attic surfaces, including the air ducts and the attic floor. A radiant barrier reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic.
Radiant Roof Barriers (cont.) A radiant barrier's performance is determined by three factors: Emissivity (or emittance) - the ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area. It's expressed as a number between 0 and 1. The higher the number, the greater the emitted radiation. Reflectivity (or reflectance) - a measure of how much radiant heat is reflected by a material. It's also expressed as a number between 0 and 1 (sometimes, it is given as a percentage between 0 and 100%). The higher the number, the greater the reflectivity. The angle the incident radiation strikes the surface - a right angle (perpendicular) usually works best. Radiant barriers come in a variety of forms, including reflective foil, reflective metal roof shingles, reflective laminated roof sheathing, and even reflective chips, which can be applied over loose-fill insulation. The reflective material, usually aluminum, is applied to one or both sides of a number of substrate materials. Substrate materials include kraft paper, plastic films, cardboard, oriented strand board, and air infiltration barrier material. Some products are fiber-reinforced to increase the durability and ease of handling."
Roof Covering Roof covering has the basic function of keeping out the rain and snow. It can also serve aesthetic purposes and adds texture and color to a house design. Here is a list of popular roof coverings arranged in order of their costs - from lowest to highest. Composition roll roofing Composition shingle Built-up rock Metal Wood shakes or shingles Cement fiber shingle Clay tile Slate Copper
Rise Over Run The slope of the roof is described as a precise relationship of the rise over run. The rise is how high it goes up vertically over a certain horizontal run. For example, if the roof rises 4 inches as it goes 12 inches sideways - the slope or pitch of the roof is 4 over 12 or 4/12. In northern climes, 4 over 12 would be a minimum, because steeper roofs are needed to combat snow loads in the winter. In Florida, snow load is not a consideration when designing a roof.
Roof Sheathing Roof sheathing serves the same purposes as the wall sheathing - strength and nailing surface, plus moisture protection. It typically consists of plywood sheets, or oriented strand board (OSB). A sheathing paper is also applied, which has traditionally been asphalt paper. Today, there are a number of synthetic roof underlayments, including some that are self-sticking. Prior to the 1950s, most roofs were sheathed with 1 x 4 or 1 x 6 planking, nailed to the rafters. If the covering was to be cedar shingles, the sheathing was typically 1 x 4 planking with air spaces in between, so that the shingle could dry out after rains or snows. Some roofs today are sheathed with wooden planks, particularly if they are to be left exposed on the interior.
Roof Framing As the weight of the roof presses down, it tries to push the side walls out. The ceiling joists hold the walls together. Conventional rafter systems consist of boards that are set at an angle and meet at the ridge. There may or may not be additional cross pieces (collar ties) to help hold the stresses.
Roof Trusses Roof truss systems resist the spreading stresses and transfer all the weight to the outside walls. They are about 3 to 4 times as strong as a conventional rafter system and none of the interior walls are load-bearing. That allows great flexibility in interior design and layout. There can be large open spaces. They are usually factory-built to custom specifications, trucked to the site, and erected with cranes. There are various configurations of trusses.
SIPs So, SIPs can be used to frame an entire house or light commercial building. The SIPs in the wall replace the conventional stud framing system with insulation in between the studs. It also would include the sheathing on the inside and outside, all in one step. It would be ready to apply the interior finish and exterior siding. SIPs could also replace the roof rafter or trusses, the roof insulation, and sheathing. This image is from the www.springtimehomes.com website. Note: there are many videos available that illustrate these new kinds of products such as Structural Insulated Panels and Insulating Concrete Forms. I found some entertaining ones on Youtube. I did not want to link to any particular one because they might no longer be available when you log on. However, I might recommend that you go to www.youtube.com and enter the appropriate phrase in their search box. For example, search for "Structural Insulated Panel." I just did that and found over 400 videos there on SIPs.
Roof Types There are many types of roofs. The simplest and cheapest are the flat and shed roofs. The shed roof has just one plane and slopes in one direction. The gable roof has two similar pitches. As the style gets more complex, the framing requirements become more complex and more expensive. The type of roof can add greatly to the overall style of the house. You can't have a Dutch Colonial without a gambrel roof or a Second Empire house without a mansard roof.
Sheathing Sheathing is applied to: Strengthen the structure Provide a nailing surface for siding Combat air infiltration Form a moisture barrier Provide some insulation The most common sheathing is plywood. We are also seeing more OSB sheathing being used
Sheathing (cont.) Sheathing paper, such as asphalt building paper or vapor and wind barriers such as "Tyvek", is applied to the frame. Vapor barriers are used to block the migration of water through building materials. Where it should be applied varies among different climates. Some parts of the country are generally and other parts are generally cold. The typical amounts of humidity in the air are also a mitigating factor. If vapor barriers are applied in the wrong way it can have serious consequences. Please click here and read an informative article on understanding vapor barriers. There are also various kinds of insulating foam sheathing that may provide up to R-8 insulation.
Fiber Cement Siding A recent innovation in siding is fiber cement. It has become popular in the South and Southwest. It is composed of cement, sand and cellulose fiber to prevent cracking and increase strength. It comes in various styles, is textured to resemble wood and can be painted in any color. Among the popular brands is Hardie Plank, manufactured by the James Hardie company. Its features include: Low maintenance Moisture resistant Won't crack, rot, buckle or de-laminate Termite proof Non-combustible 50-year transferable warranty You have to handle it differently, because of its composition. You cut it with a carbide tipped saw (with dust catcher) or shears and fasten it with hand or pneumatic driven non-corrosive nails or screws. You leave a joint at the edge and caulk to allow expansion if it meets wood - or use vinyl trim. It can be applied over wood frame and sheathing or insulation board. It can also be applied directly over masonry block or concrete. Currently installed costs are a little more than vinyl siding, about equal to hardboard siding and less than masonry or EIFS.
Siding Popularity According to the U.S. Bureau of the Census, here are percentages of new houses built in 2012, with different types of siding: Siding Type Percentage Vinyl 32.3 Brick 24.5 Stucco 20.1 Fiber Cement 16.5 Wood/wood product 5.0 Other 0.3 A check of your understanding is next.
Cool Metal Roofs Cool metal roofs are a sustainable product that has been developed in recent years. The idea is that the more sun rays that can be reflected away, the less heat will build up in an attic. Cool metal roofs are light colored and shiny. They can save up to 40% in cooling energy. Metal roofs are durable and have sustainable attributes in that most contain at least 25% recycled materials. At the end of their life, they can be 100% recycled. Depending on the specific product, the weight of metal roofing is one-third to as little as one-eighth that of conventional roofing shingles. Metal roofing consisted of about 5.5% of the roofing market in 2012.
Solar Shingles Solar shingles are Photovoltaic solar cells designed to look like conventional asphalt shingles. They are the same size and shape as conventional asphalt shingles and are applied to a roof along with conventional shingles. The first ones were introduced in 2005. Click here to see a good video on the topic. It runs just over 3 minutes (after having to sit through a brief commercial). You can even click on the symbol at the bottom and enlarge it for full screen viewing. As mentioned before, there are some good videos on YouTube as well.
Siding Wood siding, both shingle and clapboard, was the standard in this country from the 1600s through the 1800s. During the last 50 years or so, there have been many innovations in lower maintenance siding materials. Many have the color baked in and textures are available to resemble wood. As before, a list follows with sidings in approximate order of cost. Hardboard Wood clapboard Aluminum Vinyl Stucco Wood shingles EIFS Brick Stone
Stucco Stucco is a lime-based mortar finish applied to a wall. It can be easily applied over concrete blocks. Two or three coats are sprayed or troweled on. Stucco can be applied over frame walls, with the proper preparation. Wire mesh is first attached to solid sheathing. Stucco is relatively low cost for exterior applications and generally long lasting. It is particularly popular in the south and southwest. It has appeal in Spanish or hacienda style dwellings. We are seeing some applications now where stucco is being applied over existing siding; in order to provide lower maintenance than painted surfaces. It can be applied over wood, brick, concrete or metal siding. First, a water barrier must be applied and then a wire mesh. A layer of foam insulation may be applied as well.
Floor Trusses A relatively recent innovation is computer-designed floor trusses. They have greater strength and allow long, clear spans without girders or posts. The open web design allows easy installation of plumbing and wiring.
Subflooring Subflooring used to consist of 1 x 6 tongue-and-groove boards laid diagonally for more strength. Today, it is almost always 4 x 8 foot sheets of plywood or oriented strand board (OSB). 1/2 inch thick plywood may be an acceptable minimum. 5/8 inch or ¾ inch is much more desirable. A good way to combat floor squeaks and improve structural rigidity is to glue the plywood down to the joists and to use tongue-and-groove sheets.
Asphalt/Fiberglass Shingles Most new construction today employs asphalt/fiberglass composition shingles. The average life ranges from 20 to 35 years, depending on the thickness and weight of the shingles. The life may be less in the South, where the sun is more intense. The weight of the shingles is a literal term describing the weight of shingles that are sufficient to cover 100 square feet, or a square. For example, a square of 240-pound shingles would weight 240 pounds if you put them on a scale. It is more common for composition shingles to be marketed and sold based on the number of years they are expected to last, e.g., 30-year shingles. Today, newer, low maintenance products being used include metal roofs and fiberglass tiles that look like clay tiles. In 2012, asphalt shingles accounted for 57% of the roofing materials sold. Old asphalt shingles that are torn off and replaced can be ground down and recycled into products such as hot-mix asphalt additives, cold patch for pothole repair, and new shingle additives.
Wood Shingle Roofs Wood shingle roofs have been used in Europe for over a thousand years. Many buildings had wood shingles on the walls and roofs. They were popular in Colonial America and are still used a lot in areas such as New England and particularly on Cape Cod. Shingles are thin, tapered pieces of wood and are uniform in size and shape. In early times the shingles were planed smooth and uniform. Starting in the early 1800s they were milled in steam powered saw mills. Shakes are shingles that have been hand split from straight grained bolts of wood and are irregular in shape. Cedar is a popular wood for shingles and shakes, as it is water resistant. Also used is cypress and redwood. Wood shingle roofs can be installed over a solid roof deck or a "spaced" sheathing that allows some air circulation around the shingles. Wood shingles cost more than asphalt shingles roofs and there are more labor costs to install them. However, wood shingle roofs are popular in many areas due to their "rustic" appearance. They are well suited for various styles of vacation cottages, cabins, and chalets. But, they have been banned in certain areas due to their potential to catch fire from flying embers if there is a forest fire; even though they can be pressure treated to retard fires.