INSULATION AND VENTILATION

The vapor retarder is usually a heavy paper called

Kraft paper.

Several factors contribute to Mold and Rot in the Crawl Spaces including

Lifestyle choices, typical lack of attention to detail in the installation of insulation and the crawl space floor vapor retarder, and inadequate maintenance of gutters and grading.

Insulation is a means to

Maintain a comfortable interior environment, and to help make the house as energy efficient as reasonably possible.

Ventilation is a means to

Manage moisture, remove or dilute pollutants, and maintain a supply of air for occupant health and comfort.

Polyethylene and foil sheeting, Kraft paper, and vinyl and foil wallpaper are vapor impermeable, meaning

Meaning they do not allow water vapor to pass easily. These materials and others are considered vapor retarders, although wallpaper is not supposed to be used as a vapor retarder.

Mineral wool is another less common insulation type.

Mineral wool is made from natural minerals (rocks) or from waste products from steel production (slag).

Because insulation works primarily by slowing conductive heat flow, insulation must be

In contact with an air barrier that is adjacent to conditioned space.

The other source of moisture in this situation is the crawl space ventilation openings.

In warm moist climates, crawl space ventilation openings can bring in as much water vapor as they remove.

Insulation upgrades in attics with trusses are one situation where

Insulation weight could create a problem.

A blown-in fiberglass system called Blown-in Batts (Blankets) is also available, but is less common.

Its R-value is about R-3.8 per inch.

Air moving across or through insulation reduces

Its resistance to heat flow (its R-value).

A material that is installed in the wrong location, or that is improperly installed, can

Can trap moisture or allow moisture to flow where it can do harm.

It also helps to realize that each house occupant can add ½ gallon or more of water vapor to the air in the house each day by activities such as

Breathing, Cooking, and Bathing.

The R-value of a double 2x_ header would be about the same as a

2x4.

Sheet insulation is most commonly available in

4 foot wide sheets of various lengths (8 to 10 feet are the most common). Common thicknesses are ½ and 1 inch, but thicker sheets are also available.

A Class I or II vapor retarder is usually required on the interior side of walls in

5 - 8 and Marine 4. There are several exceptions to this requirement that allow a Class III vapor retarder. These exceptions involve using specific types of wall cladding and sheathing material.

The permeability of 1 inch of EPS is about

5.0, which makes it a Class III vapor retarder.

A vapor retarder may be installed on the attic floor (under the insulation) in climate zones

6 - 8 as an alternative to the 1/150 attic ventilation ratio.

Vapor drive:

A condition that occurs when heat and vapor pressure cause increased vapor diffusion. One example is when water vapor diffuses through permeable building materials from heated interior areas in the winter. Another example is when solar radiation heats wet bricks forcing water vapor through permeable building materials in the summer. Vapor drive is usually less of a factor than vapor flow by convection through openings in the building envelope.

Vapor retarder:

A material that restricts the flow of water vapor. A Class I vapor retarder is rated at 0.1 perms or less. Polyethylene sheeting is an example. A Class II vapor retarder is rated at between 0.1 and 1.0 perms. Kraft paper used as the facing on some batt insulation is an example. A Class III vapor retarder is rated at between 1.0 and 10.0 perms. Latex and oil paints are examples.

Solar heat gain coefficient (SHGC):

A measure of the amount of solar radiation that passes through a window. A lower SHGC means that less solar radiation passes through a window.

Vapor barrier:

A technically questionable term often used when the term vapor retarder is intended. Class I vapor retarders are effectively vapor barriers, but the term vapor retarder is preferred.

Basement wall:

A wall with at least (≥) 50% of its area below grade (covered by earth on the outside) and encloses conditioned space.

The R-value of EPS sheets is

About R-4 per inch.

Mass wall:

Above-grade walls made from concrete masonry units, concrete, insulated concrete forms, masonry cavity, brick (structural, not veneer), adobe, compressed earth block, rammed earth, and solid timber logs.

The easiest way to think about the house as a system is in terms of pressures and holes.

Air and water vapor will remain motionless without pressure (a force) to move them. This is an expression of Newton's First Law of Motion. Air and water vapor will remain in the same space unless there is a hole through which they can pass.

The ideal insulation installation has an

Air barrier on all six sides of the insulation to eliminate convection around and through the insulation, a phenomenon sometimes called wind washing.

House wraps and building paper are also air barriers, and if properly installed without gaps and holes and with tape applied to seams, can help reduce

Air flow through seams in the other air barriers.

Loose fill insulation is not an

Air-barrier, nor is it a vapor retarder.

A vapor retarder installed above the insulation can create a moisture trap that can

Allow water to condense between the vapor retarder and the attic floor.

Lack of insulation in these (usually) concealed spaces is difficult to detect during a visual home inspection; however, moisture stains or mold growth near these areas can be

An indication of an insulation or air sealing defect.

Moisture stains or mold growth around the baseboards can also be an indication of

An insulation or air sealing defect.

Air barrier:

Any material or combination of materials that prevents the flow of air from unconditioned areas into the thermal envelope.

A vapor retarder is not required in an adequately ventilated

Attic.

Loose fill (also called blown-in or blown) insulation comes in

Bags. The material is usually poured into the hopper of a machine that uses air to blow the insulation through a hose into the space being insulated.

Grading, drainage, gutters, and landscape irrigation are the first line of defense against

Basement and crawl space moisture problems.

Batts made from cotton are marketed as eco-friendly insulation, but are uncommon.

Batts made from recycled plastic are also marketed as eco-friendly, but are uncommon.

A room with a supply duct and no return will

Become pressurized and can force air into the wall cavity, the interstitial space between floors, and into the attic.

Heat is transferred in three ways that can occur individually, but often occur together.

Conduction occurs when heat moves through solid matter. Convection occurs when heat moves by circulation of a gas or a liquid. Radiation occurs when molecules gain heat by absorbing electromagnetic energy in the infrared part of the spectrum.

Insulation works mostly by slowing

Conductive heat transfer. It does this by trapping air in the insulation material, and by keeping the air from moving.

Powered attic ventilation fans can depressurize the attic and

Draw conditioned air from the house, and can draw moist unconditioned air from the basement and crawl space if there are openings that connect the two.

A wall cavity should be designed to

Dry toward at least one side, so a vapor retarder should not be installed on both sides of a wall cavity.

Sheet insulation is often applied as

Exterior sheathing, so it is often not visible during a home inspection. It may, however, be visible in attics and crawl spaces.

Some batts have a vapor retarder on one side and are called

Faced batts.

Cellulose insulation and mineral wool insulation are heavier than

Fiberglass insulation. The extra weight can be an issue when this insulation is applied in an attic framed at 24 inches on center with ½ inch thick drywall.

The most common type of batt insulation is made from fiberglass.

Fiberglass, as the name suggests, is made from fine glass fibers.

Imbalances in the air flow through forced-air supply and return ducts can pressurize or depressurize individual rooms or the entire house.

For example, a leak in the return duct will pressurize the house because more supply air is entering the house than is being removed from the house.

Attic moisture problems can sometimes be traced to the crawl space.

For example, a powered attic ventilation fan can depressurize the attic and draw water vapor from the crawl space through interior walls and chases. The water vapor can condense inside the walls or near where the chase or opening enters the attic.

Most loose fill insulation is usually made from

From fiberglass or cellulose.

Wet insulation loses R-value because

Heat transfers more effectively through water. Wet insulation also retains water that can provide moisture for fungal growth.

Insulation that has more, but not too many, air pockets that completely fills the space in which it is installed, and that does not have air moving around or through it has a

Higher resistance to heat transfer (a higher R-value).

The condition and adequacy of exhaust components that are part of heat recovery ventilation systems (HRV) and energy recovery ventilation systems (ERV) are not in scope of a

Home inspection.

Fenestration:

Openings in the wall and roof of a house such as windows, doors, and skylights.

The R-value of a 2x6 is about

R 6.9

Fiberglass batts values range between about

R-3 (standard) to R-4 (high density) per inch.

Loose fill mineral wool R-value is about

R-3.1 per inch.

Cotton batts values are about

R-3.7 per inch.

Mineral wool batts values are about

R-3.7 per inch.

Plastic batts values are about

R-4 per inch.

Insulation that is compressed, even a little, loses

R-value because it contains less air to slow heat transfer.

Conversely, insulation that is "fluffed" also loses

R-value because it is not dense enough to keep the air in the insulation stable.

Air that flows between the insulation and conditioned space, and air that flows through or around the insulation, can reduce the

R-value of the insulation to almost zero.

The R-value of a 2x4 (measured through the 3½ inch side) is about

R4.4

Cellulose insulation is made from

Recycled paper that is treated to make it fire retardant.

Lack of an exhaust system where required (e. g., bathrooms without operable windows) is a

Reportable defect.

Batt (blanket) insulation comes in

Rolls that are usually installed between framing members.

Expanded Polystyrene (EPS) is usually white and looks like a

Sheet of white beads stuck together (which is what it is).

Stationary air is actually a good insulator.

That is how most insulation achieves its R-value.

U-value (factor):

The ability or property of a material to allow heat transfer. U-value is the inverse of R-value (R-value = 1/U-value). U-value is expressed as a number greater than zero. A larger number equals a higher rate of heat transfer and a lower R-value. U-value is primarily used in residential construction to compare the thermal performance of fenestration. For example, metal such as aluminum has a high U-value; this is why higher quality aluminum windows have a thermal break in the frame to slow heat transfer.

Permeability:

The ability or property of a material to resist or allow the diffusion of water vapor through the material. Permeability (perms) is expressed as a number greater than zero. For example, glass is a very low permeability material and fiberglass batt insulation is a high permeability material.

R-value:

The ability or property of a material to slow heat transfer. A higher R-value number equals a higher ability to slow heat transfer. R-value is expressed as a number greater than zero. R-value is used to compare the insulation value of materials.

Humidity, relative:

The amount of water vapor that is actually in the air compared to the amount of water vapor that could exist in the air at a given air temperature, expressed as a percentage. More moisture can exist in warm air than in cold air, so raising the air temperature while keeping the water vapor constant reduces relative humidity. Conversely, lowering the air temperature and keeping the water vapor content constant increases relative humidity.

Loose fill insulation is usually installed on

The attic floor. The material can be blown into fabric suspended from the rafters in unventilated attics. Cellulose loose fill can be blown into wall cavities.

Building thermal envelope:

The conditioned (heated and cooled) area of the building. The envelope boundary between conditioned and unconditioned space includes walls, ceilings, floors, basement walls and slab-on-grade foundations. The thermal envelope may include the attic and the crawl space if these areas are designed and built as conditioned space.

Water vapor can pass (diffuse) through many materials used to build houses

The ease with which this happens depends on the permeability of the material.

An intact water and air barrier (not a vapor retarder) should always be installed on

The exterior side of exterior walls.

A vapor retarder was installed on

The interior side of exterior framed walls in all climates.

Loose-fill fiberglass, like fiberglass batts, is available in low and high-density versions:

The low density version is very light and can be moved very easily by air currents in the attic. Low density fiberglass R-value is about R-2.2 per inch. High density fiberglass is heavier and is less easily moved. High density fiberglass R-value is about R-2.7 per inch.

Codes also require that new houses be air sealed so that

The measured rate of air changes per hour is five or fewer (three or fewer in all but climate zone 1 and climate zone 2). This means that some form of mechanical ventilation is required in new houses and in houses that have been effectively air sealed.

Codes require providing outside air to houses by mechanical means if

The measured rate of air changes per hour is five or fewer.

Air sealing can have a greater impact on energy use than adding insulation.

The problem is that air sealing can have a negative impact on air quality in the house, and can have a negative impact on traditional methods of providing combustion air for fuel-burning appliances.

Vapor diffusion:

The process by which water vapor passes through a permeable mate-rial from an area of greater vapor pressure to an area of lower vapor pressure.

Ventilation (building):

The process of supplying outside air to a house or removing inside air from a house by natural or mechanical means; ventilation can be random and uncontrolled (air leaks), or it can be designed and controlled (outside air ducts, heat recovery ventilators, energy recovery ventilators).

All conditioned spaces should have insulation installed at

The surface closest to the conditioned space.

Dew point (temperature):

The temperature at which water vapor in the air may condense into liquid water. A higher dew point temperature indicates that the air contains more water vapor.

Mold and Rot in the Attic begins when warm moist air flows through the openings in the ceiling driven by the stack effect and by positive pressure in the house with respect to the attic.

The water vapor is not quickly removed from the attic because of inadequate attic ventilation. The water vapor condenses on the coldest surface, which is the attic sheathing, roofing nails, and rafters. Discoloration, mold, and rot are observed.

Brick, wood and vinyl siding, #15 building felt, and insulation are vapor permeable, meaning

They allow water vapor to pass easily.

Many types of sheet and spray foam insulation may need protection from ignition because

They are flammable and because they produce toxic smoke when they burn.

House systems and components, house occupants, and the environment in which the house exists are constantly acting on each other.

This makes the house, occupants, and its environment one complex interdependent system.

Mold and Rot in the Crawl Space begins when the warm moist air in the crawl space diffuses through the vapor permeable insulation and condenses in the insulation and on the floor joists.

This occurs because the temperature in the insulation is reduced to the dew point temperature due to the cool temperature in the house above. The wet insulation loses additional R-value and the condensation increases as the dew point temperature in the insulation travels further down toward the crawl space floor. Discoloration, mold, and rot are observed.

You can see this using an infrared camera; the framing material clearly shows as a different temperature (which makes infrared cameras great, if expensive, stud finders)

This phenomenon is called thermal bridging. One effect of thermal bridging is to reduce the total R-value of the assembly. The other effect is to provide a surface on which water vapor in the assembly can condense; this tends to occur in cold climates in the winter.

A vapor retarder installed where a vapor permeable water barrier should have been installed can

Trap moisture in the wall cavity. At best, the trapped moisture reduces the R-value of insulation. At worst, the moisture condenses into liquid water, damaging the house and providing moisture for fungal growth.

Some have no vapor retarder and are called

Unfaced batts.

Drywall, OSB and plywood sheathing, and insulation sheathing (1 inch or less thick), are moderately vapor permeable and are not considered

Vapor Retarders.

Insulation and ventilation components that are in scope of a home inspection include

Visible insulation and vapor retarders, ventilation of attics and foundation areas, and local exhaust systems including bathroom, laundry, and clothes dryers.

We now know that this one size fits all approach causes problems, especially in warm/humid climates.

Whether a vapor retarder should be installed depends on the temperature and humidity where the house is located.

Insulation that is not in direct contact with an air barrier at the insulated area is practically

Worthless.

A vapor retarder is not required, nor is it recommended, on either side of walls in

climate zones 1 - 4 (except Marine 4). A vapor retarder is not required in these climate zones because it has been shown that water vapor condensation in wall cavities is usually not a problem. A vapor retarder is not recommended in these climate zones because lack of one allows the wall system to dry both toward the interior and the exterior if water should enter the wall cavity.

To understand how insulation works, we need to recall two rules from the Cooling System and the Heating System chapters of this book:

• Heat energy transfers from some place hotter to some place colder. • Hotter air is lighter than cooler air and will rise (stack effect).

To understand how and why vapor retarders work, we need to recall two rules from the Cooling System and the Heating System chapters of this book:

• Water vapor in the air flows (diffuses) from a place with more water vapor to a place with less water vapor. • More water vapor can exist in warm air than in cool air. • Water vapor in the air may condense into liquid water if the air temperature decreases to the dew point.