L 18 insulation

insulation above the membrane

(membrane is not adhered to the underlying surface). the protected membrane roof pmr

Thermal insulation can be installed in any of three positions:

1. Below the structural deck 2. Between the deck and the membrane. 3. Above the membrane.

minimum roof deck slope

1/4 inch per foot. 1 i 50 or 2%

Membranes for low-slope roofing have life expectancies ranging from

10-30 years, depending on the membrane material, thickness, geographic location, exposure to extremes of temperature and UV radiation, quality of installation, and maintenance.

if air continues to cool, it will reach a relative humidity of

100%

ballast

A heavy material installed over a roof membrane to prevent wind uplift and shield the membrane from sunlight.

bitumen

A semi-solid compound derived from coal or petroleum, such as asphalt, tars, and pitch. It is used as a component of a waterproofing material for roofs and on the earth side of foundation walls. Usually dissolved in a solvent or heated to a liquid state and combined w/ felt paper. When asphalt or coal tar is applied hot, it saturates and binds to the felt and forms a continuous one-piece membrane. this type of waterproofing is used where appearance is not an issue.

R values/inch for common building materials

Aerogel- 10 Polyurethane rigid panel- 6.8 Fiberglass batts- 3.6 softwood- 1.41 snow- 1 hardwood, brick, glass, concrete, steel follow after

BUR process

Assembled in place from multiple layers of asphalt-impregnated roofing felt bedded in additional layers of bitumen. Bitumen or coal tar pitch is applied hot in order to merge with the saturant bitumens in the felt and form a unified, multi-ply membrane. To protect membrane, a layer of crushed stone or other mineral granule aggregate is embedded in the top surface.

BTU

British thermal unit The amount of energy needed to heat one pound of water one degree Fahrenheit

vapor retarder

Material that is used to slow the diffusion of water vapor through a building assembly.

insulation above membrane- protected membrane roof

Membrane* is protected from extremes of heat and cold, and the membrane is on the warm side of the insulation, where it is immune to vapor blistering problems. • Panels of polystyrene are either embedded in a coat of hot asphalt to adhere them to the membrane below or are laid loose. • Panels are held down and protected from sunlight by a layer of ballast: crushed stone or gravel, thin concrete layer laminated at the factory to the upper surface of the insulating board, or interlocking concrete blocks.

low slope roof best choice materials

No single material has best attributes. combination of materials or composite board materials work.

disadvantages of protected membrane roofs

Potential for diminished performance of insulation if moisture is absorbed. • Somewhat more expensive and time-consuming to repair.

thermal resistance is abbreviated as

R

disadvantages of slow sloped roofs

Small errors in design or construction can cause them to puddle and/or hold water. • Small punctures, tears, or gaps in seams can cause large quantities of water to enter the building structure and its interior. • Water vapor pressure from within the building can blister and rupture the membrane.

built up roof membrane BUR

System works on principle of redundancy - felt is laminated in overlapping layers (plies) to form a membrane that is two to four plies thick. The more plies, the more durable the roof.

In Florida, the southern U.S., and the Hawaiian Islands, the summer condition is the more severe. _ is the predominant problem to be solved

The flow of water vapor from exterior to interior

Bituminous Roof Membranes include

built up roof membrane and modified bitumen

thermal bridging is commonly seen in

cantilevered concrete slabs, steel beams, and older window assemblies

asphalt-impregnated roofing felt is made from

cellulose, glass, or synthetic fibers, and is saturated with asphalt at the factory and delivered to the site in rolls.

thermal bridging greatly reduces

overall thermal performance of entire building assembly. should be avoided

vapor retarder materials

polyethylene plastic sheet, craft paper facing on glass fiber batt inflation, aluminum foil facing on insulation, paint primers with low water vapor permeability

if slope is too shallow

ponding occurs- formation of puddles

metals

poor insulators

vapor barrier

prevents vapor from condensing within

low density insulating concrete

pumice as lightweight aggregate 9.8 R value wall. 14.1 R-value roof

If the rate of diffusion is high enough and the change of temperature within the assembly great enough, water vapor will

reach its dew point and condense within the assembly.

as air cools, its capacity to hold water vapor diminishes. this leads to an increase in

relative humidity (even though the amount of water vapor is unchanged)

topside roof vents

release vapor pressure. usu mid insulation roofs

drainage components

removes water that runs off the membrane. roof drains, gutters, and downspouts

air barrier

restricts the leakage of air through the roof assembly

envelope

roofs + walls

If properly designed and located (on warm/humid/high pressure side), vapor retarder may

slow movement of moisture into the wall assembly, reducing likelihood of condensation occurring within the cavity.

thermal resistance units

square ft/ hour / degree F per BTU. (ft2-hr-F/BTU)

roof deck

structural surface the supports the roof

relative humidity

the amount of water vapor the air contains in proportion to the maximum amount of water that it can contain

Control of water vapor in building assemblies focuses primarily on

the flow of vapor from interior to exterior.

the more water vapor an air mass contains,

the greater the vapor pressure

the higher a material's R value,

the higher its resistance to heat flow and the better it thermally insulates

the more plies

the more durable the roof.

the higher the temperature of the air

the more water vapor it can contain

thermal insulation slows

the passage of heat into and out of the building

the thermal performance of a complete building assembly depends on

the sum of the thermal resistance of the materials from which it is made

vapor retarder is located toward

the warmer side of the insulation in a building assembly

thermal breaks will prevent

thermal bridging

a material's effectiveness in resisting the conduction of heat is called its

thermal resistance

Mechanical fasteners are favored by insurance companies because

they are more secure against wind uplift.

in humid regions, locate vapor retarder

toward the exterior side of insulation

vapor retarder is inexactly referred to as

vapor barrier

above the membrane, insulation also acts as a

vapor retarder

in low slope roof construction

vapor retarders are often made of adhered rubberized asphalt sheets or roofing felts layered in hot asphalt

preliminary consideration of envelope

water and thermal aspects

low slope roofs

water drains slowly leakage is big issue

a net difference in vapor pressure acting from inside to outside, causes

water vapor to diffuse outward directly through the various material layers of the enclosing assembly.

insulation below the deck

• Batt insulation of mineral fiber or glass fiber is installed either between framing members or on top of a suspended ceiling assembly. • Building code requires a ventilated airspace between insulation and underside of deck to dissipate excess water vapor. • In cold climates or when enclosing humid spaces, a vapor retarder is recommended on the warm, conditioned side of the roof insulation to control the diffusion of water vapor into the insulated portions of the roof where condensation could occur.

low slope roofs 3 categories

• Bituminous roof membranes • Single-ply roof membranes • Fluid-applied roof membranes

low slope roof advantages

• Can cover a building of any horizontal dimension, whereas a steep roof becomes uneconomically tall when used on a very broad building. • Much simpler geometries make them easier and less expensive to construct. • Can serve as balconies, decks, patios, landscaped gardens, or parks.

between deck insulation• In cold climates, two precautions may be taken:

• Install a vapor retarder below the insulation. • Provide ventilation within the insulation to allow the escape of moisture.

PMR must be made of

• Insulation must be made of a material that retains its insulating value when wet and does not decay or disintegrate: extruded polystyrene foam.

insulation above membrane- protected membrane roof lasts

• Lasts twice as long as an assembly where membrane is not shielded from sun. 38

insulation between the deck

• Traditional position for low-slope roof insulation. • Low-density rigid boards or lightweight concrete. • Insulation protects the deck from temperature extremes and is itself protected from the weather by the membrane. • Membrane remains exposed to extreme temperature variations. • Ventilation accomplished with topside vents, one per 1000 sf. These are most effective with l

Under summertime cooling conditions

Water vapor is driven from the warm, damp outside air toward cooler, drier airinside.

dry rooms have

a lower dew point. the air can be cooled to a lower temperature before it reaches saturation

installing extruded polystyrene foam insulation over a roof membrane creates

a protected membrane roof PMR

Rule of thumb: materials used on the opposite side of an assembly from a vapor retarder should have

a vapor permeance at least 10 times that of the vapor retarder itself.

for insulation-above-membrane roofs, the membrane also acts as

a vapor retarder

Lightweight insulating concrete is

an economical insulating material that also creates a nailable roof deck. It can be applied directly over corrugated steel decking or rough concrete decks and can be tapered during installation to slope towards roof drains.

flashing

at edges of membrane and wherever penetrated by pipes, vents, expansion joints, electrical conduits, or roof hatches. special flashings and details must be installed to prevent water penetration

Assemblies with multiple vapor-impermeable layers should be

avoided; they can trap moisture and provide no means for the moisture to escape.

two principal methods to create roof slope

beams sloped by varying column heights. deck is level and slope is created by layering thermal insulation of varying thicknesses on top.

concrete and masonry

both are pretty poor insulators

the BUR makeup

bottom to top: aggregate, rigid insulation boards, asphalt, felt, asphalt primer coat, concrete deck

protected membrane roof makeup

bottom to top: roof deck, membrane, polystyrene foam insulation, polymeric fabric that separates the ballast from the insulation, and the ballast

the opposite side of the vapor retarder (cooler side of the assembly) must be

breatheable, or designed so that any moisture that does find its way into the assembly can be dispersed through vapor parable materials

Rigid Insulating Materials for Low-Slope Roofs should have a high thermal resistance and resistance to

compression, denting, gouging, moisture, decay, and fire. If part of a hot-applied system, it should have a high resistance to melting or dissolving when hot bitumens are mopped onto it.

converting water vapor to liquid by cooling

condensation

vapor retarder is made of

continuous sheets or coatings of plastic, metal foil, coated paper, or other water vapor resistant material

between deck insulation• Any moisture that may accumulate in the insulation is trapped beneath the membrane, which can lead to

decay of the insulation and roof deck, as well as blistering and eventual rupture of the membrane.

the temperature at which the air is fully saturated with water vapor

dewpoint. relative humidity is 100%

steep roofs

drain quickly materials can be small overlapping units

benefits of small roofing units

easy to handle and install easy repair of localized damage thermal expansion and contraction and structural movements supporting the roof have minimized effects easy ventilation of water vapor

wood

has a higher thermal resistance, but not nearly has high as commonly used insulating materials

humid rooms have

high dew points. the air would not need to be cooled much before it reaches 100% humidity

Moisture will move from areas of

high pressure towards areas of lower pressure.

Warmer air = more moisture =

higher vapor pressure

dew points vary based on

humidity of air masses

roof membrane

impervious sheet material that keeps water out of building

rigid insulation boards are attached to a roof

in staggered layers to provide a firm, smooth base for application of the membrane. in cold climates, a vapor retarder should be installed between layers of insulation boards.

where heating conditions predominate, place vapor retarders toward

interior, heated side of the insulation in the assembly

when air is cooled below its dew point

it can no longer contain all its water vapor.

low slope roofs ratio

less than 2:12. 17 % slope. 2:12 rise:run

roofs can be organized into 2 groups

low slope roofs and steep roofs

Cooler air = less moisture =

lower vapor pressure

thermal insulation

material added to a building assembly to slow the conduction of heat through the assembly

rigid board material

may be adhered to the deck with hot asphalt or adhesives, or fastened to the deck mechanically with screws or any of a variety of fasteners.

loose-laid membrane

membrane is not adhered to the underlying surface

in mild or balanced climates,

might not need vapor retarder

low slope roofs membrane

must be watertight.

thermal bridging

occurs when a part or parts of a building envelope assembly with low thermal resistance penetrate the thermal barrier