Chapter 3: Weatherization Materials
This chapter focuses on materials for insulation and air sealing. It begins by discussing the introductory information on air sealing and then air sealing materials, insulation building science, and insulation materials. This information supports the next four chapters on the major parts of the building shell.
Perform air leakage testing and evaluation before beginning air-sealing or duct-sealing work. Always evaluate ventilation and perform combustion-safety testing as a part of air sealing a home. See ASHRAE Standard 62.2–2016 Ventilation
Reducing air leakage accomplishes several goals.
• Saves energy by reducing unintentional air exchange with outdoors
• Reduces air leakage and convection around insulation, protecting its thermal resistance
• Aligns the air barrier with the thermal insulation.
• Increases comfort by reducing drafts and moderating the radiant temperature of interior surfaces
• Reduces moisture migration into building cavities
• Reduces the pathways by which fire spreads through a building
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SWS Detail:2.0401.1 Air Sealing Moisture Precautions, 2.0101.1 Air Sealing Worker Safety |
Air sealing reduces the exchange of fresh air in the home, and can alter the pressures within the home. Before air sealing, survey the home to identify both air pollutants that may be concentrated by air sealing efforts and open combustion appliances that may be affected by changes in house pressure.
Don’t do air sealing when there are obvious threats to the occupants’ health, the installers’ health, or the building’s durability that are related to air sealing. If any of the following circumstances are present, either postpone air sealing until they’re corrected or correct the problems as part of the air-sealing work.
• Measured carbon monoxide levels exceed the suggested action level. See Carbon Monoxide (CO) Testing
• Combustion zone depressurization exceeds the limits shown in SWS 2.0299.1 Combustion Appliance Depressurization Limits Table, or SWS Combustion Appliance Depres-surization Limits during a worst-case test. See Worst-Case CAZ Depressurization Test
• Occupants will use unvented space heaters as a primary source of heat after weatherization is completed.
• The air-leakage area has moisture damage, indicated by staining, mold or rot.
3.2.1 Air Sealing and Fire Containment
Fire, flame and smoke spread through the paths of least resistance. Many building assemblies harbor concealed voids or cavities within walls, ceilings and attics. During a fire, these pathways spread fire and make fire-fighting difficult.
In new buildings, the IRC requires builders to seal all shafts and hidden air leaks between living spaces and intermediate zones with fire-blocking materials.
The building codes define a fire-block as a material installed to “resist the free passage of flame through concealed spaces.” Fire-blocking materials don’t need to be non-combustible.
We recommend that you use rigid fire-blocking materials such as the following ones suggested in the IRC.
• Plywood, OSB or other wood sheeting (3/4 inch thick)
• Drywall (1/2 or 5/8 inch thick)
Air barriers must resist severe wind pressures. Use strong air barrier materials like structural wood paneling, drywall, or sheet metal to seal large air leaks, especially if your region has powerful winds. Attach these strong materials with mechanical fasteners and seal them with caulk or adhesive. If a technician needs to access a shaft or penetration in the future use a caulk that isn’t a strong adhesive, such as acrylic latex.
Use caulk by itself for sealing small cracks. Use liquid foam for cracks larger than 1/4 inch.
Air barrier materials should themselves be air barriers and also rated as fire blocks. See Table Table 12-1: .
Three-quarter-inch plywood, OSB, and particle board are IRC-approved fire-blocking materials, and they’re strong enough to resist windstorms. Attach these structural sheets with screws or nails along with any sealant or adhesive that effectively air seals the joint.
Half-inch drywall constitutes a 15 minute thermal barrier, and is also an ignition barrier. When air sealing a fire-rated assembly in a commercial or multi-family building, choose five-eighths -inch drywall and a fire-rated caulking. Fasten drywall with screws and construction adhesive. Don’t use drywall in damp locations where it may get wet.
Steel Sheet Metal
Being non-combustible, sheet metal is used to seal around chimneys and other heat producing components. To seal around chimneys, cut the galvanized steel accurately, with less than a 1/8-inch gap, so that you can seal the gap with high temperature, non combustible caulk labeled ASTM E136.
Foam board may be a desirable product for air sealing; however it has less structural strength and fire resistance than the other materials discussed previously.
Cross-Linked Polyethylene House Wrap
House wrap and polyethylene sheeting are air barriers. These flexible materials aren’t rated as fire-blocks, and they are structurally weak.
Stuffing materials are used to insulate a cavity, to give the cavity a bottom, or to serve as supporting part of an air seal.
Backer rod and caulking are the most reliable and long-lasting air seals. Backer rod is closed-cell polyethylene foam that creates a bottom barrier in a gap before caulking. Backer rod doesn’t bond to the caulking, and so prevents three-sided adhesion that could tear the caulking bead apart with the materials’ expansion and contraction of temperature extremes.
Fiberglass batts reduce air convection in cavities where they’re installed. However, fiberglass batts are air permeable, even if compressed. Batts can support two-part foam sprayed over the opening of a cavity. Fiberglass batting is a good stuffing material for use with non-combustible caulk for penetrations through fire-rated assemblies because of its low combustibility.
Blown cellulose and fiberglass reduce air convection and air leakage through closed cavities. However neither material is an air barrier even when blown at high densities. Both are considered fire-blocks when installed in closed cavities because they block the passage of flames.
The adhesion and durability of caulking and adhesives depends on their formulation and on the surfaces to which they’re applied. Some caulks and adhesives are sensitive to dirt and only work well on particular surfaces, while others are versatile and dirt-tolerant. Remove debris and clean the joint to prepare the surfaces for caulking.
Water-Based Caulks
A wide variety of paintable caulks are sold under the description of acrylic latex and vinyl. These are the most commonly used caulks and the easiest to apply and clean up. Siliconized latex caulks are among the most adhesive and durable sealants in this group. Don’t apply water-based caulks to building exteriors when rain is forecast since they aren’t waterproof until cured, and they stain nearby materials if they are rained upon while curing. Don’t apply water-based caulks during freezing weather.
Silicone has great flexibility, but its adhesion varies among different surfaces. Silicone is easy to gun even in cold weather. Silicone isn’t as easy to clean up as water based caulks, though it’s easier than polyurethane or butyl. Silicone isn’t paintable, so choose an appropriate color. High-temperature silicone may be used with galvanized steel to air seal around chimneys if labeled ASTM E136, meaning that the caulk is non-combustible.
Polyurethane has the best adhesion and elasticity of any common caulk. It works very well for cracks between different materials like brick and wood. Polyurethane resists abrasion and is used to seal critical joints in concrete slabs and walls. It is also good for sealing the fastening fins of windows to walls. Polyurethane is almost as sticky and adhesive as a construction adhesive. Cleaning it up is difficult so neat workmanship is essential. Polyurethane caulk doesn’t gun easily, and should be room temperature or higher. Polyurethane caulk doesn’t hold paint.
This solvent-based or water-based adhesive is used to seal laps in polyethylene film and house wrap. Acoustical sealant is very sticky, adheres well to most construction materials, and remains flexible. Acoustical sealant is used to seal building assembles for sound deadening. Acoustical sealant is also used to seal the seams of polyethylene vapor barriers and ground moisture barriers.
Water Soluble Duct Mastic
Duct mastic is the best material for sealing ducts, including cavities used for return ducts. A messy but highly effective sealant, duct mastic can be applied with a thickness of 1/8-inch with a brush or rubber glove. Have a bucket of warm water handy to clean your gloved hands and a rag to dry the gloves. Spread the mastic and use fiberglass fabric web tape to reinforce cracks more than 1/8-inch in diameter. Thorough cleaning of dust and loose material isn’t necessary. Mastic bonds tenaciously to everything, including skin and clothing.
Stove cement is a material that can withstand temperatures up to 2000° F. It is used to seal wood stove chimneys and to cement wood stove door gaskets in place.
Some elastomeric caulks are designed specifically for use in fire-rated assemblies. They are labeled ASTM E136, meaning that the caulk is non-combustible. Use this type of sealant when sealing penetrations through fire-rated assemblies in multifamily buildings.
Fire-Rated Mortar
Used with other air-sealing materials to seal various sized holes and gaps in multifamily buildings with fire-rated masonry building assemblies. This mortar often covers a foam air sealant to create a non-combustible surface for an combustible air seal.
Construction adhesives are designed primarily to bond materials together. But they also create an air seal if applied continuously around the perimeter of a rigid material. They are often used with fasteners like screws or nails but can also be used by themselves. Some construction adhesives act like contact adhesives to bond lightweight materials without mechanical fasteners.
Use specially designed construction adhesives for polystyrene foam insulation because many general-purpose adhesives decompose the foam’s surface.
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SWS Detail: 4.9901.1 General Information on Spray Polyurethane Foam (SPF), 4.1401.1 Band/Rim Joists—Spray Polyurethane Foam (SPF) Installation, |
Liquid closed-cell polyurethane foam is a versatile air sealing material. Closed-cell foam is packaged in a one-part injectable variety and a two-part sprayable variety. It has a high R-value per inch and is ideal for insulating and air sealing small, poorly insulated, and leaky areas in a single application.
Installation is easy compared to other materials to accomplish the same air sealing tasks. However, cleanup is difficult enough that you probably don’t want to clean up multiple times on the same job. Instead identify all the spots needing foam application, make a list, and foam them one after another.
This gap filler has tenacious adhesion. One-part foam is best applied with a foam gun rather than the disposable cans. Cleanup is difficult if you’re careless. When squirted skillfully into gaps, one-part foam reduces air leakage, thermal bridging, and air convection. One-part foam isn’t effective or easy to apply to gaps over about one inch or to bottomless gaps. This product can leave small air leaks because it cracks when the materials around it move or shift.
Good for bridging gaps larger than one inch. Two-part foam is popular for use with rigid patching materials to seal large openings. Cut foam board to close-enough tolerances around obstacles and fill the edges with the two-part foam. Two-part foam should be sprayed to at least an inch of thickness when it serves as an adhesive for foamboard patches over large holes for strength.
Foam Construction Adhesive
Polyurethane foam dispensed from foam guns is an excellent adhesive for joining many kinds of building materials. It works well for joining foam sheets together into thick slabs for vertical access doors and attic hatches.
Caution: Two-part foam is hazardous to installers and building occupants. Installers must wear special personal protective equipment and ventilate spaces during installation to avoid lung, skin, and eye damage. SPF can harm occupants who breathe the toxic vapors during installation. SPF requires precise mixing of the two components at specific temperature ranges. Improperly mixed or installed spray foam can emit vapors for months or years resulting in long-term respiratory hazards.
3.4 Insulation Building Science
Insulation reduces heat transmission by resisting the conduction, convection, and radiation of heat through the building shell. Insulation combined with an air barrier creates the thermal envelope between the conditioned indoors and outdoors.
Installing insulation is one of the most effective energy-saving measures. You can ensure insulation’s safety and effectiveness by following these guidelines.
✓ Install insulation in a way that enhances fire safety and doesn’t degrade it. See Safety Preparations for Attic Insulation
✓ Comply with lead-safe practices when disturbing paint in pre-1978 homes. See Lead-Safe Work Practices
✓ Prevent air movement through and around the insulation with an effective air barrier. Make sure that the air barrier and insulation are aligned (next to one another) using procedures outlined starting on here.
✓ Protect insulation from moisture by repairing roof and siding leaks, providing site drainage, and by controlling vapor sources within the home. See Solutions for Moisture Problems
✓ Install insulation to meet or exceed the guidelines of the International Energy Conservation Code (IECC) 2012 and the DOE’s Standardized Work Specifications.
3.4.1 Insulation Receipt or Certificate
Provide each client, receiving insulation products and services, a printed and signed receipt or certificate that includes the following information.
• Insulation type
• Coverage area
• Number of bags installed
• R-value
• Installed thickness and settled thickness
• Amount of insulation installed according to manufacturer’s specifications
3.5 Insulation Material Characteristics
The purpose of insulation is to provide thermal resistance that reduces the rate of heat transmission through building assemblies. Characteristics such as R-value per inch, density, fire safety, vapor permeability, and airflow resistance help weatherization specialists choose the right insulation for the job.
3.5.1 Fibrous Insulation Materials
Fibrous insulation materials are the most economical insulations for buildings. If blown at a high density, fibrous insulations aren’t air barriers themselves, but they may contribute to the airflow resistance of a building assembly that functions as an air barrier. The term mineral wool describes both fiberglass and rock wool. Rock wool is both a generic term and a trade name. We use rock wool in the generic sense as an insulating wool spun from rocks or slag. Fiberglass is wool spun from molten glass.
Cellulose was once made from virgin wood fiber under trade names like Balsam Wool. Now cellulose is manufactured primarily from recycled paper, treated with a fire retardant.
A vapor permeable air barrier should cover fibrous insulation installed vertically or horizontally in human-contact areas to limit exposure to fibers, which may cause respiratory distress.
Most fiberglass batts are either 15 inches wide or 23 inches wide to fit 16-inch or 24-inch spacing for wood studs or joists. However, manufacturers also provide 16-inch or 24-inch widths for metal stud construction.
The advertised R-values of batts vary from 3.1 per inch to 4.2 per inch depending on density. Installed fiberglass R-values may be 5% to 30% less than advertised depending on installation quality and the effectiveness of the assembly’s air barrier.
Installers must cut and fit batts very carefully. Batts achieve their advertised R-value only when they are touching all six sides of the cavity it inhabits.
See Open-Cavity Wall Insulation
Fiberglass blankets are typically three to six feet wide. Blankets come in a variety of thicknesses from 1 to 6 inches. Fiberglass blankets are used to insulate metal buildings, to insulate crawl spaces from the inside, and to insulate water heaters.
Although fiberglass doesn’t absorb much moisture, the facings on blankets and batts can trap water in the batts, which can dampen building materials and provide a water source for pests.
Facings for Fiberglass Batts
Insulation manufacturers make batts and blankets with a number of facings, including the following.
• Unfaced: Vapor permeable and Class-A fire rating of ≤25 flame spread.
• Kraft paper: A Class II vapor retarder that is flammable (Class-C or Class 3) with a flame spread ≥150.
• Foil-kraft: foil bonded to kraft paper. A vapor barrier with a flame spread of >75 (Class-C or Class 3).
• Foil-skrim-kraft (FSK): Aluminum foil bonded to kraft paper with skrim netting in-between as reinforcement. A vapor barrier available as a Class-A material with a flame spread of ≤25.
• White poly-skrim-kraft (PSK): White polyvinylchloride bonded to kraft paper with skrim netting in-between as reinforcement. A vapor barrier available as a Class A fire-rated material with a flame spread of ≤25. The white surface maximizes light reflection.
Blown Fiberglass
Loose fiberglass is blown in attics from 0.3 to 0.8 pcf and at that density range, the R-value is around 2.9 per inch. Expect around 5% settling within five years after installation.
Blown fiberglass is non-combustible as a virgin product. However, some blown fiberglass is made from chopped batt waste that contains a small amount of combustible binder.
Fiberglass manufacturers now provide two blowing products, one for standard densities of up to about 1.4 pcf, and another for dense-packing to more than 2.0 pcf.
In closed cavities, installers blow fiberglass from 1.2 to 2.2 pcf, with the R-value per inch varying from 3.6 to 4.2. Higher density achieves a higher R-value. The high-density fiberglass is typically reserved for walls where the superior resistance to settling, airflow, and convection has extra value over lesser density.
Blown Cellulose
Cellulose is the most inexpensive insulation and among the easiest insulations to install. Loose cellulose is blown in attics from 1.5 to 2.0 pounds pcf and at that density range, the R-value is around 3.7 per inch. Expect around 15% settling within five years after installation.
In wall cavities, cellulose is blown at a higher density of between 3.5 to 4.0 pcf, to prevent settling and to maximize its airflow resistance. At that high density, cellulose’s R-value per inch is around 3.4. Evaluate the strength of wall cladding before blowing a wall with cellulose to prevent damage during installation.
Cellulose absorbs up to 130% of its own weight in water. Before anyone discovers a moisture problem, the cellulose could be soaked, shrunken, double its dry weight, and far less thermally resistant. Avoid using cellulose in regions with an annual average precipitation of more than 50 inches or an annual average relative humidity of more than 70%. Cellulose shouldn’t be installed in the following places regardless of climate.
• Floor cavities above crawl spaces or unconditioned basements
• Crawl space walls or basement walls
Rock Wool
Rock wool is a type of mineral wool like fiberglass. Rock wool has a small market share in North America. Rock wool batts have similar R-values per inch as fiberglass batts and contain flammable binders. Rock wool itself is non-combustible so blown rock wool doesn’t burn.
Rock wool is also the most moisture-resistant insulation discussed here. In rainy and humid climates, rock wool is the least likely insulation to harbor moisture or support pests.
Damp Spray Fibrous Insulation
Installers mix fibrous insulation with sprayed water and a small amount of adhesive in damp-spray applications either in open cavities or directly adhered to building surfaces. Sprayed cellulose contains a non-corrosive fire retardant to prevent metal corrosion when used in contact with metal building components.
3.5.2 Operating the Insulation Blowing Machines
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SWS Detail: 4.1001.5 Dense Pack Preparation, 4.1088.7 Insulating Inaccessible Attics |
Perform these important steps before and during insulation-blowing.
✓ Verify that the electrical source can provide the ampere draw of the insulation machine.
✓ Measure the pressure created by a blowing machine by connecting the hose to a fitting attached to a manometer. Close the feed gate and turn the air to the highest setting. For cellulose, the blowing machine should develop 2.9 pounds per square inch (psi) or 80 inches of water (IWC) For other types of fibrous insulation, check manufacturer specifications for blowing machine set up.
✓ Verify that you’re blowing the correct density of fibrous insulation by using the bag’s weight or the manufacturer’s coverage tables.
Important Note: Dense-packed fibrous insulation can reduce air leakage and convection in closed building cavities. However, don’t use dense-packed fibrous as a substitute for the air-sealing techniques described throughout this guide.
3.5.3 Spray Foam Insulation Materials
Spray Polyurethane Foam (SPF) is combustible and creates toxic smoke. Foam insulation usually requires covering with a thermal barrier or an ignition barrier, discussed inFire Protection for Foam Insulation. SPF comes in two formulations: closed-cell and open-cell. Both are described below.
Spray foam is an insect-friendly material that can aid termites and carpenter ants in establishing a colony in wood structures. Mitigate all sources of ground water before installing foam near a foundation. When foam is installed on the outside of foundations, the surrounding soil should be treated with a termiticide if necessary. Inside a crawl space, foam must never provide a direct link from the ground to wood materials. The International Residential Code (IRC) forbids foam below grade in “very heavy” termite-colonized areas.
Caution: Two-part foam is hazardous to installers and building occupants. Installers must wear special personal protective equipment and ventilate spaces during installation to avoid lung, skin, and eye damage. SPF can harm occupants who breathe the toxic vapors during installation. SPF requires precise mixing of the two components at specific temperature ranges. Improperly mixed or installed spray foam can emit vapors for months or years resulting in long-term respiratory hazards.
Closed-Cell Spray Polyurethane Foam
Closed-cell polyurethane spray foam (SPF) is an air barrier and a vapor barrier and is the most expensive insulation discussed here. Closed-cell SPF is a good value when space is limited, where an air or vapor barrier is needed, or where its structural strength and durability are needed.
Spray foam professionals install closed-cell SPF from two 55-gallon containers through hoses and a nozzle that mix the material. The closed-cell foam installs at approximately 2 pcf density and achieves an R-value of 6 or more per inch. However, roofing applications call for a density near 3 pcf.
Closed-cell polyurethane foam is also packaged in smaller containers in the following products.
• One-part high-expanding foam for air sealing.
• One-part low-expanding foam for air sealing.
• Two-part high-expanding foam for air sealing and insulation of surfaces.
Open-Cell Polyurethane Spray Foam and Injectable Foam
Polyurethane open-cell foam is installed at between 0.5 pcf to 1.0 pcf and achieves an R-value of around 3.7 per inch to 4.7 per inch depending on density.
These open-cell formulations are injected into a hole, one inch or smaller, through an injection nozzle and not a fill tube. (The plastic fill tube would clog and isn’t cleanable.) The open-cell foam can subject a wall cavity to some pressure, so evaluate wall-cladding strength before injecting it.
Open-cell foam can absorb both water vapor and liquid water. Open-cell foam can hold moisture and become a medium for mold growth. We recommend that contractors don’t install low-density spray foam in the following locations.
• Underside of roof decking
• Underside of floor decking above crawl spaces
• Crawl space walls
3.5.4 Special Safety Precautions for Spray Foam
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SWS Detail: 4.1003.7 Ignition and Thermal Barriers—Spray Polyurethane Foam |
Two-part foam is hazardous to installers and building occupants. SPF can harm occupants who breathe the toxic vapors during installation. SPF requires precise mixing of the two components at specific temperature ranges. Improperly mixed or installed spray foam can emit vapors for months or years resulting in long-term respiratory hazards.
Installers must wear special personal protective equipment and ventilate spaces during installation to avoid lung, skin, and eye damage.
Consider essential these precautions for spraying foam safely.
1. Ask the occupants to leave while you spray foam for as long as a day. Power ventilate the area during installation and for at least 24 hours afterwards.
2. When spraying low-pressure polyurethane foam — either 1-part or 2-part — use a respirator cartridge designed to filter organic vapors, and ventilate the area where you’re spraying the foam.
3. You must complete training, including safety training, before spraying high-pressure 2-part foam.
4. When spraying high-pressure polyurethane foam from a truck-mounted machine, use a supplied-air, positive-pressure respirator, and ventilate the area.
3.5.5 Fire Protection for Foam Insulation
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SWS Detail: 4.1003.7 Ignition and Thermal Barriers—Spray Polyurethane Foam |
Plastic foam is the generic term used by the IRC for both rigid and spray foams. Plastic foams are combustible, and create toxic smoke when they burn.
The following fire-safety and durability issues are particularly important to installing foam insulation.
• Foam insulation requires a thermal barrier covering when installed in a living space, which might include a basement or other unfinished area. Half-inch drywall and other materials qualify as a thermal barrier.
• Foam may require an ignition barrier when installed in attics or crawl spaces or it may not.
• A thermal barrier is a material, usually drywall, that protects combustible materials behind it from heat and flame creating a fire. Intumescent paint is a proprietary latex coating that may qualify as a thermal barrier.
• An ignition barrier is designed to delay the ignition of the material it protects. Ignition barriers include plywood, galvanized steel, damp-spray fiberglass, and intumescent paint. Intumescent paint is a proprietary latex coating designed to delay the ignition of foam insulation in a fire.
The IRC requires a thermal barrier for spray foam in all living areas and storage areas. Instead of a thermal barrier, installers may use an ignition barrier (1.5 inches of fibrous insulation or intumescent paint) to cover foam in attics and crawl spaces that aren’t used for storage.
Fire protection requirements vary among foam formulations, according to the amount and type of fire retardant. Foam insulations generally fit into one of two classifications.
• Class I or Class A; ≤25 flame spread
• Class II or Class B; flame spread 26-75
If a foam product has a flame spread of 25 or less (Class I), it may require no thermal barrier or ignition barrier. If a foam product has a flame spread of more than 25, further testing may qualify it for exemption from the thermal barrier or ignition barrier requirements of the IRC.
Code jurisdictions and individual building officials vary in their interpretation of the IRC depending on these three factors.
1. Foam manufacturer’s fire-testing reports.
2. The possibility that residents might use an attic or unoccupied basement for storage or even living space.
3. The possibility that no one may ever enter the space again except for maintenance.
Foam board is combustible and creates toxic smoke if it burns. Foam insulation usually requires covering with a thermal barrier or an ignition barrier, discussed inFire Protection for Foam Insulation.
Foam board, although not an insect food, is an insect-friendly material that can aid termites in establishing colonies in wood structures. Mitigate all sources of ground water before installing foam near a foundation. When foam is installed on the outside of foundations, the surrounding soil should be treated with a termiticide. Inside a crawl space, foam must never provide a direct link from the ground to wood materials where termites or carpenter ants are common. The IRC forbids foam below grade in “very heavy” termite-colonized regions; the foam must be kept 6 inches above grade.
Expanded Polystyrene (EPS) Foam Board
EPS foam board, sometimes called beadboard, is the most inexpensive of the foam insulations. EPS varies in density from 1 to 2 pcf with R-values per inch of 3.9 to 4.7, increasing with increasing density. EPS is packaged in a wide variety of products by local manufacturers. Products include structural insulated panels (SIPS), tapered flat-roof insulation, EPS bonded to drywall, and EPS embedded with fastening strips.
EPS is flammable and produces toxic smoke when burned. It has a low maximum operating temperature (160 degrees F) that is a concern for using EPS under dark-colored roofing or siding. EPS has shrunken in some installations.
EPS is very moisture resistant and its vapor permeability is similar to masonry materials, which makes EPS a good insulation for masonry walls.
Dense EPS (2 pcf) is appropriate for use on flat roofs and below grade. Dense EPS is also more dimensionally stable and less likely to shrink. Use weatherproof coverings to prevent degradation by ultraviolet light and freezing and thawing at ground level.
Extruded Polystyrene (XPS) Foam Board
XPS is produced by only a few manufacturers and is popular for below-grade applications. XPS is more expensive than EPS and has an R-value of 5.0 per inch. XPS may be the most moisture-resistant of the foam boards.
XPS is flammable and produces toxic smoke when burned. XPS must be covered by a thermal barrier when installed in living spaces. XPS has a low maximum operating temperature (160 degrees F) that is a concern for using XPS under shingles or dark-colored siding. XPS has shrunken in some installations. Use weatherproof coverings to prevent degradation by ultraviolet light and freezing and thawing at ground level.
Polyisocyanurate (PIC) Foam Board
PIC board has the highest R-value per inch (R-6 or a little more) of any common foam board. PIC is packaged with a vapor permeable facing or an aluminum-foil (vapor barrier) facing. PIC is expensive but worth the cost when the thickness of insulation is limited.
PIC is combustible and produces toxic smoke during a fire. However some products have fire retardants that allow installation in attics and crawl spaces without a thermal barrier or ignition barrier.
PIC has a low maximum operating temperature (<200 degrees F) that may be a concern for using PIC under dark-colored roofing or siding. Use the high-density (3 pcf) PIC board for low-sloping roof insulation.
Polystyrene (EPS) beads can be poured or blown into cavities. The cavities must be airtight or the beads will escape, making an annoying mess. EPS beads have an R-value between 2.2 and 2.5 per inch. Beads work well for filling hollow masonry walls.
These expanded minerals are pour-able and used when a non-combustible insulation or high temperature insulation is needed. R-value per inch is between 2.0 and 2.7 per inch. These products are good for insulation around single-wall chimney liners to prevent condensation in the liner. Existing vermiculite may contain asbestos, and it must not be disturbed by anyone except a licensed asbestos abatement specialist.
3.6 Insulation Safety and Durability
Insulation activities require awareness about safety. Reference the following safety-related sections of this guide if necessary.
✓ See Asbestos Containing Materials (ACM)
✓ See
Moisture is the most common and severe durability problem in insulated building assemblies. Moisture fosters rot by insects and microbes. Entrained moisture reduces the thermal resistance of many insulation materials. Moisture affects the chemistry of some building materials: metals for example.
Moisture prevention includes denying moisture access to building cavities, allowing condensed water to drain out, and allowing moisture to dry to the indoors, outdoors, or both.
Retrofitting insulation can affect the preventive measures listed here. Consider the function and relevance of these building components whenever you install insulation.
• Air barrier: Air can carry moisture into building cavities from indoors or outdoors where the moisture can condense and dampen insulation and other building materials. Air leakage is an energy problem too. The air barrier is any continuous material or building assembly that provides acceptable resistance to air leakage.
• Vapor retarder: Vapor diffusion can carry large amounts of water vapor into building cavities where it can condense and dampen insulation and other building materials. Vapor retarders resist water vapor diffusion from indoors into cavities where condensation can dampen insulation and other building materials. A vapor retarder has a perm rating between 1.0 and 10.
• Vapor barrier: A very effective vapor retarder. A vapor retarder with a perm rating of less than 0.1 perms.
• Ground-moisture barrier: The ground under a building is the most potent source of moisture in many buildings, especially those built on crawl spaces. Most crawl spaces require ground-moisture barriers to prevent the ground from being a major cause of moisture problems.
• Water resistive barrier (WRB): Asphalt paper or house wrap, under siding and roofing, serves as the home’s last defense to wind-driven rain, which can dampen sheathing and other building materials. This water resistive barrier must be protected during insulation and incorporated into window openings during window replacement.
• Vapor permeable materials: Most common building materials are permeable to water vapor, which allows the water vapor to follow a gradient from wet to dry. This process allows building assembles to dry out to both indoors and outdoors. Vapor permeable materials are essential for fail-safe building assemblies in most climates.
• Flashings: Seams and penetrations in building assemblies are protected by flashings, which prevent water from entering these vulnerable areas.
• Drainage features: Intentional or unintentional drainage features of buildings allow water to drain out of cavities. Examples: Masonry veneers have intentional drainage planes and weep openings near their bottoms. Cathedral ceilings drain water out through their soffit vents unintentionally.
• Water storage: Masonry veneers and structural masonry walls have the ability to store rainwater and dry out during dry weather.
• Ventilation: Roofs, attics, crawl spaces and even some walls have ventilation features that dry out wet building assemblies.
• Termiticide: When foam insulation is installed below grade in regions with termites, apply a termiticide to the soil in amounts determined by the labeling of the termiticide.
Consult with experts when necessary to preserve, protect, or install these moisture-prevention features, according to local climate and established best practices.