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	Insulation

	Air-barrier materials

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Air-Barrier Materials

Requirements for Air-Barrier Systems

The air-barrier system is an important part of any retrofit job. It is the main means of protecting the building structure and the insulation from moisture damage. In order to be effective, the air-barrier system must be:

resistant to air movement
continuous, completely surrounding the envelope of the house and properly supported by rigid surfaces on both the interior and exterior (to prevent movement in high winds)
strong and durable

A variety of materials are used throughout the envelope to act as the air barrier. In some cases, building materials such as drywall, baseboards or structural members are incorporated into the air barrier by sealing them to adjoining materials.

Air-Barrier System Components

The most common components of an air-barrier system are:

sheet or rigid materials for large surfaces
caulking and gaskets for joints between materials that do not move
weatherstripping for joints that do move

Choosing Air-Barrier Materials

If the material offers resistance to airflow, strength and durability, consider the following installation factors:

Is it easy to install?
If installed in a concealed location, will it last the life of the building or will it be accessible and easily repaired?
Is it compatible with other materials in the system? Can it be successfully sealed to adjacent materials?
Is the choice of material appropriate for the other work being done on the home? Some renovation work will permit the installation of a new sheet-material air barrier, while other jobs may require comprehensive air-sealing work instead.
Does it serve other functions such as acting as insulation or as a vapour barrier?

Sheet Materials

Polyethylene Sheeting

Available in wide sheets, minimizing the number of seams required.
Seams and edges should be supported on both sides to maintain the seal.
A thickness of 0.15 mm (6 mil) now commonly installed as an air barrier because it is more durable on the construction site.
Should be protected from exposure to sunlight. When exposed to sunlight over extended periods (when wrapping the exterior of a house, for example), a UV-stabilized polyethylene should be used.
Should be clear, made from virgin material and labelled. Should conform to the Canadian General Standards Board standard for polyethylene.
Can also function as a vapour barrier.

Caution: Exterior products should not be used indoors – they may be hazardous when their volatiles are inhaled in a confined space over an extended period of time. Check the manufacturer's literature carefully.

Housewrap

Available in wide sheets, minimizing the number of seams required.
Acts solely as an air barrier; does not function as a vapour barrier.
Generally used to wrap the exterior of a house; often bonded to exterior glass-fibre sheathing.
When installed on the exterior, acts as a wind barrier, preventing wind from reducing the effective RSI value of insulation.
Should be protected from extended exposure to sunlight.

Rigid Materials

Most solid building components will act as barriers to air. These components include drywall, plaster, plywood, glass, wood and poured concrete (not concrete blocks). Insulating materials such as rigid foam boards also act as air barriers. To be effective, however, the seams between these various materials must be sealed with the appropriate caulking, weatherstripping or gasket. For example, caulking can be used between the baseboard and a wall as well as between the baseboard and the floor, linking the air-sealing qualities of three different building components. The combination of rigid air-barrier materials forms the house's air-barrier system as long as the joints are well sealed.

Sealants

Make sure that the caulking you use is compatible with the surfaces you are applying it to.

Caulkings are not permanent and will have to be maintained. They also vary in durability, compatibility with other materials, suitability for painting and curing time. All sealants will require some extra ventilation of the house after application to let the material cure. Typical curing time will be no more than two or three days for interior applications.

Acoustical Sealant

Bonds to most surfaces; excellent for use on metal, concrete and gypsum board.
Excellent for sealing the joints in polyethylene air and vapour barriers, but should be used only where it is sandwiched between two materials.
Mechanical support (e.g., staples) required when acoustical sealant is used to seal the joints in polyethylene.
Maximum joint width of 16 mm (3/8 in.); accepts some joint movement (10 percent).
Very durable (20-year life expectancy).
Non-hardening and not paintable; use should be limited to unexposed applications.

Acrylic Latex

A water-based emulsion sealant.
Excellent for non-porous surfaces such as aluminum, glass and ceramic tile, but may be used to seal joints with wood surfaces.
Maximum joint width of 10 mm (3/8 in.); limit use to joints where little or no movement is expected
Durable (10-year life expectancy).
Available in a wide range of colours; paintable.
Can attract dust over time, especially when used next to floors.

Butyl Rubber

A synthetic rubber sealant.
Bonds to most surfaces; particularly suited to metal and masonry.
Appropriate for a joint width up to 13 mm (½ in.); accepts some movement of joint (5 to 10 percent).
Durable (10-year life expectancy).
Available in a variety of colours; paintable after one week's curing.
Ventilation required during application and curing (up to three days).

Silicone Sealant

Solvent-free silicone compound; produces a flexible, watertight seal upon curing.
Good adhesion to most surfaces; primers may be required on wood, steel or anodized aluminum.
Excellent for large moving joints: up to 25 mm (1 in.) joint width and 12 to 50 percent joint movement.
Highly durable (over 20-year life expectancy).
Most types not paintable.
Available in several colours and clear; clear silicone is particularly suited for sealing highly visible joints where the caulking should not be noticeable.
Ventilation required during application and curing.

Polysulphide Sealant

Produces a flexible sealant upon curing.
Ideally suited for use on stone, masonry and concrete surfaces when used with a special primer.
Maximum joint width of 25 mm (1 in.); will accept joint movement of 12 to 25 percent.
Excellent durability (over 25-year life expectancy).
Available in several colours; paintable.
Ventilation required to remove potentially toxic vapours.

Urethane Foam Sealant

Available in a dispensing system with spray nozzles or individual aerosol spray cans.
Foam types are available with different rates of expansion depending on ingredients and the amount of pre-curing. Check the cans carefully for details on sizes of cracks that can be filled. Some types expand slowly and moderately; others expand quickly and greatly. Use gloves and a drop cloth.
Bonds well to most surfaces except polyethylene, Teflon or silicone plastics.
Very good for filling larger joints and cavities where conventional sealant materials would not be suitable (i.e., header/joist intersections and around plumbing and vent openings).
Should not be used at window headers since it can transfer structural loads if the wall settles.
Good durability (10- to 20-year life expectancy).
Like all insulating foams, must be covered with a fire-resistant material.
Ventilation required to remove potentially toxic vapours.

High-Temperature Stove or Muffler Cements

For use in areas where there are high temperatures but no joint movement.
Typically used in conjunction with other materials for sealing around masonry or factory-built chimneys.

Gaskets

Several specialty gaskets have been developed for sealing joints where caulking may not be appropriate.

Sill Plate Gasket

Polyethylene foam strips.
Installed between the foundation and sill plate during construction or where existing house walls meet a new addition.
Available in widths of 152 mm and 203 mm (6 in. and 8 in.) on 24 m (79-ft.) rolls.

Outlet Gasket.

Electrical Outlet and Lighting Fixture Gaskets

Foam gaskets are designed to fit behind the cover plates of electrical receptacles, switches and lighting mounts, reducing air leakage into walls and attics.
Electrical outlet gaskets are more effective when caulked and should be used in conjunction with child-safety plugs to reduce air leakage through electrical sockets.

Foam Backer Rod

Closed-cell compressible foam "rope."
Excellent for filling deep gaps before caulking.
Available in diameters of 6 to 51 mm (¼ to 2 in.).

Foam backer rod.

Neoprene Gasket

Flexible and very durable.
Excellent for sealing joints and penetrations where movement is to be expected, such as plumbing stacks.

Weatherstripping

Weatherstripping.

Weatherstripping is used to block air leakage around doors and the operable parts of windows. Weatherstripping comes in a variety of shapes; it can be a flat strip, tube or "V" shape and can be designed to work under compression or by sliding along the joint. To be effective, the product must close the gap and not allow air to pass.

When choosing weatherstripping, consider the size of the gap to be sealed and the durability, ease of installation and appearance of the product. Look for products that are flexible and that spring back to their original shape quickly and easily. Avoid products that make it difficult to operate the window or door.

Compression Strips

Use compression strips where there is a pressure stress, such as at the bottom of vertical sliding windows, along attic hatches or on hinged windows and doors.

Closed-Cell Foam

An adhesive-backed foam stripping available in rolls.
Easy to install.
Available as a high-performance compressible polyurethane strip with its own carrier.

Ribbed Closed-Cell Rubber

An adhesive-backed stripping available in rolls.
Very durable; easy to install.
Good for irregular surfaces but less appropriate for accommodating long or varied gap widths.

Tubular Stripping

Tubular material made with either its own attachment area or on an attachment strip of a different material.
Rubber type (as opposed to plastic) should be used because it is more durable.
Generally used as a window or door weatherstrip; installed with nails, staples or screws, depending on the type of attachment strip.
Highly noticeable when installed.

Tension Strips

Spring Vinyl

Can be used in the same applications as compression strips as well as in sliding joints in double-hung windows and doors.
Adhesive-backed; easy to install.
Two types available:
- small-format "V" strip for narrow gaps, such as tight-fitting double-hung windows
- large format for wide gaps, such as loose windows and doors
Good durability; polypropylene type should be chosen over other plastics.

Spring Metal

Generally used as a door weatherstrip; most effective when under light compression.
Installed using small tacks.
Metal can permanently deform.

Combination Types

Spring-Loaded/Self-Adjusting Weatherstripping

Uses a spring mechanism that allows it to adapt to unequal distances from the weatherstrip to the door or window.
Effective for doors and hinged windows.
Installed with screws through an attachment strip.
Can be used in conjunction with" V" strips.

Magnetic-Strip Systems

Magnetic attraction between a magnetic strip mounted on the door/window frame and a metal strip mounted on the door/window provides the seal.
Effective for doors and hinged windows in moderate climatic conditions.
May not provide good seal in cold temperatures due to condensation and frost formation (the vinyl case may stiffen and split).
Good durability; highly noticeable when installed.

Door Bottoms, Sweeps and Thresholds

The bottoms of doors can be sealed using a number of systems: door sweeps, door thresholds and door bottoms. Door bottoms and sweeps are usually more durable than thresholds, although they often provide a less effective seal.

Door Sweeps

A vinyl pile or rubber sweep.
Screwed via attachment strip to door bottom.
Effective where a carpet has a low pile or is absent altogether.

Partial Threshold

A vinyl or rubber strip, attached to the door threshold.
Provides an excellent seal.
Can become damaged by traffic and weathering.

Full Threshold

A combination strip, attached to threshold.
Requires at least 16 mm (5/8 in.) clearance below the door to be effective.

Door Bottoms

Combination strips of vinyl pile or compressible rubber.
Attachment strip fits over door bottom.
Requires a clearance of 8 to 13 mm (1/3 to 1/2 in.) under door.

Taping air ducts.

Tape

Duct Tape

Vinyl and foil tapes can be used to seal around the seams of heating ductwork to reduce air leakage, especially where ducting passes through unheated areas of the house.

Sheathing Tape

Available for sealing the seams of housewrap wind-barrier material and polyethylene air-barrier material.

Other Items

Electrical box.

Plastic boxes are placed around electrical outlet and switch boxes before installation.
Equipped with a flange for sealing to the main air barrier.
Also act as vapour barriers.