Air Barrier Applications for Sealants and Adhesives
This is my second blog in the ASC Building Products series and will continue the theme set in blog #1...sealants and adhesives used to air seal the gaps and joints between the many installed building products used in construction. Buildings are complex structures that are often impossible to adequately completely seal on the external façade like a picnic ice chest with only the lid seal in question. These are the basics of building sealing for air leakage control…
- Seal the bottom of the wall
- Seal the wall roof connection
- Seal all wall, roof, and attic or roof penetrations e.g. conduit and pipes, windows and doors, chimneys and roof vents etc. (also see list below)
- Seal all gaps and joints in the exterior faced material or sheathing
- Seal the many air leakage paths that interconnect within wall or floor cavity, and under ceiling or within attic spaces. These paths are related to the routing of many utilities like HVAC, electric, plumbing, etc.
Obviously there are numerous adhesive and sealant products that are utilized in the above…elastomeric sealants, foam sealants, adhesive tapes and mastics. These products will enhance building energy performance and often fire safety as well.
Air infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors, windows, and numerous other penetrations in the building envelope/enclosure. Many associations have been involved in creating standards for testing and for setting desirable levels of air leakage in various building types. The Air barrier Association of America (AABA) has been a champion in education, standards creation, and certification in this area. ASHRAE has standards for commercial buildings. ASTM has developed numerous air leakage test methods for materials and assemblies. The Canadian Government Standards Board (CGSB) was early in promoting information on building air leakage. Other involved groups now include USGB and LEED, Oak Ridge BEP, Building Performance Institute, RESNET, the Canadian Construction Materials Council (CCMC), and our many building codes.
Air infiltration/exfiltration is caused by wind, building pressurization and by air movement forces known commonly as the “stack effect” wherein internal building pressure is negative at the bottom (sucking unconditioned air in) and higher at the top (expelling conditioned air out) creating an unintentional chimney effect for the building air flow. If you are standing by an elevator door in a tall building and hear a hissing sound this is the stack effect, DOE sponsored research has shown that up to 30% of the building energy costs can be saved by sealing air leaks around window and door frames, electrical outlets and switch covers, baseboards, plumbing and electrical penetrations, duct work and other vulnerable areas of the building. In addition, the building is more comfortable with less unpleasant drafts while building durability is enhances by reducing moisture condensation from unconditioned air on air conditioned wall, floor, and enclosed ceiling surfaces.
A typical high rise building offers many opportunities for air sealing. Some examples include the following:
- Roof/wall intersections (first illustration below)
- HVAC equipment
- Wall penetrations (second illustration)
- Roof penetrations
- Attic penetrations
- Interior and Exterior wall top/bottom plate penetrations to unconditioned spaces (third illustration below)
- Underground parking access doors
- Exhaust and air intake vents
- Soffits and ground floor access doors
- Service penetrations
- Inspection hatches
- Slab/wall intersections
- Stairwell fire doors
- Fire hose cabinets
- Elevator cable holes
- Elevator room doors
- Garbage chute perimeters and access hatches
- Hallway pressurization grille perimeters
- Elevator shaft smoke control grilles
- Vented mechanical rooms
- Garbage compactor rooms
- Door and window installation practice and trim and weather-stripping (forth and fifth illustration)
- Baseboard heaters (sixth illustration)
- Electrical receptacles on exterior and or interior walls.
Some common air-sealing products include many types of sealant but often latex or silicone caulk is used along with aerosol expanding foam products, and adhesive weather-stripping or tape. Exterior wall wraps called WRB (weather resistant barrier) are utilized and also require sealing adhesive tape at the joints. Insulated sheathing, used for air leakage control, will also require a butt joint/tong and grove joint seal-tape and/or a sealant or foam sealant to maintain air barrier continuity.
In the next blog I plan to describe the many air barrier standards that have been created, along with the specific test methods used. Also we will explore the issue of air barrier durability, and the codes being developed around this building performance issue. Indoor air quality will also be on the agenda as well.
I suggest you may want to also view this video related to building air leakage evaluation.