Eragorn Northe

Attic Insulation
The attic is often the most cost-effective place to add insulation. Usually, a contractor blows loose fill into and over the top of ceiling joists. For the do-it-yourselfer, batts laid sideways on existing insulation are an easy alternative.

• The air barrier at the ceiling line must be tight to ensure warm moist air from the house does not get into the cold attic and condense in the winter. Check ceiling light fixtures, the tops of interior walls and penetrations such as plumbing stacks for air leakage.
• Ensure that soffit venting is not blocked by added insulation; baffles may have to be installed.

Wall Insulation for Existing Construction

The two most common wall types are wood-frame and solid brick. In a wood-frame wall, insulation (loose fill and some foams) is typically blown into the cavities through holes that have been drilled through the drywall or siding. In solid brick, the largest cavity is usually 25 mm (1 in.) wide, which is not enough for any significant increase in R value. The builder must create a cavity. Usually, a new cavity wall is built inside and insulated as a new wall, or board stock and new siding are applied to the exterior. When planning a cavity wall retrofit, remember the following:

• The cost of getting at and repairing the walls is a significant part of the work and cost of the project.
• Both air and vapour barriers are required. The interior painted drywall can be both an air and vapour barrier, but details at windows, electrical outlets, floors and other penetrations must be done carefully to reduce air movement through the wall as much as possible. Air movement can lead to mold growth and decay of the walls, as well as loss of insulation efficiency.
• An insulation must be selected that will completely fill the cavity and not settle. Some insulations, such as foams, can provide reasonable air barriers themselves.

Typically, this is a wood-frame wall with the potential for insulation in the stud cavity (batts or spray-applied) and on the exterior face of the studs (rigid insulation). See Figure 1. During planning and installation, note the following:

• The vapour retarder should be at or near the inside surface of the insulation and would most commonly be 6 mm (0.2 in.) polyethylene sheeting at the inside face of the studs or vapour-retardant paint on the finished drywall.
• The air barrier can be provided by the polyethylene vapour retarder, by the interior drywall or by air-barrier sheeting on the exterior face of the studs. In all cases, the air barrier must be carefully detailed to be continuous at all penetrations.
• Adding rigid (board-stock) insulation to the outside face of the studs minimizes thermal bridging. Spacing the studs at 610 mm (24 in.) rather than 406 mm (16 in.) where possible will also reduce thermal bridging.

Effective Insulation Systems

Effective insulation systems slow the movement of heat and deal with the movement of moisture at a reasonable cost. To do this, they have the following:

• An air barrier, which prevents the movement of interior or exterior air through the system.
• Carefully filled cavities, which leave no gaps in or around the insulation and which do not compress the insulation.
• A minimum of thermal bridges. These are parts of the wall that, with a lower R value, extend from the warm side to the cold side of the insulation, giving heat an easy escape. The structural members in the wall will often be thermal bridges.
• A vapour retarder, such as polyethylene sheeting, which prevents moisture from moving from warm interior spaces into a colder building envelope where it could condense.
• Drying potential, which is the ability of the insulated assembly to release

Insulation Effectiveness

R values and their metric equivalent, RSI values, are a way of labelling the effectiveness of insulating materials. The higher the R value or RSI value, the more resistance the material has to the movement of heat. Insulation products sold in Canada are labelled with R and RSI values. Provincial building codes specify minimum R (or RSI) values for new construction, with different values for different applications. It is important to know what your local building code requires when planning new construction.
Note: The way the insulation is installed plays a large role in its effectiveness. Compressing the insulation, leaving air spaces around the insulation and allowing air movement in the insulation all reduce the actual R value of the insulation.