Between a wall and a cold space
Walls can account for about 20 per cent of heat loss in houses. In addition to heat loss through the walls, there are many cracks and penetrations that allow uncontrolled air leakage into and out of the house.
Solid walls – built of brick, stone, concrete block, log or wood plank – do not have a cavity that can be insulated. The only option is to add insulation to the exterior or to the interior. Many solid walls, including double brick walls have a small cavity, generally less than 25 mm (1 in.), which is a drainage plane that collects and drains water out of the wall. Never insulate these cavities or plug their drain holes.
Concrete-block walls usually have hollow cores that allow air circulation within, increasing convective heat losses. Insulating the cores offers minimal thermal resistance since the blocks’ internal webs and mortar will continue to act as thermal bridges. Instead, seal all possible air leakage routes into the block wall and ensure that the top course of blocks is capped. Where block walls form the party walls between housing units, air leakage often occurs in the space between the block wall and the interior finish. Make sure the space is fully air sealed.
Frame walls have a cavity that may be insulated. Different construction techniques determine the size of the cavity and ease of access from either the interior or exterior. The wall construction also affects details that can interfere with the insulation, including top and bottom plates, fire stops, blocking, plumbing, wiring and heating ducts. A frame house with a brick veneer usually has a 25 to 50 mm (1 to 2 in.) air space between the bricks and the frame wall as part of the drainage plane. Do not insulate this space. Furthermore, insulating over the surface of an exterior wall that includes a drainage plane air space will simply not be very effective. It is better to add the insulation directly to the exterior of the frame wall and then incorporate the appropriate air barrier, drainage plane and siding, unless the specific product and its installation directions account for these requirements. The larger cavity in the frame wall can be insulated.
Opportunities for upgrading
Using dense-pack insulation techniques, empty cavity and some partially insulated cavity frame walls can be insulated from the top and bottom or from the interior or exterior.
Walls can be insulated as part
of a major repair job or renovation. Interior work includes wall repairs, electrical wiring upgrades, insulation and vapour barrier installation, drywall and finishing. On the exterior, insulating can be combined with residing.
Address any moisture or structural problems before insulating. Indications of problems include staining, mould growth, rot, cracks on the inside and exterior wall finishes, and windows and doors that do not operate properly because they are out of square. It is important to consider both vapour barriers and air barriers, especially when adding insulation to the interior or exterior of an existing wall.
The vapour barrier must be on the warm third of the finished wall.
Also consider the location and condition of old vapour barriers, which could be as simple as plaster walls with several coats of paint.
Today, professional insulation contractors can blow in loose-fill insulation or inject approved foam insulation into even partially insulated wood-frame wall cavities. Using dense-pack tech- niques, cellulose, glass fibre and approved foams will compress existing batt insulation and fill all the remaining voids while also offering good air sealing values. Since the stud space is likely only about 89 to 102 mm (3 to 4 in.) thick, thermal resistance gains may be limited, especially if the wall already contains some insulation. However, next to adding either interior or exterior insulation, good results can be had. Before proceeding, try looking behind electrical outlets – with the power off – to find out what already exists in the walls.
To insulate, small holes must be drilled into each stud space. In most cases, one to five holes must be drilled per storey, including those above and blow windows and doors. A long tube is inserted through each hole into the cavity from the top or the bottom of the stud space. The hose is then withdrawn in stages to allow the space to be filled to the proper density.
Choose your insulation product and installation method carefully. Consult closely with a contractor with a proven track record to obtain the best results. Stipulate the manufacturer’s recommended densities for the material in the contract with the installer. The contractor will need to verify the amount and density of the application and then you and the contractor should agree on the number of bags or containers to be used.
Only a small variation from this target is acceptable as too little will leave voids and/or settling gaps in the walls. If too much is used, some of the insulation may be escaping from the wall into the floor space or some other area where it is not needed. Too high a density can cause walls to bulge. Also verify with the contractor exactly how the holes will be sealed, patched and finished.
Installing the insulation
There are three ways to install the insulation: from the inside, from the outside, from the basement/attic.
From the inside
Small holes of 15 to 50 mm. are drilled through the inside wall finish and the insulation is blown or injected directly into the wall. The holes must then be completely plugged and sealed.
If you must replace or re-cover the interior finish, it should be possible to drill the holes, blow in or inject the insulation, install a well-sealed air and vapour barrier on top of the old interior wall, apply new drywall and finish.
From the outside
Most types of exterior siding can be drilled, lifted or removed to access the stud wall behind. In some cases, brick siding can have single bricks temporarily removed leaving sufficient space to repair holes in the sheathing. Ideally, two stud spaces can be filled from one brick space, though each stud space may require two or more holes with this method. Do not insulate the drainage cavity between the brick veneer and the stud walls. Make sure the installer patches the holes section by section rather than leaving them all until the end to avoid water entry if a storm occurs.
From the basement/attic
This can be the easiest approach if access can be gained and if the cavity is open from top to bottom such as with balloon frame construction. All stud spaces need to be filled, but there should be allowance for windows and doors, fire stops, cross braces and other obstructions in the wall cavity. The contractor will check to see if the wall should be filled from the top, bottom or both, depending on obstructions. After the wall is filled, ensure that the access holes are tightly sealed.
Insulating the interior involves insulating the old wall, extending the electrical boxes, applying the air and vapour barrier, crossstrapping, horizontal insulation between the strapping.
Renovating the interior
If your plans involve extensive renovation, you have two options: you can rebuild the existing wall or build a new wall on the inside of an existing one.
Remove the existing wall board or plaster from a wood frame wall, add or upgrade the existing wall cavity insulation and then install the vapour barrier, new drywall and finish.
Alternatively, after filling the cavity with insulation, screw or nail the rigid foam board directly to the exposed studs. Foam board materials, with their high RSI (R) value, use less interior space and provide a thermal break. Depending on the type and thickness of the foam board used, either seal the foam board to act as a vapour barrier or install an approved vapour barrier.
If you are considering having spray-foam installed, there are two basic techniques – one that uses low-density spray foam and the other, high-density spray foam.
For low-density applications, you can choose to remove any existing wall cavity insulation and fill the cavity or better yet, strap the wall and then fill the full, deeper space. The low-density foam will act as an air barrier, but you will have to install an additional vapour barrier before covering the wall with drywall and finishing.
For high-density spray foam, first strap the wall to create a deeper cavity. Then spray a continuous layer of foam (minimum 50 mm [2 in.]) against the exterior sheathing and also cover the framing members. Fill the rest of the cavity with your choice of insulation ( e. g. low-density spray foam, glass, mineral or cellulose fibre).
Build a new wall on the inside of an existing one
With both wood frame and masonry walls, you can build a new insulated wall onto the existing one.
The new frame wall can be installed any distance from the old wall as long as all cavities are filled with insulation.
If you ensure that a new, wellsealed vapour barrier is installed, there is no need to remove or damage any existing vapour barrier.
In both options noted above, follow the relevant part of the instructions for insulating a basement from the inside.
This includes sealing air leaks, framing the new wall, framing around window and door openings, insulating (ideally in two layers so there are no gaps), installing an air and vapour barrier, and applying the new finish.
FILLING THE GAPS: Spraying foam insulation is a good way to fill gaps while in other spaces, rigid insulation or batts will do the job.