Insulating Existing Walls

The cost of heating or cooling a house is a serious consideration. Energy rates increase on a regular basis and when your energy bill is higher than usual, it may be that your home is not properly insulated. More often than not, new homes are cost effective and energy efficient as wall insulation is invariably integrated into new homes. However, insulation on older existing walls is sometimes doubtful.

Houses built from the 1920s onwards are likely to have cavity walls or double-walling. The external wall is usually of brick, stone, wood or any synthetic board such as vinyl or fiber board. The interior wall’s finishing could be made of any finishing material such as gypsum.  The gap in between the two walls is the cavity.  Insulating this gap is not easy.  Thermal insulation is impractical to use as the whole interior wall has to be taken down piece by piece to roll out and caulk the thermal matting. A more practical approach for insulating existing walls is by using loose-filling or blown-in insulation. Insulating existing walls is commonly referred to as dense pack insulating.

Insulating existing walls will definitely cut on utility bills. Though double-walling is a solution for permeating moisture, it is not a solution for insulation. The “gap” in between the interior and exterior walls has outside air circulating within. A house needs to be airtight for it to be cost effective and energy efficient.

Best Materials to Use for Existing Walls

The most common materials for filling existing walls are fiberglass and cellulose. Both fiberglass and cellulose can be blown into existing walls with great effectiveness. Insulating an existing wall is quite straightforward.  Blow-in insulation into existing walls means cutting or drilling a hole into either the exterior or interior wall to accommodate the insulation machine’s nozzle. If the exterior of the wall is a brick veneer or stone, cellulose is the choice material. It is able to be blown through a 1” nozzle (pictured).

Filling up the hopper with cellulose fiber then attaching the blower’s hose into the cavity to insulate the gap seems quite easy. It is, as long as the resolute DIY-er knows what he is doing.  Cutting a hole into the wall for the nozzle needs to be precisely in between wall studs to ensure that the spaces between are properly insulated.  It is best to cut a 2” hole halfway up the wall and another at the top. The DIY-er needs to be extremely careful that electrical, plumbing and ducts are missed to avoid a catastrophe. Seriously consider a professional who has experience in filling cavities.

The nozzle of the insulation machine should fit quite snuggly into the hole and the air turned up on the machine. Use a piece of fiberglass around the nozzle to prevent the material from coming back through. This is a two-person job as one needs to hold the nozzle while the other person feeds the hopper with the insulating material. Once the cavity is filled, a plug is used to seal the hole.

Should You Insulate Your Walls?

It is our opinion that insulating your walls is a last resort. If your walls have the minimal insulation (R-11) then additional insulation may not be cost effective. BEFORE you insulate your walls, consider improving your attic insulation to current recommended standards. Then make sure you have good windows and doors. If your outlets are bleeding air, use a gasket to stop the leaking air. You can use a smoke pencil to detect drafts (pictured below).

With a R-11, it will take a long time for you to recuperate the cost differential between your energy savings and hiring a contractor. Since this is our opinion, you are always encouraged to seek the advice of a contractor who can visibly inspect your situation. Besides, if current tax credits and money being given by utility companies and certain states dramatically reduce the cost, we would definitely encourage insulating your walls.

Testing the Quality of an Insulated Wall

To make sure that a wall has been completely insulated, an infrared camera will show hot and cold spots. Some contractors have this equipment.