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Attic insulation reduces heating bills and prevents ice dams; you can't have too much, but too little will cost you!

Research shows that ice dams are caused mainly by poor attic insulation, and that attic ventilation has little effect on their occurrence. Improving attic insulation is an economical way that you can often do yourself, to both reduce your heating costs and prevent ice dams

Ice dams occur when snow melts on the roof, and the melt water freezes where it is obstructed by snow or ice at the eaves. This can occur on sunny days when the extra heat from the sunlight, combined with heat escaping from the ceiling below the attic, is sufficient to melt the snow covering on the roof. The meltwater runs down the roof, and when it comes to the eaves overhang, which is often not as greatly heated from the ceiling below, the water freezes when it reaches the unmelted strip of snow. This ice causes water to back up and may cause to to find a way underneath the shingles, into the attic space. You'll notice this as a leak stain on the ceiling below.

If this happens, be careful about how you attempt to remove the dams. Pulling snow off the roof while you're on a ladder can lead to a fall if the snow comes off unexpectedly and falls on you. It's better to use a melting compound, one that's not harmful to your roof and the environment. Urea and ammonium fertiliser compounds are ice melters that are not environmentally harmful according to CMHC.

Wall Insulation Retrofits

We recently inspected an insulation retrofit for a homeowner. The retrofit was a ‘drill and fill’ installation, in which Icynene™ expanding foam insulation was installed in the cavities of the exterior walls of the house. This foam was chosen because of its low to non-existent off-gassing characteristics, and its reported environmental friendliness. It is foam with a low-rate of expansion, suitable for pouring into existing cavities without high risk of popping the interior wall apart. Much depends on the ability of the installer to control the amount of foam to fill the cavity without overfilling it. The insulation can be installed form the exterior, without going into the house, or from the interior, or a combination of both. If no workers are to enter the house, someone must be available on the inside to report on the expansion of the foam.

To assist homeowners who may be considering this type of installation, the photographs we took can be viewed here.

Wall Preparation for Foam Injection
The walls are prepared by drilling about ¾ inch (about 20 mm) diameter holes in the mortar joints between the bricks. These holes have to penetrate the brickwork and the interior backing of the wall cavity, but not the interior face of the house wall! It is possible that one or two holes may go right through the inside wall, due to factors beyond the control of the crew. Whether your interior wall construction is plaster or drywall, any such holes are patchable and when repaired properly, virtually impossible to detect afterwards. It is advisable to take down any wall hangings (plates, paintings, photographs or other pictures, fabrics etc) from the walls, and to move furniture away from outside walls, just in case.

Foam Injection
The foam is injected using a mixing gun that controls the proportion of the foam components, to ensure that the foam mixture is consistent and as specified by the manufacturer. During the injection, someone on the inside is needed to monitor the expansion of the foam. Listen for the injection squirt, and then the effects of foam expansion. There may be some creaking or cracking as the foam expands to fill the cavity. If there is too much foam, you will hear the sounds of the wall being stressed by the expanding foam. The crew needs to know about these noises to judge the amount of foam to be injected. We use cellular phones (or two way radios if necessary) to maintain contact between the house interior and the crew.

Patching and Clean-up
The drilled holes are patched with mortar, but it may not be possible to match the colour of the existing mortar, depending on its age and weathering. There may be some foam over spray on the brickwork, which the crew removes easily, and also on windows. Any faint marking left on the brickwork should disappear with time.

Blown-in Insulation
Blown-in insulation can be done from the exterior or interior. In this installation, one area was insulated using blow-in insulation through an interior surface (the garage ceiling), and the attic was topped-up to R50 from originally about R10, through a gable vent.

Surface preparation
Holes of about 2 in (50 mm) diameter are drilled through the plaster (or dry-wall) surface to allow the insulation to be blow into the cavity to be insulated.

Blown-in Insulation
The insulation comes bagged, and is poured into a hopper from which it is blown by air pressure into the cavity to be filled. Basically, the cavity is filled until it will take no more insulation, or until the added depth of attic insulation reaches a pre-determined amount.

Patching and Clean-up
The holes are plugged with an appropriate diameter wooden plug, which is tapped into place and left just below the surface of the surrounding wall, or ceiling in this case. It may be left to the homeowner to do the final patching of these plugs, as it was in this case. There is very little clean-up required after this work, which mostly comes from the drilling of the holes. In a garage, this entails just sweeping the floor; however in any other area of a house, this could require much more work unless dust sheets were used.

Performance Results
Expanding foam installed in the wall cavity both seals the cavity against air movement, and increases the insulation value of the wall. In this case, the insulation will have been increased from originally zero, to somewhere between R15 to R20, which will greatly reduce heat transfer through the walls, as well as air movement through the walls into and out of the house.

Topping-up the attic to R50 reduces heat transfer through ceilings, decreasing the heat load of rooms below. (The rate of heat loss into the attic space is lower in winter, and the rate of heat gain from the attic space is lower in summer.)

It is still too early to assess the increased comfort level in this house, for although the performance improvement can be measured by a blower door test, the real assessment lies in whether the house is more comfortable, and less expensive to heat or cool.