Are You Insulated?

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For example, you may have a rafter of 4" depth and you want to add 3" of insulation board, then it would be possible to do this if you attached a lath of about 1". Otherwise the procedure is very similar to that above.

Above the Rafters

This particular option is only worthwhile if you are having your roof renewed. It is also the most complicated method, because it almost certainly involves some redesign of the eaves to allow for the added thickness of insulation. The basic principle is to strip the roof of tiles and tile laths; to lay a rigid insulation board on top of the rafters; and lay a building board or roofing laths on top of this to take the tiles or shingles. If you are choosing to lay a thicker layer of insulation than can be accommodated by the existing roof, it may be necessary to obtain the advise of someone knowledgeable in the building business. It is treatment of the eaves and gable end that requires special attention. Another important point to watch for in all these cases is the ventilation of the timber rafters. If there is any doubt that there will be sufficient airflow, then it is advisable to install a vapor-proof barrier of polyethelene sheeting just behind the finish boarding to prevent water vapor traveling through from the inside.

Wall Insulation

Wall construction is predominantly timber frame, and the simplest way of insulating this type of wall is by blowing cellulose fibers into the cavities between the inside and the outside lining or boarding. Achieving this is likely to be the single largest fuel-saving measure for most houses, and if you rent a blowing machine and do the job yourself, the payback time can be reduced significantly. Lumberyards sell cellulose fibers, and many will loan you the blower for nothing if they are in a reasonable mood. If you decide that these fibers make sense, you need to make a decision on whether to gain access from the interior through 2" holes cut in the plasterboard or through the exterior by removing some clapboards or shingles.

To guard against the cellulose becoming damp, the exterior boarding should have vents and interior walls painted with vapor-barrier paint, such as an oil based paint. Another option is to remove the existing interior finish boarding and install rigid sheet insulation or baits between the studs before replacing the internal finish. This procedure allows you to install a polyethylene vapor barrier between the insulation and studwork and internal boarding, but requires a major renovation investment in time and money.

Brick Walls

There are three possible ways to insulate masonry or brick walls:

(1) Insulating the internal cavity
(2) Insulating externally—the most effective form of insulation
(3) Insulating internally—the most involved

Cavity Wall Insulation

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