Insulation -Just do it!

Here's the next installment from my articles for the Sheffield Star green pages.

As I said in my last post, insulation is essential. Once you have addressed air leaks your next best investment will be insulation. Primary areas to insulate are the loft, the walls, and the floor. If you are re-roofing be sure to get a layer of insulation installed under the tiles. This may need an air gap between it and the tiles as well. Additionally, you should insulate any hot water pipes that you can get to.

The Loft - If a loft renovation has been done and the actual flat space above the ceiling is minimal then doing more than 10 to 16 inches may not be worth it as the pitched portion of the roof will be the largest area of loss. If you are planning a loft renovation be sure to plan in a method to insulate the entire roof area. One solution is insulated drywall for the pitched sections, to avoid losing too much headroom, and at least 10 to 16 inches of recycled denim or cellulose insulation in the flat section. If you have a large flat area consider going up to 24 inches of depth for best performance. Be sure to fill all gaps while still allowing for eaves ventilation and cover the ceiling joists. Make sure you insulate all the flat spaces at floor level that are sealed off behind new walls. Typical payback periods for loft insulation will be short, particularly if you do it yourself or get a grant for it, in some cases as little as one winter.

The Walls - Most walls in England, particularly in older homes are stone or brick. Most brick walls built since the turn of the century, 19th to 20th, are built as two walls side by side. These are known as cavity walls. Stone walls, while thicker tend to be a single layer or solid.

Grants for cavity wall insulation are available and well worth the effort to get. Cavities should be filled with a waterproof insulation and due to the nature of the job will likely need to be done by a qualified contractor. If you are doing a renovation, have a look at your lintels. A single stone or concrete lintel that spans the cavity will act as a cold bridge, draining away heat from the inside. Plan to replace the single lintels with separated lintels.
If you have solid walls there are two options, insulate externally or insulate internally.

External, though more expensive, can be breathable and will allow the internal masonry to act as a heat store, known as thermal mass, and will not reduce the interior space. It will however change the appearance of the building. There are other issues with external insulation that you don’t face with internal. Roof overhangs will need to be addressed to insure that the top edge of the insulation is covered. A good time to do an external insulation job might be when you are replacing the roof. Also, external plumbing, guttering and wiring will have to be removed and rerouted afterwards to accommodate the extra thickness.

Internal insulation, typically achieved through the addition of a layer of insulated drywall, will require removal of floor and ceiling molding, skirting boards, and the remounting of electrical fixtures and outlets. Ideally, it should happen as you are installing double glazing as you will want to insulate reveals and lintels as well. It also means that you will lose interior space, in a small victorian terrace this may be a high price to pay. But this method will cost less than exterior insulation and can be accomplished on a room by room basis. Unfortunately, it will reduce thermal mass and won’t address cold bridging from external to internal walls. As you will be reducing the breathability of the walls you may encounter damp problems which can be addressed with a vapour barrier on the warm side of the insulation.

The Floor- While not the first priority for insulation as it is only responsible for up 20% of heat loss, once the loft is insulated and the cavity walls have been filled it is well worth doing. Plan on at least 8 to 10 inches of insulation between the floor joists. This is usually easily achieved in a a Victorian era house with a cellar. If you are doing a major renovation and replacing the floor be sure the insulation overlaps the wall insulation if internal.


References:
Harris, C. and Borer, P. 1998 - The Whole House Book; Ecological Building Design and Materials 2nd edition