It seems to me that the energy debate is biased towards the supply side, e.g. should we build more nuclear capacity, if not then what? While on the demand side we have a building stock that is extremely poorly insulated on the whole. Double walls (cavity walls) didn't really appear until the 1930's and only relatively recently have building regulations been squeezing the energy footprint on new builds.
Old solid(single) wall buildings (which make up a large proportion of UK housing) will typically have 9" thick walls (U≈2), with some as narrow as 4" (U≈4). The U value there indicates heat loss per unit area per temperature differential for a typical brick. So for a temp differential of D degrees Celsius and a wall with area A m2, heat loss in Watts is given by:
For a small terraced house this amounts to something like 2 * 80 * 10 = 1.6KW that you need to burn in order to maintain a 10°C differential, and that's not including heat loss through the roof, windows, doors, draughts, etc. Multiply these losses by several million homes and there's a big chunk of the demand side of the national energy equation right there. For the record the regs for new builds demand U values for walls of at least 0.3 (2006 regs) and 0.2 (new regs just coming into force).
The amounts of energy are vast - in the order of gigawatts of continuous consumption. Furthermore the cost/benefit ratio of insulating the most leaky buildings is much better than investing in solar panels and quite likely even wind turbines - especially when you consider how many homes have no or very poor loft insulation which is cheap and easy to install. If as a nation we're ever going to knock a hole in our energy footprint then to my mind building insulation is priority #1. The government recently scaled back on grant money for home insulation - you now have to be on some form of benefits to qualify. Fair enough I suppose, those with higher incomes can invest based on their own cost/benefit analysis and make money over the long term. But less grant money => less incentive => lower upgrade rate.
An alternative and cheaper incentive might be to increase the VAT differential between energy and insulation upgrade work. Energy VAT has a reduced rate of 5% as does insulation. I figure increasing the energy rate would be political suicide (frozen pensioners in news), which leaves reducing VAT on insulation products and services to 0%. Not much but a cheap and easy step to take.
As it happens you can get grants for something called sempatap, which is a 1cm thick heavy foam that comes in rolls and is applied to walls in a similar manner to wallpaper (only a lot more fiddly). It has been widely used to upgrade housing association stock, but having looked at the maths it's actually a pretty poor win. For starters (A) it's easily damaged and thus probably has a short lifespan, (B) it's not actually that cheap at £15/m^2 and (C) it's not even a very good insulator (U=6 @ 10mm thick). If we're going to make a significant reduction in energy use then we need something better and sempatap is just a time and money wasting distraction - it's going to take effort to strip all this stuff away and replace it with what we should have used the first time.
Right now you can get Polyisocyanurate (PIR) insulation panels with good thermal resistance (about U=0.4 for a 50mm thick panel) for about £17/m^2 (excluding VAT). That's about a 13x improvement in thermal resistance per unit cost and also a much longer term solution as this stuff is intended to be adhered/fastened to brick and plastered over. At this point I'm even wondering if there's some corruption going on with these sempatap subsidies (probably not though, see Hanlon's razor). I refer to the 50mm PIR panels as they'll get an old solid brick house more or less up to regulation standards (the standard for renovations is slightly less than for new builds). And if you need to fit them internally you can justify some of the depth by replacing the old plaster, which in old houses is usually 2-3cm thick if it's still the original plaster (which is typical).
Current makes of PIR insulation board that I could find for sale in the UK are Kingspan and Celotex.