The cost of comfort

Footprint carries the story of another PassivHaus retrofit costing £200,000. All part of the Technology Strategy Board's Retrofit for the Future strategy. 86 projects up and down the land, each funded in this ludicrous way, proving absolutely nothing at all, except that it costs more to retrofit an existing house properly than it does to rebuild it.

The whole scheme is an embarrassment and I am surprised that anyone is brave enough to court publicity for their endeavours. Long before this scheme was first dreamt up, we knew the answer. Yes, it's difficult but not impossible to retrofit existing houses to these incredible standards but, no, we can't afford it.

The question should be what can we afford? Or, to put it another way, what standard of retrofit should we roll out? At the other end of the spectrum, we have the Green Deal taxiing for take-off, looking hopelessly lightweight. A Green Deal retrofit (cost around £6,000) will save householder's very little energy: it will simply make their homes more comfortable. Most homes these days are a hotch-potch of warm spots and cold spots, heated rooms and unheated rooms, times of the day when the temperatures are comfortable and other times when they are not. We juggle with our central heating controls in a futile attempt to balance comfort against cost.

The Fuel Poverty standards don't help: Adequate warmth is generally defined to be 21°C in the main living room and 18°C in other occupied rooms during daytime hours. Very few people now have the wherewithal to meet these supposed World Health Organisation standards, and we don't have enough money to be able to get to everyone to these standards, and we should stop pretending we do. The higher we set the hurdle, the less homes we will be able to treat.

We need an adult debate about just what is affordable, and how much comfort we can deliver. There must be a sweet spot between the T-shirt slouching 21°C suggested by the Fuel Poverty standards and the mould-inducing 12°C where things start to get genuinely ugly. What is the average internal British house temperature in January? What should it be? Big policy questions currently not even being asked, let alone answered.

The Big K Battle: Knauf v Kingspan

Part L has long since given up on giving us elemental U values and has left it to us to work them out from first principles. The insulation manufacturers have no such qualms and are happy to go into print with their views on what the position is. And, surprise, surprise, they don't agree.

In one corner is Knauf, who run the old Pilkington plants in St Helens, and specialise in glass and mineral wool (now re-branded Earthwool). Plus a little extruded polystyrene (Polyfoam). In the other is Kingspan, makers of phenolic foam and polyisocyanurates (I hope I've spelt that right): high performance plastic foam boards which sell for twice as much as Knauf's products but get the job done in less depth.

You don't have to be a rocket scientist to figure out that low U values tend to favour Kingspan products, because the space consumed by their insulation is much less than Knauf's, and as insulation gets thicker, the space used becomes more of an issue. This is particularly true for cavity walls, where Kingspan products have to be installed with a 50mm air gap, the so-called partial fill solution.

But Part L is scientific and unbiased, so surely the manufacturers can't play fast and loose with the U values. Can they?

Well here's what they reckon the maximum U values should be for various elements. Kingspan here. Knauf here.

External Walls: Knauf 0.25, Kingspan 0.18
Pitched Roof (rafter level): Knauf 0.18, Kingspan 0.13
Ground Floors: Knauf 0.16 to 0.20, Kingspan 0.13