17 Apr 2012

The Case for Consequential Improvements

From the debate so far, you'd think that consequential improvements were designed purely and simply to get up the noses of aspirational, squeezed-middle, Daily Mail reading home improvers. They weren't. There is a good case for them and it's not being heard.

At the heart of the matter is the question of energy saving and the law of diminishing returns. It states that the first inch of so of insulation saves a mass of energy, but each subsequent inch saves less than the one before. This is expressed in mathematical terms in U value calculations which show that if you want to halve the heat loss, you have to double the amount of insulation.

It's relatively easy to halve the heat loss of an existing wall with no insulation in it. Adding around 50mm of insulation will reduce the U value from around 1.2 to around 0.6 (that's half). It's much more demanding to halve the heat loss in an extension which is being built to modern standards: getting a wall from a U value of, say, 0.3 down to 0.15 would involve widening the cavity from around 80mm to nearly 200mm, and forking out for 120mm extra insulation. There are other details to consider here as well, but for simplicities sake, I'll ignore them.

In doing this, your extension may have halved its energy loss but it's done it from a much lower starting point. The total energy saved in the new extension will be far less than you might save in the existing house where you've only had to add 50mm of insulation. You've also, incidentally, lost a significant floor area from your extension as the walls have to be so much wider to cope with all that insulation.

The financial calculations are even more compelling. Adding 120mm of extra insulation onto a 30m2 extension is complex and relatively expensive: it could easily add a couple of thousand onto build costs. Cavity wall insulation on an existing house usually costs between £300 and £500. The cavity wall insulation will result in far more energy being saved, and have a far greater effect on fuel bills. Like an order of magnitude.

Financially, it's a no brainer. It makes sense to insist that the existing house is upgraded rather than pouring money into building an ultra-low-energy extension.

There is more. Any energy saving you might hope to get in the newly-built extension will be mostly lost via the existing house, meaning that the expensively constructed low-energy extension will probably not save any appreciable amount of energy at all. And the whole house now risks being uncomfortable to live in, neither fish nor fowl. It would be like wearing a coat where the left side is made of a thin cotton and the right side of thick sheepskin. What a crazy design? Who would choose such a coat? Who would choose to live in such a house?

Like it or not, consequential improvements make sense, at least when the house is being extended. If it was to really have teeth, Part L would be insisting that anyone extending the heated floor area of an existing house should ensure that the overall heat loss of the new should be no more than the old. Now that would be draconian (but it would also make a lot of sense).

As it stands, the suggestions for improvements as set out in the Part L consultation are very watered down so that only four actions are required:
• cavity wall insulation (only if you've got an unfilled cavity)
• extra loft insulation (big deal)
• cylinder lagging (again, it's a nothing job, and over half the country doesn't even have a cylinder, they use a combi)
• draft proofing

It's very hard to see this lot costing £10,000 for anyone, unless you happen to own a huge country house. It's hard to see it costing much more than a grand on most homes. With or without the Green Deal, it's not going to be very expensive to install these and it makes sense it terms of overall comfort, if nothing else.

Up till now, Part L has tried to maintain some sort of parity of standards between new build and extensions, but it's reached the point when the two are about to separate because (as discussed) it makes little sense to build extensions to new build standards if the existing house is a drafty old pile. What should Part L do for extensions? Should it insist that they continue to ape new build standards (cost maybe £2,000 per extension, energy saving negligible) or should it branch out and insist that the equivalent money is spent in the existing house? The answer is obvious: consequential improvements are logical, sensible and justifiable.

200,000 extensions a year represents a huge floor area, comparable with the floor area arriving via newly built homes each year. Are we just going to give up on trying to get these homes fit for the 21st century? High energy bills are not going to go away anytime soon and Part L is one of the very few tools at the government's disposal to protect people from them. Ditch consequential improvements and you leave a gaping hole in energy policy.

As a footnote, I do think it was a mistake to add replacement windows and boilers as triggers for consequential improvements. I wonder whether they were placed in the consultation as a negotiating ploy, so that something could be conceded before the final version of Part L was published. If so, it has backfired badly. The principle of consequential improvements should be simple to grasp: if you chose to extend the heated envelope, you must improve the energy performance of the existing house. Adding window and boiler replacement as triggers muddied the simplicity of this golden rule.


  1. I'm totally with you on the absurdity of achieving building regs level insulation on an extension to a draughty uninsulated house. The only way I could avoid building a windowless (nearly) bunker was to make my extension a "garden room" with an insulated door into the main house. The irony is that the extension will be much better insulated than the house.

    I would totally welcome expert advice on how to insulate and draught proof an Edwardian property, but I expect I would be sent a leaflet about cavity wall insulation.

    1. Hi Commentor

      There are lots of companies (us included) who can provide advice on making older properties more efficient. They will look at what the planners will be happy with, how much space you're willing to lose, your budget and ways of avoiding condensation. It's also worth using an installer who specialises in older properties so that they preserve what makes these properties so great!

    2. Thank you. I'm stingy though and don't want to pay £450 for the energy report.

      I reckon draught proofing my suspended timber floors would be the best thing I could do to my flat, as that's where most of the heat escapes (I think), but don't know how to do it 'properly' (avoiding damp issues). BTW this is not me angling for free advice. :)

    3. Do give us a call, you don't need a whole energy survey just for insulation. We'd rather that you spent the money on insulation!

  2. The inclusion of boilers and replacement windows as triggers gave me the impression that the whole point of the new consequential-improvements requirements had nothing to do with the logic you describe. Rather, they'd been slung in after it had dawned on the GD architects that the market they'd envisioned was not going to materialize after all. The idea was to force some people into GD plans. No?

    1. Cons impvmt is not a new idea. It's been in the last 3 Part L consultations and it therefore predates Green Deal.

  3. Alan ClarkeApril 18, 2012

    Frustrating how some decent debate only comes out after the consultation is closed! So sensible suggestions here are:

    boilers & windows help efficiency anyway, so drop those,

    if you extend a house then improve the existing house so that total emissions aren't increased (provisos being that improvements are such that can be funded by green deal, if you want - though if you have some low hanging fruit this may be cheaper than getting the extn to newbuild standards)

    I was quite negative about the original proposal, but put like this it makes sense!

  4. I completely agree with you about the pointlessness of making people build highly insulated extensions to current part L standards onto leaky old houses and also show why there is little to be gained by pushing those standards any higher.

    But then you say "Like it or not, consequential improvements make sense," No they don't. There is nothing consequential about them. Insulation and draught proofing in a leaky house is always makes sense, extension on not. This is just an excuse to wield a big stick and strike poses.

    There is a thread running through the current Building Regs that seems to assume people have to be forced to do work on their own houses by a Government that knows best. I think this is wrong on both counts. Firstly, there can be very few houses that have not had a fair amount of insulation work done. I did a rough count in our unfashionable little Derbyshire town and found just 5 houses out of more than 400 that did not have double glazing. I bet they have some loft insulation too. People are making changes but need some intelligent guidance as Commentator says not a kick in the teeth.

    Secondly, I don't think the Government does know best. You rightly lampoon the draught proofing/cylinder lagging tick-box nonsense but then go on to say that without consequential improvements "....you leave a gaping hole in energy policy." Really? Not much of an energy policy of that motley collection of clich├ęs are central to it.

    The way the building regs operate now is at least fairy logical - when it's built, it's built. The start date sets the regulations that must be met and that's it. The idea of 'consequential' anything makes a nonsense of it all. Why limit this to part L, why not make people change their staircases to meet modern requirements, or make them fit part M style level access instead of all those nasty door steps? Surely we should make people rewire the whole house too, when they extend, they'd be so much safer. If you go down that route it'll never end.

  5. Stoat,

    I hear what you are saying and you know from past musings that I am sympathetic to many of them, esp on Part G. But take a look at my next post. There really is no clear cut line that separates new work from consequential work and there never has been.