3 Apr 2006

What the ODPM won’t tell you about the new Part L

Walls — 0.27
Flat ceiling — 0.16
Pitched roof — 0.20
Floor — 0.22
Windows — 1.8
A-rated boiler
Pay close attention to air leakage paths
Be prepared for an air-tightness test but don’t be worried about it

That’s it. Those are the U values and the details you will need to get your new detached house through the new Part L of the England & Wales building regs, which came into play at the beginning of April.

Funnily enough, you won’t find this information in the section of Part L that looks at building new homes, Part L1A. This is because we are meant to be moving to a whole house heat loss approach. This is a fine thing in principle as it recognises that the energy performance of a dwelling is dependent on a variety of factors. The regs suggest that you should have a target carbon emission figure for each house and that it’s up to the designers to figure out how they meet that target. But that doesn’t help designers a great deal because you have to put your designs through a process known as a SAP calculation in order to know what your emission rate is likely to be. You can do this manually via the BRE’s SAP 2005 calculations sheet (warning: it’s six pages and has 120 different steps to go through, many with look-up tables, before you get an answer) or you can do it using software but this is stuff you have to purchase. It’s not the sort of process a house designer is really geared up for: they want to know how much insulation they have to squeeze into the fabric.

But contacts of mine in the insulation business have been busying themselves with the new calculations and are coming up with model designs that will meet the new regs. And that one at the top of this article looks like the dog’s bollocks as regards detached new houses.

Oh, and it looks like bad news for Actis and the multifoil kids. Despite my contact Charlie Duke showing that Actis works pretty well, the powers-that-be are going to require that all insulation meets standard BR443 after 1 Jan 2007. BR443 states that thermal insulation has to have a European Technical Approval to be permissible. That means, in short order, that the insulation has to pass muster with the standard test, the guarded hot box test, which the multifoils don’t do.

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