25% and a B2 BER

antiskeptic · 25-01-2020 6:33pm #1

Just came across mention of some recent legislation regarding building refurbishment and new demands re BER that need be achieved.

There is some mention of 25% (as in this B2 rating for whole of house needs to be achieved once this threshold is crossed.)

I thought to ask here first as I'm sure folk will have parsed what it means in practice

What's this 25% about? If the house is extended, say, by more than 25% then you need to B2 the whole house? I can fixer uppers dropping in price!

I also came across the caveat 'if cost effective'. What does that mean?

Thanks in advance..

mad m · 26-01-2020 12:41am

Interested in this as well. Check out section 2 for existing dwellings. Table 6 & 7

TGD Part L

Alf Veedersane · 29-01-2020 12:53pm

Table 6 above defines what works qualify, e.g. replacement of roof structure would mean the roof area is included in the calculation of the 25%. Insulating at ceiling level wouldn't. Internal/external wall insulation is included. Cavity wall insulation isn't.

Table 7 outlines what works are required where the 25% threshold is hit. Getting a B2 is one route, the right-most column outlines the alternative route, i.e. what works are required.

In terms of extensions, the 25% threshold is "Where a new extension is added to an existing dwelling and affects more than 25 % of the surface area of the existing dwelling’s envelope" (section 2.3.6 of TGD L).

If someone is insulating their walls internally or externally, then they're looking at having to bring up their roof insulation (if it's greater than 0.16 W/m2K) and upgrading their boiler if it's < 86% efficient. I'm not entirely sure that will put off a lot of people upgrading their walls. But I can see how it might put off some.

If you're extending where the threshold is hit, then you'd be looking at doing roof + boiler + walls. That would be more likely to put people off but doesn't apply to all extensions.

Penn · 04-02-2020 4:31pm

The idea is that the works you're undertaking, considering you're affecting more than 25% of the surface area of a building element, should be such that it'll bring the dwelling to a BER of B2. There is a cost-optimal provision however, in that if you can prove that the works you plan to take is feasible but that the additional works required to bring your house to a B2 are not feasible, then you don't have to achieve a B2 rating.

But the reason behind it all is that if you're doing substantial works to the dwelling anyway (whether via fabric or services), it should be more cost-optimal to do enough works to reach a B2 level, and you may be eligible for further grants if you do, or better loan terms for energy upgrades. It might cost a bit extra up front, but would save more money in the long run due to the greater energy efficiency of the house (a cost-optimal study would be required).

25% and a B2 BER

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