Did you know there are usually restrictions on how much glazing is allowed in an extension project? This is governed under the Building Regulations and is related to heat loss and energy conservation.
Glazing is often a weak spot for energy efficiency as it lets out more heat than say a floor or wall + it can often overheat in the warmer months. Usually it is limited to a maximum of 25% of the floor area of the extension. So, for a 60m² extension you would only be allowed 15m² of glazing. This applies to doors + windows + roof windows, all glazing needs to be assessed.
With a lot of modern extension projects there is increased demand from clients to have loads of glazing, to bring in natural light, offer large views outside to nature and to provide a lightweight feel to the building. This often means the amount of glazing required exceeds this maximum 25% floor area limit.
However, there are ways around this so you can increase the amount of glazing past the maximum 25% floor area limit.
There are optional approaches with more design flexibility in the Building Regulations. Part L1B makes reference to using an Area-weighted U-value method. Essentially, what this means is that you can beef up the insulation elsewhere [floor, walls and roof] to compensate for the extra heat lost through the glazing. As long as the total heat loss is no worse than if using an identical project built to the standard regulations it’s ok. We’ve successfully used this method on loads of projects over the years.
To do this you need to calculate the heat loss of a notional building with the same floor area as your building, that uses the 25% floor area limit. You then complete a further calculation for your proposed building that uses the actual glazing area which is more than the 25% floor area limit. You then tweak and increase the U values of the other bits of your actual building [floor, walls and roof, possibly the glass as well, triple glazing etc.] until the heat loss is no worse than the notional building or even better.
To help you we’re giving away our very own Excel schedule template, Area-weighted U-value Calculator, free of charge, no strings attached. Instructions for use + a worked example are included so hopefully this is all easy enough to use. Best to download and use the desktop version of Excel – File > Save as > Download a copy.
We’ve spent a fair amount of time creating this and then updating and tweaking it. We sometimes feel like we want to keep all our own hard work to ourselves but in the spirit of open collaboration and helping others, please feel free to download, use and share with others. Spread the love my friends. We hope this is useful.
Ikonografik Design – Free – Downloadable Area-weighted U-value Calculator – click the link below. 👇
Contact us about any questions you may have or how we can fulfil your requirements