Why u-values are not enough – eliminating thermal bridging is key…

This is a bit of a continuation of the Blog Post on DEAP, BER ratings, DEAP, Part L and Building Regulation Compliance So you’ve been working your design through DEAP and no matter what you do, you can’t jump from say a B1 to an A3, what’s missing?

The fabric u-values are not the only aspect of thermal performance to your building; the next big step the construction industry needs to take is with eliminating Thermal Bridging. It’s something the PassivHaus has addressed from the beginning and it’s only really now (since the 2011 Building Regulation changes) that the Irish Regulations are addressing the problem.

The excellent article by Joseph Little – low energy architects and building fabric consultants goes into brilliant detail here, and understanding and then implementing a successful thermal bridge strategy is key to creating a low energy and healthy building.

The above article explains how the DEAP software is at fault by allowing only a single number for thermal bridging (Building Elements>Heat Loss Results):

Also, the above article goes onto show the inaccuracy of using the higher 0.08 W/m2k figure IN THE SAME HOUSE!

As an example I was working through, by simply changing the Thermal Bridge factor from 0.15 (the default) to the higher (0.08) it jumped from a B2 (non compliant) to a B1 (compliant). To obtain more accuracy however in your DEAP calculation you can obtain certified thermal bridge values or calculate them yourself using specific Ψ Values /thermal bridge calculation software.

But this isn’t just about the numbers, what is required is a complete strategy from the design, detailing and then on-site supervision, inspection and certification throughout the entire building process. Something that the Irish construction industry finds hard (if not impossible to do ~ see all the pieces I’ve written on the Building Regs & Priory Hall!); it is also something the public is not used to paying for; the days of getting your planning and construction drawings done and then letting the builder get on with it are over! Especially with the banks not lending (not having?) any money and having the architects effectively taking full responsibility for the finances and entire construction/supervision of the project.

Comments as always welcome…

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