Compare Apples with Apples – nZEB & Passivhaus #ThermalBridging #24intphc

I wrote THIS yesterday on my presentation at the 24th Passive House Conference on nZEB & Passivhaus in Ireland and the question is that surely they must be close now in terms of performance?

As I said in my conference you need to make sure that you are comparing Apples with Apples.

Let’s look here at just one aspect – Thermal Bridging:

In order for the BER Assessor to provide calculations for the house that meet the nZEB threshold – the architect/engineer needs to provide ‘signed-off’ details that are in compliance with Acceptable Construction Details (ACD’s) in order to obtain the improved value of 0.08 W/mK as opposed to the default value of 0.15 W/mK. The problem with this is fourfold:

1. The details provided are essentially from 2006, are out of date and poor-performing. The detail for a foundation detail is shown below:

There is a cold bridge occurring at the sole plate – this would have been reduced with the use of a thermal block at this location (of suitable strength for the timber frame)

2. The value for the ‘improved’ thermal bridge is still considerably poorer than the ‘Thermal Bridge Free’ requirement of Passivhaus of <0.01 W/mK - This value is modelled at design stage and verified during the construction process in order to become a certified Passive House. 3. There is no guarantee that the detailed construction (as poor as it is) is constructed EXACTLY as the modelled detail – Passive House Certification requires complete documentary evidence which includes photographic records of the entire construction ensuring that what is designed and detailed is EXACTLY as the construction drawing.

4. Any cold bridges in a Passive House are accurately thermal modelled and the results of the model are input into the PHPP software as a component of the heat loss.

So let’s look at a few examples:

The poor example from the ACD is shown above, let’s now look at a thermally modelled detail where the results were input into the PHPP calculation. The first image is the details as deigned and drawn and the second image shows the thermal model.

Special thanks to Darren O’Gorman Msc Cpm for the thermal modelling

This is then checked on site during the construction process to ensure this detail is constructed as drawn:

The following infographic shows the Passive House certification process from The International Passive House Association:

If you are contemplating a Passive House building in 2021 (Passivhaus covers all types of buildings – not just houses) then why not CONTACT US…

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