Recently I’ve been analysing the energy demands on proposed houses designed by others and existing houses ( I do this type of analysis on my own designs as a matter of course to check Building Regulation compliance at all stages). The results I’ve come to are interesting and thought I’d share:
1. Every little helps
Every small improvement in U-value, air tightness etc.. makes a big improvement in the end result; with every small change meaning the difference in rating from a B1 to a B3 for example.
2. Airtightness is key
By improving the air tightness from a crappy Building Regs standard (10m3/hr/m2) down to a respectable 3m3/hr/m2 you will improve your energy value by 5.59kWh/m2/yr, which could mean the difference from a B2 to a B1 rating.
3. Get certified values
You’ll need to do quite a bit of research on specific items such as windows, doors, solar panels, boilers, heat recovery units – by obtaining these certified values you’ll obtain a more accurate result rather than relying on the default values.
4. High performance windows are good, but…
Getting the best windows you can afford (see point 1 above) is good but surprisingly the end result may not justify the additional cost. On one example, changing from a high performance triple glazed window to a reasonable triple glazed version only resulted in a downgrading of performance of 0.22Kwh/m2/yr. In todays ecomomic disaster it’s essential to carefully work out the energy savings you get and how much they are going to cost.
5. Yes, but I want an A rated house !
Sometimes you can tweak the u-values, window specs as much as you want and you can never jump from a B1 to an A3 rated house. The answer is to implement a renewable technology that produces or saves energy such as wind turbines or photovoltaic panels. With this in mind, see point 6 below:
6. The BER rating is significantly different to a Passivhaus result
The items discussed above apply for improving your BER rating, it should be remembered that BER ratings are significantly different to how the energy efficiency of a Passivehaus is calculated which (I believe) gives a more accurate model for creating a house with low energy demands. Unfortunately the Building Regulations (currently) are based on the BER rating and not the Passivehaus standard and this should be borne in mind when any ‘sign-off’ is required by banks etc…
If anybody disagrees with the above, please comment and I’m happy to edit !