As you may or may not know Part L of the Irish Building Regulations (Conservation of Fuel and Energy) changed in December 2011. Normally the actual Regulations (as opposed to the Technical Guidance Documents) are quite broad, for example Part M (Access for People with Disabilities) will simply state:
Adequate provision shall be made to enable people with disabilities to safely and independently access and use a building.
And the Technical Guidance Document (TGD) then goes on to describe Prima Facie methods of achieving the Regulation.
Part L is somewhat different as it now says:
A building shall be designed and constructed so as to ensure that the energy performance of the building is such to limit the amount of energy required for the operation of the building and the amount of carbon dioxide (CO2) emissions associated with this energy use insofar as is reasonably practicable.
All fine so far…
For new dwellings, the requirements of L1 shall be met by:
…both energy consumption and carbon dioxide (CO2) emissions are calculated using the Dwelling Energy Assessment Procedure (DEAP) published by Sustainable Energy Authority of Ireland.
The TGD then states the performance criteria:
The Maximum Permitted Energy Performance Coefficient (MPEPC) should be no greater than 0.4
The Maximum Permitted Carbon Performance Coefficient (MPCPC) should be no greater than 0.46
What’s interesting is that the above figures are the standard we have to work to; it’s not the actual BER energy rating; as this can vary depending on the different approach taken. As a guideline a compliant house can vary from an A1 down to a high B1; to emphasise the key figures you’re working to are MPEPC <= 0.4 and MPCPC <= 0.46. Generally however, to meet Part L Building Regulations you should be aiming to achieve an A1 or A2 rated house – not easy and I suspect the majority of self-builders (and builders?) have no idea the level of insulation, airtightness and lack of thermal bridging that is required to be compliant.
Now this has big repercussions on how the design is approached, how it is detailed and how it is built:
It means that you’ll need to be understanding and using DEAP and you’ll need to be using DEAP at a much earlier stage.
It means that you will be working alongside DEAP to ensure your house complies throughout the design, detailing and construction process.
You will need to be constantly entering and checking values for things like window u-values, boiler type & efficiency…
You will need to be working closely alongside your architect (with DEAP experience (ahem)) or your energy assessor that evaluates your design at each stage of the design and construction.
It means there are various approaches you can take to still achieve compliance; from the fabric insulation to the ventilation, from the heating system to the airtightness…
So back to the title of this post ‘Why you can’t rely on backstop u-values’ – What this means is that the time of simply adhering to a specific wall construction to ensure compliance have gone. The house is now treated as a whole and it’s the figures described above that ensure compliance. Part L however does give MAXIMUM u- values for the fabric elements (Table 1 below) but to ensure compliance you’ll need to be significantly better than these figures Appendix E for example gives a specification set for an example dwelling where the wall u-value is 0.13 W/m2K):
There’s a lot more that Part L covers regarding airtightness, thermal bridging etc… but I guess that’s for another blog post and this is enough to get you thinking…
As always comments welcome…