Why you can’t rely on backstop u-values, Part L, DEAP and BER rating

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


DEAP Screen grab showing permissible MPEPC & MPCPC values (on latest version with blank project)

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):


Table 1 Part L Building Regulations – Maximum Elemental U values.

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…

12 thoughts on “Why you can’t rely on backstop u-values, Part L, DEAP and BER rating

  1. I like the line “You will need to be working closely alongside your architect (with DEAP experience (ahem)) ”
    If you look at the current publication of construct Ireland you will see that there are over 3,500 published BER’s for new houses and only 1,000+ are Part L compliant… What’s going on here eh..!!

    Its a joke really, you get 2 points on your license for being on the phone or you get threatened with prosecution if you don’t pay your TV license but build a €300,000.00 house anyway you like without any consequence…

  2. Hi Mark
    Who is going to inspect the building to ensure compliance? I had conversations with two selfbuilders, one today and one yesterday who quite clearly stated they will not be in complient with the new building regulations and dont care either ways as no one will inspect what type or levels of insulation has bee applied to the building envenlope. Inspection can only be carried out correctly during construction and it cannot be checked properly after the building is closed up and decorated.

    1. Hi Dermot

      This doesn’t surprise me one bit; the bank will need a cert to release money and the certifying architect/engineer is pushed into sign-off to get paid – Professionals need to get much tougher in keeping a complete check on Building Regs & money at every stage of project and refuse to sign-off when things are looking bad.


      1. Hi Mark
        I agree with your comments I believe the rules should be laid down at the very start of each project. There should be a fee included to cover unannounced inspections. I am working on a project at the moment where the architect has said the client will not pay him to carryout inspections I believe this is crazy. The project is 4500 sq foot home.The client must be made aware of the serious problems that arise from poor quality application of building materials and the incorrect levels of insulation materials. I have two clear statments I make iF YOU DONT INSPECT THE INSULATION – Don’t expect the best results. Pay cheap – Pay twice

  3. Mark, I have learned a lot from your site. For that : Muchos Gracias!
    Ok….. My brother has house that fits the bill with a lot of what you have talked about in past 2/3 years.
    Completed 2013 to 2008 Regs. He has had had INCREDIBLE draughts in the house.( this is important with what comes next).

    -Architect signed off house as Compliant( design only basis)
    -BER guy xml files shows Part L Non Compliance
    -Surveyor and Engineer we got in both agree house is Non Compliant.
    – developer of site submitted / signed off on Thermal Bridging Details in General Guidance Documents to the BER guy who in turn used .8 factor towards BER calculation.

    Problem is , the Thermal Bridging Details ticked off on Guidance Doc were NOT actually what was built on site with a far inferior and v different form of wall construction than ticked. These thermal bridging details were not inspected or ever recorded by an outside Architect/Engineer .
    Examples : no air tightness tape at junctions, regular plasterboard was used rather than the ticked insulated plasterboard etc……

    In light of the unbeleivable draughts/ cold air infiltration inside the (porous) envelope , my brother is kicking up a storm. What does seem to be v grey area is if signed off thermal bridging guidance docs are not followed through on site , if there is any legal recourse. Brother is mortgaged and his bank manager red faced as they feel they have got wool pulled over eyes.

    based on your experience and your prophecy in 2012 original blog posting that stuff like this is coming down the line to Solicitors/ Banks – who is ultimately responsible and at fault if anyone? I thought the guidance doc was just that ie a guide and builder free to change but if then used as part of BER , that doesn’t sound right ie
    ” we will use the doc to get a nice BER score to sell the house but we won’t build to this as its too much hassle/ expensive”

    Your thoughts Mark?

    VanMarke or thomas for De Ronde!!

    Kenny G

    1. Hi Kenny

      Many thanks & Tricky, BER guy is relying on details from architect so he gets out

      Architect is Design only so didn’t inspect what the contractor built, he could get out

      Only way is through court.

      This is why SI9 came about to have full finger pointing paperwork


      All advice online is remote from the situation and cannot be relied upon as a defence or support – in and of itself – should legal action be taken. Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.

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