What is DEAP and why does it matter for your design?

How it works in Ireland

DEAP is the software-based method published by SEAI for calculating how much energy a home needs for heating, hot water, ventilation and lighting, and the carbon emissions that result. The same method sits behind two things you will meet on a self-build: the compliance check against Part L, and the BER certificate.

Technical Guidance Document L uses the DEAP result to test a new dwelling against its energy and carbon limits and the minimum share of renewable energy. Your designer enters the planned wall, floor and roof build-ups, windows, the expected airtightness, the heating and ventilation systems and any panels, and reads off the result. Small changes, such as a different window or a heat pump instead of a boiler, can move the answer a lot.

A BER assessor repeats the calculation on the finished house using what was actually built. The as-built result produces the BER, so it can differ from the design stage figure if the build changed.

You do not run DEAP yourself, but you should see the output. It also gives an estimate of delivered energy that you can multiply by an electricity price to get a running cost.

What to ask

Ask your designer three things: what the preliminary result is for this design, how much margin it has against the Part L limits, and which choices drive it most. Then ask how the result would change if you swapped the heating system or window specification. Keep the design stage report with your planning and building control papers, and give the BER assessor the final drawings and product details so the as-built calculation reflects what you actually installed.

A common mistake

Asking for the DEAP result only once the house is built. Ask for a preliminary result before the drawings are finished, and for a margin against the limits, so changes are cheap.