The AECB Building Standard certification FAQ

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Is there a small dispensation for retrofits?

No. There is no dispensation. Furthermore, there are a number of reasons why this may not change in the future:

1) Moisture risk – the greater the air leakage the greater the risk of condensation risk and mould damage
2) Energy use is increased
3) The air tightness standards are (relative to EnerPHit) fairly relaxed

For new build dwellings, is there a requirement for triple glazing?

There is no specific requirement to use triple glazing (just as with Passivhaus). It is however expected that you will give due attention to thermal comfort. To this extent particular attention should be given to the risk of downdrafts from the glazing systems that are specified.

Further guidance: Page 12 of the following presentation from the AECB Annual Conference may be of assistance (for information only. No liability is accepted):

Is triple glazing mandatory?
Triple glazing is recommended, but not required, in order to avoid cold down drafts (where glazing is 2.1m or more), reduce overheating risks, improve comfort and optimise the space heating demand.

Page 19 of the AECB energy standards addresses the performance requirement for the installed and uninstalled window U-values.

You will see that the U-values (uninstalled and installed) permit double glazing.

On this basis for the AECB Building Standard triple glazing is not mandatory.


If we choose an MVHR that is not Passivhaus certified, does AECB Building Standard impose the Passivhaus ‘penalty’ of 12% on the heat recovery efficiency?


PHPP using EnerPHit suggests primary energy (PE) of 144, depending on what percentage I assume for woodstove contribution to heating. How rigid is AECB Building Standard criteria on PE?

The quality assurance for AECB Building Standard is just as rigorous as Passivhaus. The only real difference is the numerical targets are more relaxed.

As a retrofit I can’t guarantee every detail is up to scratch, but airleakage was only 1.45ach. I may not be able to provide every detail or photo as built.

AECB Building Standard certification rests upon your professional indemnity insurance –  it is your responsibility to ensure that all assumptions are appropriate. Without appropriate supporting data the AECB recommends that you assume a worst case scenario for each detail.

The house has PV, would the use of an Immersun™ for hot water be acceptable? I don’t know how to input this into PHPP.

Refer to the primary energy demand sheet “electricity demand (without heat pump).” You can enter the fraction of immersion heating in one of those cells.

My client is inclined to use an air source heat pump but CarbonLite guidance does not suggest this option.

It is true that CarbonLite would suggest that an ASHP is not ideal. This is because of the challenges arising from design, product quality, install and commissioning. The crucial thing is having a rigorous and reliable means of verifying that the Air Source Heat Pump does what is intended once in place.
With this in mind, strictly speaking, other than electricity, AECB Building Standard is agnostic about which kinds of heat source are used – providing you can be confident that they will perform appropriately.

Ultimately, as certifier, AECB Building Standard certification rests upon your professional indemnity insurance.

Can the AECB Building Standard be used for retrofit?

At this point in time AECB Building Standard can be used as a target for retrofit. Once the CarbonLite Retrofit (CLR) progresses to certification stage, AECB Building Standard will only really apply to new build. The critical difference with CLR is the greater degree of attention that is given to moisture related concerns.

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