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SAP & Air Tightness Energy Savings In Naturally-Ventilated Dwellings

We discuss the Government’s response to the Future Homes Standards Consultation (Questions 48 & 49).

The Government’s response to the Future Homes Standards Consultation has been keenly awaited by the UK construction sector. The response document, published in January 2021, covers many aspects of home construction with a view to meeting the nation’s carbon-zero targets.

Air tightness – and therefore air tightness testing – plays a significant role in building’s energy efficiency, and so formed a key part of the consultation and response documents.

Here we’ll look at the government’s response to Question 48: Do you agree that there should be a limit to the credit given in SAP for energy savings from airtightness for naturally ventilated dwellings?

The consultation document stated that currently “increased airtightness is rewarded in SAP due to an improvement in energy efficiency.” It pointed out, though, that very high levels of air tightness can result in poor indoor air quality, or the need for added ventilation. The consultation suggested there should be a limit to the energy/CO2 credit in SAP as regards naturally-ventilated properties in relation to bettering air tightness over a certain level. The proposal was designed to discourage extremely airtight homes that do not have appropriate levels of ventilation.

67% of respondents answered ‘no’ to this question.

A proportion of respondents that said ‘yes’ to this proposal suggested “only mechanical ventilation with heat recovery should be used for an airtightness of 3m3/(h.m2) or below, and most proposed that all homes should only be constructed with an airtightness of 3 m3/(h.m2) or below.”

It was suggested that the air tightness test should be based on actual air tightness test results – which could be different from the intention of the original design. It was also suggested that if a building fell below the required threshold, the nature of remedial work should be stipulated.

A number of respondents suggested that Part F of the Building Regulations provide recommendations for different strategies for different levels of airtightness. With this in mind, it was suggested that if “Part F was clear that natural ventilation is not

suitable for the most airtight homes, there would be no need to amend the energy

calculations in SAP.”

In response to question 48, and the related question 49 (Do you agree that the limit should be set at 3m3/(h.m2)?), the government stated it will introduce “a credit limit

of 3m3/(h.m2) for both as design and as-built air permeability in SAP for naturally

ventilated dwellings.”

The government response went on: “Guidance will only be provided

for naturally ventilated homes where the design air permeability is leakier than

5m3/(h.m2) @ 50 Pa.”

Will the limit be applied to the design, or the as-built SAP calculations?

For the sake of simplicity, the government has proposed “a credit limit of 3 m3/(h.m2) for both the design and as-built calculations”. This should give peace of mind to developers as regards their design-stage SAP calculations benefits. Further, the response provided guidance on remedial action should a test reveal that a building is too airtight (detailed in Section 1 of the response).

Let us help you navigate the UK’s air tightness testing regulations

With many years of experience in conducting air tightness testing on buildings across England, Air Tightness Testing Ltd. is ideally placed to handle your testing needs in a timely and efficient manner. Our vast knowledge of air tightness will prove invaluable in relation to any remedial requirements – and getting your new developments prepared for sale or rent.

Get in touch with Air Tightness Testing today.

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We are registered with iATS (Independent AirTightness Testing Scheme) and use equipment calibrated by UKAS laboratories. Our testing procedures are also recognised by UKAS.