17. Is the EcoBungalow the most airtight retrofit in the UK?

A big day in the evolution of the EcoBungalow: the interim airtightness test.

We’d established that the original draughty, cold bungalow had an airtightness of 11.75 Air

Changes per Hour (ACH). At the start of the design process, we set a target of achieving AECB Level 2 but ideally aiming for the higher standard of EnerPHit (the Passivhaus retrofit standard). This is a maximum of 1 ACH. We were blown away with a result of 0.2 ACH – better than even the new build Passivhaus target of 0.6 ACH.

Why are we so excited by this? Airtightness achieves three key things:

• Reduced heat loss. Once the insulation levels in a building have been increased, heat loss through uncontrolled ventilation become significant. An airtight building prevents uncontrolled movement of air by closing the cracks and gaps in the building where warm air can escape and cold air can get in.

• Improved living comfort, especially through the elimination of drafts through cracks and gaps. As mechanical ventilation is usually used in an airtight building, fresh air is provided from outside the building via filters. Air quality is therefore much better than in a home where air enters the building randomly.

• Protection of the building fabric. Any warm air escaping the building will contain moisture. As this air passes through the construction, it will meet cold air and condense. The water from this interstitial condensation can damage the building fabric and cause it to fail. An airtight building reduces the risk of this type of condensation. 

So a high level of airtightness means we’ll be able to achieve an extraordinarily energy efficient, extremely comfortable and long-lasting home. This is why we’re excited!

Why is the airtightness result so good? Four reasons:

A simple building form: We started with a building that’s a simple box-like form. This makes life easier by avoiding awkward junctions and ensures that the ratio of external wall area to floor area as small as possible. We’ve made the building even simpler by removing the conservatory.

Teamwork: We brought the contractor on board early in the design process. Buildability and ease of creating an airtight building drove the strategy of stripping the bungalow back to one single space, then insulating it, creating an airtight box, and finally putting internal walls back in.

This strategy was only possible because I could move out of my home for the duration of the build. So the team has included the people who are kindly putting up with me as their lodger for eight months. Many people won’t have this luxury, and will need to take a phased approach to retrofit. This inevitably means that achieving high levels of airtightness is more challenging.

Quality products: We’ve been especially impressed by the Viking triple glazing supplied by EcoSpheric – excellent quality and requiring no adjustment at all after installation. Thoughtful details, such as a completely flat frame, make taping to achieve airtightness much easier than windows with grooves or steps in the profile.

Superb workmanship: Alex Burn takes a huge amount of pride in his work, with phenomenal attention to detail. The quality of workmanship is fantastic. He was always confident of the outcome of the airtightness test and – indeed – his first response to the result was “I think I can get it down to 0.15 ACH.”

Is the EcoBungalow the most airtight retrofit in the UK?

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