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Passivhaus with Helen Seymour-Smith

Helen Seymour-Smith

Helen designed and lives in Underhill House in the Cotswolds, the very first Passivhaus in England. This groundbreaking project was shown on Grand Designs, featuring a Sto system carefully put together by our technical team.

Helen's practice now tends to work mainly on Passivhaus projects, including the recently completed refurbishment of an interwar detached house in Moseley, Birmingham, and a small replacement dwelling in a Conservation Area in Cheltenham, which is currently on site. They have many other Passivhaus projects on the drawing board, and recently came second with an Honorable Mention in the Bulgaria Passive House Design Competition.


What are the pros and cons for self-builders of achieving Passivhaus?

Why wouldn't you want your house to have such a thermally efficient envelope and design that it only required very minimal heating?

By achieving the following:

  • very good levels of insulation with minimal thermal bridges;
  • well thought out utilisation of solar and internal gains;
  • excellent level of airtightness;
  • good indoor air quality, provided by a whole house mechanical ventilation system with highly efficient heat recovery


You produce a house which does not need a traditional heating system to be comfortable to live in. It seems to me to be a no-brainer.

The only downside is that you have to invest more money and effort to achieve this. But if you are able to look at it as simply front-loading your utility bills, then it makes perfect sense.

How does Passivhaus compare to the Code for Sustainable Homes?

Passivhaus concerns itself principally with getting the fabric of the building right, creating a building which requires minimal energy to run, whereas the Code for Sustainable Homes primary aims are to reduce CO₂ emissions from a building, taking into account the whole life cycle. The Code encourages renewable energy sources, although these may be wasted if the building envelope is not adequately sealed.

Is the method suitable for refurbishment projects? What are the challenges?

Yes, it's certainly suitable for refurbishment, although it is much more challenging to achieve – hence the less stringent EnerPHit Standard. Airtightness is particularly difficult in existing properties if the airtightness layer is on the inside, working around existing joist penetrations etc. Continuity of insulation is equally challenging when the insulation is internal, and the potential for condensation problems is a minefield. External insulation is a better option, but it is often not suitable in sensitive areas to change the external appearance of a building. Other challenges include the existing orientation of the building and openings which may not be suitable, and the routing of MVHR ductwork.

What is the future for Passivhaus in the UK?

It's looking very bright indeed. With organisations like the Passivhaus Trust championing the cause, and lots of training available, the awareness and uptake seems to be rapidly increasing with an impressive number of completed projects in the UK.

How does the EWI help in Passivhaus constructions and why would someone choose EWI rather than a standard insulation solution?

Externally insulated masonry construction makes perfect sense, in eliminating the risk of condensation and keeping the thermal mass of the structure exposed internally to help regulate the internal temperature. It also makes eliminating thermal bridging relatively easy.

Has your Passivhaus delivered how you expected it to?

Absolutely! The indoor air quality is excellent. It's completely draught free, and the temperature stays very constant. It's an absolute pleasure to live and work in such a space, not to mention satisfying how little energy is required to run it.