What is it really like to live in a Passivhaus Retrofit?

Q.

What made you decide on an EnerPHit retrofit?

A.  

Our aim was to reduce our long-term ecological footprint while simultaneously reducing and future-proofing our fuel bills, with a welcomed side-effect of improving the house’s comfort levels.

After reading reports about failure to perform in 'eco homes', which seemed to address vastly under-predicting energy use, leading to disappointed clients , we chose the EnerPHit certification route as it was the only low energy retrofit method with proven post-construction performance.

Q. 

Who were the key team & were they experienced in Passivhaus?

A. 

As clients we did have to learn a lot about building in general and Passivhaus methods in particular, and we were unable to find a local architect or builder with prior experience of the standards. We were fortunate to find Redesign Architects who were enthusiastic about learning to design to EnerPHit, and able to recommend an equally enthusiastic builder, Burton Building Solutions.

We were able to follow the lessons learned from the earlier Grove Cottage EnerPHit project, the Totnes Passivhaus, and we used AECB details to refine elements. This helped make most of our building details work as well as planned.

We were not rushed in the design stages of our retrofit, so although ensuring build compliance was complicated and took over a year, by the time we started we were confident the design would work. The hardest part was ensuring that what we had designed actually got built.

Paul Jennings from ALDAS conduct an invaluable airtightness training day on site which ensured the main build team understood the importance of careful detailing and repairing mistakes.

• Architects: Redesign Architects.

• Main Contractor: Burton Building Solutions.

• Passivhaus Consultant: Alan Budden of Ecodesign Consultants.

• PHPP calculations: John Trinick of WARM.

• Airtightness training: Paul Jennings of ALDAS.

Q.

In your opinion what are the key differences between living in an EnerPHit home, compared to a standard home?

A.

We thought that the advertised level of improved comfort of an EnerPHit home was probably exaggerated.  However, since completing the works, we've been really surprised by the difference in quality of living EnerPHit provides. The comparison between living in an EnerPHit home and a building-regs level home is like the difference between living in a home with open fires and one with central heating. Not only is the house warmer, drier, cleaner and draught free, but the housekeeping chores needed to keep the house comfortable take a fraction of the time: We never have to wipe condensation off windows, laundry dries overnight on airers, smells vanish, and there is never any black mould anywhere.  An unexpected benefit of maintaining a good air quality without having to open windows in summer is great for hay fever suffers.

Q.

 What was most challenging?

A.

Occupying the house with 2 small children during construction was difficult; but the greatest worry was the airtightness layer, and maintaining the quality of construction to achieve this was a challenge. We ended up achieving 0.32ACH rather than the 1.0ACH we were aiming for by:

• Choosing an external airtight layer: As we would be fixing lots of furniture to the walls, which would inevitably damage the airtightness of internal plaster, we decided upon an external cementitious parge coat. This meant we could keep the airtight details as simple as possible and avoid joist penetrations. Having the relatively fragile airtightness materials protected from damage both inside and out seemed a very good idea to us.

• Training and supervising sub-contractors: To maintain high quality workmanship on building that would not usually require such detail, and could be easily covered up was a continuous battle. Camera phones were an absolute lifesaver!- the builders were able to photograph anything they were unsure about, so if I was unavailable they could text through a photo, ensuring that every detail was completed to a high standard. It also meant that there was no excuse for covering up a mistake. Team atmosphere was greatly helped by a no-blame attitude to mistakes, and we were able to spend evenings and weekends helping out, mainly doing the airtight taping and general labouring, to help keep the project moving.

Insulation and taping at window. Photo credit, eco design consultants.

Q.  

Passivhaus retrofits are usually dismissed as not cost effective. What are your opinions on cost?

A. 

Our gas bills have gone down from £128 to £28 per month, in spite of price rises, a large extension, two extra adults living in the house and the building being on average a generous 5 degrees warmer all winter than before the retrofit.

Retrofitting regardless of which standard you aim for, is costly, in no small part because VAT applies to retrofits but not to new build, which makes retrofit relatively expensive in comparison. An advantage was that we were able to live in for all but two weeks of the works, saving thousands on rental of another house. Our project, cost about £950/m² inclusive of 20% VAT. The external insulation costs totalled £28k alone.

We estimate the payback time will be 5 years due to income from 2 housemates, reduced fuel bills and the solar PV feed-in tariff (though Architects/Builders believe we are pessimists.) We have no idea what kind of premium, if any, an EnerPHit home would attract. Of course, we hope that if we ever do have to sell, the demonstrated cost savings and comfort will attract a considerable premium.

Q.  

What would you do differently and why?

A.   

We hadn't quite anticipated that some rooms would be slightly warmer or cooler than others. This isn’t shown on the PHPP modelling as it is a simple Excel tool to work out the heat input required for the whole building- a task it has managed admirably. The old parts of our house are brick built, while the new extensions are timber framed. The timber framed parts have noticeably bigger temperature swings than the heavier parts, due to their lack of thermal mass. We could probably have reduced or eliminated this effect by using insulates with more thermal mass (such as wood fibre, rather than polystyrene) and by having radiators in more rooms: Currently, the temperature of the 13 rooms and 173m² of the house is maintained by three or four radiators, which means that some rooms are one or two degrees colder than others in winter as the MVHR is not able to redistribute quite enough heat.

Q. 

Would you do it all again?

A.     

Having lived in a functionally completed (if not entirely decorated) EnerPHit home for the last year, we are convinced that if we ever need to move, we will either retrofit another house, or build a new Passivhaus  ourselves. As more architects and builders become familiar with Passivhaus, the self-education required by clients  should become less and less, and this should open the option of EnerPHit to a far larger number of households. We  recently heard that one of the Architects, who were uninterested in Passivhaus as a standard when we were  asking around, is now designing a Passivhaus new build for another family- a very reassuring progression.