NSBRC - Case Study | Guy & Susan Hargreaves

Kinver: Victorian Terrace transformed to Passivhaus Standard

Guy and Susan were already experienced renovators when they undertook their eco renovation / extension project in Oxford. Their new home was a mid-terraced late Victorian home, constructed of brick and stone with a plain tiled roof and a poor-quality extension, in need of some modernisation. Their aim to make it a light, bright, comfortable space fit for the 21st Century, which was as environmentally sustainable as possible.

Guy attended the Passivhaus Workshop at the NSBRC in November 2019 where he first met with Alan Budden of Eco Design Consultants. At that stage Guy and Susan were awaiting planning permission, but took the decision to step back and optimise the design to align with the Passivhaus Standard, and resubmit their plans to the local authority. The process began by analysing the building, proposed changes, and specifications in the Passivhaus Planning Package (PHPP).

After obtain planning permission for the revised design, and the completion of the detailed design, construction started on site in January 2021. Work commenced with stripping out, which inevitably highlighted some unplanned issues - which was expected given the property was built in 1906. The construction methods used reflected a desire to be environmentally sustainable and sensitive to the existing structure.

The principal contractor had a dedicated site manager and Eco Design Consultants worked as contract administrators. Everything else was managed by Guy and Susan, attending site as frequently as restriction at the time allowed. The whole project was also documented by Ben Adam-Smith of Regen Media, with film, photographs, interviews and podcasts found on Ben’s houseplanninghelp.com website.

As a terraced home on the outskirts of Oxford, access to the site was a challenge. The contractors had to wheelbarrow rubble from site to their vans through the house, removing everything daily. When the windows arrived, these needed to be craned in over the back garden.

An important goal of this Passivhaus project was achieving a high level of airtightness. Attaining this was very time consuming, but contributed considerably to the final comfort of the home.

Could you tell us any interesting facts or remarkable features about your project?

The property is a 1906 mid terrace, and is not in a conservation area.
The ground floor of the main dwelling (being all levels ground and above) was converted into open plan living, kitchen, and dining area across the full building footprint.
There are three bedrooms, a bathroom, and a laundry / utility on the extended first floor, and a master bedroom and ensuite on the expanded dormer second floor.
The basement was converted into a self-contained apartment with a separate kitchen and bathroom, and external access only.
The property’s airtightness tested at 0.94 ACH across both main and basement dwellings.
Both dwellings are ventilated via two separate MVHR systems.
One ASHP provides hot water (through heat batteries) to both main and basement dwellings, and heating / cooling to the main dwelling through its ventilation system.
Modern triple glazed tilt-and-turn windows and sliding doors to the rear were fitted.
Mock-sash triple glazed tilt-and-turn windows have replaced all front and most rear original sash windows.
The rear ground floor flat roof has an attractive sedum garden.
Solar PV and battery providing 95% of the net electrical needs of the main dwelling across the seasons (excluding EV charging) has been installed.
An EV charger and participation in the Oxford Gul-e trial allows EV charging on-street (no off-street parking).
The property has an all-electrical specification with gas closed off at the street main.

Please click here to see the floorplans in full.

Guy and Susan’s Experience at the National Self Build and Renovation Centre:

How many times have you visited The National Self Build and Renovation Centre before?

Three

What would you say is the most helpful feature or resource at the NSBRC?

The ability to view many different technologies and meet a range of professionals in one convenient space, with EV charging and close to Oxford!

Did you use any exhibitors at the NSBRC? If so, who?

Yes, Eco Design Consultants (EDC), Worcester Renewables and Zehnder.

What did you enjoy most about your visit to the NSBRC?

Listening to the many experts there, and learning about the latest products and techniques appropriate to our climate and conditions.

Would you recommend the NSBRC to a friend, and if so, what aspects of the Centre would you recommend and why?

I highly recommend potential retrofitters spend time looking and learning about products of relevance to them. For me insulation, ventilation, and building materials were of great interest. Also I attended a Passivhaus Workshop where I met my architect and learnt more about the standard.

Before Photos:

Under Construction:

The Finished Property:

Guy and Susan's Retrofit Experience:

What first inspired you to undertake your project – what did you hope to achieve?

We bought our property knowing it needed a fair deal of renovation. As we worked through the project and developed plans our ambition grew, and we finally settled on aiming for Passivhaus standard. We wanted to fully electrify the property and futureproof it as much as possible for a warmer and more volatile future climate.

What was the cost and size of your retrofit project?

We bought the property in late 2019, which in hindsight proved to be the post-Brexit low in property prices. We felt we paid a fully unrenovated price without premium. As a result, we felt confident we could spend a bit more than were we simply aiming to achieve standard UK building certification level, and not significantly overcapitalise the property. I would estimate achieving Passivhaus enerPHit standard added an additional 20-30% to total costs. Separating Passivhaus from generic building costs differences is not easy – things like kitchens, fittings, and finishes can vary massively in cost depending on whether one specifies high or lower end products.

How did you find your land or conversion project? Do you have any tips for others currently searching for something similar?

My wife Susan put in a massive amount of legwork visiting properties before we found the right place in the area we wanted at a fair price. There is no substitute for hard work finding the right property in our opinion. We preferred properties with south or west facing gardens, which reduced the number of potential candidates a lot! We are from Australia and New Zealand, and when buying property down there we preferred north or west facing gardens, which served us well. Our philosophy is when buying property put in the time and effort to buy the right property, and it will more desirable and easier to sell when that time comes.

Did you have any issues getting your planning permission granted or with building control? If so – why was this?

As we were not in a conservation zone and were doing external works that had a lot of precedent in the area, we had no problems with planning permission. Our first approval took less than six weeks, and a subsequent variation to that approval took around a month.

What factors influenced the selection of your method of construction?

We were heavily guided by our architect Alan Budden of Ecological Design Consultants (EDC). Alan’s team were Passivhaus specialists so naturally specified plenty of insulation, airtightness and other such products. Where possible we used ecologically sustainable products, but at other times - e.g. the new kitchen floor slab – traditional concrete was used. The property was stripped back fully internally, but externally much less work was required minimising the carbon footprint of the project.

Did you use a project manager, or did you choose to self-project manage?

I was fortunate to be able to spend a lot of time onsite every day so in a sense I self-project managed it. We had a foreman from the primary contractor and EDC administered the contract, visiting every two weeks. No formal project manager was appointed.

What was your budget and were you able to stick to it?

We ended around 10% over budget, almost entirely by choice.

If you didn’t stick to your budget, what was the main reason for the overspend?

We found three main surprises during the building works – a hidden steel joist needed moving upon discovery, the front bay window brickwork was in poor condition and needed pulling down and rebuilding, and the front basement level needed underpinning. All other overspend was from increased specification or some minor plan reworking.

What is the value of the finished project?

Probably around what we paid for the property plus the cost of the works we have done.

Did you reclaim the VAT, and if so, how much were you able to reclaim?

Being a retrofit there was limited scope to reclaim VAT. We did qualify for the Green Homes Grant to offset the cost of the ASHP.

What aspects of the process did you find stressful – and do you have any tips on how to avoid the pitfalls you encountered?

Generally I found the building process stressful, mainly because spending significant money on a project that can go wrong creates a constant amount of stress. We had a fixed price contract which reduced our uncertainty in overall cost, but whenever our own contractors e.g., the mechanical engineer, renewable installer, or window supplier caused any delay that could create costs for our primary contractor (builder). Fortunately all parties had similar delays, and so we all absorbed our own delay costs. Probably good luck over management! We built in 2021 when the COVID-19 pandemic was beginning to subside but the labour and supply markets were very dislocated. With a Passivhaus project there are a lot of additional requirements, and the most stressful of these for me was staying on track to deliver a high-quality airtightness result. This was a daily struggle, and I highly recommend asking the builder to appoint an airtightness champion whose only job is to focus on ensuring all work done is airtight. This person could ideally report to the building company owner directly – similar to a compliance function. If airtightness quality weakens for any reason then action needs to be taken immediately before final finishes go on and the leaky areas become inaccessible. Airtightness testing will find 100% of the leaks, and it doesn’t take much to fail Passivhaus certification. Happily our builder delivered a sound airtightness result.

What did you find most enjoyable about working on your project?

I enjoyed the science of building to Passivhaus certification. As a former engineer I found much of the design process very interesting. Seeing the project coming together was very satisfying, and while we were aiming for a new build Passivhaus airtightness result from the beginning, going through the build and recognising the practical difficulties of making a retrofit airtight meant when we got the EnerPHit result we were thrilled.

What is one of your favourite features about your project?

There is so much we love about living here now – the open plan style, the flexible lifestyle, the control over heating and cooling, the low energy bills, the freedom from gas, the EV charging, the consistent temperature throughout the house, the flexible use basement flat.

How did you tailor your home to suit your lifestyle?

Open plan living with full height and width glass sliding doors flowing onto a stone patio and perfectly sized garden was how we loved to spend our days. The house is light and modern but from the outside fits the existing townscape beautifully.

Is there a possibility you would ever undertake another project in the future?

We may do a Passivhaus new build if we ever go back home to Australia. The project hasn’t put us off property development, but it was stressful nonetheless.

If so, is there anything you would do differently?

New build with SIP construction just to simplify the building process. Otherwise I imagine the design and execution process would be similar.

What would your top tip be for other NSBRC Visitors about to embark on their first self build, conversion or home improvement journey?

Chase your dreams and don’t give up. A beautiful, comfortable, future proofed home is worth every effort!

Guy & Susan Hargreaves