HPH322 : An EnerPHit standard retrofit of a Victorian mid terrace home – with Guy Hargreaves
Homeowner Guy Hargreaves reflects on adapting and expanding his Victorian mid terrace home, retrofitting the whole building to EnerPHit standard.
Interview with Guy Hargreaves
Initially we chatted with Guy Hargreaves (episode 297) about his aspirations for upgrading his period property for energy efficiency, comfort and to future-proof it for a less hospitable climate. He had gone through the design process and gained planning consent to adapt and extend the property, and targeted Passivhaus standard (largely helped by the form or shape of the building) for the project.
In this episode Guy returns after the renovation and reflects on the construction stage as well describing what the house has been like to live in.
Guy has been fantastic in sharing the journey in our membership community, The Hub.
Go behind the scenes of this deep retrofit. Get access to our in-depth video case study in The Hub
Access issues meant a lot of manual labour
The project began in February 2021 with the strip-out but initially everything had to be removed through the front door! As the one-way street was narrow construction waste had to be dealt with immediately, so it was placed into the back of a truck, driven to the builders' yard and sorted there.
Access improved after a ‘win win' arrangement
As time went by, Guy managed to negotiate access through a private car park at the rear (on an adjacent road). In return he offered to resurface the car park at the end of the process, fix the lights and replace the fence.
Before the renovation
Visualisation of the proposed scheme (at the rear)
New foundations were prepared for the extension
At the rear of the property a small lean-to extension was demolished and fresh foundations were dug for the new extension which would be the width of the property. A digger was craned into the garden from the car park to make the excavation work easier.
Tonnes of soil was removed to prepare for the new foundation.
Then the concrete went in, followed by a layer of insulation and a floating concrete slab.
Steels help open up the old house, but were not necessary for the retrofit
A key element of the brief was to open up the space and so a couple of walls on the ground floor had to go. Structural steels spanning the width of the house were added to take the loads from above.
Some steels already existed in the house from previous renovations but these needed to be replaced.
A contingency is always essential on a retrofit
It is impossible to predict everything that may crop up during a retrofit which is why a healthy contingency fund is always required. One ‘nasty' on this project was the condition of the bay.
Although a homeowner's survey was conducted when the property was purchased it did not flag up any issues. However as the building was stripped back cracks around the windows and crumbling brickwork were revealed, and it became clear that a structural engineer would have to take a closer look.
The outcome was that the bay needed to be rebuilt at ground level with some underpinning necessary at basement level.
Insulation and airtightness strategies change around the building
With a mixture of new and old, brick and timber, combined with planning constraints the technical design utilises several difficult wall build-ups. For example, at the front of the property the appearance had to be preserved and so an internal wall insulation strategy was necessary. This breathable build-up has several layers including a diathonite plaster (the airtightness layer), wood fibre board and a lime based plaster.
The ceiling height in the basement was not as generous as the floors above but removing a 75mm screed layer gave them a bit of wiggle room to add 40mm of rigid insulation.
Up in the attic room rigid insulation was used in the roof. And at the back of the house softer wool batts were filled the timber frame.
Larsen truss built on site for rear extension
The new extension is timber frame and uses a twin stud Larsen truss (300mm) to create a decent size cavity for the required insulation. Cutting and erecting it on site is a simple and cost effective route to achieve high performance.
The room at the top of the house was expanded
A previous owner had converted the loft but the sloping ceilings made it slightly awkward space so Guy planned to open it up on the garden side (south side), which also affords the best view in the house.
The skylights before the renovation
Guy understood the overheating risk of the dormer room
That whole south side we glazed in a rather aggressive and somewhat controversial scheme that is going to be a work in progress over time because that dormer is the top of the house… The heat in the house tends to rise into the dormer and add to the solar gain.
External blinds will be installed if ever needed
While over-glazing will lead to overheating Guy did not have his eyes closed. Instead he made sure that there was a strong back-up plan. So there were plenty of window ventilation options as well a reverse cycle heat pump, which can be used for cooling. However, if the temperature becomes unbearable then the ultimate solution will be external shading.
Guy stepped in as quality control
Much like Mike Coe's experience in Portree, Guy decided to monitor quality.
He was on site every day checking how the airtightness layer was coming together, highlighting potential weak spots.
Airtightness became a personal challenge
I knew that we would get the insulation right. But I had absolutely no idea that we would get the airtightness right. And the airtightness, it's like a stop go thing. It's like blowing up a balloon. If there's a hole in it you will get found out.
The biggest worry would be areas where the airtightness layer gets hidden by the construction.
Interim airtightness tests highlighted areas that needed attention
Guys likens airtightness to ‘compliance' in the corporate world. He suggests that those in charge of the results should almost be separate from those doing the work.
Pressurising the fabric of the house and using smoke pens to identify leaks was essential to eliminating draughts and improving airtightness.
Airtightness is really about chasing down your problems.
Pausing construction to perfect the airtightness is not realistic
In an ideal world the required airtightness would be achieved before any finishing work was carried out.
With a team of builders on site it becomes increasingly difficult to address small airtightness issues without progressing work elsewhere in the building.
Delays in ordering increased pressure
With supply chain issues the sequencing on this project added another layer of complexity. Lead times could change overnight.
Architects' contract administration a good call
One of the more valuable things we did was to engage with my architect in an administration contract, which included a fortnightly visit on site, and that kept a level of professional focus on what was needed, what was coming up, where the timing was, what was being realistic, etc.
The Passivhaus standard became a step too far
EnerPHit is the retrofit standard for a reason. It is hard to modernise existing buildings and this is why it's a slightly less stringent target.
Although Guy held onto the goal of achieving the Passivhaus standard target of 0.6 air changes per hour (@ 50 Pa) until the ‘grim death' there came a point where he realised it was too much of a stretch.
Work in the basement apartment had been halted to focus on the main house so that Guy and Susan could move back in as soon as possible.
So the first ‘official' airtightness test of the main house was after they had moved back in (March 2022). At this point it became harder to carry out remedial work.
And an airtightness test for the basement was still needed for an overall result (which came a few weeks later).
The final result for the whole house was 0.95 (ACH @ 50 Pa).
Knowing the ‘Hurculean' effort that went in Guy is immensely proud.
That's what the EnerPHit standard is about… recognising the almost exponential effort in getting from 1 ACH to 0.6 ACH (@ 50 Pa) in a property that's already built.
Comfort tops the benefits
Guy laughs about being able to wear shorts and a t-shirt almost all year round!
He also points out how quiet and still the house is.
With an all electric house the bills are likely to be 1/5 of what they were before, but clearly there has been a massive upfront investment.
Solar PV is the only missing element!
In some respects the people I'm feeling most envious about today are those who have 10 kilowatts of solar PV on their roofs.
With an efficient heat pump providing heating and cooling for the house as well as the hot water, Guy has got nearly everything for the resilience and future-proofing he wanted.
However, there were not many good options for a solar installation. The flat roof at the top of the house was the obvious one but it only had a couple of kilowatts potential.
I didn't think that that was worth the trouble, to be honest. But given everything else that we were doing, it was just probably the straw that broke the camel's back.
Good communication and a stable relationship with your builder is vital
Having been through building processes before Guy has been reminded how important it is to have a stable relationship with your builder. The key to this is staying calm and talking through any challenges.
Changing your builder is a vastly complicated process and it's made even more so when you're halfway through a Passivhaus. And you wouldn't find another builder to want to take it on. So having a strong relationship with the builder is super important.
There is an appetite for retrofit in the UK
Guy has already opened the doors of his home to local community groups interested in retrofit.
There is an enormous appetite in Oxford, and I think probably UK wide, for all or some or most or half of the things that we've done to our property.
Find out more
Check out part 1 – our interview with Guy before construction began
Visit the website of Eco Design Consultants
Visit the website of Equus Design and Build
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