Alan Budden explains how a phased retrofit might work and what preparation is required. He also shares how he's retrofitted his own home, which includes trialling an innovative roof solution.
The house (after the retrofit)
Interview with Alan Budden
Alan has been on the podcast before. Last time he explained how simple design decisions can impact on energy performance and cost.
In this session he reflects on his own retrofit which is getting towards the final stage.
Get access to our in-depth video case study of the Kinver retrofit in The Hub
If you have the funds, tackle a retrofit in one go
Nobody ‘chooses' to do a staged retrofit because it's a better option to do all the work in one hit.
Not only will it be cheaper overall (for example tradespeople might have to make a few more visits during a phased retrofit) but the disruption will also be minimised.
And from a planning perspective it will be simpler too.
There's lots of junctions you have to consider in terms of how it's going to be weathered and work during that stage, as it could be six months, it could be 10 years between stages. That's one of the issues. So you end up detailing things, then for the final construction detailing it back.
Retrofitting in stages is a way to progress with the money you have today
Recently Alan has noticed a lot more enquiries from young families who are keen to upgrade their homes.
Unfortunately they lack the funds for a comprehensive retrofit so Eco Design Consultants recommend tackling it in stages.
The most important aspect is to have a whole house plan before you start.
A staged retrofit could allow you to stay put during building work
Depending on the size of the house one benefit of a phased approach is that you might be able to move around the house while the work is being done, thus save money on moving out and renting accommodation.
Retrofit at an appropriate stage in the maintenance cycle
All houses require maintenance and upgrading so there will naturally come a point where you'll be spending money on your home anyway.
The house still had single-glazed windows
The single-glazed windows were not fit for purpose and had been something Alan had wanted to change ever since he bought the property. While he could have upgraded to double-glazing he bided his time so that it would be a switch straight to triple-glazing. His cladding was also tired and needed replacing so doing all these things together can contribute to the project costs.
Think of a deep retrofit as creating a house for life
A deep retrofit is significant work so it's unlikely that you'd just want to sell the house straightaway afterwards. So you should be trying to make the house work for you now and into the future.
Think carefully about how you want to live in the house. Could you also add a bit of value (by increasing floor area, if needed)?
Can the house shape be simplified?
Alan wanted to do the design work himself
Despite having an architecture practice at his disposal, Alan thought the ethical approach was to do the design work and modelling himself. Consequently progress was slow, being confined to evenings and weekends.
Modelling the house in PHPP is a key step
Alan says that after deciding how you want to live in the house and optimising the layout, the next step is to begin modelling it in the Passive House Planning Package. Setting an energy target for the project, such as the Passivhaus retrofit standard EnerPHit, helps inform decisions about insulation, windows, etc.
The shape (or form factor) of the house was improved
Where the first floor was slightly smaller than the ground floor Alan decided to square up the building. This increased the floor area, allowing for a new dressing room and increasing the size of the en suite. but also simplified the shape of the building.
Alan's knowledge meant he could optimise his approach
When selecting materials Alan was always looking at a balance between cost, performance and embodied carbon.
I looked at some interesting things with the external wall upstairs. Timber frame work projects off the wall with GRP brackets with just ordinary cavity wall insulation inside. So I've looked at the DriTherm 32, the DriTherm 36 and a couple of others, so it's different types of mineral wool. And as it was less… the thermal conductivity was worse, the density was less, and the embodied carbon was less and the cost was less. So trying to optimise how thick the insulation was, and which ones I used was quite interesting. And depending on what sort of brackets I could get as well for the timber frame. So it was quite a complex lot of options.
Think how you can stretch funds
Alan planned to do parts of the work himself to save money and therefore, hopefully, take the project further.
He was also planning to test a new roof system which would be manufactured off site and placed onto the existing trusses, but it had a few teething problems. Knowing there would be a delay in the programme there was nothing to be gained by hiring builders to get through the work quickly.
The builder was happy to step in as required
Alan describes how he and his family put on the membrane (from the scaffolding). The builders then came and put the brackets on and the timber framework. And then it was back to Alan and family to fill it with insulation. And so on.
After taking the roof off the utility room and building upwards, they stripped the tiles off the rest of the building and made a few adjustments in preparation for the new roof cassettes.
A stick-on airtightness membrane, Siga Majpell 500, was installed.
A multi-purpose roof was manufactured off site
Alan has always been interested in how retrofit might be tackled at scale and as such he's been part of a group developing an innovative roof panel system.
With funding from Innovate UK the project has progressed and he has become the guinea pig for the first full installation.
The idea was to develop a structural roof panel that includes PV and solar thermal, using that to heat the house.
Off-site manufacture comes with benefits
Using a crane the panels were lifted into place in just one day.
This is a big health and safety benefit because it reduces the amount of time that people are working at height.
Alan comments that making the roof panels have more than one purpose should bring about some economies of scale.
Unfortunately some of the technology underneath the panels that was being used to cool them didn't work as planned, so they are looking at an alternative and hoping to lift off two of the panels off and replace them with new ones. Then they can get them plumbed in and see how much energy they are reaping from the roof and how that's helping to improve the performance of the PV.
Project delays meant Alan was without a roof for 6 months!
With development delays and then the pandemic Alan was caught in a tricky situation. He had taken off his old roof, added a membrane and then discovered the roof panels were not ready!
The manufacturers of the membrane normally suggest that it can be exposed to the elements for up to a month.
So Alan had a challenge on his hands, particularly when a big storm came along.
My roof was left exposed for just over six, including the winter, which is not the best of times, which meant that I was getting condensation forming on the inside because the insulation was planned to be put on the outside and I had some insulation left in the loft to keep us a little bit warm in the winter. So I was having to mop it down, which shows you really, the amount of water I was taking off was quite considerable. At the worst times, I almost had a bucket full of water. I was at the end of it with my mop! And it does show you how much moisture you're putting out as a family. And if that's going to condense somewhere that could cause all sorts of problems. Luckily I could see it, I could deal with it. And now obviously that's gone away.
The membrane did survive and seems to be doing its job.
Get the MVHR online as soon as the house becomes airtight
In a new build the MVHR might be commissioned towards the end of the process but in a staged retrofit it needs to go on sooner, otherwise moisture and CO₂ will build up.
The only downside of that is you will probably go through more filters as they get clogged up with the dust and the dirt from both the outside and the inside. Alan has been switching off the unit altogether if there are particularly dirty or dusty jobs going on.
The insulation will go internally on the ground floor
Alan wanted to keep some of the brickwork visible externally to match other houses in the estate, which means an internal insulation strategy is required downstairs.
The windows downstairs will open outwards to maximise insulation on the frames
All the windows upstairs have been changed because they went within the external insulation so they're opening inwards. On the ground floor we're doing internal insulation and those windows can open outward so we can maximise the insulation onto the frames on the insides. So there's a number of windows downstairs still to be done. I did, we did take a few opportunities to insulate some of the windows on the ground floor, for instance outside our snug and the downstairs toilet because there's some external cladding there with some vertical battens instead of horizontal just to emphasise… a bit of architecture! And also squeeze in a bit more external insulation.
There's added motivation as they near the end of the project
The final stage of the project will be to insulate internally on the ground floor and replace the windows.
One of the things that's happened because of the extended programme is that we've been able to keep going. We weren't necessarily expecting to do the ground floor stuff straightaway but it's carrying on now! And because upstairs is so much warmer than downstairs, it's really given us an emphasis to say we need to get this done. You realise the difference. Generally upstairs has been about three to four degrees warmer than downstairs. And that shows all the Passivhaus physics that air moves when there's three to four degrees difference.
The builders will come back to replace the windows
With a house that's getting warmer as the project progresses, the builders will be coming back to install the windows.
This will get the changeover done quickly.
Then it's back to Alan and family to tackle the internal insulation room by room.
So we'll put some studwork up, insulate it, membrane it, re-plasterboard and finish it off. And also on the ground floor, what was going to be phase three that I think might happen at the same time is the floor insulation. The plan is to dig up the screed, put down a phenolic insulation and the board on top.
A preliminary air test was conducted before the roof went on
Having installed all the airtightness membranes as a family, Alan wanted an airtightness test before the roof panels went on.
There were a few reasons for this. While they are always interested in an overall score, it's more about identifying key leakage hotspots that can then be fixed.
As with the Kinver project, once the roof is on there will be little hope in fixing leaks in this area.
That's why attention to detail is important. The number on this first test was 1.7 air changes per hour at 50 Pascals.
Biggest risk with retrofit in stages is having to redo work
Alan says one takeaway from the project is the importance of a well thought out initial plan.
One thing I'm not enjoying quite so much is in our utility room and kitchen, I had already insulated some of the wall there with 50mm of polystyrene, mainly because at that stage, I was worried about the interstitial condensation. So I was limiting it to what I could do. But because now I'm insulating some on the garage side as well, I can increase the thickness of insulation internally. So I'm having to take out some insulation to put different stuff back in, which is a little bit frustrating to be honest. So get the whole plan done, make sure that works, and then do bits towards it, because that way you're not going to be replacing those bits.
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