Ian McKay from BBM Sustainable Design shares how to find a property that will lend itself well to an eco retrofit.
He also contrasts two very different projects, the retrofit of a 1960s terraced house and the upgrade of a Victorian villa from the 1890s.
Interview with Ian McKay
Futurehouse, Milton Keynes
Minimise Energy Demand Before Generating Energy
An eco retrofit is a way of taking an existing building and reducing its energy demand to make it comfortable during the extremes of weather and so forth.
This is likely to include adding insulation, making sure the windows are airtight and insulative in their own right, and considering whether the heating sources are as efficient as can be.
The key thing is about minimising the energy demand first rather than thinking about how you're going to make the energy.
Fussy Architectural Details Make Retrofits Expensive
Choosing the right candidate building to start with can make the project simpler and thus more cost effective.
Very complex forms, lots of roof shapes and little bay windows are beautiful but will be incredibly expensive to eco retrofit.
Simplicity is at the Heart of Houses that are Cheap to Treat
Ian gives an example of how he did a project for his family on a two-storey timber frame ‘shoebox' built in 1969.
Ian says: “We just knew immediately when we first saw the building that's going to be cheap to treat.”
In total (with solar panels, etc.) it cost £70,000 (whereas a low carbon refurbishment of a residential property can often cost £250,000).
Barons Down has a simple form
A Terraced House Will Have Fewer Walls to Treat
In a terraced house it would be unnecessary to treat the shared walls because the neighbours will be heating their spaces and so there would be very little energy loss.
Even if the neighbouring property was vacant the temperature would never get down to outside air temperatures.
Older Properties May Have More Irksome Problems
As older houses tend to be a little bit out of plum certain jobs might take slightly longer in an old house compared to a modern house.
Ian gives an example of how a carpenter might need an extra half an hour to hang each door because the frames are out.
In the UK, Refurbishments are Heavily Taxed
While the new build option is 0% VAT in the UK, refurbishments and extensions are taxed at 20% VAT.
Ian explains that there is a loophole: “People should be aware that it's 5% VAT if it's strictly speaking just eco retrofit, low carbon refurbishment. If you are mixing it up with an extension or creating a loft conversion or extensive alterations in the house which are not to do with making it energy efficient then it makes the contract impossible to segregate out the 20% from the 5% .”
By splitting it into two contracts, doing the extension first and then the eco retrofit as the second, it is possible to take advantage of the 5% rate. However you have to make sure that you're not going to run out of money.
Internally Insulating to Very High Levels Can Damage External Masonry
When Ben asks whether it's best to avoid buildings that need to be insulated internally Ian explains one of the issues associated with a solid masonry construction.
Internally insulating means that the external wall stays cold and damp through the winter and it hasn't got the ability to release that moisture quickly. This can result in increased frost damage on the outside faces of the brick.
On the inside where there's a cold face up against the insulation or maybe a small air gap, this can be susceptible to mildew and fungal growth (which is very bad for internal air quality).
So another rule of thumb is to make sure the internal insulation does not have a very, very good U-value.
If You Have to Insulate Internally, Use Breathable Materials
By using breathable insulation products, such as calcium silicate boards, the moisture is able pass through.
Ian continues: “It's applied directly onto the masonry face but it allows that moisture to come through and you put a lime plaster on the face. That also breathes. Don't, for goodness sake, put emulsion paint on. Put a mineral based paint onto the lime plaster because that also breathes. If you fill up the pores with an emulsion paint then it can't breathe any more. But that helps to keep the wall healthy, it helps bring the moisture out of the wall into the internal heated space and then it can ventilate that way.”
Cutaway graphic of Barons Down
Sheep's Wool Insulation was Used in the Studs
The Barons Down project was a timber frame house which was insulated from the inside. The old plasterboard was taken off, the walls were built in slightly and the depth of the studs was increased to 150mm. Then these were filled with sheep's wool insulation.
Studding into the room to form a deeper insulation void
A Perimeter Channel of Insulation was Dug Around the Ground-Bearing Slab
As the ground-bearing slab at Barons Down had no insulation on it and the ceiling heights were very low, it was not an option to build on top.
So they dug a perimeter channel of insulation at the edge of the slab to make a little thermal break.
They then used 8mm of cork right across the ground floor which itself is a good insulative material.
The perimeter floor channel which formed the thermal break
Consider the Different Solutions Upfront
Before buying a property, it's important to have an idea of the different wall and roof solutions etc. that could be applied.
Hiring a professional is likely to pay off.
Conservation Orders May Limit How a Building Can be Treated
Ian talks about a project called The Nook that was part of the Retrofit for the Future programme.
Built in the 1890s, this Victorian villa is a solid wall construction. As it's located in a conservation area, that meant that the front elevation could not be treated on the outside.
A Hybrid of Internal and External Insulation was Used
Three of the walls were treated externally but because of the architectural features (the two bay windows) the front elevation had to be treated on the inside face.
Therefore that front elevation is not insulated quite as well as the side and back elevations (which were treated from the outside).
External insulation going on
Upgrades Like This are Expensive
It cost £130,000 just to treat the external fabric of the building. It did also get a new boiler and mechanical ventilation system with heat recovery.
Although it achieved the target for the Retrofit for the Future programme which was roughly around that 17kg of carbon per annum per m2, it is hard to justify from a cost benefit analysis.
Floor insulation to ground floor to full depth of first step of staircase
Our Housing Stocks Needs to be Evaluated
Ian believes there is a case for evaluating a large amount of our housing stock.
If it is uneconomic to treat so that people can live comfortably and affordably, then we ought to consider large-scale renewal.
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