EnerPHit: How Glasgow's green tenements slashed bills

Tenants moved in just over a year ago and have seen an "astounding" drop in energy bill costs, according to Southside Housing Association, which acquired the flats.

Sign me up -  what exactly did they do?

Around 450 millimetres of insulation was added in the roof and on the ground floor, between and beneath joists. In the loft, insulation was almost half a metre deep.

Outside walls were bolstered with 200 millimetres of insulation and inside the street facing walls, 100 millimetres of wood fibreboard over lime plaster was added.

"We also did a lot of work on reducing thermal bridging," says project leader and architect Chris Morgan, "trying to reduce heat loss through the bits that are very difficult to insulate and installed triple glazing to all windows with  MVHR (mechanical ventilation with heat recovery). 

"We took all the floor joists out of walls where indoor insulation wasn’t working, so they now go into a beam that is fixed back to the wall so nothing can rot inside those stone walls. 

"We didn’t quite achieve EnerPHit standards – the contractors weren’t able to get air tightness we needed, even though it reached the right number when we modelled it. This was a lesson learnt for future projects."

Engineers also made a number of changes to increase the building's resilience to climate change with gutters oversized so that when rain falls more heavily, they are less likely to be blocked.

Any stumbling blocks?

"Perhaps the client would say finding the money! But it is worth saying that even standard retrofit is expensive now," says Mr Morgan.

"The question I would ask is not how expensive it is, but what’s the difference between this approach and what we might ordinarily do.  

"Our EnerPHit approach is more guaranteed to deliver savings – and more or less, we have achieved these savings, and you wouldn’t find this in buildings that haven’t followed this. 

"It’s important to note that if you only say we are undertaking retrofit to save carbon, there’s a limit to how much you should spend. 

"However, if we are also reducing fuel poverty, improving Scotland’s heritage, reducing health inequalities, improving fuel security, addressing climate change impact, residents’ comfort etc – then there’s arguably more reason to support this sort of work. 

"Achieving the necessary standard of air tightness was a challenge. With Niddrie Road, this was difficult to achieve, due to various reasons around construction and planning".

We are in a cost-of-living crisis, what's the damage?

"When we went to tender for this project, we divided the costs into three sections, one of which was energy efficiency, the others were more to do with general improvements, …and it came back at £88,000. Of this, only £36,000 was energy efficiency. 

"The remaining costs (e.g. for walls, or plastering, redoing electrics etc) got more expensive over time - partly covid restrictions, partly demolition requirements - but the cost of the energy efficiency didn’t increase. So in my head it was £36,000. Other similar projects have ranged from £25,000 to £100,000. 

"It’s costly but so is everything else. If everything is expensive, surely we should choose the thing that has the best and biggest long-term impact on fuel poverty, health, heritage, carbon reduction etc – and that’s the approach we took, on the basis that it was the most cost effective way to go forward. 

"I believe the government should be meeting the retrofit costs, and the tenants will reap the benefits of long-term savings."

Can I go it alone with one tenement?

"EnerPHit standard can only be achieved on a block-by-block basis which is one of the reasons we did this project as we had a whole block and it’s so much more cost effective to do this," says the architect.

"But you can do a lot of the things to one flat and taking these measures is always a perfectly sensible idea.

"To make a tenement more energy efficient and warmer, I’d look at the suggestions I made earlier – so adding insulation, making the property more air tight, using heat pumps, sealing up gaps.

"Loco Home Retrofit are working with people in Glasgow to achieve these changes by supporting energy conscious home improvement, so I’d recommend reaching out to them."

Chris Morgan is Director/Architect at John Gilbert Architects with over 25 years' experience and is certified in Passivhaus, Permaculture and Building Biology.