When I was in my twenties, I worked out in Africa doing low cost self-build housing, which helped to inform my political outlook on the world. Coming back, I became aware that development issues and global issues were linked not so much to policies out in Africa but to a lack of understanding back in the West. And it seemed to me at the time – I’m talking about the eighties – that green issues, which were often regarded as fringe issues then, were in fact very central issues to a global outlook. So those issues have been very important to me since, and my architectural thesis looked particularly at energy and green building issues. I’ve been very interested in green issues throughout my years in architectural practice, and in this zero carbon house we’ve been able, as combined architect and client, to take them even further.
As a growing family we were looking around at first for a site to build a new zero carbon house. However, there were no vacant sites because the locality we’re in is very dense urban housing. It very quickly became apparent that it would be much more interesting to take an existing house and attempt to retrofit it, to the very demanding Code for Sustainable Homes Level 6 zero carbon level, than it would be to build a new house. Once I had embraced that idea, and saw that in fact it had much wider sustainability potential and implications as there are many more old houses than new ones, each using much more energy, I became very interested in how we could pursue it.
This semi detached property built in the 1840s has been substantially extended and converted from the original 2 bedroom house to a 4 bedroom house with a studio loft. Completed in 2009, the UK’s first retrofit house to “zero carbon” standard (Code for Sustainable Homes level 6). It generates all its own renewable energy with no use of fossil fuels, and has won six design awards including Civic Trust Commendation and RIBA Architecture Award. This is a private family home.
“quirky, delightful…a thoughtful design of exceptional quality” – RIBA
“I’ve seen the future – and it’s in Birmingham” – The Times.
Designing Zero Carbon Buildings Using Dynamic Simulation Methods by Ljubomir Jankovic (Routledge, 2012), features this house as an extended 22 page case study. It also features in a BBC TV Inside Out episode.
As part of the substantial extension made to the original property, we installed certain measures to get the house to zero carbon. Insulation is a key factor in reducing heat loss; therefore we installed it in internal walls, ceilings, floors and the roof. Triple glazing was also used extensively throughout the property. We utilised specific materials such as clay blocks, rammed earth floors and the existing Victorian brickwork to regulate internal temperatures. Combined, this allowed us to make the switch from central heating to using just a wood stove along with solar thermal panels. The other major change was a Mechanical Ventilation Heat Recovery system installed throughout the whole house.
The new triple glazed roof lights and windows allow large amounts of high quality natural light all the way through the house. The triple glazed windows also utilize solar radiation whereby the low angle of the sun in winter transfers heat through the windows. In summer the windows are shaded from the higher angle of the sun by an ash tree, therefore keeping the house cooler. The house doesn’t overheat in summer (even during July 2013) and the day time and night time internal temperatures are relatively even due to the use of the high thermal mass materials (clay, earth, etc.).
The insulation installed in walls, floors and the ceiling has resulted in the current walls and roof being 16 times better than in the old building. The windows are 14 times better and the air-tightness of the house – which is particularly important – is 28 times better than in the old building.
A combination of the above measures means that no central heating is needed and 80% of the heat produced by the stove is used to heat water whereas only 20% is needed for heating.
There are tiny things like switching we might have done slightly differently but overall, I think it’s exceeded our highest expectations. We had no idea whether it could be done – retrofitting an old building to this standard. No one had done it, computer software was not available to model it, and so we didn’t know if it was really possible. On the latest figures, the home is not just 100% zero carbon, it’s 183% carbon negative!
So difficult to pick one, but the quality of the natural light and the quality of the materials like the earth floors are favourites. The natural and reflected daylight and sunlight changes dramatically through the day and through the year. Even after four years here we’re still surprised by new effects of light we haven’t previously seen. We like the fact that we’re so in touch with the seasons. I think we notice the rhythm of the year much more living in this house than we did previously: we can touch a button and see how much solar electricity we have generated that day, or see what the temperature is in the solar hot water cylinder. That makes us conscious of the abundant “free” energy available most of the time, and helps us to think about whether we want to boost the hot water and the choice between having a bath or a hot shower.
The house is designed to hold the heat and to keep an even temperature. Solid heavy floors (as well as walls) are an important part of this. They warm up when the sun shines, and store that heat to release it again at night. In the winter if the temperature outside dips, it stays warm inside; and in the sumner it stays cool. The heavy floors prevent excessive temperature swings by holding and releasing heat slowly.
It’s important first to explain that our earth floors have insulation underneath them. The ground floor build up is 250mm of insulation, a damp-proof membrane, 100mm floor slab, and then 75mm of rammed earth.
The earth is red clay sub-soil (not the black sub-soil) which was dug to make the foundations of the new house. We had to import some extra red earth to supplement it. We sieved to 10mm to remove larger stones. The earth is mixed to a workable consistency with a little water – as little as possible to keep the mix fairly dry – and then laid like a cement screed with a trowel finish. As the earth dries out, it shrinks slightly. This leaves the small cracks and fissures which run across the floor and give it character and texture. If the mix is laid too wet, too much shrinkage and too many cracks will result. If it’s too dry, it won’t be possible to work it to a smooth finish with a trowel. It may need a bit of experimentation to achieve this.
During the drying period – several weeks, but probably extending to 6+ months until it’s fully dry – we used a whacker-plate compacter to “ram” the earth to make it as dense as possible. During drying, we protected the floors with hardboard.
After it had dried, we primed the floor with citrus and linseed oil, and finished with a natural beeswax-based floor polish. This ensures it’s reasonably waterproof and sealed. When it’s fully dried, the floor is almost as strong as some sandstones – which after all are just sedimentary rocks firmed by compaction in the same way. We’re quite careful with table legs etc to avoid heavy point loads on the floor, which it wouldn’t appreciate.
The good news is that engrained dirt simply becomes part of the floor! In heavily used areas, the floor polish needs renewing more often, but generally just vacuuming or sweeping is enough. If there’s a real problem – someone put a stiletto heel through a soft spot in our floor before it had fully hardened! – you can simply break out a small area and remake it again.
The eight-year payback or whole life cost analysis that I was quoting is from the book by Professor Lubo Jankovic, Designing Zero Carbon Buildings Using Dynamic Simulation Methods.
The study looks at the “extra” cost of the energy efficiency measures in the old 1840 part of the zero carbon house including insulation, triple-glazed windows, solar panels etc. It then shows a method of accounting which recognises these construction costs and financing, and also that there are no fuel bills in the house, and also that cash is generated from the PV solar panels. This is the general principle of where the quoted 8-year payback comes from.
We used a firm called AMB Glass who were ok. They are in the Malvern direction, but I think any reasonable glazier could do it, not too complex. I have heard First Glass Birmingham are ok although I don’t have personal experience of them.
AMB supplied and installed our frameless triple-glazed units (ie. these normally go into window frames).
We sealed them straight into the building, which was less expensive and makes excellent airtightness. Elsewhere we gave opening windows which are slightly different.
Our builder then sealed the frameless units to the building airtight membrane with special tapes.
The specification of our units is 6-16-4-16-6, ie. two 16mm cavities which are argon filled, also two Low E coatings and warm-edge spacer bars to the cavities. All these measures greatly reduce heat loss.