The sleeper walls have been stripped out of the ground floor; the chimneys are down and we are installing hardcore, sand blinding and 300mm of EPS before casting the new concrete slab.
We have installed a 600mm deep x 100mm thick strip of XPS (Extruded Polystyrene) to the inner face of all the internal masonry walls. This mitigates the thermal bridge created by the walls where they pass through the floor insulation.
The roof is stripped of tiles, but we are leaving the felt and battens to provide weather protection until ready with the new membrane, insulation and roof covering.
We need to extend the width of the roof at the sides (verges) and also at the gutterline (eaves) to “receive” the additional thickness of the EWI (external wall insulation). My builder has built additional verge ladders and extended the existing rafters at the eaves. The eaves is a tricky detail for a number of reasons: we need to wrap the airtight membrane around the ends of the rafters and tape it back to the walls; we also need to be careful that we are not extending the rafters to far so they will get in the way of the first floor windows.
The builder has made a mock-up of the eaves detail and also constructed a plywood box in the window reveal – the ply box will make it easier to get a really good airtight installation for the window AND crucially help us to locate the window within the EWI insulation zone which will achieve a much better thermal performance than if the window was installed within the brick reveal.
As we will be installing 200mm of external wall insulation, the scaffold has to be erected in such a way that it can be easily modified to allow enough room to install the wall insulation and render at a later date. In practice, this means a scaffolding board or two closest to the house can be removed later, without having to re-do the whole scaffold.
The chimneys are coming down – chimneys are not great if you are trying to make an airtight house. Luckily, ours are on the outside, so demolishing them is not too disruptive.
One big piece of work is to replace the existing suspended timber ground floor (joists and floorboards) with a new insulated concrete floor slab. The builder has taken the timber out and you can see the supporting “sleeper” walls below. The depth of the void under the floor varies quite a lot and follows the natural slope of the ground. It varies from about 450mm to 1100mm.
The reason we have done this is that it is very difficult to insulate a suspended timber floor without creating thermal bridges – every joist is a thermal bridge. The concrete floor will have 300mm of insulation (Expanded Polystyrene, or EPS) underneath it. True, the insulation is interrupted by internal masonry walls which are built off their own strip foundations – but we have a way of mitigating those thermal bridges – more later.
Being an architect, I have always wanted to build my own house. We all do! There is always something about an “off the peg” house which isn’t quite right – not enough light, poor flow, mean windows etc. The chance to design everything from scratch would be wonderful.
The snag however, which is a common problem for aspiring self-builders, was finding an affordable plot of land in SW Sheffield. After about 15 years of trying, we realised that our budget was probably about £100k short of being able to complete the project.
Plan B was to buy a “wreck” in an area close to where we currently live and adapt it to our needs – to provide a 4 bedroomed family house with a well-insulated fabric and healthy internal environment. I have been interested in the Passivhaus approach to building design since hearing about it in 2010. I became a certified Passivhaus designer in 2012 and now apply the approach to as many buildings as possible in my architectural practice – Lomas + Mitchell Architects.
My wife Jill found the house – she never gave up on the dream of doing a project. The house is an early 1960’s brick-faced, detached house. It is quite boxy, with an attached single garage to the side and has a tiled, pitched roof which has a bedroom within the roof space.
The house and garden had both been neglected for about twenty years – the man who lived there before us suffered from health issues and hadn’t done any maintenance or improvements.
The bare bones of the house are pretty good with large rooms and generously-sized windows. The rear garden is large and SW-facing.
Our primary focus is making the house as energy-efficient as the budget will allow. Yes, we would like to extend the ground floor and take some existing walls out to provide larger, open plan spaces on the ground floor. We need a new kitchen and bathroom and would also like an ensuite on the top floor. Getting a handle on our budget and working out what we can afford to do was/is critical.