The work described here is part of package of measures being embarked upon, to reduce heat loss from a 1960's semi-detached house in Frome, Somerset. The work has been jointly designed by myself and Paul Buckingham - we are both graduates of the Centre for Alternative Technology Architecture course Advanced Environmental and Energy Studies (PG Dip/MSc).
Top left shows roof plate of my 1960s semi-detached house - uninsulated and with a large area of cold wall inside above all the top floor windows. This is where condensation occurs and mould grows - a problem with all the 1960s houses built to this design.(See my post Save before Generating for more on this.) Windows are below the soffit boards at the base of the roof. Battens attached to the outer blocks support the soffits. The top row of outer blocks is has been used to close up the 50mm cavity.
The picture to the right shows the party wall with an uninsulated cavity that is exposed to the cold where it joins the roof - a major problem. To address it will require pumping insulation in via the internal wall or taking all the roof tiles off to expose and fill it that way. We are exploring the possibility of insulating from inside but have yet to find a company willing to do it. They seem to be few and far between.It is mad that if cavity wall insulation is done (often under a government grant scheme - now it is free to anyone) the party wall is not. As a consequence, this type of house will have only one brick skin between the internal part of the property and the cold winter air.
100mm polystyrene insulation has been used - cut in steps up to and including the first 500mm into the loft space. Loft insulation has then been overlapped. An air gap has been left to allow for air to circulate in the roof (inflow via vents in the soffits). Ventilation - moving air - in the roof is vital to prevent condensation occurring in the loft. A section of roof felt had to be replaced with a suitable membrane, although we were able to reuse the battens for fixing the tiles.
Vermiculite was used to fill in gaps between the steps of insulation. The insulation sytem used is Knauf-Marmorit - 100mm polystyrene stuck down with a lime-based mortar (also used to insulate the rear exterior of the house). The down side of this system is the huge quantity of polystyrene waste, and the impossibility of controlling where all the bits go. Despite our best efforts, there are bits of polystyrene all over the place in the garden. With hindsight I would in future prefer to use a wood-fibre product - much more sustainable and environmentally friendly (although nowhere near as good an insulator).
Cavity wall insulation
The house was cavity-wall insulated in 2008, but we know that the insulation did not reach many areas, including under windows and beside doors. Thermal imaging of other properties has shown that insulating cavity walls, especially those with 50mm cavities, is not an exact science. However, leaving bits of uninsulated walls means small areas of cold surface where condensation will readily occur. I have begun the process of seeking restorative work on my property by the company responsible for the insulation - there is a 25-year guarantee.However, they don't seem to be able to find contractors to do the work, as yet.