Today we installed the new bathroom window, and true to the retrofit mantra of doing it once and doing it right, the window is made from Accoya timber so is dimensionally stable and will last perhaps 60 years plus, the glazing is triple with krypton gas to reduce sash thickness, high performance airtight seals all round, concealed balances within the sashes (which are not visible at all) and reduce air leakage and cold bridging. This is a window developed over 2 years for another project and should be rolled out to the retrofit market! Manufacured by Westgate Joinery. Period detailing to match existing windows and you really can’t tell it’s super high performance. Beautiful installation of expanding foam airtightness to the frame.
The party wall where the chimney has been removed was in a terrible state (as expected!) with holes visible into the neighbour’s chimney flues so a brick skin (shown partially complete) has been added to strengthen the structure and give a basic level of airtightness. Additionally both party walls are being plastered in lime which will allow any existing and future moisture from the brickwork to migrate into the void between the new stud wall and escape through the roof (details to follow) and to further improve airtightness. There is also a strip of Perinsul blocks (black on the photo) above the steel to reduce cold bridging and the second photo shows how this integrates with a Purenit sleeve to form a continuous thermal envelope around the steels (in grey) in this tricky configuration. Note there is also a Spacetherm blanket around the back of the steel which can be seen in an earlier blog. These hi-tech materials are rarely used in traditional buildings but are tools of the trade for high performance buildings and while they are expensive both in material and labor costs there is a significant reduction in heat loss, improved thermal comfort and additional safeguarding of the building fabric, and I would expect a payback over the lifetime of the building.
The steels supporting the new loft floor bear into the party walls and until the neighbours undertake loft conversions this will be a significant heat loss. The beam ends have been encased in Purneit (a structural insulation left over from another job) with 10mm of Spacetherm blanket behind. Without going to the expense of 3D thermal bridge calculations it’s impossible to determine the improvement but simple U value calculations suggest both the Spacetherm and Purenit reduce the heat loss by a factor of 3. The black paint is Blowerproof which provides the airtightness which is especially critical here as the brickwork is thin and weak. The second image shows where the Purenit has been routered to seat the steel bearing plate with the Spacetherm behind