Fantastic news today, the rebuild of a Victorian cottage in Brighton has achieved an airtightness of 0.35 ACH so way below EnerPhit and acheiveing full Passivhaus performance. The homeowner has toiled on the project for 5 years and the result of a lot of hard work and dedication has paid off.
Retrofitting airtightness to eaves is always a tricky detail. The joists were boxed under and around with OSB / ply which was sealed first with Orcon F and then taped with Tecson Vana. Solido SL was used to continue the airtightness to the wall as the fleece backing and can be plastered. The black above the joists is 6mm acoustic strip.
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.
An Intello membrane has been wrapped around the sole plate (support for the new dormer facade) which will be taped to the plaster below and to the wall / fenestration above which makes this awkward detail airtight for minimal effort and cost. Keen eyes might notice that the floor joists are not treated to avoid unnecessary chemicals. The tin roof is proving be be a great investment, allowing protected & dry working conditions and saving £££s every day by reducing temporary works.
Has anyone tried to model airtightness for a building and predict the buildings overall air change rate at the design stage? I’ve done this by making educated guesses for each element, such as walls, floors, roof and windows and then multiplying by the areas to give a whole building infiltration rate and then comparing against the ventilation volume. I’m looking for some pier review to see if it could be used reliably. Any thoughts…? I’m happy to email my model to anyone who’s interested. Please get in touch