There has been a debate about the floor strategy for the project but in the end we have gone for a floating floor strategy, which is basically putting insulation on top of the existing floor. We added a damp proof membrane and then adding 100mm of phenolic board insulation and then a 22mm plywood deck.
Raising the floor
We were able to do this because there was considerable ceiling height to play with in the older part of the house. In the kitchen extension it has been a bit more challenging but we've managed to add 100mm of insulation, whilst also maintaining a 2 metre head height. Of course, raising the floor in this way has also had a knock-on effect on the entrance door for the house, but this needed to be replaced anyway, so was (just about) doable with the new head height.
Budgetary considerations
The floating floor strategy has the advantage of being a lot cheaper and easier to install and has probably saved at least two weeks of labour on site, compared to if we had gone down the route of digging up and replacing the floor. The disadvantage is that we've had to use oil-based phenolic board insulation, rather than natural alternatives. It was a cost and budget-based decision and compromise.
Effect on overall energy efficiency
Camilla Govan is working as the Passivhaus Consultant for the project and is using PHPP (Passivhaus Planning Package) software to model the retrofit and hopefully get the project through AECB Retrofit level 2 certification. The PHPP modelling of the project has shown a dramatic improvement in floor U value with our chosen floor strategy, with a U value of 5.405 W/m2K being improved to 0.204 W/m2K. This confirms the clients' experience of living in the home pre-retrofit and how cold the floor had felt before.
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