55. A big blue week

The damp proof membrane goes down

17th December 2014

The pace has picked up a bit this week, principally thanks to Szymon and Jarek, our two-man team of cheerful and hard-working electricians. There are cables everywhere. First fix electrics is all about finding the best way of routing your cables so as to provide lighting and power where it is needed without obstructing later parts of the build, which often involves wiring seriously circuitous circuits.

While they have been on the top floor, reaching for the rafters, I have been on my knees on the ground floor, installing the big blue sheets of the damp proof membrane. Ford helped me get going on Sunday, rolling out two 4m wide plastic sheets and taping them up the middle. Since then I have been working on the tricky details around the edges where corners have to be turned and turned again. It’s a bit like wrapping Christmas presents, inside as well as out, using thick blue plastic on a cold concrete floor. Festive joy!

As well as keeping the damp from rising, this membrane is also a critical part of our airtight envelope, preventing warm air escaping and cold draughts getting in. We hope to achieve an exceptionally high standard of airtightness (the Passive House standard in fact) so every junction and connection has to be properly sealed, one way or another. The blue membrane is carefully taped to the plastic damp proof course that was installed on top of the blocks of the plinth before the timber frame went up. This takes the envelope to the outside, where the tongue and groove sheathing boards of the walls continue the airtight envelope upwards. Every detail has been thought through in advance by our architect, Peter Smithdale, and our timber frame company, Touchwood Homes, so I have no excuse if I screw up.

Having laid the membrane and strapped the frame down – we wouldn’t want the house to blow away – I started laying the subfloor today: huge sheets of Kingspan insulation. Two layers of 150mm insulation ought to add up to a seriously warm floor. Our ground floor will be a ‘floating floor’, with nothing between the floorboards and the concrete than insulation, so there will be no easy routes for heat to escape. The insulation is solid and can be walked on but definitely has a bit of a bounce to it. I’m assuming this will be gone by the time we have laid tongue and groove boards and a parquet finish on top. If not, our parties will be a fraction more animated than usual.


  1. What have you done with your husband?! Ford looks like a gnome!

  2. So no underfloor heating then? Are you having any heating, or will the insulation be so good that you don't need any?

    1. That's right - no need for underfloor heating as the predicted demand for active heating is so low. According to our PHPP (Passive House Planning Package) calculations, the maximum heat demand for the entire house in midwinter when it's freezing outside will be 800 Watts, so we are installing four small programmable, thermostatically-controlled electric radiators to meet this (which should be way more than we need, if the house is built properly, but this allows us to control different rooms at different temperatures and heating schedules).

    2. Will, that is as awesome as it is amazing.