Tony's House

Traditionally when we have built houses we have built in massive airleakage paths in the void between the ground floor ceiling and the first floor boards.

This gives rise to a plethora of problems. Drafts enter this void round the joist ends and through the infill block work and mortar joints. Later as the timbers shrink due to drying out more leakage paths open up and existing ones enlarge. The drafts (sometimes gales) resulting from this air leakage path are massive and are getting right into our homes from an area where it is very difficult to carry out remedial work due to inaccessibility. Even if the area were opened up I’m not quite sure exactly what could be done to fully remedy the problem even if cost and time were not considerations.

We say that we would like to build tight. I would like to see us get it right in this area first time. We need in some way to draft proof this area when it is built allowing for shrinkage of joists (joist hangers do not solve the problem and add unnecessary cost).The solution should be simple and easy to do, it should be built in as we go, cheap and essentially idiot proof.

It’s no use talking without suggesting a remedy. So here it is:-

Set the joists on a breathable wind proof membrane. Build in the joists with blockwork infill. Flap the membrane up over the joist ends protecting a 75mm flap above them. Repeat the process all round the house parallel as well as perpendicular to the joists. Provide any service ducts through the barrier in readiness for future use and seal to membrane. Seal the joins in the membrane (by welting or taping) and ensure all the joins and corners are air leakage tight. Later in the building process fix expanded metal over the flaps of the membrane up the wall behind the skirting and at the top of the walls just below the ceiling. On wet plastering an airleakage tight seal will be formed (in my opinion the dabbing on of plasterboard is not an acceptable titleernative in a built tight house).

The plugging up of this area is something we should have done long ago. My hope is that the above will enable us to head towards building for a future more airtightly.

Click here to read the ful article from the Green Building magazine.

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