Improving airtightness of our house

An air tight downlight cover glued over a spotlight

Our house has a lot of unintentional leaks. As part of our larger retrofit project, I’ve been improving airtightness to ensure that air only enters where we want it to.

Bathroom spotlights

We have four spotlights in the bathroom and they’re anything but airtight. They were installed into holes in the plasterboard, with mineral wool insulation placed directly on top.

Inside the loft, a spotlight enclosure fitted into plasterboard with a floating wire

There were lots of problems with this setup:

  • During a shower, moisture was entering the loft and going into the insulation. There were dark stains on the bottom of the mineral rool insulation which looks like mould.

  • When the extractor fan system pulled air out of the bathroom, it was likely sucking air back in through the spotlights, rather than under the door. This undermines our ventilation strategy in which the bathroom pulls air in through the bedrooms.

  • The floating wires meant the insulation couldn’t lie flat against the plasterboard.

I found these Thermahood airtight downlight covers and bought a pack. (I think they’re a whitelabel version of the Partel IZOTHERM Cover).

They sit on top of the downlight and have little mouseholes for the wires to run through.

I rearranged the wiring to lie flat and tested the covers in position.

Air tight downlight covers positioned on top of plasterboard with wires running flat

I taped up the unused mouseholes for covers which only needed one.

I cleaned up decades of dust, random nails and rat poo and wiped down the surface of the plasterboard.

I drew round the caps with a sharpie then ran a splodge of grab adhesive along the plasterboard and the bottom of the cap.

An adhesive gun beside a line of white adhesive ready to stick down the downlight cover

I pushed the cap down into position and ran my finger round the edge to make sure there was a good seal. I squeezed big slodges into the mouseholes around the wires and sealed up the unused ones blanked with tape.

An air tight downlight cover glued over a spotlight

They stuck down nicely. It’s hard to tell how air tight they are, but looking with an infrared camera may help.