We’ve got our second child on the way, so it’s time to shift the nursery from the box room to something bigger, and the room could do with some more insulation. We’ve been using it as a study (and to be honest a bit of a dumping zone) but it’s a good size and will be much better used as the kids’ bedroom. The project would also be a nice little experiment for me in internal wall insulation.
This room is cold and ugly. It has nasty old metal-framed single glazed windows and a giant hole in the wall (air brick). There was a hideous mauve wallpaper peeling from the walls. Something had to be done.
- Re-line the external wall with internal wall insulation.
- Seal the air vent.
- Strip wallpaper and paint a neutral colour. We’ll be applying stickers that the kids can change as they grow or we move things around.
- New double-glazing
I opted for Kingspan K17 insulated plasterboard for the internal wall insulation. I like the way everything is integrated into one slab. It gets stuck straight onto the walls with adhesive and has a vapour control layer to prevent condensation inside the wall (a genuine problem when adding insulation). Thermal conductivity is 0.021W mK-1.
Getting it done
Luckily the old wallpaper was in such poor condition that most of it came away by hand. We’ve got an el cheaper wallpaper stripper from B&Q and used that on the stubborn bits. Underneath we found an unpleasant green paint/primer/something that we’ve struck elsewhere in the house. It’s nasty flaky rubbish that turns to mush when steamed, and alternately sticks like shit to a blanket or falls off the wall at the drop of a hat. We gambled and didn’t remove it all, just a bit of a sand on the loose bits, and most of it seems alright. If all the paint falls off in a year’s time I guess we’ll know we ballsed that up.
I stuck the Kingspan K17 to the outside wall using Insta Stik MP. Very easy to use, but if you’re using the “self applicator” type with a little plastic tube instead of a gun be aware that you can’t stop half way through as it keeps seeping out of the nozzle, so cut all your boards and check them for fit before you start gumming them to the wall. I used a continuous bead of the stuff around the edges to try to prevent vapour getting behind the insulation slabs from the joints.
Doing the actual insulation slabs was easy, but I underestimated the amount of work that changing skirting boards, coving, radiators, and fitting new window boards would create. I was limited to quite a thin type of Kingspan K17 by the piping for the radiator, so could only fit 25mm (plus plasterboard makes 37.5mm). Make sure you plan your cuts around the windows carefully, so that you can use the parts you’re removing to do inside the window reveals (otherwise they’ll act as cold bridges). You don’t want to have to buy extra sheets just to do details.
The cavity in the wall for the air brick was stuffed with offcuts of rockwool and I simply stuck the Kingpsan K17 over the top. Should be well insulated and air tight.
For paint we went for some Dulux one coat. I’d not used one coat paint before and was skeptical, but it covered really well. A couple of spots needed a quick second coat after half and hour, but otherwise it covered really well.
Moving the wall inwards meant shortening the skirting boards on the adjacent walls, and new coving as the old stuff doesn’t survive being pulled off. The change in depth of the window reveals also means the old window sills were too short, so new PVC window boards went on.
The nasty old metal Crittal windows might as well have been a hole in the wall, so out they went and in their place came in some nice new double glazed units supplied by Unique Windows Doors and Conservatories, a local company. I highly recommend this father and son team if you’re in the southeast of England. Very good standard of parts and workmanship, nice blokes and a good price to boot.
The wall was composed of three heat-losing elements:
- Brick wall with cavity wall insulation inside it
- Single glazed metal-framed windows
- Air vent
|Before||After||Max heat loss before||Max heat loss after||Annual heat saving||Annual cost saving||Annual CO2 saving|
As you can see, most of the improvement actually comes from the windows and the ventilation. The thin layer of Kingspan K17 adds relatively little. This is because the wall was already insulated and the layer of internal wall insulation was very thin.
Was it worth it?
To be honest, the internal wall insulation probably wasn’t for the amount of extra work it involved compared to the energy savings. If you have to re-do your plasterboard anyway or you’re able to fit a more worthwhile thickness of internal wall insulation then go for it. I’ve canned any further internal wall insulation plans for rooms that simply need a lick of paint. On the plus side there’s a couple of cold bridges around the house that will benefit from applying the offcuts of Kingspan K17.
Apart from that, the room looks great and feels warmer and lighter and will make a really nice bedroom for the kids, so we’re chuffed with it.