Insulating the walls

Filling the walls with Warmcel

Very early last Friday, a couple of vans turned up on site with Dave and the Sustainable Energy Scotland team. Their mission was to fill the downstairs exterior walls with 140mm of shredded newspaper which would form the main ingredient in our insulation system.

The usual solution to insulating the walls of a new timber frame house like ours is to put rigid “board” insulation 150mm thick in between the studs (wooden uprights). Kingspan supply some very good but pricey boards for just such a purpose. However well you cut the boards though, you can’t be sure of completely filling the gap between the studs. So you have to go round with expanding foam to deal with the holes later which is a fraught process if you’re aiming to have the house meet current standards for air tightness.

Andy Black introduced us to the Warmcel product at a meeting in Dundee a while back. The man from SES explained how the shredded cellulose (newspaper to you and me) was blown through a long tube into the wall panels. They carefully check the density of the blown material to ensure that there can be no “slumping”. Nothing to do with slopy shoulders; it refers to the eventual development of cold spots as the insulation slides down the stud. Get the density right, no slumping, no cold spots.

And the process of filling the studs with shredded material means no gaps at the corners or down the edges. In theory.

Time will tell!

Left, filling the studs with Warmcel. Right, stapling the scrim into place

So the first task was to cover the studs over with a lightweight scrim, stapled carefully into position. The lads ran the scrim over the whole of the ground floor walls – shades of George Clarke on the TV with his white spray paint. Then, very scientifically, they cut a hole in the scrim in each panel and fed in the hose from the pump outside into each one in turn.

Controlling the flow from a remote controller, they filled each panel. To keep the panels from bursting open, they then stapled over them a strip of damp proof membrane.

To check their work, every so often they stopped and took what looked like a core sample from one of the panels. Using a metal tube with a serrated rim, they pushed it through the scrim and into the Warmcel. Extracting it carefully, they put the tube on a set of scales and checked the weight against a target chart.

They were aiming for a minimum density of 60; they were achieving just under 80. So we have about 30% more fill than we need to prevent the dreaded slumping. Then they replaced the contents of the sample in the wall and stuck a patch over it – more like a punctured tyre than anything.

The finished Warmcel-filled living room wall.

When they were done, the walls looked rather like a very large mattress stood up on its side. In fact, the right way up you could have a comfortable night’s sleep on a bed of Warmcel. Inevitably, the panels bulge a little under the pressure of the fill but since we have a couple more layers to go, the plasterboard walls will end up flat as planned.

The next steps are for the joiners to come back and lay 25mm of Kingspan board right across the studs to reduce any thermal bridge effects through the wooden studs themselves. Then they’ll place 25mm battens over the Kingspan on top of which goes 12mm thick plasterboard ready for taping and painting.

So, not only warm and toasty but handy for installing the electric wiring, on which more shortly.