Insulating our bedrooms

Back in February, we insulated the two bedrooms in our end-of-terrace Victorian solid-walled house. This blog post attempts to document the process, including lots of photos. The detailed plans for this project (including some CO2 calculations and a complete shopping list) are described in a previous blog post. A quick re-cap of the plans:

  • Our upstairs walls are not damp so we can just attach the insulation directly to the plastered wall, we didn't bother with wooden battens.
  • Use Fermacell instead of plasterboard. Fermacell is much stronger than plasterboard, so it should be possible to hang shelves directly from the Fermacell.
  • 65mm insulation + 12.5mm Fermacell
  • Use 160mm "frame-fixing" screws to mechanically secure the Fermacell to the brick. These come with their own wall plugs. To use, just drill straight through the Fermacell + insulation + brick, then hammer the wall plugs into place and screw in the long screws (i.e. you don't need to pre-drill the wall and then try to align holes in the insulation with holes in the wall).

In total it took about three weekends to install the insulation for both our bedrooms, MUCH less time than it took to insulate our living room. (This time does not include the time taken to plaster and decorate, which we had done by some excellent local decorators - I just installed the insulation & Fermacell.)

On to the details...

The insulation waiting to be installed:


I tried two different permutations. In our daughter's bedroom, I first attached the the 65mm celotex insulation to the wall (using expandable foam and long nails), then cut the Fermcell to size and secured the Fermcell to the brick using frame fixings.

In the photo below, two sheets of insulation are attached (the far right sheet of insulation is behind the Fermacell sheet which is temporarily leaning against the insulation). I applied the expanding foam in a grid to try to minimise the chance of any air being able to convect in big loops behind the insulation.


And I added some expandable foam to the edge of the insulation to the gaps between each insulation sheet is as airtight as possible:


Attaching the insulation before attaching the Fermacell gave me the opportunity to tape over the gaps in the insulation to create a vapour barrier. This probably isn't necessary though:


Here's the insulation and Fermacell fully installed in our daughter's room:


In our main bedroom, I tried a different method. I tried to make my own laminates of insulation and Fermacell by glueing the Fermacell to the insulation before cutting:

Here's the glue applied to the insulation just before the Fermacell is about to be attached:


And here's the laminate drying (I put three sandbags onto the laminate to make sure the Fermacell is pushed onto the insulation).


Attaching the insulation to the Fermcell prior to cutting has the advantage that you only have to cut and attach to the wall once. But it does take a while to glue the sheets. And you need a lot of glue! Oh, and the glue sinks out the house for a good day.

Just to emphasise: all the glue used in this project is just to temporarily hold components in place while I'm working. All the mechanical strength comes from the frame fixing screws.

Fermacell is very tough stuff so I hired a jigsaw from HSS to help me cut the shapes for the windows:


Here's the "window wall" in our main bedroom (prior to insulation):








Woops, a frame fixing screw sheered while being screwed into place!


The finished product:

More photos on Flickr.

I used the special Fermacell "jointstick" sealant between the boards (which sets remarkably solid). We used a local plasterer to skim over the boards. It is possible to get a good finish completely DIY but our walls are so wobbly and my work so rubbish that we decided it would be best to get a professional skim finish!


  • 2.4 x 1.2m Fermcell sheets are very heavy. My wife and I really struggled to move the sheets upstairs. I just about managed to install the sheets myself but only by "walking" the sheets across small distances. If you're going to install Fermcell yourself then it might be better to get 1200x600mm sheets.
  • Our walls are terrible. Usually about one in every two holes I drilled was too crumbly to support a frame fixing. I got into the habit of pushing a thin wooden chopstick into the hole prior to hammering the wall plugs in. This seemed to slightly increase the chance of the wall plug "gripping".
  • Expandable foam very quickly loses its stickiness (maybe 10 minutes?) so you have to be very quick if you're going to use expandable foam in the same way I did.


This has been tremendously helpful to me, I've used your suggestions and done much the same with 75mm celotex and fermacell. If you want I can send some pictures :-)

Glad it was useful! It'd be great to see your photos on Flickr (or similar) to share your pain / experiences!!

Thanks so much for writing all these posts about your various insulation projects, it's great to see someone DIY'ing this kind of work and you seem to have done an amazing job. We're renovating a Victorian house in Manchester and are about to start insulating. I was slightly terrified reading your living room posts so it's good to see it can be done in less than 18 months :-) I have a couple of questions if you don't mind? Firstly - did the insulation in the bedroom extend past the profile if the window frames? If so, how did you deal with that? Secondly - did you do anything to maintain airflow behind the bedroom insulation so the bricks can continue to breathe? Thanks so much in advance!

Hi Alice,

Thanks loads for getting in touch. I'm glad the blog posts were useful!


I'm afraid I don't know enough about window frames to know exactly which part constitutes the "profile" of the frame. The insulation stopped a short distance (~20mm) away from the wooden frame of the window. This gap was filled with expandable foam and then covered with the architrave / nosing. Hopefully these photos will give a better feel for what we did:


I concluded that our upstairs brickwork was not damp and hence I didn't leave any ventilation between the upstairs insulation and the brick. In fact, I deliberately tried to prevent air moving in that space.

Good luck with your own project! Thanks, Jack

Do you have any problems with moisture after you installed the fermacell boards ? I did the same in my house and it looks like there is mould behind the boards

Hi Moller,

I haven't noticed any signs of damp or mould. But I'm not able to look behind the boards.

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