We have a bit of a confession to make – we still haven’t completely finished taking down our cellar ceiling! But, we’ve not been as lazy as it may seem, as we’ve already started on insulating it!
Progress has been fairly slow, but we’re finally starting to see some results. The back cellar room, which we’re planning on using as a little workshop, is almost finished. The other rooms are still a work in progress.
For the most part, we’ve finished removing the lath and plaster ceiling. It made a huge mess and it took us over 5 trips (with a fully loaded car) to the tip in order to get rid of the rubble.
There are still a few heating and gas pipes that need to be removed/ repositioned so that we can finish removing the rest of the ceiling, but it’s already a huge improvement on the cracked and damaged plaster that was there before.
We also had a good clear out (it’s surprising how many almost empty paint cans and random junk we managed to collect in just a few years), removed two ugly old & unused radiators and had a bit of a clean.
It took a surprisingly long amount of time (probably because of the amount of cables and pipes) to remove the ceiling, but luckily the insulating part was a bit quicker. We already insulated under our living room floor a few years ago, so had a bit of practice which maybe helped a bit, too.
Adding extra insulation to your floors is a job that’s easily DIYable, but you will need to comply with the relevant Building Regulations for where you live. In England, if you are upgrading your floor, you will need to achieve minimum a U-Value of 0.25 W/m²K (for new floors it’s 0.22 W/m²K).
This is the method that we found worked best for us:
1. Measure the distance between your joists. At both ends – ours were almost never parallel.
2. Transfer your measurements onto the insulation panel.
3. Cut off the piece of insulation you need with a saw. We just used a standard hand saw which worked perfectly. There was really no need to buy any special equipment.
Our tip: We sometimes cut the insulation slightly too big. We found that the easiest way to trim it to size, was to insert it (as far as possible) between the joists and then, using the joists as a guide, cut along the edge of the insulation panel with a saw.
4. Squash the insulation into place. If you’ve cut it properly, it should stay between the joists on its own. If it slips, use some battens at the side of the joists to hold it up.
When insulating your floor, you basically have two aims: Windtightness (Cutting down on draughts and minimising the passage of air around the insulation which will result in heat loss) & Insulation. That’s why it’s important that there are no gaps around the insulation boards. If you find that you’ve cut a board a bit too small, you can fill the gaps with draught excluder tape (the same kind that we used to fill the gap between our skirting and floorboards) or, if you have any larger gaps, you can use expanding foam filler and mineral wool insulation.
After a few calculations, we decided to insulate under the floors using PIR insulation boards. These rigid insulation boards are roughly twice as effective as mineral wool insulation, which effectively means you only need about half of the thickness. According to our calculations, we would have only needed about 90 mm of insulation, but we decided to increase the thickness to 110 mm. In our case, that means that we actually comply with the Building Regulations specification for new builds.
There is absolutely no need to insulate the floors of your upstairs rooms in your house, when the rooms underneath are insulated. It’s only important and effective to do when the rooms or space below aren’t heated.
Hopefully we’ll manage to finish insulating the cellar this weekend. It’s really starting to get cold here in the north of the UK and with our heating and radiator situation not being ideal (hopefully that will be sorted soon, too) we really need to make sure that our house can retain as much heat as possible.
Are you doing anything in order to insulate your home before winter kicks in? Or, if you’ve already insulated your home, has it made a difference?
Hi guys
Just wondering what you will do with the pipe work and cables. Will these sit on top of the insulation, rather than between the joists?
Good question,Tim! All of our pipework and cables sit under the insulation, so luckily it’s not too much of a problem. Where the pipes go up and through the floorboards, we’ve cut holes into the insulation which we’ll then be filling with expanding foam filler.
Cx
Nice job with the insulation. Since your doing such a good job of making sure the heat stays upstairs, how will you keep your pipes in the cellar from freezing? Or isn’t that a problem in your neck of the woods?
Thanks for reminding us about that, Cindy! You’re exactly right of course. We already insulated most of the pipes in the cellar and we will definitely be taking care of the new ones that we’re replacing and moving before it starts to get very cold.
I wish we did live somewhere where it was warm enough not to worry about stuff like that!
Have you considered the ‘breathability’ of the house with all this gap sealing and insulation.
Like yourselves I have often considered insulating but despite the mass amount of propaganda that encourages us to insulate everything, I found a few people who would argue this case. When you read into it in more detail, breathability makes so much sense. There are already many horror stories out there where people have over insulated.
This article is a great insight into what i’m talking about, which I urge you to read.
http://climatechangeblog.historic-scotland.gov.uk/2013/09/traditional-buildings-are-cool/
What IS a traditional building? It’s very simple – an ‘traditional building’ is a structure built with solid walls (stone, brick, timber frame) using breathable materials.
Thanks Russ! We completely agree with you! There’s a trend to over insulate everything. We constantly have people coming round trying to sell us cavity wall insulation. Our cavity is only about 4cm, so it makes absolutely no sense and would almost certainly cause more problems! Insulating is definitely something that should not be undertaken be lightly and we check ours on a regular basis to make sure everything is still bb okay. At the end of the day, as long as you still have enough airflow too remove any moisture, you should be okay.
Cx
Great looking project. You’re obviously doing the research to do a quality job. PIR is a new material to me, I’ll have to go take a look. Thanks for the tip!
Thanks Jeffery. There’s no point doing a job if you’re not going to do it properly!
Cx
How long did the project take you? It’s something I’ve been wanting to do in my cellar for some time
Taking down the ceiling probably took about a day and insulating another 1-2 days. Using ridged insulation is probably a bit more involved as you have to cut it exactly to fit between the joists.
It was definitely worth the work though – the room above is much warmer now.
Cx
Fantastic images; especially the animated one. Really makes me feel like I’m with you observing the work. Best of luck with the project!
Great walkthrough. Can I ask how many square feet (or meters) the space was that you insulated? I am looking to insulate my cellar and am debating between fiberglass and a solid material, cost effectiveness, and efficiency etc. I would be insulating approximately 1,000 square feet of floor. over a concrete cellar where my boiler lives.
Thanks Roger! I’d say we insulated about 60m² of which we insulated about 20m² with mineral wool and the rest with ridged insulation.
Cx
Hi, thanks for this handy post :)
We’re thinking of doing the same thing in our basement. We’re in an old Victorian terrace with a big, draughty and very cold cellar.
A question: Did you leave space between the top of the insulation boards and the floorboards? I’m concerned about cutting off ventilation around the joists and floorboards.
But if you used 110mm boards there should have been some space left between insulation and the boards, right?
Thanks!
Thanks Matt!
Our insulation is butted up directly against the floorboards and in my opinion that’s the way it should be done. Our joists are still ventilated from below and I think that you’d probably create a thermal bridge if there’s a gap. Opinions on this do seem to be divided though. If you’re unsure I’d recommend getting in touch with a company that supplies underfloor insulation like Kingspan. They’re usually really helpful and can advise on the best build up for your floor.
Cx
Hiya, we’re going to be undertaking pretty much the same project over the coming months. The same insulation has been suggested by a friend. I was just wondering have you over boarded insulation underneath? Also in relation to pulling down the old stuff – I know how messy it can be as I’ve already pulled down a section. Did you have anything other than a mask and eye protection on?
The insulation was easy to work with and we didn’t overboard it because we were concerned about blocking the airflow which could possibly end up creating condensation. Yes, pulling down the old stuff is really messy but we didn’t take any precautions other than masks and eye protection (I think I may have worn a hat, too).
Cx
Fantastic, thanks a million. Will be starting over the next couple of weeks.
We too have insulated our cellar ceiling with celotex insulation which is butted up to the floorboards of the room above. Like yours our joists in the cellar are still ventilated from below so I’m thinking this should be okay, just worried when I see other sites recommending leaving a gap. We have also put wooden batens on the walls and screwed foil backed plasterboard onto them to cover the brick. There is an open air vent to the outside and a radiator in the cellar. Do you think this will be okay or is there a risk it may cause condensation/damp problems? Thanks for any advice
I believe that not having a gap is the right thing to do but it will, of course, depend on your home and your exact circumstances. If you’re unsure it’s probably a good idea to get someone to look at it. We had no problems with our insulation and we checked every now and then to make sure there was no condensation – maybe that would be a good idea for you, too?
Cx