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Insulating under the floor - a photo case study

Posted by Cathy Debenham on 27 November 2013 at 10:16 am

When insulation is mentioned we tend to think about lofts and walls, but insulating under the floor can make a significant difference too. When we did up our house, we didn't do anything to most of the floors - except lift the carpets and sand them.

Since then, annoyed by the howling draughts in our living room I have tried, with little success, to prevent them. It's a cold room with three outside walls and it had big gaps between floor boards, even larger gaps between the floor and the bottom of the skirting board, and holes where radiator pipes used to poke through.

As well as being draughty, the pine floorboards were not in great condition and didn't look good, so we eventually decided to replace them. And as we were taking the floor up anyway it made perfect sense to insulate at the same time. 

Here's how we did it in pictures:

Taking up the floorboards

My husband ripped up all the floor boards. It took about a day. Then we handed over to a local carpenter we know and went away on holiday...

Laying insulation between the joists

He cut the insulation and fixed it between the joists. 

Taping the joins in the under floor insulation

Taped the joins, so that it was all airtight. We also asked an electrician to come round and put some sockets in the floor under where the sofa goes, and hide the speaker cabling.

Sealing the edges of the insulation with expanding foam

He put expanding foam around the edges.

Laying new floor boards

And layed the floorboards on top.

And we came back from holiday to a beautiful new floor (and quite a lot of painting and decorating to do).

Already we notice that the insulation is making a difference. You can sit comfortably in there with no shoes on, as the draughts are no more. The floor feels warm to walk on. The room holds the heat much better than it did, and seems to heat up faster. So, if you are thinking of replacing flooring, it's definitely worth insulating at the same time. 

When I got my green deal assessment earlier this year, the advice report suggested underfloor insulation. It wasn't clear whether the suggestion was for the whole of downstairs or just one room. It gave a guidance price of £1,000. Our experience demonstrates how unrealistic that is. The cost of labour and materials for making good the joists, insulating, taping and laying the new floor was nearer to £1,500. If we had paid someone to lift the floor too that would have been another day's labour. Then there was also the cost of the new floor on top. The time spent lifting boards would have been much longer if we were trying to do it so they were in good enough shape to re-use. 

More information on underfloor insulation on YouGen

YouGen guide to insulation

Is it worth insulating under the floor

Get snug: a DIY case study of underfloor insulation

Is fleece or board best for underfloor insulation?


If you have a question about anything in the above blog, please ask it in the comments section below.

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5 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 1 April 2014 at 2:59 pm

Hi John

We wanted to replace the floorboards anyway, as they weren't very nice and were seriously draughty. We wanted to get better looking, and tongue and groove. It certainly wasn't a cheaper option! However, if you replace them, you (or whoever you get to do it for you) will take much longer getting the old ones up, as it is much harder to get them up in a good enough condition to relay them.

I'm afraid I haven't ever heard of retrovivefloor, so can't comment on that.

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John Broad

John BroadComment left on: 27 March 2014 at 1:08 pm

If you google underfoor insulation one of the first things that come up is retrovivefloor - have you heard anything about their effectiveness/value? 

ps we have a similar situation with our suspended floors. Did you decide it was cheaper to replace rather than renew the floorboards?

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Cathy Debenham

Cathy DebenhamComment left on: 28 November 2013 at 8:58 am

Thanks @Teagle. Too late for us, but hopefully useful to someone else.

@MuppetKeeper I agree. I tried to get proper quotes from various green deal providers to see what they would actually charge, but none was able to give me one!! 

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MuppetKeeperComment left on: 27 November 2013 at 7:40 pm

i too have an "estimate" from an energy survey, suggesting to insulate under my floors, suggested cost £1200.  I have seven rooms on the ground floor, all with concrete floors, you can imagine I'd be delighted to get it all done for £1200!!!

These wild guesses seem daft to me.

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TeagleComment left on: 27 November 2013 at 6:25 pm

Even better, you could plaster in some airtightness tape to the walls around the edge rather than just the foam. 

nice blog post



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