Tuesday, 12 June 2012

Insulating the floor

For the floor I opted to use 50mm Celotex PIR board. This should provide a decent level of insulation underfoot.

I started by lining the floor (Which was basically the HawkLok shed base, and the floor rafters) in a damp-proof sheet. Basically this is just a very thick black plastic sheet. It covered the floor completely, and will stop any water from under the shed damaging the insulation.

The Celotex was laid between the rafters. To cut the Celotex up I used a standard saw, however a kitchen knife or knife with a vert fine set of teeth will be better, and leave much less dust - never, ever cut Celotex up without an asbestos-grade face mask. It's not in any way cancerous, but it will cause breathing problems for a couple of days, and from my research it turns out that the cheap paper masks dont actually do bugger all, so make sure its asbestos grade (they are around £5 each).

Once the insulation was fitted, any gaps were filled with expanding foam. I didn't need to worry about using foil tape around the edges as the celotex was on the sealed plastic sheet, so no air or liquid restriction was needed.

Shed Floor Insulation
The floorboards were then laid from front to back, they interlock a bit like laminate flooring but are made of solid wood. They are then nailed down to the rafters.

I was actually pleasantly surprised at how stable the floor was. I expected a bit of 'bounce' to it, but it was pretty rock solid.

Once the floor was done, it was time to work on the ceiling, which I'll cover in the next post!


  1. Your build is almost exactly what i plan to do. Insulation is key i feel.

    I would welcome some feedback if you get a moment. i (now possibly) plan to use a plastic base and use pressure treated wood (probably 60-70mm) as a base for my cabin to sit on. this would go all round the outside and also provide a cavity floor inside much like your pictures of the floor.
    I then plan to use insulation and then underfloor heating on top of that before the wood floor is laid. I was thinking of keeping the insulation about 10mm off the base for air flow - Do you think this is important if i go the plastic route as i expect there will be ample air due to the design of the base? i will of course seal any gaps to stop air coming up and into the cabin.

    1. Airflow shouldn't be too much of an issue if you're going for the plastic base. You dont really need much air flow down there to be honest, as long as its dry it'll be fine. The biggest thing is making sure that you've got a decent damp-proof plastic sheet down to seal the floor. I've basically got the plastic base, with the pressure treated floor runners. Then I laid the plastic damp-proofing down on top of that, followed by the insulation. Then he floorboards just locked into place on top.

      I really wouldn't worry about any kid of air gap under the insulation though. There will be air flowing under the damp-proof layer if you use the plastic base which will be ample.

  2. The air flow never occurred to me until i read about it on another site but perhaps that was just for a concrete base and they were worried about damp as water sometimes finds its way :)

    You also read different advice on how big to have the base, some day exact size others say keep it 10cm bigger all round (i assume they plan to use guttering and put gravel on the excess?)

    I think my design is much the same as yours just a little bigger once the walls and roof is on i will add create a framework for insulation on the walls and ceiling and then plasterboard on top and then finish the electrics.

    Lots of different advice out there - common sense plays a big part i think

    do you have a link for the plastic sheet you purchased?

    1. Yeah most of it is just common sense. I spent a lot of time getting opinions on forums, most of which was really only applicable if you were working in a proper brick-built building. Most of my threads turned into different forum members arguing at each other! Even a simple thread asking for suggestions for heating turned into a 9 page thread of people slagging each other off!

      The plastic sheet I used was one of these: http://j.mp/OohS2n

      I think most of my materials came from ebay. Even the plasterboard! I did plan on getting the plasterboard from wickes, but they wanted £25 to deliver it! Ended up paying £54 for 10 sheets, including delivery!

      It was the same situation with the celotex. I bought a batch from eBay for half the price Wickes wanted. The second batch came from condell-ltd.com. Both the celotex and plasterboard ended up being delivered on the back of a Travis Perkins lorry so I guess these places all dropship!

      One thing I will say - shop around like crazy! Its unbelievable how much prices can vary. For example, Wickes charge £28.99 (+ £25 delivery) for 1 sheet of 50mm celotex. That condel ltd site sells it for £22.07 with free delivery if your order is over £100. If you've got the space to put it, get all your celotex and plasterboard in bulk from somewhere like this as it works out a fair bit cheaper! I was lucky on my first celotex order (The 100mm stuff for the ceiling) as the company I bought it from had only just joined ebay and had it on sale.

      I think I spent around £40 with them and it included delivery from yorkshire to north london! They probably spent more getting down here than I paid!

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