Expanding Foam as Insulation
 

I'm trying to figure out a way to insulate my workshop floor. Unfortunately before I had chance to place anything down prior to the workshop being erected has left me with a 3 inch gap between the floorboards and the concrete the workshop sits on.

I thought about putting some 50mm polystyrene sheets down and then making a false floor on top of this, but after consideration it doesnt seem practical.

My final thought is that i could block off both ends of the workshop, at the base, and drill some holes into the floorboards, then squirt expanding foam into the floor cavity.

Below the 6 inch concrete base is a layer of plastic sheeting, so its damp proofed.

I was thinking of using Gorilla Filler http://www.ebay.co.uk/itm/GORILLA-FI...#ht_978wt_1163

I would appreciate any thoughts on this. Has anyone used this expanding foam? does it act as insulation?, does 750ml cover a large area? :dozey:

Re: Expanding Foam as Insulation
 

Cavity wall insulation used to be expanding foam, but it's been replaced by fibre blown in. Just remember that if you use expanding foam that any work you need to do under the floor (pipes/wiring) will be impossible to get at without hacking away a load of foam.

Re: Expanding Foam as Insulation
 

Is it possible to lift the floorboards, and then use rockwool?

Re: Expanding Foam as Insulation
 

Is this outdoors? If so, an air gap would be great for stopping rot in the floor.

Cans of SEF don't go as far and therefore become very expensive very quickly. You can buy rockwool slabs, but it would have to be laid between load-supporting joists that a second floor would be laid upon (polystyrene would be too much of a fire hazard AFAIC).

Re: Expanding Foam as Insulation
 

It isnt, the floorboards go underneath the base of the walls, or should i say the walls sit on the edge of the floorboards, either way, i cant lift them up. I wish i could because i could save money insulating then.

Re: Expanding Foam as Insulation
 

You can always get a cavity wall company to blow in rockwool fibre.. Should be the same cost as getting the walls done

Re: Expanding Foam as Insulation
 

Gets my vote,

Expanding foam is good for some circumstances but I wouldn't dream of using it as insulation under a floor because as it expands it will lift the floor boards up, then once it's set your buggered.

Also I would recommend leaving the joist's air to breath, you don't want moisture getting trapped and rotting the timber.

In my man shed at the side of the house I just used the moisture resistant tongue and groove type MDF sheet's you can get from builders merchants but it can be a bit expensive so my money is on the rockwool just for cost and ease.

---------- Post added at 12:44 ---------- Previous post was at 12:42 ----------

Good thinking Bat woman, I like your thinking :)

---------- Post added at 12:53 ---------- Previous post was at 12:44 ----------

Ooooops, only just saw this sorry :erm:, then either Kymmy's idea or build a new floor are your only options really.

That I can think of

Re: Expanding Foam as Insulation
 

I think Kymmy's idea is by far your best option:

Re: Expanding Foam as Insulation
 

thanks for the replies, i will look into how much it will cost for the rockwool.

---------- Post added at 13:46 ---------- Previous post was at 13:24 ----------

The boards are 1" Thick between joists of 1 1/2 ft, you sure that expanding foam will push those up? They seem pretty solid.

What about the plastic sheeting under the concrete? Isn't that supposed to be the damproofing?

Also, this timber is treated, its not supposed to rot for 10 years. Wont that also work in my favour?


I've attached a few pics so you can see a bit of what im referring to.

Floorboards

http://i55.photobucket.com/albums/g1...sponia/ws2.jpg

Underfloor

http://i55.photobucket.com/albums/g1...sponia/ws1.jpg

Re: Expanding Foam as Insulation
 

I use this stuff all the time ,there are different types of expanding foam for different purposes .Gorilla filler foam is exactly that ,a filler with no thermal properties at all .Insulating expanding foam is about £11-15 per tin and you would need quite a few tins looking at the photo .Also drilling holes in the floor will only lead to patchy instalation and you could easily end up with too much in one area which WILL DEFINATELY lift the floor.Filling the void will lead to early rotting of the timbers not as quickly as usual as the timbers are treated but they will rot .Your best bet given the practicalities is to overlay 18mm ply sheeting over the boards and screwing them down keeping the joints tight to stop draughts .You will find this much more effective that trying to retro fit insulation .Wood is a natural insulator so you will definately notice a difference

Re: Expanding Foam as Insulation
 

After looking at the pictures now, I think your idea of using polystyrene sheets (or something similar) would be better, as long as your not planning on putting anything really heavy on the floor it shouldn't be too springy if you use a decent grade particle board (MDF) on top.

Picture No2 shows the air gap under your shed, this IMO should be left alone and not boxed in and filled with expanding foam or whatever.

Re: Expanding Foam as Insulation
 

Even in modern conventional house construction the void under a timber floor would be ventilated to reduce the risks of rot from excess moisture. Remember that in an external environment, unless you have the ground fully sealed with an impervious barrier to the walls there will be moisture both from the ground but also the general side entries. Even the timber flooring will not be imprevious. Thus damp can arise, including condensation moisture. Any plastic sheet under an external paving concrete slab is laid simply to aid the construction process and rarely would it be of sufficient grade and fully lapped that it could act as a reliable damp proof membrane. I can't therefore recommend you fill this void with any insulation materials.

As stated above expanding foam of the types available in aerosol cans will be very costly. It isn't intended to fill anything more than small voids. It also doesn't resist weather and damp very well and could actually entrap moisture making things worse. I doubt you'd get even coverage and if you overfill you risk distortion of timbers.

If you must fill the void then I'd suggest the polystyrene beads that have been used as retro fill by blown injection, rather than rockwool or other fibres. Most of these insulants are more intended from cavity walls or to lay over ceilings, so in the underfloor location may not perform well and again could actually cause problems with mositre entrapment. You certainly won't get a guarantee, and for the small area involved the installation costs could be prohibitive.

The best option would be an overlay to the current timber floor. Lay a vapoud check plastic sheet, place rigid foam boards over that (Wickes now sell the polyurethane type boards, as well as other foams for use with loftsapce boards that should work), and you can if needed place some timbers between these insulations, ideally crosswise to the current joists so the loads are spread, before you lay new timber flooring, perhaps of moisture resistant 19mm chipboard, or if you are being extravagant plywood.. The cheap job, which would simply reduce draughts would be a simple overlay of thin 3-6mm sheet plywood, to the existing flooring to block up any gaps.

Re: Expanding Foam as Insulation
 

We plan on using the workshop during winter months, the reason i'm insulating. Do you think an overlay of MDF would keep the floor warm enough?

I dont really have a problem with putting a false floor down. I was thinking of doing this originally by laying 50mm poly sheeting, or at least using 30mm, and using plywood as the floor base. MDF would be cheaper I think.

Would using ONLY MDF be enough?

Re: Expanding Foam as Insulation
 

Your biggest problem is draughts so going all out with thermal insulation on the floor will be a waste of money unless you are going to do the roof and walls(or already have done) .Very little heat if any will escape through the floor you are more likely to get cold draughts blowing up through the floor.My advice would be to eliminate the draughts rather than insulate and a ply/mdf floor covering can be very effective .You can buy T&G chipboard flooring with foam insulation already attached

Re: Expanding Foam as Insulation
 

I see what you mean. The roof and walls are insulated with a combination of polystyrene sheeting and bubblewrap, I was on a tight budget, but it seems to have worked. The wall cavity was about 2 1/2 inches which was jam packed with insulation.

I dont want to overspend on floor insulation if its not necessary, the cheapest option would be the best for me, ive already spent way too much on the workshop as it is.

This insulated MDF sounds good, i will have to look out for that. It would be ideal.