# Under floor insulation



## Lisa Murray

Hi everyone,

We've just bought ourselves a van and are in the very early stages of converting it. We haven't done anything like this before so all hints and tips would be most welcome.

We'd love to know your advice on how to best insulate the floor of the van. We're going to lay a water resistant floating laminate floor over a layer iof ply, but we're stumped on how to  insulate down there? The hardware store dude said a 2mm layer of foam between the ply and floating floor would do the job. We don't think so, its the sort of white foam sheets that new computers/TVs come wrapped in.

The hardware store dude also pointed out that some foam underfloor insulation is a fire hazard but didn't expand on this point further. Do any of you know the do's and don'ts regarding floor insulation and fire safety.

Do we need to give any special consideration to the floor ionsulation in areas of the van where the shower unit and fridge will go?

Cheers.


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## mostin

Hi Lisa.

There is more than one way to skin a cat but this is how i did it.

The first thing you need to ask is when & where are you going to use your van?

i.e are you going to be going to Scotland in the winter or just use it in the better weather for the odd weekend? The colder it is the better you need to insulate.

First of all you will need to map out your services layout (cable / pipe runs) on the floor then battern it out.

I've insulated by van using "kingspane" (polyurethane foam) you can get it at most big DIY stores. Its the suff they use to insolate new houses when they build them. (not the wooly stuff) It comes in sheet / board form. 

I used 25mm thick sheets & on the sides i used it up to 75mm to build out some of the contures.

As for a fire, it has a degree or fire pretection but i would think the ply wood floor covering it would burn first!!

A good site to look at is SBMCC ~ Self Build Motor Caravanners Club it is full of info for self builders. I found it to be full of info.

Have fun.
Mostin


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## al n sal

Good advice from Mostin, and definately look up the SBMCC.

loads of really helpful people there


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## Byronic

If you're using ply then use WPB (waterproof/boilproof) exterior grade. 9mm thick is sufficient if you fix battens to the underside at say 400mm spacing
the battens should be as near possible the same thickness as the insulation say 12mm to 20 mm  so as not to compress the insulation when you add weight. 

If the floor has shallow corrugation


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## Byronic

Sorry about the incomplete reply blame 3uk dongle setup....useless. Message
lost in the ether.


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## kell

Hi Lisa

I used the green fibre underlay tiles that are normally used with laminate flooring.


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## Deleted member 207

Floor insulation done well can be fantastic - done badly and it will ruin a good vehicle with a rusted out floor in a few seasons.

You need to make sure that whatever you use fills all the ribs/indentations in the van floor as condensation will be trapped under the insulated surface. 

Treat the floor with an anti rust paint before fitting the insulation.

The thin foam insulation that you refer to is a normal part of laying a floating floor over concrete/steel and is more about a moisture barrier and making the boards quiet to walk on than provide insulation. Wood is a good insulator in its own right but can be heavy and you might end up pushing the weight limit of the van by the time you've put the rest of the fittings in. 

My Westfalia has a layer of polystyrene closed cell foam about 10mm thick, with a vinyl floor stuck on top of that about 5mm thick. Its soft to walk on, not so good when I dropped a heavy box a few years ago and put a dent in the flooring.


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## ssstuarttt

*floor insulation*

I have recently insulated my t4 transporter, for the floor i used expanded polystyrene. The t4 has a step in the floor betweeen the driver cabin and the rest of the van of 110mm, so i put down 100mm of insulation and 10mm of ply. lovely solid base and warm to lie on as it is so insulated too. Also handy to get rid of the step. Hope  this helps and well worth the effort.


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## jacks906

We used sound deadening stuff on a mates t4 to keep damp an noise down then ply over that and click together laminate on to has no road noise coming threw and along with the 35mm foam sheets in the Walls an roof it really is quiet and warm in the cold and cold in the warmth


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## Firefox

My floor had an original 9mm ply lining. On top of that I layed 25mm thick celotext sheet and 6mm ply on top of that, then carpet.

Celotext (or kingspan foam/foil) is really for cavity walls not floors, but it will take the traffic with the ply cover and if you put battens down at 400-500mm centres to support the ply and all round the edges too. 

You can get 25mm Celotext, 25x38 battens and 6mm/9mm ply in Wickes DIY.


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## roamer2

*airtec double insulation*

all good advice from other members we used airtec double insulation same as 55mm polystyrene and only 5mm thick so not using your headroom .hope this helps


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## Bernard Jones

Since heat rises I would be more concerned about insulating the roof (and water getting under the floor)  I used 18mm softwood exterior ply just laid on the floor (about £25 per 8' x 4' sheet, very strong so you can screw into it to fasten things down, and not very heavy) with a few holes drilled in the floor to let any water out.  Wood is a good insulator, and when you get your floorcovering and everything else on as well I doubt if you would lose much heat through it?  Or get to much heat in through it when the sun is too hot?


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## jogguk

*another radical option*

The Canadian converters of my M/H (panel van) used a different method all together. The underside of the floor including water tanks & wheel arches are coated with a few inches of spayed on expanding foam the type of stuff used extensively for wall roof insulation in house building. It is then sprayed over again with a heavy black underseal It even is injected between the floor and the various alloy heat shields above the exhaust cat and silencers.

The GRP hi-top roof is double skinned with presumably more foam between the two shells. It is very strong, I have crawled on it without it deflecting. The walls are just common pink glass wool loft insulation.

I was a little concerned initially that this foam may hold water and latter cause corrosion, however, this has not proved to be a problem even around the wheel arches and van now 10 years old.  I did find out while repairing the polyethylene waste water tank outlet with a blowlamp and soldering iron that the foam (which is normally self extinguishing) when coated with underseal actually burns like hell I was very, very lucky I had a fire extinguisher under the van with me at the time.

John


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## Bernard Jones

jogguk said:


> The Canadian converters of my M/H (panel van) used a different method all together. The underside of the floor including water tanks & wheel arches are coated with a few inches of spayed on expanding foam the type of stuff used extensively for wall roof insulation in house building. It is then sprayed over again with a heavy black underseal It even is injected between the floor and the various alloy heat shields above the exhaust cat and silencers.
> 
> The GRP hi-top roof is double skinned with presumably more foam between the two shells. It is very strong, I have crawled on it without it deflecting. The walls are just common pink glass wool loft insulation.
> 
> I was a little concerned initially that this foam may hold water and latter cause corrosion, however, this has not proved to be a problem even around the wheel arches and van now 10 years old.  I did find out while repairing the polyethylene waste water tank outlet with a blowlamp and soldering iron that the foam (which is normally self extinguishing) when coated with underseal actually burns like hell I was very, very lucky I had a fire extinguisher under the van with me at the time.
> 
> John



Yes I think spraying in foam is the best way.  I read on another forum of a cavity wall insulation guy who injects vans for around £200 (sorry, have lost the link)  More of a pain to arrange it, and more of an initial cost than the cheap stuff you can put in yourself. But probably £200 is cheapest in the long run?


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## caspar

You don't say where you live, but if you're anywhere near South Wales give me a shout as I can get insulation (the high density foam silver backed stuff) legally for free. I'd be happy to help out. Done two vans myself with it but used it on the walls and ceiling, not on the floor. Don't know whether it would do for this or not. Can get all thicknesses, so if you're near enough let me know - pm me or e-mail davidlindley@sky.com with some contact details!


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## vwalan

the idea is to use a closed cell cavity foam then it cant take in water . even if its torn apart only the outside holes get wet and the inside stay dry. water falls ut of the open cells as well. if you use a normal sponge tyoe foam it will suck up the water just like a sponge. most can be bought with a fire retardant finish these days . 
cheers alan.


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