Floor Insulation - as in UNDER the floor. Can anyone advise please?

[GRWXJR]

Ok... this is just an idle thought (cooked up while I was underneath my van tinkering with something).

As we like to get away in the van at any opportunity and in any season, it'd be good if the camper had some better floor insulation. However, I have already done the inside floor and in any case can't really afford to/don't want to lose any height.

Now, my LDV has a lot of ground clearance, and also a fair amount of clearance even between the running gear/exhaust etc. and the floor.
The floor is the usual sheet steel, and is reinforced by box section struts (as well as the main chassis rails). The suspension is leaf spring with masses of room between it and the floor, so there's not much getting in the way of most of the floor.

The underside has been recently undersealed (Waxoyled) throughout. Inside there is a thin foil type insulation barrier on top of a ply floor, and the top finish is laminate flooring.

So... my thinking was... could I get a much better insulated floor by using all that dead free space between the strengthening struts and insulate the floor from UNDER the van - outside instead of inside - sort of 'cladding' the floor? Can I 'fill in' the spaces between the crossmembers etc. with something like 50mm Sellatex to insulate (most) of the habitat area floor?

I thought about potential to trap water etc., but the floor is undersealed, plus I thought I'd coat each piece of infill Sellatex section with underseal before sticking them into place. I don't think fitting insulation is a difficulty - but the consequences for causing rust of other issues are my concerns.

Anywhere where the exhaust might get a bit close for comfort I can leave, or I can easily heat safety wrap/lag the pipe (I already have done the front section as an extra noise insulation move. As a bonus I thought the floor insulation would give welcome extra noise insulation as well when travelling (Tranny Di engines and transmissions/axles do make a bit of a racket).

So... is this viable or a "bad idea"? If I'm talking nonsense - is there a better under-body solution or material to use that would accomplish this? Or, do I just live with it and burn a bit more fuel through the Webasto instead?

(BTW - the rear part of the van is storage/services, and the main fuel tank and the night heater are under this area, so I don't need to worry about doing anything anywhere near these things anyway, and I wouldn't be daft enough to cover/bury any of the fuel lines etc.)

Thanks in advance of any assistance / advice rendered!

G.

 

[izwozral]

Have you considered spray foam insulation? You could add as little or as much as is viable.

 

[GRWXJR]

Have you considered spray foam insulation? You could add as little or as much as is viable.

I thought about it, but (apart from knowing nothing about it, and that chances are I'd have to pay someone else to do it) there seems like a couple of potential shortcomings with external spray insulation.....

1. Seemed more likely if (IF) water got behind it to trap it there and cause corrosion etc.
2. I have NO idea if this stuff is suitable for external environments anyway
3. I couldn't easily take a section off/out if I needed to to gain access to the floor for whatever reason.

I know that they make external Kingspan / Cellatex type stuff, as its used to externally clad older single skin construction houses to improve the insulation properties (Lisa's mum's house got done a year or 2 back). I'm just not sure WHICH product, not IF its remotely suitable for this idea.

I'm guessing more people would have done this already if it was that good an idea to insulate the underneath from the outside (cos someone cleverer would have thought about it long before me)..... but I thought there might be something to it (& the materials wouldn't have been available not so long ago either?), and no harm in asking, right?

I have sent a cheeky email to Kingspans technical dept asking them which (if any) of their products they might deem suitable. I don't know if I'll get a reply, but if I do I'll share what they say on here.

 

[mark61]

Have thought about insulating that way too. I just wonder how long most insulation would last having road grit, mud, etc chucked at it, and being soaked for long periods. No doubt there will be a suitable product, but you can bet it's a fortune.

 

[GRWXJR]

Have thought about insulating that way too. I just wonder how long most insulation would last having road grit, mud, etc chucked at it, and being soaked for long periods. No doubt there will be a suitable product, but you can bet it's a fortune.

I built a raft over a decade ago for the local charity race using 6", 6-metre duct pipe to build a catamaran. I didn't know if itd work, but I sealed the rear ends (which were in the water permanently) by inflating kids balloons stuffed up the pipe 18" or so, then filled the ends with expanding foam. We then painted some pond wall sealant over the faces and that was that.

That raft still works today, and where the UV has got at it the foam has aged and bits have come off - but the stuff still keeps the river out.

I'm thinking that the chemical composition of expanding foam HAS to be something similar to the material in these insulating boards, right? So, if it can stand the abuse my raft gave it, then I thought maybe the floor of the van, (which gets wet, but surely nothing like as much water as a fully submerged raft?) just might be something with some mileage in it.

Hopefully someone will know, and also I'm hoping kingspans' boffins will in the spirit of the season, bother to reply to some dopey member of the public sending them daft emails with something useful!

This is what I was looking at earlier:Kingspan Insulation - Therma Insulation - Kingspan Insulation UK

 

[K9d]

I've contemplated the same on my Hymer, there's loads of space under there too, sounds similar to yours but a Fiat Chassis.
My thoughts on material would be polystyrene, because its light and a very good insulator, I'm not sure what the material is your thinking of using.
With regard to the expanding foam I can see a few issues, firstly how do you get it to stay there initially and secondly if you have to remove it it'll be a pig of a job. But on the plus side window fitters use it to fill gaps around windows and doors so I would imagine its durable. I have used it in the past and its easy to use but it expands a lot, a lot more than you might think and suddenly your confronted with masses of foam that won't stop getting bigger.

As for trapping water in there, as long as its dry when you fit the insulation I can't see it being an issue, if it can get it, it can also get out. If you did use expanding foam that uses water to activate the expansion so it would probably absorb any water in the process.

 

[GRWXJR]

I've contemplated the same on my Hymer, there's loads of space under there too, sounds similar to yours but a Fiat Chassis.
My thoughts on material would be polystyrene, because its light and a very good insulator, I'm not sure what the material is your thinking of using.
With regard to the expanding foam I can see a few issues, firstly how do you get it to stay there initially and secondly if you have to remove it it'll be a pig of a job. But on the plus side window fitters use it to fill gaps around windows and doors so I would imagine its durable. I have used it in the past and its easy to use but it expands a lot, a lot more than you might think and suddenly your confronted with masses of foam that won't stop getting bigger.

As for trapping water in there, as long as its dry when you fit the insulation I can't see it being an issue, if it can get it, it can also get out. If you did use expanding foam that uses water to activate the expansion so it would probably absorb any water in the process.

The same raft race has seen constructions using thick 6" polystyrene sheet, screwed together and braced with aluminium sheet (sort of a sandwich. like a side of a caravan). It floats well, but it does seem to absorb water too - the things weigh several times what they did when you come to drag them out of the water.

This leads me to think that Polystyrene is a "bad idea" for underneath the van.

The stuff in Kingspan and Cellatex though is more like compacted and dried Expanding Foam, and seems to be less keen on soaking up water by far than polystyrene. Kingspan do some stuff designed for cladding air ductwork, and states it is for external use only, plus they make the stuff for external wall cladding, so hence my leaning towards this material (which also has aluminium foil faces on both sides for extra water resistance and increased thermal performance, and is available in various thicknesses).

Oops! Just put the link in the wrong post above. DOH! Here it is again.... Kingspan Insulation - Therma Insulation - Kingspan Insulation UK

 

[K9d]

Well you learn something everyday, I didn't know polystyrene would absorb water.

Hymers are built with something that resembles polystyrene but isn't, and its also impervious to water so could be similar to what your looking at.

http://www.hymer.com/medien/pdf/1287653343-Broschuere_HYMER_Reisemobil_GB.pdf

 

[Norm De Plume]

LDV vans are metal - the top half of the van would conduct cold down to the floor and you would have the mother of all 'cold bridges'.

I wouldn't bother, TBH.

 

[GRWXJR]

Well you learn something everyday, I didn't know polystyrene would absorb water.

Hymers are built with something that resembles polystyrene but isn't, and its also impervious to water so could be similar to what your looking at.

http://www.hymer.com/medien/pdf/1287653343-Broschuere_HYMER_Reisemobil_GB.pdf

"PU Foam" is Polyurethane Foam. The thing is, PU seems to cover an awful lot of ground, from the stuff they package breakables or electronics in, to acoustic foam, and the sort of stuff i am on about - it looks like its a very broad church, and so its probably easy to pick one that's totally wrong!

Like polystyrene, I think part of the issue is the amount of porosity of the material, as of course this is how the water gets absorbed - the more dense or 'closed cell' the type of material, then the better a chance it'll be effective at keeping the water out of its construction (too dense of course though, & it'll be rubbish as insulation!).

My thinking was to 'assist' the water resistance by using the foil covered Kingspan boards, and where you have the exposed foam ends, paint the ends/sides with underseal before fitting, to try and seal the section before fitting it in place under the van.

Hymer obviously use the sort of stuff that seems right by the sound of it though - so that at least gives me cause to hope that there is something suitable out there (although theirs is probably formed and moulded as a single construction with the aluminium skin rather than sourced as a flat sheet product which is then bonded to the skin) - if it can be tracked down & identified!

 

[GRWXJR]

LDV vans are metal - the top half of the van would conduct cold down to the floor and you would have the mother of all 'cold bridges'.

I wouldn't bother, TBH.

I read something about 'cold bridges', yes, so I think I know where you're coming from (the van shell would simply conduct all the cold down into the steel floor, thereby 'inserting' cold into the floorpan and so then getting the cold to 'bypass' my thermal barrier underneath, yes?).

My (unqualified) thinking though was, that it seems a heck of a lot of the 'cold' is coming through the floor from BELOW, and that the floor is a massive surface area exposed to the coldest part near the ground, and which has the least insulation.
So... even allowing for the fact that I would not be able to stop SOME cold leaching into the floorpan from the walls (Hi-Top is Glassfibre btw) that I could greatly REDUCE the cold arriving in the habitat area from the outside by cladding the surface area of the floor (plus I do have the bit of insulation on the inside under the laminate with foil and ply as well).

Do you have any tangibles that tell you that the results definitely would be negligible / nil / wouldn't warrant the cost and hassle to do?

BTW - On Sunday morning, packing away, the floor under the bed was way, WAY colder than the surrounding floor - even though there is some large gaps under the pull-out frame. That tells me that our body heat and the rest of the insulation etc. was keeping the rest of the room and the floor several degrees warmer than the area under the bed (3/8" ply base and 5" thick foam cushions, plus bedding). So...(seeing as this part of the floor gets as much 'cold bridge' effect as the rest of the floor from the van body), this suggests to me that maybe the floor under the bed being extra cold was due to the bed insulating that part of the floor from the rest of the van space? So... if you can insulate the floor from WARMTH from above with a marked difference... then can't we also do the reverse and insulate it to a marked effect from the COLD underneath it - even taking the 'cold bridge' effect into consideration?

Or am I just clutching at straws?

 

[GRWXJR]

This from Wikipedia....

"Thermal bridging is created when materials that are poor thermal insulators come into contact, allowing heat to flow through the path of least thermal resistance created, although nearby layers of material separated by airspace allow little heat transfer.

[2] Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging; the bridging itself needs to be treated carefully, rebuilt with a reduced cross-section or with materials that have better insulating properties, or with a section of material with low thermal conductivity installed between high conductivity components to retard the passage of heat through a wall or window assembly, called a thermal break."

Bugger!

Looks like Norm de Plume is on the money (dammit!).

If I understand it correctly, the sides of the van will simply funnel the cold air down into the floor. So, any insulation On TOP of the floor can help KEEP that transferred cold out of the inside of the van (as of course does the insulation on the sides and the roof), while any insulation below the floor is ineffective against this cos its on the wrong side!

So that just leaves the question of just how much of the cold in the floor comes via 'cold bridge transfer' from the walls, and how much is directly from underneath the van (as its only THIS aspect that any external cladding can address, plus I suppose it'd help prevent some heat from inside the van leaving through the floor as much).

I think I need for the floor to suffer much more from the cold directly onto the sheet steel floor than it does from transfer from the walls if any external treatment is to bring any real benefits? (Feel free to agree / disagree and educate me here please!)

I'm still tempted to give it a try if it'd not work out too pricey!

I'd welcome all the brains and experience I can get on this? Has anyone tried this before and got some comments? I was hoping that NBrown and the mega-experienced self-builders will weigh in with their 2-pence worth!

 

[hextal]

I agree with the others and definitely wouldn't.

It will be a faff, fairly ineffective and get covered in all sorts of crud to help it degrade quick.

 

[mark61]

LDV vans are metal - the top half of the van would conduct cold down to the floor and you would have the mother of all 'cold bridges'.

I wouldn't bother, TBH.

I think you are probably right. My van warms up very quickly, open the sliding door for 5 seconds and all the heat as gone, lol. I won't be blocking off the rear doors on the next van.

 

[GRWXJR]

I knew there had to be a reason why no-one did it, and the thermal bridge thing is the clincher - I just couldn't see it until it was put in front of me and I'd had a chance to get my head around it.

I already plan to stick some of that 'camping roll' type foam with foil on one side (sort of like the stuff they bung behind radiators) onto the bed /sofa base sections to add a bit of extra insulation there, and a couple of other tweaks to the insides, so it seems that its best I stick to the inside!

Ah well, guess its easier to take a bit off the bottom of the loo door so it'll open over the top of a rug than it would be to bung chunks of insulation material under the van anyway eh?

 

[blackbird100]

seems like a good idea, but remember you must be able to remove it easy, if it covers any part of the underside which comes under MOT..Testers don't like it, and will fail the vehicle if they cant see it . also if you have to weld it,at any point, the hazzards speak for them selves, especially with spray foam,,hope it helps

 

[mandrake]

there may be plenty of room under the van to insulate the floor ,but you have big problems for a start off all the fuel lines ,brake pipes and wiring loom also run under the van you cannot cover them ,for obvious reasons . also if you restrict an mot testers access to the underside, the van will be rendered un motable i would have guessed .

 

[Teutone]

I would just stick a nice thick carpet down over he colder period wih some neoprene backing.

 

[GRWXJR]

Yes, all in all it seems that its a non-starter.

I don't think that the MOT would be an issue - they can't fail it if they cant see it (my tester told me that they aren't allowed even to poke around with a screwdriver or hammer anymore - visual only - so like my van is undersealed and it might be covering a multitude of sins - but if he cant se it, he cant fail it. It isn't covering disasters btw - my LDV is sound underneath I'm glad to say).

The issue is simply that all the information says that it simply wouldn't make enough difference to warrant bothering - if (IF) I did get around to putting anything under there it'll be in the search for better sound insulation rather than heat insulation.

It was just an idea, and the this thread exercise has done the trick and answered the question - its not really worth doing.

Thanks to all for your contributions - much appreciated!

G.

 

[Roger]

Westfalia use a 25mm (approx.) fibreboard on top of the metal van floor, then a vinyl covering stuck onto the fibreboard. Only issue is water ingress and fibreboard, but its a lot lighter than the equivalent thickness of ply. They use a series of appropriately thick strips to even out the ribs in the floor. They don't stick the fibreboard down either.

Putting anything underneath the van is a recipe for rust, you may think that you got all the holes but water will get in behind the underfloor insulation and eventually rot the steel floor out. Even under sealing can allow water to collect behind the seal and cause rust.

Wall and roof insulation is taken care of with fibreglass wool - water repellent, light, easily suck to metal walls.

Heating, any of the cab heaters from Eberspacher and the likes - also get hot water at the same time and runs off diesel.

Biggest area of heat loss is the windscreen so any sort of insulated screen wrapping around will do the job and then a curtain to isolate the cab from the living area.

My two bobs worth.