Insulation under van floor, rockwool rigid boards

Thinking outside the box. My researching of options to insulate the floor of my econoline, and have a bedliner utility option, lead me to under floor insulation. Then to the rockwool rigid board insulation. From what I can tell, it is a "perfect" option for this. Fire resistant, noise control, moisture repellant, and breathable in order to air out any environmental moisture, water crossing, etc. Being exerior is nice for lack of concern with fibers or health issues that often are brought up with the different materials for interior build outs.

The floor ribs under my econoline are 2" thick, which may be just right to stuff one end of 2" rockwool board into and attach on the other side. If not, 1.5" is available. Either a tab screwed into the opposing ribs, or 2.5" screws from the inside of the floor with a dab of sealant and fender washers/screw nuts to hold it in place. I dont have time to order it and give it a try, if I have to pull the transmission again I will plan ahead and order the peoduct. But maybe this will get someone else to try it or get some feedback from those who have used it in house construction. I also dont know what product would be best for the seams, or if it is needed(can foam, a type of tape, glue.. 🤷‍♂️)
 

Roaddude

Long time off-grid vanlife adventurist
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Rockwool can be an irritant and in some cases be more problematic than that: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711883/ . Might not matter to you being underneath, but having worked with it, and asbestos, and fiberglas, I wouldn't use any of it in my van.

Here's a potential alternative to consider that is inexpensive, effective, and very comfortable for van living.

I've used my current GMC Savana van for over a decade both for traveling work all over the continent and adventuring/living in through winter months as far as northern Quebec and Fargo NoDak. Before that a Chevy Express for the same thing. Ford Econoline before that with a different insulation set up.

What's evolved for me for best sound barrier, insulation, and overall comfort has been to leave the vinyl/rubber flooring the van came with and screw plywood down over it. Nothing under the van. Too much hassle to install, no fun to maintain, and potentially problematic. Anything underneath is unnecessary and overkill, is what I've learned.

Over the plywood--which has been given a couple coats of Polycrylic--I keep a simple indoor-outdoor mat that I can easily remove when I want to clean it. Or when I need to haul something I want to strap down to my e-track. The mat rarely needs more than a good sweeping, to be honest, when camping and going in and out of the van in all seasons. Moisture has never been a problem either, from me tracking it in or from it trapping condensation.

Here's an aftermarket vinyl/rubber flooring for older Econolines: https://www.factoryinteriors.com/news/ford-e350-econoline-vinyl-flooring/

This set up is very comfortable under foot. I never feel the cold from underneath the van or notice thermal bridging, etc, even bare foot. Been the simplest, most effective, and least expensive floor solution I've found in well over twenty years of wandering North America in vans.

GM-van-floor-liner-900.jpeg
OEM flexible vinyl/rubber floor covering for cargo vans. Can usually be purchased new for most vans.

interior_2802-900.jpeg
Birch ply with a couple coats of Polycrylic; comes in gloss or satin. Rugged. The image above is some 6 or 8 years after it was applied. Screwed right through the rubber flooring into the van floor with e-track set in.

vannery-int_6042-900.jpeg
Set up for adventuring with a rugged indoor-outdoor mat over the plywood that is already trimmed with a rubber flange, though could be cut to size.

Easy to remove; not glued down or stapled.

I'll be interested in seeing what else you consider and what you end up doing.

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It is a lot of work, but paired with removing the fuel tank for other reasons it doesn't seem as terrible.

I think I only found one example of under insulation, using foam panels. Maybe a mention here or there without doing it. So for those that would be interested in it, they might find this topic and product discussion searching the web. I wouldn't want the fibers inside the van either.. but just like the insulation around the dog house and under most hoods, it isn't in the livable space and only a concern for installation. Although that is a good point to consider with working under the van after.

As a side note, but still under insulation topic..
For my van, I had to take the Transmission out and dropped the tank to plumb in a rear tank. It was wide open for it, but was not the original plan. I intended to do bedliner with a ceramic additive underneath, then do the same on the inside and hope it would do "enough". After degreasing and pressure washing, there was still a bunch of grease and prep that would be necessary. I doubted I could get proper adhesion and I couldn't justify putting the project on hold waiting for Rockwool panels. So I went with foil covered rigid foam panels and butyl foil taped seams. Closed cell foam in the braces except for by the body mounts and the drain holes next to them. I will periodically check behind one that is easy to access for moisture accumulation. If it is a total disaster, because of using foam instead of Rockwool panels, Removing it would be possible with everything installed. For install, I cleaned and prepped the floor braces and butyl taped at the edges of the panels.
 

Roaddude

Long time off-grid vanlife adventurist
It is a lot of work, but paired with removing the fuel tank for other reasons it doesn't seem as terrible.

I think I only found one example of under insulation, using foam panels. Maybe a mention here or there without doing it. So for those that would be interested in it, they might find this topic and product discussion searching the web. I wouldn't want the fibers inside the van either.. but just like the insulation around the dog house and under most hoods, it isn't in the livable space and only a concern for installation. Although that is a good point to consider with working under the van after.

As a side note, but still under insulation topic..
For my van, I had to take the Transmission out and dropped the tank to plumb in a rear tank. It was wide open for it, but was not the original plan. I intended to do bedliner with a ceramic additive underneath, then do the same on the inside and hope it would do "enough". After degreasing and pressure washing, there was still a bunch of grease and prep that would be necessary. I doubted I could get proper adhesion and I couldn't justify putting the project on hold waiting for Rockwool panels. So I went with foil covered rigid foam panels and butyl foil taped seams. Closed cell foam in the braces except for by the body mounts and the drain holes next to them. I will periodically check behind one that is easy to access for moisture accumulation. If it is a total disaster, because of using foam instead of Rockwool panels, Removing it would be possible with everything installed. For install, I cleaned and prepped the floor braces and butyl taped at the edges of the panels.
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Yeah, bedliner underneath and inside would not dampen sound much at all, or provide any kind of desired level of insulation from heat and cold.

I don't understand the desire to insulate underneath, exposed to not only weather but an increase in wind, wet, and other forces that may cause premature failure while driving. Perhaps if stationary, living in a vehicle which rarely moves. It is so much easier, more efficient, and better maintained to insulate effectively inside without losing noticeable space.

I hope it works out the way you want - be sure to post up images. Best of luck with it!
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PlethoraOfGuns

Adventurer
Interesting concept. To me, underbody doesn't make much sense as a thermal insulator. Sound, maybe. But the steel floor will act as a thermal bridge and bring temperature past the insulation via conduction. Also when insulating vans, people should consider the sheet metal of the body as a vapor barrier in itself. I don't think it matters if you have vapor barrier inside or outside the insulation, but you don't want insulation between two vapor barriers.
 
I get that bedliner isn't a good insulator. I am putting a lot of hopes and dreams into the "insulating additive", lol. I don't expect too much but I'm willing to try something different to find out. I'm mostly going to be dealing with hot weather insulation needs. Thought the underside being insulated would work decently against radiant road heat. Maybe ill conceived? I started doing the butyl tape for sound deadening and then kept going thinking the foil layer and butyl separation wouldn't hurt.

My preference of bedliner inside is for a clean utilitarian style instead of the cabin stuff that is trendy right now. I found other people's discussion of the topic in an attempt to save as much height as possible. But my emphasis is on a durable floor that I can abuse and work out of when finished.
 
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_hein_

Observer
Our minicell kits are very popular and fairly easy to install. We don't go with thick insulation (high R value) simply because it doesn't help. A van is not sitting on a foundation with dead air space so keeping the floor warm in cold is a loosing battle. The minicell system is comprised of two thicknesses. One is cut into strips to fill the valleys between the corrugations. Then a full layer of minicell. You can add an optional layer of thin 3M thinsulate TAI1547 between the strips and full layer. This will improve acoustic and thermal performance a bit. Then 3/8 to 1/2 inch thick good quality (5-ply birch) plywood over the top. Make sure to seal the underside with a water based polyurethane. We have used ordinary porch paint as a top coat and recently used epoxy garage floor coating. Both are very durable. The porch paint can be renewed just by rolling on another coat. We also like an area rug or mat on top. Great for more comfort, catching spills and looks. For ultimate in comfort in cold climate put some seat heating elements under the rug/mat and plug those into a 12V outlet.

All the best,
Hein
DIYvan

 

Roaddude

Long time off-grid vanlife adventurist
Our minicell kits are very popular and fairly easy to install. We don't go with thick insulation (high R value) simply because it doesn't help. A van is not sitting on a foundation with dead air space so keeping the floor warm in cold is a loosing battle. The minicell system is comprised of two thicknesses. One is cut into strips to fill the valleys between the corrugations. Then a full layer of minicell. You can add an optional layer of thin 3M thinsulate TAI1547 between the strips and full layer. This will improve acoustic and thermal performance a bit. Then 3/8 to 1/2 inch thick good quality (5-ply birch) plywood over the top. Make sure to seal the underside with a water based polyurethane. We have used ordinary porch paint as a top coat and recently used epoxy garage floor coating. Both are very durable. The porch paint can be renewed just by rolling on another coat. We also like an area rug or mat on top. Great for more comfort, catching spills and looks. For ultimate in comfort in cold climate put some seat heating elements under the rug/mat and plug those into a 12V outlet.

All the best,
Hein
DIYvan

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Sounds like a great system. Cool to see someone else doing something so similar to what I've been doing for so long, outlined in my post above. That you've done it with several types of vans is validating.

- Thick vinyl/rubber OEM flooring left in place, which fills the valleys between floor ribs nicely and floats a layer over, too. I've used that instead of the Minicell you suggest, though I'd love to experiment with some (I took the liberty of linking it), and would no doubt get that if I didn't have such an in-great-shape floor covering already.
- A layer of good birch ply over. I've found Polycrylic to be the best water-based poly finish for this, at least for me. I like it's durability, ease of application, and the way it cleans up. I use it on all interior bare birch; applied lightly in two or three coats for cabinets, 3-4 on the floor; sanded in between coats. It provides an impervious, easily kept, surface and does not yellow like some polys.
- Ply floor topped with a good grade removable indoor/outdoor mat where needed.

I've had terrific success with this simple cost-effective system with no moisture problems under ply or OEM mat, for more than 10 years in my present van and for several years in another van before that. I never notice a cold floor and have no acoustic issues.
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s.e.charles

Well-known member
yeah; i would not put anything substantial on the floor either under or over the steel. even filling the stamped floor recesses is risky to retard allowing anything spilled or leaked finding its way clear or at least spreading out enough to dry of its own accord.

go over as you please and invest in an area rug or two. and some UGGS - you'll be on Pinterest before you can say "van-life".
 

Joe917

Explorer
Roxul board soaks up water like a sponge when submerged. It will weigh a ton and take a long time to dry. It is designed to be installed vertically and act as a drainage/insulation layer behind a rain screen.
 
My bedliner kit sitting on the shelf had an issue, the activator began hardening up. So I got another kit of raptor liner, added some of the hocus pocus ceramic sphere stuff and started applying it. I then ran out and had to use the thickened activator and some clearcoat hardener to get it finished with the old kit... So it isn't very thick.

But anyways, I got to drive it to work and grabbed the thermal imaging camera to see what the floors looked like after my commute on a cool low 40's morning.

I have not put insulation behind the steps yet, and no snake oil insulated bedliner applied there yet either. The majority of the heat will be on the passenger side, and close to the dog house. The few inches before the dog house opening doesn't have foam, but it does have a peel and stick heat shield and the factory heat shield. I also did not spray bedliner where the dog house gasket seals to the floor.

Drivers floor close to the dog house


Drivers floor away from dog house or step


Drivers floor step area uninsulated, and further away from the exhaust( about where the fuel filter is)

 
Passenger side, the most heat from the collector and motor being closer to that side.

Front Step area


Floor area, darker(cooler) spot


Hot spot seen better in the other picture because I had my cup holder thing in the way, but square is where the color variation showed more heat.

 
And the passenger rear seat and step area



So.. it kinda works. Like the factory heat shield underneath.. trapped moisture is a concern with the foam boards I used instead of the rockwool stuff I was optimistic about for discussion. Before everyone pooped on it because it's not the way its always been done. lol.

Hopefully I will have time to do the foam underneath half of one step and just the bedliner over the other to compare them separately.

When I build out the interior I will touch back to see how dramatic the thermal bridging transition is from the rocker panel exterior, to interior insulation. But that was inadvertently shown some in the thermal imaging camera within a few inches. If that is confined to the rocker area then it shouldn't make a big difference for the occupied space. As the transition is about 8-10" of unused rocker area.
 

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