Yet another subfloor question: Insulation Compression, Subfloor Rigidity, Noise

Hi All,

I completed my subfloor months ago, and am unfortunately considering ripping it out and replacing. Looking for advice on addressing some issues I have with my first iteration.

My subfloor is 1x2 pine slats, both horizontal and vertical, creating a lattice structure at an elevation 3/4” above the highest ribs. These pieces are adhered to the van floor with marine adhesive. Then, the voids were filled with standard Thinsulate SML 600 (non-compressible), and the stud/lattice structure was skinned with 1/2” BB primed ply.

Overall, the floor is extremely level and solid. There are no low spots, and I can bolt through the body pretty much where I choose without the floor deflecting much (close ribs, pretty rigid BB ply tied down with *many screws into the studs.

But-every time I walk on it, it makes slight creaks/noise. It sounds like an old hardwood floor in a house. I’m noise sensitive and it annoys me a ton. I think the adhesive perhaps is not a great solution when the body flexes, resulting in glue failure. Then there is independent movement between the studs and metal floor, and the movement creates noise.

I am debating mini cell or the other kind of Thinsulate (au400 I believe); filling the low ribs with minicell, then a single layer, then 3/4” or 1/2” BB ply and bolting it down. For those of who have done this: is it *solid? Does the floor feel rigid like a slab, or is there give? Do I have to block areas where I will bolt cabinetry/batteries etc, and the doorways so the minicell doesn’t compress? I want a solid floor like I have now, but without the moving pieces/noise.

I know this topic has been discussed at length, but I’m wondering about specifically noise/compression properties.

I used 3/4" BB for the floor. 3 sheets, biscuit joined and glued together at the seams. This is laid on top of a full sheet covering of 1/4" minicell foam from Hein. The rib recesses are filled in with strips of the same minicell but in .300 thick. The floor is bomber and never makes any noise. Very solid and very happy with the outcome.

Montucky said:

I used 3/4" BB for the floor. 3 sheets, biscuit joined and glued together at the seams. This is laid on top of a full sheet covering of 1/4" minicell foam from Hein. The rib recesses are filled in with strips of the same minicell but in .300 thick. The floor is bomber and never makes any noise. Very solid and very happy with the outcome.

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Good to hear. My 2019 has varying rib depths-did your van have different depth ribs as well? Did you double up?

When you bolt the stack down, does the minicell compress to a point and then it’s solid/no deflection beyond that point? Or does the minicell have very little compression capacity even before bolting the floor down?

Marie adhesive inherently has flex built into it vs construction adhesive which can become brittle and break down line you describe. Boats move non stop...houses do not (hopefully).

Did you put marine adhesive between stingers and plywood as well as between ply sheets? That is the location that most floors squeak.

While you may not feel it, 1/2" is very flexible ply in a flooring application.

I have wood stringers to floor using marine adhesive then 3/4" ply screwed down. Zero squeaks.

Anywhere you have wood to wood or wood to metal contact throw down a bead of adhesive. That may be a cheaper solution than tearing he whole thing out and stating over.

kfo said:

Good to hear. My 2019 has varying rib depths-did your van have different depth ribs as well? Did you double up?

When you bolt the stack down, does the minicell compress to a point and then it’s solid/no deflection beyond that point? Or does the minicell have very little compression capacity even before bolting the floor down?

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I don't recall doubling up on the strips that I put into the recesses between the ribs, but it can't hurt. You just want to be sure that the foam doesn't protrude above the plane of the top of the ribs.

The support of the minicell is perfect IMO. It doesn't feel squishy at all. Although the foam seems like it might squish under the floor, we're dealing with distributed loads on the foam, under a very rigid layer of 3/4" ply... so in reality the 3/4" plywood is supported about as well as it would be if it we laid directly on top of a rigid underlayment.

I used the factory fastener locations to bolt the floor down, and I didn't torque mine down too tight (until I squished all the foam). I tightened the floor bolts until the plywood was secured tight to the foam, and left it like that. I obviously don't want it flopping around, but it doesn't need to be torqued down crazy tight. I have L track in the back which helps pinch the floor down tight, and I did add a single fastener from the underside to secure the area immediately behind the passenger seat.

Yes the floor grooves vary in depth. I believe the 3 deeper grooves are 1/2” deep while the remainder are about 1/4-3/8”. I also filled the grooves with mini-cell foam flush with the top of the sheet metal ribs. I then installed the OEM rubber floor from my crew van over the mini-cell. My factory 3/8” composite wood floor was reinforced at select locations with 1/2” Baltic birch, the remaining voids were filled with 1/2” poly-iso, before being bolted down. No squeaks at all. More details on my build thread “Baby Shamu”.











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Montucky said:

I used the factory fastener locations to bolt the floor down, and I didn't torque mine down too tight (until I squished all the foam).\

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Quick question-did you use contact adhesive for the final sheet of Minicell? If so, was it in a few places just to tack it in place, or full coverage-spraying the floor fully and then the top sheets, and adhering them completely? Thanks.

kfo said:

Quick question-did you use contact adhesive for the final sheet of Minicell? If so, was it in a few places just to tack it in place, or full coverage-spraying the floor fully and then the top sheets, and adhering them completely? Thanks.

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I didn't use any adhesive. It's just floating. I did tape the seams using gaffer tape so that it held the pieces together as one continuous piece. You may be able to see the tape in the photos.

I don't think you'd have any problems if you hit a few spots with adhesive to hold the layers in place while you install the floor. I dropped my floor in as one piece, so nothing really had a chance to move.

In older homes they used solid wood joists and you are right - they do squeak. The question is - why do they make noise? The reading that I did indicated that it is from the wood moving up and down the shaft of the screw, and the wood joints moving relative to each other.

Some builders use laminated / engineered joists to make the boards more consistent - and frankly also to hold fasteners better.

We had a few rooms that had floors that made noise. Obviously it would be difficult to replace the joists in our house, so I added a LOT of screws to the floor and put down the carpet again. I also added some talc powder as a lubricant - not sure if that helped or not, but the noise level is much less.

I suspect that the pine is just not hard and strong enough to really hold the screws well. Laminated wood such as good quality baltic birch is rather dramatically harder and holds fasteners better than pine.

Especially if you get the 13 laminations / 18mm thick, it is super dense and holds screws pretty well. You almost have to drill a pilot hole before it will accept a screw.

Montucky said:

I don't recall doubling up on the strips that I put into the recesses between the ribs, but it can't hurt. You just want to be sure that the foam doesn't protrude above the plane of the top of the ribs.

The support of the minicell is perfect IMO. It doesn't feel squishy at all. Although the foam seems like it might squish under the floor, we're dealing with distributed loads on the foam, under a very rigid layer of 3/4" ply... so in reality the 3/4" plywood is supported about as well as it would be if it we laid directly on top of a rigid underlayment.

I used the factory fastener locations to bolt the floor down, and I didn't torque mine down too tight (until I squished all the foam). I tightened the floor bolts until the plywood was secured tight to the foam, and left it like that. I obviously don't want it flopping around, but it doesn't need to be torqued down crazy tight. I have L track in the back which helps pinch the floor down tight, and I did add a single fastener from the underside to secure the area immediately behind the passenger seat.

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I have this thread saved and following a very similar formula for my floor. I just finished gluing the mini cell strips into the corrugations over the weekend. I am surprised that the 3M 90 isnt adhering as good as I thought it would. Question for you on the ply wood. I am going to go with a 3/4" baltic birch. Did you use any kind of sealant or mold prevention? Is it needed? I wish I could find the grey stuff Mercedes uses to coat their floors.

mike183 said:

I have this thread saved and following a very similar formula for my floor. I just finished gluing the mini cell strips into the corrugations over the weekend. I am surprised that the 3M 90 isnt adhering as good as I thought it would. Question for you on the ply wood. I am going to go with a 3/4" baltic birch. Did you use any kind of sealant or mold prevention? Is it needed? I wish I could find the grey stuff Mercedes uses to coat their floors.

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I live in a pretty dry climate (Montana), and applied no finish to my plywood. The Loncoin is bonded right to the raw wood using their epoxy adhesive. I also biscuit joined and glued each of the sheets at the seams so the whole floor is essentially one-piece. It's been 2 years and I've not had any problems, but I suppose that if you live in a wet/humid environment and/or if you expected some spills and water to get under the floor, then it's probably not a bad idea to prime it or paint it with something to protect it. Overall I'm really happy with the floor. Can't testify the the specific performance of the insulation, but it doesn't squeak, and we have no problems controlling the temperature in the van both in the heat and in the cold.