Subfloor suggestions

[0Wanderlust0]

Hi All! I'm starting to look at subflooring options for my bus. I know that I want to at least have some rigid foam insulation for the floor, but I am unsure of how thick to make the insulation and plywood. I definitely want the floor to feel solid, but I'm cheap and want to do this for a reasonable price. I'm debating between 1/2 and 3/4 ply with possibly 2x4 framing underneath. I really just want to make sure that the floor is solid and isn't too cold to walk on in the winter. What would be the most cost effective way to do this? I've been reading that the main issue with buses is the windows. I do plan on keeping them, minus some deleted ones, and may even be doing a roof raise by cutting under them. ( I like the bus look and the light the windows let in). I do plan on taking the bus into mild weather, but not below 0. My plan was to make thick insulating curtains and just blast a diesel heater or two. I plan to be connected to shore power with the option to go off grid, but on shore, efficiency of heating/cooling wouldn't be as big of a problem. Any pointers is greatly appreciated!

[ChurchBuz]

I have been sawing through the posts (I have not read them all by a long shot).

I am going to use the 2” XPS foam on the floor.

My issue is with interior height. I am not tall, but I don’t want to live in a small tube. I want as much interior height, with as much efficiency and strength as I can get.

My plan is to cut 4” pvc drain pipe (thin wall) into 2” lengths and press (with the cores) into the foam every four or so inches, in a grid. This will keep the foam from crushing/getting spongy, and have insignificant heat transfer. Then put down a 1/4” hard core waterproof laminate floor.

Total height off of the metal is about 2 1/4”. Sturdy under foot with better insulation than wood, without the height.

The downside is the cost of the 1/4” hard core laminate floor is high, but it gives me advantages I am willing to pay for.

For what it is worth: I have successfully pressed in 1/2” CPVC (with its core) into the foam in a close grid pattern. I used a sharpened tube as a punch. It was fairly fast and worked well!

I expect that the 4” wouldn’t be too much more difficult, a hole saw with the curf ground off might just whip through there. Much fewer to do with a larger diameter.

[musigenesis]

Originally Posted by ChurchBuz

My plan is to cut 4” pvc drain pipe (thin wall) into 2” lengths and press (with the cores) into the foam every four or so inches, in a grid. This will keep the foam from crushing/getting spongy, and have insignificant heat transfer.

There's no reason to do this. XPS foam board is typically 20 PSI (or higher), more than enough to resist crushing if there is a plywood layer on top.

I did something sort of along these lines, welding upright wood screws to the floor and spinning 2" long pieces of dowel onto the screws through holes in the XPS. But this was to provide a mechanical connection between the plywood layer on top and the steel floor on the bottom, not to provide unneeded compression resistance (the dowels keep the plywood down without relying on glue and they also in places keep the rust-damaged steel floor from sagging).

[bus-bro]

Yeah, I used 1" polystyrene (pink foam board) topped by 3/4" tongue-in-groove plywood (the stuff used for residential sub-flooring), and painted it with latex porch paint. Worked well. It cost about $10 a foot of floor length, though I suppose it'll costs over twice that now.

[ChurchBuz]

Yes, I agree that the foam is strong, especially if there is a layer of plywood to spread out the load.

I am 5’ 8” with my boots on and I do not want to be any closer to the ceiling than I have to be. That 3/4” plywood is thicker, heavier, and more expensive than I am willing. The 2” foam is already more than I want height wise, but the insulation is worth it (to me), the plywood is not.

[HamSkoolie]

Owens Corning (Pink Panther) "Fomular 150" pink foam insulation sheets can handle 15 PSI before compressing. Under 1/2" plywood (which spreads out the load) you will be hard pressed to exceed 15 PSI. You can glue (use compatible construction adhesive) the foam to the floor and then the plywood to the foam. pay particular attention to the joints between plywood sheets to ensure they are well secured, and then cover with your choice of flooring material. Or save money and just seal the plywood with your choice of materials (keeping in mind you don't want an ice rink if it has water on it).
I believe the Owens Corning product is R7.5/inch. It might be R5. Check home depot or lowes websites for that number.

[0Wanderlust0]

These are some new ideas I've never heard of! I didn't realize that xps has a relatively high compression resistance. I'm thinking that would allow me to go thinner on the plywood with less fear of extensive "squishiness". Id keep framing in 2x4 just so I have something solid to frame walls onto. I still want to roof raise just for height as I'm 6' 2" with no shoes and the bus is 6' 5" in the center off the steel floor. Height of the floor isn't much of an issue I just don't want to be excessive and waste un needed cash.

[HamSkoolie]

Originally Posted by 0Wanderlust0

These are some new ideas I've never heard of! I didn't realize that xps has a relatively high compression resistance. I'm thinking that would allow me to go thinner on the plywood with less fear of extensive "squishiness". Id keep framing in 2x4 just so I have something solid to frame walls onto. I still want to roof raise just for height as I'm 6' 2" with no shoes and the bus is 6' 5" in the center off the steel floor. Height of the floor isn't much of an issue I just don't want to be excessive and waste un needed cash.

We're going with 1" Pink Owens Corning, 1/2" plywood, and 1/4" or less finish floor and then reinstalling the original perforated steel ceiling panels after spray foam (we'll take the thermal hit at the ceiling because the goal is minimal loss of headroom as I'm 6'1" and we didn't want to avoid the roof raise. If there's a thermal issue with the ceiling, we will remove the steel and install something thin (plastic wall panels, 1/8" luan, or similar.
We hope it will work out okay but if it doesn't we'll bite the bullet and remove the steel.

[Mercuric Mind]

I'm putting in a radiant heated floor and I wanted to keep the overall stack height to a minimum. I first put down 2 layers of R8 (so says the manufacture) mylar coated closed cell foam for R16 at 1/2" and then 3/4" plywood cut with the heating tub channels in it. This is screwed down to the metal floor and then covered with 1/2" plywood screwed to that. Last ~1/4" vinyl plank flooring. I hope it works.

[ism minerals]

I used 2x3 lagged bolted into the bottom seat rail with a small spacer to keep it slightly off the rail around 2'' and and also glued the crossmembers to the floor using constructive adhesive. I also put a couple of lag bolts from the underside of the bus into some of the 2x 3 cross members. I filled the spaces in between with 2'' XPS pink foam board r10 and sealed all joints with expanding foam. Looking back I would have made sure all my walls would have a 2x3 under them for added support. When I laid the advantek board, i cut it longs ways so it had to slide under the lip on the chair rail. It was a pain, but may provide additional protection in a rollover.

[musigenesis]

Originally Posted by Mercuric Mind

2 layers of R8 (so says the manufacture) mylar coated closed cell foam for R16 at 1/2"

You're absolutely not getting R16 out of a 1/2" layer of anything. In special circumstances a layer like mylar will reflect some of the radiant heat produced by direct sunlight, but this requires that the reflective layer face a 1" air gap (where the air in the gap freely circulates to outside the living space) and the equivalent R-value effectiveness is only about a +R2. Placed on a floor with no air gap, only the closed cell foam part will provide any insulating value, which at 1/2" will be R3 (at best).

[Rucker]

Originally Posted by musigenesis

You're absolutely not getting R16 out of a 1/2" layer of anything. In special circumstances a layer like mylar will reflect some of the radiant heat produced by direct sunlight, but this requires that the reflective layer face a 1" air gap (where the air in the gap freely circulates to outside the living space) and the equivalent R-value effectiveness is only about a +R2. Placed on a floor with no air gap, only the closed cell foam part will provide any insulating value, which at 1/2" will be R3 (at best).

I respectfully disagree. If you can pull a perfect vacuum in that half inch you can even do better than R16.

But then again, a vacuum is .... nothing. So maybe your statement you can't get R16 out of anything still stands.... Is Nothing still anything?

:-')

[HamSkoolie]

Originally Posted by musigenesis

You're absolutely not getting R16 out of a 1/2" layer of anything.

Even AeroGel is only a little over R10/inch. R16 in 1/2" would seem to violate the laws of physics.

[musigenesis]

Originally Posted by Rucker

If you can pull a perfect vacuum in that half inch you can even do better than R16.

I stand corrected lol. R∞ would be pretty dang toasty in wintertime.

[HamSkoolie]

Originally Posted by musigenesis

I stand corrected lol. R∞ would be pretty dang toasty in wintertime.

R∞ isn't possible since radiant heat needs no atmosphere to move though.

[musigenesis]

Originally Posted by HamSkoolie

R∞ isn't possible since radiant heat needs no atmosphere to move though.

Except that radiant heat transfer isn't part of R-value calculations, which only take into account heat transfer via thermal conduction.

[DeMac]

For insulating a steel bus with windows on both sides, there are other values which are more impactful on the performance of a particular product's R-Value rating.

K-value, C-value, R-value, and U-value can be summed up in the following rules:

The better insulated a system, the lower its U-value.
The greater the performance of a piece of insulation, the greater its R-value and the lower its C-value.
The lower the K-value of a particular insulation material, the greater its insulating value for a particular thickness and given set of conditions.

In a skoolie we ought to be particularly concerned with thermal conductance & transmittance. Both heat and cold conduct through bus window glass, solar radiation transmits straight through. The dense steel construction conducts the outside heat and cold more efficiently than most building materials.

A continuous, homogenous layer of uninterrupted, insulating barrier to seal the building envelope. Testing reports a 40-60% loss in R-value from not taping fiberglass seams. Just like a winter coat. Zipped up, no slits.

Which brings us to Convection. School buses have hundreds of hidden perforations, gaps, & holes that breath, suck, blow the temperament air right out. I could create an entire thread on seam sealer, fire calk, foam sealant, adheasives, patches and gap stopping. As far as I can tell, school bus manufacturers have zero concern for insulating a school bus.

Insulate all of the exposed steel & remove or cover as many windows as you can live without. Big gains.

[Mercuric Mind]

Originally Posted by musigenesis

You're absolutely not getting R16 out of a 1/2" layer of anything. In special circumstances a layer like mylar will reflect some of the radiant heat produced by direct sunlight, but this requires that the reflective layer face a 1" air gap (where the air in the gap freely circulates to outside the living space) and the equivalent R-value effectiveness is only about a +R2. Placed on a floor with no air gap, only the closed cell foam part will provide any insulating value, which at 1/2" will be R3 (at best).

Yes I didn't believe the manufacture's overly optimistic rating. I never knew R value rating was such a hot topic! drum roll please...

[Happy Feet]

No mention here of iso board ("Polyiso Foam Board"). Compared to good quality styrene (such as OC Foamular), it features:

• Higher R values (R6-7 /in vs R5 /in)
• Slightly higher compressive strength (16 psi vs 15 psi)
• Does not melt and is less flammable
• Similar cost

Two other notes:

• Some studies suggest that water saturation makes iso board more heat-conductive, but no longterm effect on its lifespan is expected.
• The 'iso' in iso board (polyisocyanurate) reportedly takes no longer to break down in landfills than styrene (which takes a notoriously long time).

Earlier discussion is here. I'm hoping to find out how those who have it installed feel about it. (Currently in conversion planning phase.)


Last thought: To DeMac's point on relative heat leakage, we're planning to go with just 1/2" of iso board (and thin subfloor over it). Only the thermal break is needed. I wouldn't expect a floor insulated with 2" material to be any warmer.

(P.S. Thanks to wife for letting me hijack her account to post this.)

[musigenesis]

Originally Posted by Happy Feet

No mention here of iso board ("Polyiso Foam Board").

Polyiso gets used (and mentioned on this forum) all the time. One of its disadvantages is that its R-value drops precipitously in colder temperatures, making it most suitable for hot climate insulation. Or it can be used to advantage in a layered situation with XPS/EPS against the skin or floor of the bus and polyiso on the inside.

Just 1/2" of polyiso on the floor would be much worse than 2" of XPS. Even in warm weather (above 75°F) it would be R-3.5 vs. R-10, and that R-3.5 would drop the colder it gets.