Floor insulation thickness - quick opinion needed

[Douggy]

Hi guys,

looking to get a quick opinion on floor insulation and sub-floor thickness. Spent many, many, many hours digging through the site, but seem to see varying opinions.

Background - standard bus height (6.2?) with metal floor. I removed the rubber and ply original floor (absolutely rotten, with some metal pitting underneath - removing the original floor is great advice to take!!). Metal floor was ground, phosphate-treated, primed, and painted. Looking to insulate, then add plywood sub-floor, and vinyl planking top layer. Bus is mainly for weekend/week vacations, intermittently - not fully-timing in it. Located in the Louisiana, so it’s basically hot as hell most of the year. Mainly looking to stop too much heat getting in and too much a/c cooling getting out. BUT, looking to loose as little interior height as possible.

Options:

1..... 1/2” XPS, with 1/2” ply, then vinyl plank top
2...... 1/2” XPS, with 3/4” ply, then vinyl plank top
3..... 1” XPS, with 1/2” ply, then vinyl plank top
4...... 1” XPS, with 3/4” ply, then vinyl plank top

I know option 4 is going to be the best of them all, but is it that much better than option 1? ......thought I would throw it out to the community to get some real-life experience from y’all!

Cheers

[Mark_In_MA]

I wouldn't bother with anything over 1/2 plywood, especially if it's just going to be a sub-floor.

I'd do the 1/2 XPS and 1/2 Plywood.

I think you'll loose more cooling through the windows, etc. - keep the headroom.

[Douggy]

Thank for replying Mark - I was thinking with the 1/2” ply and vinyl planking, things would be fairly rigid up top, but its good to ask and get opions - Cheers!

[CoryBodiker]

I did 1” foam with 1/4” 3ply plywood and just laid my flooring on it it worked grate.and There hasn’t been any warping Of any kind.

[Johnny Mullet]

I used 1/4" foam and 5/8" plywood to save roof height. Still made a HUGE difference in road noise.

[brokedown]

I went with option #4. So far so good.

[djdalfaro]

Man, I have gone over this exact question so many times (my floor is still not ripped out). Here's what I'm thinking.

The floor is going to be the surface that sees the least radiation, and anywhere you park it is going to be cool as the shade of the bus is over it. As such, my thoughts are that if you are looking for the most bang for your buck the additional thickness of insulation will do the most good on the ceiling and walls.

Of course this is only taking into consideration the hot outside/cool inside situation. The cold outside/warm inside is different and you will probably notice the lack of adequate insulation in the floor if you spend time in cold climates.

All that being said, I ran some rough heat transfer calcs and realized that no matter how much insulation I put in the floor/walls/ceiling, if I didn't skin over the windows (I'm not going to), the difference between the insulation thicknesses didn't matter much when you consider how much heat transfer is going through the glass windows.

*Rough heat transfer calculations ahead*

The difference between an uninsulated floor and an R3 floor at a temperature difference of 20 F is about 8000 BTU/(hr*sqft), apply that over the entire floor, say 200 sqft and it's a difference of about 1,600,000 BTU/hr.

The difference between an R3 and R5 is only 2.66 BTU/(hr*sqft), apply that over the entire floor, and it's only a difference of about 500 BTU/hr.

Consequently EACH un-insulated window flows about 650 BTU/hr.

In short, unless you are dealing with extreme temps, full timing, have skinned over all your windows... IT DOESN'T MATTER.

Of course, that won't stop me from going with option 4. Why, because I like to make my life difficult and expensive.

[somewhereinusa]

I have 2" insulation over top ot original wood floor with 3/4" wood on top of that. Heat is in grooves cut into the insulation. My floors are warm when it's below 0°.

[thrifty1]

Option 4 for me as well. Tongue and groove advantec ply

[Douggy]

Thanks for all the input guys.

Thinking I’ll play with Option #4 - buy a board of 1” insulation and board of 3/4” ply, stick it in the bus, and wander around on it seeing how many times I bash my head on things - there is little to get damaged inside of it.

[Ninjakitty]

I think it depends on how tall you are. I ended up framing my floor with 2x3 because of how crazy uneven it was. So inlayed down 1" and 3/4" foam board and compressed it by screwing down 1/2 inch ply. However, I'm 5'5" and my wife is 5'2" (maybe) so losing an inch of headroom wasn't a huge deal for us. I think you can go with 1/2" foam and 1/2" ply if you're looking to save headroom.

[EastCoastCB]

Originally Posted by Douggy

Thanks for all the input guys.

Thinking I’ll play with Option #4 - buy a board of 1” insulation and board of 3/4” ply, stick it in the bus, and wander around on it seeing how many times I bash my head on things - there is little to get damaged inside of it.

I'm not gonna live in my bus, but I'm going with 3/4" insulation and 5/8 or 3/4" marine grade ply.

[thrifty1]

Totally posted this in wrong thread

[atthebeginning]

Literally the foam people just left an hour ago. With all the windows open and no fans the bus is comfortable. Yesterday the metal roof was hot enough that you didn't want to leave your hand on it. The ceiling closed cell foam is almost two inches. The walls are almost three inches. The floor is metal + 1/2" dense blue foam + 3/4" plywood flooring. 5 windows were eliminated on each side of an 11 window bus. The foaming was $1250.00. I'm impressed, better than I thought it would be.

[Wildfloweramanda]

On a stationary skoolie in southwest Florida what would everyone recommend for the thickness of

Foam Insulation

Plywood

And final flooring (we are thinking of using cedar that we got a good deal on and will need to have it cut)

I see most people seem to use 1" in insulation, but would it be a good idea to go thinner for my Florida skoolie(to preserve headroom)?

[BarnYardCamp]

I went with 3/4" foam board and 3/4" plywood. Main focus was reducing road noise, any thermal improvements are just icing on the cake. It helps that I have a "high roof" bus.
What ever you go with, make sure every sheet is properly secured to the floor. You don't want sheets of plywood (or anything else) to become projectiles in a collision.

[Rucker]

Originally Posted by djdalfaro

Man, I have gone over this exact question so many times (my floor is still not ripped out). Here's what I'm thinking.

The floor is going to be the surface that sees the least radiation, and anywhere you park it is going to be cool as the shade of the bus is over it. As such, my thoughts are that if you are looking for the most bang for your buck the additional thickness of insulation will do the most good on the ceiling and walls.

Of course this is only taking into consideration the hot outside/cool inside situation. The cold outside/warm inside is different and you will probably notice the lack of adequate insulation in the floor if you spend time in cold climates.

All that being said, I ran some rough heat transfer calcs and realized that no matter how much insulation I put in the floor/walls/ceiling, if I didn't skin over the windows (I'm not going to), the difference between the insulation thicknesses didn't matter much when you consider how much heat transfer is going through the glass windows.

*Rough heat transfer calculations ahead*

The difference between an uninsulated floor and an R3 floor at a temperature difference of 20 F is about 8000 BTU/(hr*sqft), apply that over the entire floor, say 200 sqft and it's a difference of about 1,600,000 BTU/hr.

The difference between an R3 and R5 is only 2.66 BTU/(hr*sqft), apply that over the entire floor, and it's only a difference of about 500 BTU/hr.

Consequently EACH un-insulated window flows about 650 BTU/hr.

In short, unless you are dealing with extreme temps, full timing, have skinned over all your windows... IT DOESN'T MATTER.

Of course, that won't stop me from going with option 4. Why, because I like to make my life difficult and expensive.

Good way to approach this. I agree that for both cold and heat, window coverings matter more than almost any surface since they have the least resistance to thermal transfer and contribute directly to solar gain.

For the cold, insulating the floor (and in shuttle buses the lower part of the wall below the chair rail) is probably more about comfort--unless you have really good air circulation the air at the floor will be substantially colder than the air at head height.

I'd focus on sealing air leaks even before worrying about the floor-unless you are prepping for very cold environments.

[atthebeginning]

There is a chuck cassady YouTube on flooring that you should review. I did my bus this way and it’s great.

[musigenesis]

Originally Posted by Rucker

the air at the floor will be substantially colder than the air at head height.

I just measured this the other day in my bus with a space heater on. The air at floor level was 70°F and the air at the ceiling was 76°F. If the outside temperature is, say, 20°F, that means the ceiling is experiencing a 56° temperature differential and the floor is experiencing a 50° differential (heat loss will be proportional to the differential).

While the difference isn't nothing, it will be even smaller the colder it gets, and also smaller with just some circulation going inside (I'm going to measure the effect of this next time it gets cold here). It's not really enough of a difference to justify not insulating the floor (which I'm not sure is what you're saying anyway).

Incidentally, this temperature gradient works the opposite way in hot weather: because the ceiling air will still be warmer than the floor air, the temperature differential will be smaller at the ceiling (discounting the heating effects of direct sunlight) so more heat will be coming in through the floor than through the ceiling.