insulate tiny house with styrofoam

[Engblomarn]

Hi, I'm new here and could use some smart advice.

I'm currently building a tiny house-like structure on an old caravan chassis and have encountered some questions regarding insulation.

At the bottom, I've laid form-plywood, and on that, I've placed a 120*45 floor framework that I plan to fill with styrofoam. On top of the styrofoam/wooden framework, I was thinking of laying plastic and then floor chipboard.

Now my concern is whether there's a risk of moisture/mold developing between the plastic and the form-plywood since it becomes quite airtight.

I've been considering whether I should drill some holes in the form-plywood and create an air gap between the styrofoam and the form-plywood, but I'm not sure if that's wise either, as moisture could rise up through the holes, and I would lose a couple of cm of insulation.

In the walls and roof, I have an air gap on the outside, so there shouldn't be any risk of mold if I place plastic on the inside, but as mentioned, I'm more worried about the floor.

What do you think?

 

[fribygg]

I don't have answers to your questions but I'm wondering if it isn't unnecessarily difficult to seal between the insulation and the joists if you do as you describe.
Are you going to foam between wood and frigg or how are you going to seal it?

 

[Engblomarn]

I don't have an answer to your questions but I'm pondering whether it might be unnecessarily difficult to get a seal between the insulation and the flooring if you do as you describe.
Are you going to foam between wood and frigg, or how are you going to seal it?

Yes exactly, in hindsight, I regret choosing styrofoam as insulation, I never thought it would be so time-consuming. I had assumed the U-value would be better in styrofoam, but apparently, it isn’t.

I have already insulated the ceiling and most of the walls (the picture I posted is from the early stage of the build) and I've already used almost 6 bottles of foam, and I haven't even foamed the most tight seams 🥲

 

[fribygg]

If I were to make such a floor, I would clamp the styrofoam with the wooden batten, continue compartment by compartment and maybe foam the last compartment while sealing any knot holes and penetrations, then one can would be enough.

 

[Engblomarn]

If I were to build such a floor structure, I would clamp the styrofoam with the wooden joist, continue section by section, and maybe foam the last section while sealing any knot holes and penetrations, then a can would be enough.

yeah, that's not a bad idea; unfortunately, it's a bit too late since everything is already framed

 

[fribygg]

Formplywood?
Won't that be very heavy on such a chassis?

 

[Engblomarn]

Form plywood?
Won't that be very heavy on such a chassis?

all in all, it shouldn't be more than 2.5 tons if I've calculated correctly... the chassis has double wheel axles, then I've reinforced it a bit... should hold to drive at 30km/h

 

[fribygg]

After a tractor, 2.5 tons is not that much, but what are you going to tow with?

 

[Engblomarn]

After a tractor, 2.5 tons isn't that much, but what will you be towing with?

with an SUV, I was thinking