Is Denser Foam Worth it?

[leblanda]

Hi guy's,

I did't start the built still workinbg on the trailer.
The build will be 6x12 feet with 6 feet high
I plan using 1.5 inch foam with 2x2 reinforcement.

We can get:
Owens corning
NGX codeboard density 20psi 2x8 and 4x8 ship lap edge
Foamular c-300 30 psi 2x8 only ship lap edge
Ngx F400 40 psi 2x8 Butt edge
Ngx F600 60 psi 2x8 Butt edge

Do you think the denser foam is worth it

Thanks

Dan

 

[KCStudly]

No. Most of the strength comes from the skins, and, since you need to ensure good ventilation, any differences in R value will be moot. IMO, the foam is important to separate the inner and outer skins (for rigidity), makes good sound deadening, and provides some insulating value that hopefully mitigates condensation on the interior walls. (Posted while waiting for return flight from Honolulu... Huzzah!)

 

[leblanda]

Thanks have a good trip back

D

 

[iamroot]

Commercial roofing uses high-PSI polyiso foam board designed to be walked on with skins designed to be adhered to, and it doesn't cost much more than XPS IIRC.

Polystyrene is known to have extremely poor tensile strength (it's an inadequate core material for FRP, for example). I don't know about these stronger grades of polyiso.

 

[QueticoBill]

Plain old EPS is used for sips. All it does it keep the skins spaced apart and not let them slide.

 

[iamroot]

Plain old EPS is used for sips. All it does it keep the skins spaced apart and not let them slide.

They're not used for much shear loading. In house walls, there's approximately none; and in roofs, they seem to have rafters/truss for load below them as often as not; and besides that, they're sized for insulation and nail holding, not load.

But, I missed something on the first post: "2x2 reinforcement"

Use the cheapest thing possible because you don't need core strength!

(I've been searching if it makes sense to use higher-strength XPS for a foamie, and I missed this post was about a wood-framed trailer -- my research says XPS makes an inadequate core material for FRP laminates if you are attempting to optimize strength-to-weight ratio, but with PMF the foam is likely stronger than your skin.)

 

[QueticoBill]

The houses with sips I've seen built have no rafters or trusses supporting the roofs. I'm sure some do.

 

[CanuckShooter]

I used foamular because it won't hold moisture like the less expensive foam insulation. For my build it was worth it because the first thing to destroy a trailer is water getting into the walls. I built like a boat, ribs, thin ply, 1 1/2 foam then PMF over it all.

 

[leblanda]

I used foamular because it won't hold moisture like the less expensive foam insulation. For my build it was worth it because the first thing to destroy a trailer is water getting into the walls. I built like a boat, ribs, thin ply, 1 1/2 foam then PMF over it all.

what you mean by rib? Roof spar?

 

[CanuckShooter]

Yes, 2x2 framing, 2x3 roof spars, 1/8 panel then 1 1/2 styrofoam