I have a small 64 year old beach house in Galveston Texas. The house is on stilts at 8ft, no heat and no A/C so therefore no insulation.
I’m considering insulating the bottom side of the floor with foam board insulation in the hopes to alleviate one large issue of frozen PVC and CPVC pipes and maybe also reduce the the cold draft up through the floor in late fall and early spring. I’m on my 2nd re-pipe in 3 years.
My question is this, can I place the foam board up against the floor between the rafters and cover it with a corrugated fiber glass and have adequate air circulation as not to create a mold problem?
I am not sure which type of insulating foam board you are considering, but normally venting of this type of insulation board is not required, that is the reason that it is used under roofs, or immediately secured to vertical sheathing. So my answer would be that this should not be an issue. I have to question why the use of foam board and not simply spray foam? There are several products that can be sprayed under the home and if appearance is an issue, painted over the top. Have you tried PEX tubing for your water lines? I have a lot of experience with modular construction and in the Northeast, the majority of homes are now using PEX tubing. What is nice about the PEX is that it can expand quite considerably if frozen and when thawed return to its original shape without a rupture. Good luck