Originally Posted by yacht_planb
I am currently refitting a 1976 Hudson
Force 50 and I am putting 2 inch blueboard in the ceiling for insulation. This provides approx an R10 value. We are in south florida
where humidity is 90% or higher. The boat has a lot of 4 inch deck
supports that run from port to starboard that are made of mahagony. The ceiling panels
will cover the insulation both of which are sandwiched between these horizontal beams. My question is this, should I make sure the insulation is tight against the wooden beams to prevent the moist air from staying stagnent or is it better to have a 1 inch gap to allow air next to the wood?
Any advice would be much appreciated.
Seems like so far no one has any thoughts on this. I am not positive on this either, but in building houses in our cold climate you try to keep the humidity out of the insulated walls with a vapour barrier. The vapour barrier goes on the warm side of the wall and nowadays quality builders seal it tight to the framing with acoustic sealant
to try and avoid air leaks
at all cost. It is sealed around electrical
receptacles and so forth. The cold side has an air barrier that is moisture permeable so that any moisture that does manage to get in the wall from the inside can pass through and out of the wall to avoid rotting the framing. I believe but not 100% certain that rigid insulation is vapour tight, but since most houses use fibreglass batts in the walls the vapour barrier is always there. We have 2" of rigid insulation outside a 6" wall full of resin infused blown in fibreglass, and we still have a tightly sealed vapour barrier inside all that and a vapour permeable air barrier outside all that. It seems the thrust is to keep the moisture out from whatever side is the more humid side.
That's the only similar situation I can think of and I'm not sure how or even if it applies in your situation. If you had air con inside the boat then wouldn't the warm moist side be at the outside and you would therefore want a vapour barrier at the top above the rigid blue panels? But that's going to be very hard to seal with those beams already there. But if you didn't have air con then both sides are going to be warm and moist so then what?
Just guessing, but if I was doing this I *think* I would seal the rigid panels as tight to the roof and beams as possible and try to keep humid air out, if that's even possible. Hopefully someone who actually knows how this might be done properly in your climate will jump in here.