We are planning the following roof/first floor construction (urban villa with a hipped roof):
— Concrete ceiling instead of wood construction on the upper floor
— Insulation on the concrete ceiling
— No roof insulation.
Now our general contractor has offered us a 35mm thick fiberboard (possibly an underlayment board?).
Reason: If the shingles are damaged in a hurricane and it rains, our entire attic will not be under water.
The cost of this fiberboard is $4,000.
What do you think? Is this board necessary?
Well, you do have the advantage of being able to store more temperature-sensitive things there. Whether the one is worth the extra cost must be considered.
Then you can consider directly insulating the roof, if it's already being worked on so diligently. Otherwise, leave it alone.
I would also prefer to properly insulate the roof and leave the upper floor ceiling insulation out.
Three levels of rain protection?
3. wood fiber insulation board
Water is silly when it comes through the roof, but I don't see it as a risk. For protection against summer heat, 35mm doesn't do much good, but it's better than nothing.
But assuming this (unlikely) case happens.... the water will still go somewhere.
We have the same roof. The ceiling is insulated, the roof is not insulated. We only have fiberboard over the ceiling insulation so we can access the attic. After the storm, we're just checking to see if everything is still okay.
For that kind of money, I would have thought of much better. The benefit is close to 0.
The underlay can then be omitted. Double makes no sense.