Will I Have Condensation/Dampness Problem In Attic Crawl Space?

Southern Comfort

I'm about to insulate the crawl space in my converted attic. My joists are 4 inch (100mm). My plan was to put 100mm of Rockwool or Metac between them, place 100mm of some form of rigid insulation across the joists and cover this with chipboard flooring for storage.

Could I have problems with condensation/dampness in the long run, given that the rigid insulation board won't breathe?

Is there a better way of doing it, apart from raising the rafters another 100mm or more, and just filling this with Rockwool or Metac before putting down the chipboard flooring?

Poor Uncle Tom

If this is the Crawl Space (the low space just above the eaves) then there should be enough ventilation in the soffit boarding to stop any condensation happening in this area, unless I am missing something with your construction.

Southern Comfort

Poor Uncle Tom wrote: »

If this is the Crawl Space (the low space just above the eaves) then there should be enough ventilation in the soffit boarding to stop any condensation happening in this area, unless I am missing something with your construction.

Hi Uncle Tom. The area I'm talking about is the storage behind the plasterboard partition on both sides of my converted attic. It extends about 7 ft from the eaves to the plasterboard. The area was floored years ago but there's no insulation under it. Effectively, it's part of the ceiling of the bedrooms underneath. Hope you get what I mean..... Maybe it's just called a storage area and not a crawl space. Thanks.

Poor Uncle Tom

No, you are right it is known as a crawl space and the joists should be insulated here. If there are strip vents in the soffits then there should be enough ventilation for the timbers with the insulation as you describe, because the rigid board insulation can only be fitted out to where the rafters meet the joists leaving a space for air access.

However, you would be best advised to get a good local Architectural Technician to have a look at it with you.

Southern Comfort

Thanks again, Uncle Tom.