DIY Doctor UK DIY Forums

Hi - hope you can advise a solution to the following issue - the fibreglass insulation placed between the roof rafters is wet due to condensation build-up. How can I insulate the gap between the rafters without the build up of condensation. There are two roof vents in cut through the tiles and small vents at the base of the roof, also my bathroom fan vents in to the roof and this could be the main cause of the condensation. Will it be possible to insulate the roof space - rerouting the fan through an external wall isn't an option (the house is listed) and I cant find an extractor fan with an inbuild condensator/drain so I dont know what my options are

Hi pcarter
If you have insulation between your rafters it will be difficult to stop condensation forming even if you have a roof without slaters felt.
If you have a roof with insulation between the joists you must vent your bathroom to outside - fit a tile vent and connect to this. This may improve the problem in first situation above.
Regards S

Thanks for your reply - in summary, as long as I have the warm, wet air from the bathroom vented in to the roof the condensation build-up will continue regardless of how the insulation is applied?

Hi pcarter
Basically yes, cross ventilating the roof will reduce condensation but venting a bathroom into the roof space will increase it beyond natural removal methods.
Regards S

OK - many thanks for your advice

Yes, your issue is the bathroom fans dispensing into the attic. You need to install a Flexi pipe onto the fan and then connect the other end to a vent tile or a wall vent. If you keep ventilating the bathroom into your attic, this will keep getting worse no matter what you do. This high humid air needs to be directed out of the house.
Regards,
Build4less