Damp joists what should I do ?

[Gary111]

Thanks again Jonbey, I’ll look into the airbricks to improve airflow.

Out of interest what sort of insulation did you use ?
Would that help with the dampness or could it make it worse ?

 

[JP_]

I put kingspan between the joists. Every room is a bit different ... the best combo of effectiveness and keeping costs down was putting 50mm kingspan in first then 50mm rockwool slabs on top. The bathroom got 100mm kingspan though. The first room I did only had 25mm kingspan + 50mm rockwool, and my bedroom had just 50mm kingspan. Don't ask why, there is no logic to it!

I think the best option is probably the 50mm kingspan + 50mm rockwool - with the kingspan at the bottom it creates a flat undersurface which means better air flow. Also, less joist exposed to the cold side. Also easier to fit - I screwed trellis poles under the joists for the kingspan to sit on, then foamed and taped any gaps.

Re. dampness - the kingspan stops living moisture (breathing, showers, cooking etc) passing through the floor, so should reduce dampness below the floor. Combined with more air bricks, damp should vanish.

 

[Gary111]

Thanks Jonbey for the in depth replies, at least I know what I need to do now.