damp ply layer under roof

[spoonse]

i've had a new roof laid on to ply and i've painted the underside of the ply with a fungicidal wash as there was a few signs of mould getting into the wood,this was around two months ago but the underside of the ply is still damp in places ,i soaked it decently but i thought it would have dried out by now.By the way its an outhouse and has no heating down there at the moment..any ideas how to dry it all out?i thought about a fan heater but would it cause condensation to settle?
thanks Lloyd

 

[^woody^]

This seems like typical condensation, which a roof like this will experience no matter what you do.

If it was penetrating rain, then it would be sodden after rain.

The only way to stop this will be to insulate tight underneath the deck

Heating and some ventilation will promote some drying of the water you have introduced, but otherwise it will stay a bit damp for quite a while at this time of year

 

[spoonse]

thanks for reply Woody,i thought as much,i need a few mildish days really to help it along but we have snow maybbe next week i'll just hang on till spring

 

[JohnD]

ventilation will help. Heating won't as it will just enable the air to hold more water vapour, which will then condense when it hits the cold surface.

the air outside, if cold, will be drier than the air inside, so ventilate to outside.

Is there a ceiling in this outbuilding?

Look out for sources of moisure, e.g. wet washing, concrete floor without DPC, new plaster, concete or brickwork, unvented tumble drier (including condensor type).

//www.diynot.com/forums/viewtopic.php?t=160032.

 

[spoonse]

at the moment i have just the roof joists and the ply above that but am waiting for it to dry out so i can get on with the inside,i've done like you suggested and left open the window and the door(when we get a decent days weather)but as we all know its been so cold and damp of late so its a bad time of year to progress with it,i'll still leave the window open a touch and wait for weather to change

 

[spoonse]

by the way is it good to use a fibreglass rockwool type insulation or a rigid type ,kingspan for the ceiling or does it matter

 

[JohnD]

kingspan is more expensive, but more effective insulation per thickness. I would go for whichever you find it easier to install.

I use a light industrial building where they put kingspan on top of the rafters, then tiled on top, which seems to me a good method (too late for you, sorry)