concrete roof and condensation issue

[max3d]

hi all
i am using an outhouse ( small singled walled building built onto our house ) as an office. Due to it having a concrete roof , floor and single walls i thought i would need insulation so i sealed the walls with aquaseal and then batoned and added 30mm phonelic foam insulation boards. I also added this to the ceiling but as you guessed there is a small gap between the boards and ceiling so i am getting condensation forming and dripping onto the boards and coming through the seams. i thought if i remove the boards and add some loft insulation to the boards so there no gap between the ceiling and boards this will cure the issue as the warm air will not be able to touch the concrete ceiling as there will be loft insulation sand wiched between. will this work. i need it to end as my computers dont need the moisture dripping down onto them. i also leave the window open and have a dehumidifier running which gets a lot of water but still not enough. so will adding the loft insulation ( rockwool) idea work ?? is there anything else i can do ??

thanks in advance
i have removed one of the phonelic foam insulation boards today and the ceiling is very wet so i have to do this in the next couple of days, so if you think this will solve the issue i shall bang on with it but if it will not work i need to know before i actually do it.

 

[ladylola]

Couple of things.
You seem to say that there is quite a quanity of water causing the problem. Are you sure that the problem is condensation and not water coming through the concrete roof? Many of these outhouse were simply used to store coal where a little damp wasn't a problem as such. I'd check on top of the roof as well to see if it needs covering or if there are defective flashings. You need really to sort out from where the water is coming from before putting in the insulation as all you will really be doing is putting up a giant sponge to soak it up.You could of course just put the insulation up there and then take down you sheets in a fortnight or a month to see if the insulation is wet or not, a sort of saracifical test.
Also there are a couple of other points to think about. Having a window open whilst running a dehumidifier is pointless, all you are trying to do is dry the outside world. Also what kind of heating do you have in there? Hopefully it's a dry heat like electric and not something like a parafin heater which chuck out a lot of water.

 

[max3d]

hi there and thanks for taking the time to reply. there isnt a leak last winter there was the odd bit of condensation around the ceiling where it met the outside walls. also since i have taken down one of the middle boards the ceiling is drying up. the dehumidifier is running on a night time when the window is shut. i have a large rad which is linked to my house gas central heating. hope this helps
also i have come up with a plan
( please tell me if you think this is going to be ok )
1, take all boards down and leave batons up in place
2, aquaseal the concrete ceiling ( i used aquaseal on the single brick walls to seal out any moisture before installing the foam boards) so its nice and water proof and black lol
3, add the loft insulation ( rockwool glass)
4, add the phonelic foam boards 30mm foil backed
5, grab a coffee

what do we think?

i mean i could just leave the ceiling as it is (naked ) and use the dehumidifier without any boards but its pretty cold( not as cold as it was due to the single brick walls now being insulated)

 

[ladylola]

Sometimes problems like this can be something of a suck it and see affair. I certainly don't think that your approach will be detrimental, but equally I can't for sure say that it would work but here's hoping. I would definatetly leave at least a panel with the screws easily accessable so that a check can be made as I said in my former post.
A rather more time consuming approach would be to lower the ceiling, if possible, and install a couple of air bricks to ventilate the void thus created.
Whatever happens I do hope you cure your problem and do keep us informed as to the progress.

Pete

 

[max3d]

thanks mate, thanks for the advice. i would love to make the false roof lower but the concrete ceiling aint that high as it is :/
i shall let you know what happens and thanks again

 

[Homesafe]

. Having a window open whilst running a dehumidifier is pointless, all you are trying to do is dry the outside world.

you are causing global drying , mate close the window.

 

[croydoncorgi]

You need to stop the warm, moist air from the room reaching the cold concrete roof surfaces.
Presumably, there's no vapour barrier between room and insulation layer. Fit one.
Cheapest option is perhaps a single piece of polythene DP membrane held in place by plasterboard sheets attached to your existing battens.
BUT before wasting your time on this make absolutely sure there's no leak in the roof itself.

 

[BobKbta]

the only answer I've ever seen to a concrete ceiling is spray urethane foam which keeps the humid air from contacting the cold concrete.