Advice needed. It's raining in my new garage!

[Tim Reid]

I have just had a new garage built. Detached, 6m by 4m, single skin brick walls, Onduline corrugated roofing sheets. Insulated roller garage door. UPVC rear door.

I have got a dehumidifier running constantly which is extracting about 1l per day but there is excessive condensation on the inside of the corrugated roofing sheets. So much that it rains inside! 

 

I guess the solution is to insulate the roof???

 

[Thrustyjust]

My dehumidifier takes about 6 ltrs a day out at the moment. Mines a tiled roof and I floored the eves and single brick, although a double. I guess its not pulling the moisture out as too cold for it to work and dehumidifiy. I have a humidity meter in the garage and has shown nearly 90 % humidity recently.

[Westford]

Compressor type dehumidifiers don't work very well at lower temperatures, you need to get a dessicant one such as https://www.meacodehumidifiers.co.uk/meaco-junior-8-litre-dehumidifier-dd8lj?gclid=Cj0KEQiA4o3DBRCJsZqh8vWqt_8BEiQA2Fw0eW-dMuzrX4MCXFh1IZtqQIhdC_NeDa5ablgwCr-2zcAaAlxr8P8HAQ or similar. They will pull out the moisture at any temperature and knock spots off the compressor type.

[TAFKARM]

Has it got decent ventilation?

What has the builder said?

[Andy (Sycho)]

You will always get condensation on the sheets especially if you have heat in the garage, the sheets are the dew point where cold meets warmer air.

You could insulate the sheets with kingspan or you can get a spray on foam to help stop the condensation.

[JulianE]

When I worked from home I had the internals of my workshop sprayed with foam insulation as I had that problem , all fine afterwards and noticeably warmer too .

 

[Northwarks]

My garage is an internal garage, has a dell server and chest freezer in it to 'take the chill off', currently the temps are low but humidity about 50%

 

 

[Andy (Sycho)]

This is simlar to what I've used on steel roof sheets in a factory that we built offices in.

https://m.abbuildingproducts.co.uk/touch-n-foam-200---spray-foam-kit-pr-5203.php

You do need to heat the bottles up for it to spray correctly & cover yourself up head to toe.

[Tim Reid]

Thanks for the replies.

I have added a heater set to 8degrees to help the dehumidifier but will have a look at the other type.

I was thinking about putting up 100mm celotex to insulate as it's easily available and to fit. A good idea?

 

There is little ventilation. The builder isn't interested in helping.

[Olliebeak]

I think you seriously need some air bricks

[Man On The Clapham Omnibus]

Remember that it has been particularly mild recently, followed by a sudden cold spell. The air is moisture laden and as soon as the temperature drops, it reaches dew point almost instantly. After a few cold days with frost the moisture will have precipitated out and the air will be drier. If you insulate the roof you must prevent moist air reaching the cold side from the warm side or you get trapped condensation. 

[Tim Reid]

I understand this is a bad time of year but this is really bad. I think I'm going to insulate the roof.

If using celotex will it be ok to have a small gap (10-20mm) between the corrugated roofing sheets and insulation? Like the following...

 

--_--_--_--_--_--_--_--_-- roofing sheets

******************** Celotex

 

[Mark (smokey mow)]

1 minute ago, Tim (TimDave25) - Joint Thames Valley AO said:

I understand this is a bad time of year but this is really bad. I think I'm going to insulate the roof.

If using celotex will it be ok to have a small gap (10-20mm) between the corrugated roofing sheets and insulation? Like the following...

 

--_--_--_--_--_--_--_--_-- roofing sheets

******************** Celotex

 

So long as you provide ventilation to the void so condensation doesn't form between the celotex and roofing sheets then thats fine.  But if you don't ventilate the gap then you could find yourself with an even bigger problem than the one you have at the moment.

[David Oxfordshire]

8 hours ago, Northwarks said:

My garage is an internal garage, has a dell server and chest freezer in it to 'take the chill off', currently the temps are low but humidity about 50%

 

 

OMG a seasonal time vs humidity plot of your garage.....!

[AndrewBClarke]

Ok - here is the technical 'building' solution from a building surveyor (me!). Insulate under the roof and/or the walls. On the inside face of the insulation there needs to be a moisture proof membrane - this is sometimes built in to insulation boards (or they are inherently waterproof). The 'dew point' is where the temperature is at the point where airborne moisture with condensate. By insulating alone, this may be within the insulation layer so to stop this moisture condensating, you need to stop it getting there hence the membrane. On the brick outer walls, insulated plasterboard (foil lined to act as a membrane) can be stuck on the walls with plasterboard adhesive. Celotex is moisture resistant so ok for underside of roof. Gaps need to be avoided and joints between Celotex boards should be taped over with moisture proof tape supplied by Celotex (not electrical insulation tape or gaffer tape!). Ventilate the space (with cross ventilation if possible). Heat would not be so necessary except for the comfort of the car, and a dehumidifier redundant unless the car is wet! Good luck. Andrew