New Garage - condensation issues

[GreenBrick]

My new garage is wood and a few of the joists are getting mouldy, the OSB on the roof is not, the side walls have a vapour barrier and are dry and mould free.

There was quite a bit of water getting in under the doors, so I have a temporary fix for that, put a greenhouse heater in on low and fitted a couple of PC fans running on the end vents to increase airflow.

I am also fitting a window as light is supposed to help prevent mould.

Long term though I need to stop condensation on the joists, so do I need to do something special when encasing them in plasterboard, as someone suggested, vapour barriers etc?
Is there some sort of treatment I can spray on, or is fence paint good enough to stop rot?

I will be following this thread closely...

Cheers

[100K+]

Originally Posted by GreenBrick

There was quite a bit of water getting in under the doors, so I have a temporary fix for that, put a greenhouse heater in on low and fitted a couple of PC fans running on the end vents to increase airflow.


Cheers

I have water seeping under my roller door too, but have an ingenious solution. An aluminium patio door wheel chair access thresboard. The door seal beds down on the patio door channel and the raised profile at each side stops water flow in under the door. The strip some 125mm wide will be bedded down on a stiff mastic, and drain holes will be made in front edge.
I'll let you all know how it goes
Cheers Bob

[100K+]

As promised a picture of the door seal fitted to my garage. The actual profile is spot on, but the seal was laid on a slightly damp day so the silicon has not bonded to the concrete as water gets under the seal. Its to be resealed on a dry day. However the concept is spot on. The car tyres do flatten the profile slightly but I can live with that. The channel the door fits down into can clearly be seen

Cheers
Bob

[GreenBrick]

Update on my damp issues...

The couple of PC fans have dried the garage out nicely and the mould vacuumed off with my shop vac nice and easily, leaving only a very slight sign there was any at all. I will get a dampness gauge before next winter, so I can monitor it more closely.

The channel across the doorway for me would not help as I have wooden side-hinged doors, but the idea of something sealed down just behind the doors' weatherstripping is a good one. I am also going to fit a drip edge on the doors that are big enough so the rain falls into the drainage channel infront of them and not onto the concrete.

[I-S]

Need a bit more information...

Is there a DPC, either below the concrete raft (that I assume the floor is made up of) or within the walls?

How recently was the garage built - has all moisture from construction had a chance to dry out? If it was built during summer or autumn then this won't happen until into summer this year.

The walls are single skinned, therefore any blown rain on the walls can come through as dampness. Try coating the walls, especially on any more exposed face with something like Thomsons Water Seal Ultra - this will lessen the amount of moisture within the walls.

Is there guttering to prevent water coming off the roof from running down the walls?

Ultimately it's a matter of the source of moisture - As you're likely to have the door open when you are in there there aren't huge internal sources of moisture (unlike a house where you have showers and hours and hours of people breathing and cooking etc). If the problem persists once the structure has dried out then limiting the amount of moisture coming into the walls is the next step.

[Grimble]

I know its too late, but what on earth possessed you to have a flat roof? In the UK!

A proper pitched roof would have cost very little extra, given you overhead storage and would be unlikely to suffer the damp issues.

Plus it will never need maintenance in your lifetime.

Architectural rant over.

[Simmy]

Originally Posted by 100K+

I have been lucky enough to replace my old wooden garage with a new 20ft x 12 ft detached single skinned brick garage, to work inside on my V70 AWD R. My 60yr old bones had enough of lying outside.
The roof has11inch deep roof joists supporting osb roofing sheets covered with a rubber membrane. However, the underside ( the osb) is suffering badly from condensation.
I have tried to read up/seek a solution, but the more I read the more contradictory the offered solutions become and so the deeper my confusion.
My garage has a roller door, which has an approx 1" gap at the top which allows air into the garage and I have added two 6 x 4 " ventilation panels to a side door near the opposite end to the roller door. There is no additional ventilation within the structure or heating.
Something I feel must be done as if left unchecked won't the roof rot away in double quick time??
My thinking is thus :
Leave/don't leave a 50mm air gap between the lower osb face and insulation placed between the joists.
Use Rockwool as insulation between the joists as its a "vapour permiable insulation" where as "Kingspan" is not, but possibly easier to fit.
Place/don't place a "Vapour control layer" on the underside of the insulation selected.
Ensure this VCL is sealed/not sealed to the joists to ensure a "full layer" of protection.
This work can/cannot be undertaken with the roof in its current situation ie damp.
Thoughts/ suggestions welcomed.

Cheers

Bob

if you go with the plaster board idea make sure you use fireline boards . the pink ones available from bq and all builders merchants aswell as being fire resistant they are stronger as they contain fibers and less likley to sag if any moisture gets on them hope this helps

[100K+]

Originally Posted by I-S

Need a bit more information...

Is there a DPC, either below the concrete raft (that I assume the floor is made up of) or within the walls?

Within the walls yes. Don't know about the main raft, as the floor is a mix of old and new flooring (old garage 18' x 10 new garage 3' overlap and 20@ x 12') new flooring no DPC

How recently was the garage built - has all moisture from construction had a chance to dry out? If it was built during summer or autumn then this won't happen until into summer this year.

Nov 2017

The walls are single skinned, therefore any blown rain on the walls can come through as dampness. Try coating the walls, especially on any more exposed face with something like Thomsons Water Seal Ultra - this will lessen the amount of moisture within the walls.

That was a job for the Spring or first prolonged dry spell we have

Is there guttering to prevent water coming off the roof from running down the walls?

Yes, on lower back edge and there is a upstand to stop water cascading onto wall on the other 3 sides.

Ultimately it's a matter of the source of moisture - As you're likely to have the door open when you are in there there aren't huge internal sources of moisture (unlike a house where you have showers and hours and hours of people breathing and cooking etc). If the problem persists once the structure has dried out then limiting the amount of moisture coming into the walls is the next step.

Hope this answers your querries
Cheers
Bob

[100K+]

Originally Posted by Grimble

I know its too late, but what on earth possessed you to have a flat roof? In the UK!

A proper pitched roof would have cost very little extra, given you overhead storage and would be unlikely to suffer the damp issues.

Plus it will never need maintenance in your lifetime.

Architectural rant over.

Lol...... The main reason for flat roof was to avoid the need for planning permission. I thought ( rightly/wrongly) need max height to be under 2.5m. Also neighbours have flat rooves and I was told flat roof would be cheaper, so I spent the money saved on building extra floor area. The roof is rubber not felted - do I get some brownie points at least?
Hindsight is always 20/20...Lol. and I'd still probably still go flat.
Cheers
Bob

[Grimble]

True about the hindsight, however the money you are spending on the condensation issues may well have offset the higher construction cost.

Not having a go, its just that I hate flat roofs. Our ancestors realised that water runs off a pitch, and it certainly rains here!

More seriously, as you built the garage in Nov 17 I'd suggest that a lot of your damp issues are to do with 'drying out' of the structure and come this time next year, all will be well.