[Closed] Garage Roof replaced and gone mouldy. Advice please.

Who bought the materials? If he did, he is responsible and needs to sort it out. If it's his supplier at fault it's his problem.

Old Garages generally are damp places.

Rarely have correct dpc in floor and are not temperature controlled.

If the dew point is on the roof surface and you have not sealed the wood. Air will condense there moisture will form.

This will cause mould.

Unless the roof is leaking it's hard to pin this one on the builder imo.

Builders still being a bell end though

Who bought the materials? If he did, he is responsible and needs to sort it out. If it’s his supplier at fault it’s his problem.

He did, and that's my line of thinking. He puts it on his supplier if needs be.

Unless the roof is leaking it’s hard to pin this one on the builder imo.

No leaks apparent. The mould covers every board, not a patch.

Thanks.

Garage roofs are generally pretty low tech and don't have insulation, their only function is to stop water falling out the sky. If the roof is fully sealed without leaks then I'm not sure any damp beneath it can be blamed on the roofer.

We have a beach hut with a marine ply (curved) roof which had a GRP roof for about 20 years and now has a rubber roof.
There no insulation and ventilation in the winter is fairly minimal.
Over the winter the worktop can get mildew and there's some black marking on the ceiling.
It's fairly normal and just cause by the damp, static air.

I'm not sure your issue can be blamed on the roofer.
You said the job was "technically sound" by which I presume you mean it didn't leak.
If this is the case then he's done his job.

If there's poor ventilation and moisture getting in somewhere else then that's not his fault.

Apply something to kill the mould (bleach, etc) and try to improve the ventilation.

To my mind, he's used substandard materials. Not your fault - or his - that the ply was badly stored and was therefore going to go mouldy the moment it got a bit of moisture. But it is his fault that he chose to use it presumably knowing it was defective.

Having said that, I'm not sure what you can do. Doesn't sound like he's going to remedy it without being forced to. You could get a damp expert in, see what they say.

Mould grows on damp organic surfaces. Not the builders fault but perhaps he could have advised creating airflow to mitigate. Also not his job.
However he has admitted an issue with the materials he used so perhaps scope there to resolve.

As for cleaning, bleach isn't a long term solution to mould.

As for cleaning, bleach isn’t a long term solution to mould.

Never said it was….. I suggested using bleach [initially] and then to improve ventilation to keep the mould away.

You really need ventilation at roof level on opposite side to encourage cross-flow of air.

Has it got fascia boards? I fitted a new L shaped fascia above the main front door and incorporated a hidden mesh covered slot behind the lip of the L. Then on the rear / opposite wall fitted small circular plastic vents in the fascia board (simple job with a holesaw). Plywood was previously damp from condensation - now dry.

As for cleaning, bleach isn’t a <strike>long term </strike> solution to mould.

Sorry, fixed that.

suggested using bleach [initially]

Don't use bleach.

The roofer suggested using bleach.

The garage has air bricks at roof level, the previous roof didn't go mouldy in 20 years.

He has said it's down to the ply, which firstly he said was marine ply and we've been told independently it isn't. I'm not sure I believe the bit about extended storage causing a build up of spores which have since gone mouldy. He's just making stuff up to shift blame which actually lays it on him as the provider of the materials.

But I don't really think it's enough to get him to do anything about it.

Where are the "air bricks"?
You need two vents, one at each end, at least, up high, to benefit air flow through the building.

EDIT: He bought and supplied materials "suitable" for the job.Their suitability is his responsibility...

Bleach is old school. It works but it's a bad idea. Get some of the spray which kills the mold by crushing the spores and roots. One if the original versions was called Concrobiun or something odd like that. You spray it in, no brushing which means it contains the spores and it doesn't spread.

If you want to find out what's happening, as long as the under side seems dry, get a couple of square feet of 6mil poly and tape some squares of it using the proper vapour proof tape. Leave it for a while. If you get moisture between it and the wood, that's were it's coming from. If you get it on the underside of the plastic it's from humidity in the garage.
Once mould is established though, it doesn't need an external source of moisture to grow and spread. So if the wood was wet and now isn't, the mould could still be growing. So it's possible that if you kill it, it won't come back.

It's marine ply, clue is in the word 'marine', it's rated for use in contact with water, mildew or mould comes from poor ventilation, the roof is sound, a roofer, especially one that is good enough to fit marine ply rather than the cheap option of chipboard to get the job, is not responsible for mould growing in the garage.

And bleach is the most effective remedy, it kills mould more affectively than the various sprays and does last if the space is vented and dried out properly to stop it growing again, I like the roofers honesty in saying where the spores were picked up.

Same in a house, mould grows where the conditions are right for it, on any surface that will harbor it, just varnish the ply and it can't, it will continue to grow on plasterboard, not the plasterboards fault or whoever fitted it.

Sorry if this sounded like a rant, its just that when anything is mentioned here someone is to blame rather than just ask for a solution, quick spray with bleach and it will vanish, then seal it with anything that comes to hand, paint, varnish, whatever, if it had been anything but marine ply it would have rotted out by now, from the inside where the damp seems to be, the roofer was smart enough to spot that and not use chipboard.

Don't spray it with bleach.
5 minutes on Google will explain why this is not what you want to do.

So what changed that has made this happen now, with the new roof? As far as I can tell it's what the roofer did/supplied.

It’s marine ply, clue is in the word ‘marine’, it’s rated for use in contact with water,

All marine ply is.,...is regular ply with a couple extra layers is put together with waterproof glue that's guaranteed to have no voids. It's not rated for water contact without appropriate sealing on the outside surfaces any more than regular ply. Rots just the same without treatment

A garage in general is a damp environment, especially in the winter. I had some ply shelving which also developed some mould, had to take them off, remove the mould and paint them.

More than water ingress, I think its more the damp, cold environment.

garage roof replaced.
What was wrong with the old roof?
Was it covered in mould due to dampness?
Why is the garage so damp?

I’d put it down to garage construction / lack of ventilation and a couple of air bricks probably isn’t enough. I used to have an old concrete garage with a flat roof - it absolutely ran with water in winter and everything inside got covered in mould. Replaced it with a pitched roof with cedar shingles and vented eaves - no more damp.

What was wrong with the old roof?

Was it covered in mould due to dampness?

Why is the garage so damp?

The old roof had chipboard panels which had disintegrated over time. I don't remember seeing mould, maybe it wasn't so visible. I don't think the garage is particularly damp, there's nothing in there except the car and a fridge and a few old bits and bobs. The floor isn't damp/wet.

Spraying with a fungicide and sealing I think is the way forward. I'm not looking to blame the roofer per se... unless he's at fault. All opinions appreciated to help think it through. Thanks.

Don’t spray it with bleach.
5 minutes on Google will explain why this is not what you want to do

Bleach is really bad for you, you shouldn't inhale it and minimise contact with it, it's also the most popular domestic cleaner and women put it on their hair in far higher strengths than you would spray on mould, vinegar also works if you can stand the sink, both less toxic than mould treatments.

I have used a number of mould sprays and mould resistant paint, not great, the most effective I find is a weak solution of bleach sprayed on and left, when dry the mould is gone, plasterboard is particularly susceptible to mould because it's porous, nothing works on that because the mould is rooted right through it, needs to be replaced because anything left produces spores inside the wall and spreads even after being treated.

Also worth walking round the wall and checking if the air bricks are clear, garden debris builds up and blocks them and no one ever clears them, the source of many a damp house(and garage) for the want of 10 mins with a spade.

First thing i would worry about is the damp proofing in the garage, water is getting in, is it at ground level as the roof sounds like it's still watertight?

as others say, you can treat it and get rid of the mould, then maybe paint or spray to protect.

We had our garage roof replaced 18 months ago, was leaking like a sieve and damp proofing had gone, new roof went on, but only during a dry period where we could dry out the garage with a dehumidifier and so on, put new damp proofing on the brickwork and hopefully it'll survive for a few years, unfortunately it's rarely just remove and replace the roof that's required, there's a lot of work to keep it from failing early as well.

plasterboard is particularly susceptible to mould because it’s porous

Plywood is also porous.
Bleach wont kill the mould below the surface and ultimately will feed the regrowth.

Plywood is also porous.
Bleach wont kill the mould below the surface and ultimately will feed the regrowth.

So spray it every 6 months until someone can be bothered sealing it.

Ply is glued laminates, it won't reach the other side till the glue line breaks down.

" there’s nothing in there except the car and a fridge "
A-ha!

the old roof had chipboard panels which had disintegrated over time.

sounds to me like they had got damp as well

there’s nothing in there except the car

Car goes in warm*

Air temp in garage raises

Outside temp cools quickly.

Warm air inside trapped condenses on the roof.

* Unless car literally never moves or is cooled down outside and pushed in.....

Ply is Laminates of a thickness greater than the surface. Could easily be 1/8" of wood before the glue. Bleach can only treat the surface and won't penetrate the ply layer(s)..but the water component will still wet the wood further and heavy repeated application of a diluted solution may end up causing ply delamination if exterior grade (waterproof adhesive) ply wasn't used. Plus heavily wetting a poorly vented unheated space at this time of year wouldn't be ideal.
Bleach may also leave a surface film behind they prevent the appropriate mould eradication solution from being effective.
Bleach still isn't the right solution here, I'm unsure why that's not clear or why increasing the workload is a suggestion.
Concrobium, +ventilation, dry, seal if necessary.