Waterproofing a Roof?

And now for something completely different! Nothing to do with model engineering or workshops, but sort of related.

I rent a small single lock up garage off the local council. It is brick built but has a corrugated roof. Years ago I would have said asbestos roofs sheets were used but these days it's probably some sort of cement board. I house my end-of-life crisis car in there, a Mk1 Eunos MX5.

But the roof leaks in winter time, with the constant damp and heavy rain we experience the roof sheets get damp all the way through and drip water onto anything stored below. I complained to the council last year and they said they had waterproofed it, but it is nearly as bad this year. I will moan at the council again, they might put a coating of something on the outside of the sheeting, or they might not, but:

What could I do to stop water penetrating through the roof sheet and dripping down to what's stored below. I am thinking solutions like possibly coating the underside of the roof sheets, when dry, with some sort of waterproofing solution, or some form of underside sheeting, or WHY.

What does the team suggest?

Chris.

This is sort of related because it could just as easily be a workshop roof that is so affected!

Edited By ChrisH on 17/01/2015 20:27:34

My own thoughts have got as far as:

Waterproof solution on the underside, will that help rot the roof sheets? They would have to dry up the same way they got wet,

Sheet the underside with poly sheet of a suitable grade and support with cheap boarding of some type, but how would I / should I, ensure drainage?  And what sort of poly sheet and cheap boarding?

Chris

Edited By ChrisH on 17/01/2015 20:34:24

Are you sure it is water penetration or could it be condensation which this time of year on a single skin roof can easily occur.

I had that very problem with my last garage. After climbing up with some boards to walk about on I found that some of the flashing was dud at the front too. Since it was mine i wanted a good repair so cut in some lead for the flashing and then wire brushed/cleaned off the surface of the sheets and painted them with bitumen.. solved it for years.

Now I realise this is a rental but if there's anything worth storing in there then it might just be worth some aluminium tape over dodgy flashing and the bitumen job just to protect your stuff. Anything you put underneath is still going to allow the water into the space with the associated high humidity - it'll still be damp.

My garage has a corrugated roof which appears to be of a similar material, it also leaks badly.

The problem in my case is that the sheeting is laid at a fairly shallow angle, as the sheeting and support system has sagged a bit over the last 30 years the water now runs backwards along the overlap between the sheets, (I have stood inside and watched)

I have tried sealing the joins with fillers and even foam, nothing I've tried so far seems to work for a long period of time.

All the above plus the condensation as mentioned by Bob makes me think that the long term solution is probably replacement.

I shall obviously be watching this thread with considerable interest!

Chris, there is a clear liquid that you can spray on the outside, the name eludes me but its in B & Q. I bought a pump up spray can and the sprayed the surface twice and it seals OK. I do not recommend any thing inside except a plastic sheet over the car and supported. I had a problem with wind blown rain going under the lead flashing so I used water seal bitumen and stuck it down, no problem since.

Clive

Chris ,
I've recently been through the loop over re roofing and where you can re-cover the roof there is a steel corrugated sheet, vinyl coated on the outside and available, as optional extra, with a flock coating on the underside. The theory is that the flock coating slows down/prevents the formation of droplets which is the main problem from condensation. As you don't own this garage maybe a gazebo style erection inside your garage would keep the wet off your little mx5.
My answer was straight forward, plain steel corrugated on top of the existing felt over marine ply so I get an extra air gap for insulation and 20+ years life expectancy. Cost just over 200 pound for an 8x12 workshop and that could be sustantially reduced by taking overstock/offcuts from your local industrial roofing firm and cutting to size yourself.

I also have a shallow sloping roof that gathers moss on the troughs of the corrugations and the moss serves to make dams and that leads to back flow through the overlap joints. Short of replacing with end to end continuous sheeting I keep a shaped scraper on a long pole and have an annual descaling ceremony.

Bob D

Edited By Robert Dodds on 17/01/2015 23:05:53

I think you are in the hands of the Local Authority as to what can be done - Yes there are numerous Tar and or Silicon based liquid preparations that are readily available and applied to the outer face of the sheeting to a water repellent surface, but this does not stop any condensation drips from forming. One way to stop the condensation is to spray the underside of the roof with an expanding foam compound (Unfortunately costly and specialist applied), again many firms regularly advertise this product.

How about considering a good quality protection (waterproof) tailor made if required to fit over the car when the inclement weather is about

My own experience has been very similar to that of others. In my case the roof slope angle is very shallow and the sheets drained slowly. A lot of moss was also encouraged by the slow drainage which only dried out in the summer months. Painting with bitumen failed utterly to seal it, even after baking in the sun, it just soaked in and left it porous despite giving it 3 coats.

My roof was in asbestos sheeting circa 1940s having been over pig pens before convertion to a garage and leakage was such that I had to enclose a consumer unit below, at one time water was actually dripping out of the fuse holders!

Severe spalting from frost damage over decades had lifted the surface on outer and inner skins and in the worst section what was left was actually flexible.

I tore it all off last year and reroofed in box section steel sheeting, remarkably cheaply to my surprise and fortunately our local dump will accept old asbestos sheeting if double bagged. The replacement roof is also about 1/3 the weight of the old roof and sagging has actually begun to recover.

Chris doesn't have the luxury of that route available to him; the story may though be of use to others.

But in his case he might be able to rent alternative storage with a better roof; the Council are very unlikely to do anything of value to fix it.

Regards

Brian

I have experience of treating thousands of sq metres of roof with this problem (whilst working for my father as a teen). Farm suppliers stock a bitumen type glupe which you apply to the roof using a (non PC!) turks head brush! Do it only on warm days. It completely waterproofs the roof for decades!

The old asbestos roofs do get porous with time, the spray mentioned, some sort of silicon last time I used it, does work but not for very long. Roof needs cleaning and de-mossing first. Long term for your own shed double skinned insulated steel sheet is good and easy, can be cheap if seconds or offcuts can be found. In your situation I would be looking at a sheet inside, tented to keep clear of vehicle. PS the old sheets had a min. slope of 15deg. to work properly.

Thanks for all the replies.

Firstly, the car suffered last year and the paintwork required rubbing back. Last year was far wetter and there was masses of cement coloured drips all over the place. Leaving it for months whilst we were/are in France doesn't help! This year I have put a tailored cover over it, so the car is OK (I think - haven't looked but the cover is very good, the material proved itself on another car that was left in the open for months) and there are not so many drips anyway.

I can't really do anything to the outside of the roof. The garage is in the middle of a block, so access from the sides is out, as is from the back (the back wall forms the boundary to somebodies garden), so can only attack it from the front. I did think of something to spray or brush on as per Clive's suggestion, but in reality access makes it a no-no.

It may be a condensation problem, in fact I am sure it is, in part at least. I can see drips in places on the underside, but it is not only cold but we have also had a fair bit of rain in recent days, so difficult to say one way or the other. Although the gaps between the corrugations and the wall plate have been sealed there are two air bricks in the rear wall, which could be blocked up. The door is an up-and-over door, so that also lets cold moist air in. Unfortunately, there is no electric supply, so a dehumidifier is also a non-starter, literally, even if it was all sealed up!

Where the roof sheets overlap, the underside of the overlapped sheet is dry, which could be that it doesn't get so cold as the rest of the sheets so condensation doesn't happen there, or rain only penetrates the top sheet.

I did wonder whether a layer of insulation on the underside of the sheets might help, but it would need to be cheap, very, and stiff so it doesn't need anything up there to support it. Any ideas anyone?

As has also been suggested, another dry garage would be the answer and am looking, but they are a bit thin on the ground here. There was one in the local town, dry (only the door was exposed to the elements), with electric, but they wanted nine grand for the lease - How MUCH? ! So far, drawn a blank asking the locals who have a spare garage too.

Also as has been pointed out above, it is the council's garage not mine, so I am a bit limited to what I can do. If it were mine I might be tempted to reroof it; wouldn't mind spend the cash on that if it were mine.

Doing something cheap to the underside seems the only option, but what to use is the question?

Chris

I would still say- make a tent like structure over the car. Cheap woven plastic "tarpaulins" are available, put a rope down the middle of garage to hang over, the rest is up to you!

Think I would be having a serious talk with the council. If you wanted to park your car outside and get it wet why bother hiring a garage?

Regards Ian.

> make a tent like structure over the car

Hasn't the MX5 got one built in

Neil

(Actually they are lovely cars and a delight to drive).

My old mate George ( now in the final resting place in the sky) had a similar problem in his garage workshop. He got some corrugated iron sheets and we made another roof inside if you see what I mean. Water came in and we arranged the sheet and some plastic spouting so that the drips had a away out and it worked. It would have been difficult for the two of us to work on the outside of the roof, in the end we didn't need to. Ted

Hi Chris,
I would not bother building a tent inside the garage, if you're going to do that you might as well build a tent on your own property and save the garage rental. What about putting a sheet of polythene right over the roof and holding it down with planking?
Good luck (you're probably going to need it).
Peter.

Humm, I understand the idea of a tent inside the garage but don't like the idea much.

Ian, I am going to have a strong word with the council. The cost goes up year on year and it's now £34/month for the privilege, the roof should be dry for that. But,

I am thinking perhaps of taking the tent idea a step further, adapting John's idea and maybe explore the possibility of a roof inside the roof, using a cheap plastic roofing sheet, if I can find it, screwed to the underside of the wooden joists, and work out a way to lead the drips outside, if all else fails.

Neil. You are quite right, the MX5 is a delight to drive, I have a huge smile on my face every time I drive it. It's not particularly fast, no faster than a modern saloon car, it's just the way it does it. Such a delight! Definitely a Big Boy's Toy!

Chris

If you can dry the roof a bit there are some good repair paints, IMHO the main two are "Cromapol" & "Acrypol" neither though are particularly cheap, and are not what I would class as a permanent repair.

Paul

That's good value Paul, It cost Chris near £400 a year for the pleasure of trying to find a remedy to a problem created due to poor maintenance? Pity that in the recent "Blows", something very heavy didn't fall on said roof (While the garage was empty of course) and destroy it. Wonder if TV watchdogs would be interested?

Regards Ian.