Green/Black film on concrete roof tiles

flocker

I presume this Rooferpete's domain or his specialist subject.

The roof has this build up of slime that is very slippy. We are very close to a number of trees and I'm assuming that is coming from them. One year l cleaned the roof using a hose and scrubbing brush and it worked OK (I didn't want to use a pressure washer as l was told that it could take off a protective layer on the tiles and make matters worse).

The roof is quite discoloured at the moment and l want a more permanent way of keeping the roof clean rather than the hosepipe and brush routine.

Will a strip of copper sheet running under the ridge tile keep the tiles clean or is there a specialist product that l could use?

TIA

rooferPete

Hi flocker,

Depending on the type of tile, (profiled or flat) it is possible to fit a copper strip an both sides of the ridge provided it's concrete or baked clay.

If the roof is on a two story house it won't be noticed after a while when the shine dulls down.

It can be difficult fitting copper under an ridge already in place, even a "dry fix" system, if the roof is a modern concrete roof tile the colour should be right through the tile. so unless you are using very high pressure it should not damage the tiles.

If you are describing new fibre cement the colour is a paint finish and can be damaged by both power washers and cleaning with a stiff bristle brush, older asbestos / cement (pre 1995) should be treated with greater care as they become brittle over time.

The one advantage a flat slate effect finish has is the copper will keep it all clean.

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flocker

The tiles are flat and it is about 15 years since they were fitted. They are a red colour with a vein running through them. I'm almost sure that they are coloured all the way through.

Is the copper idea the best way to go and if so could you recommend a supplier?

Thanks for the info Pete.

Cheers

rooferPete

Hi flocker,

There are a lot of suppliers for sheet copper many plumbing merchants carry it as do builders merchants.

The correct fixing method is hard to explain, there is more involved than rolling out a piece of copper, it must be welted on both sides and fitted in pieces not exceeding 600 mm long.

Done properly the copper will stay on and give years of service, if the panels are too big or not fixed properly they can blow off or cause leaks.

One advantage you have is the colour of the tiles, the copper will dull down and be hardly noticed unless you are looking for it.

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gregos

Hi Pete.

this is an interesting technique which I have not come across before. It seems like a great solution. How does it work? I'm guessing that rainfall on the copper creates an environment that kills the algae on the tiles. Would that be right?

rooferPete

Hi gregos,

An oldie but a goodie copper oxide keeps the roof clean, you may notice on chimneys flashed with copper the roof is clean in line with the chimney also copper roofs very seldom have any build up of moss or lichen in the gutters.

The gutters get dirty if not to the correct fall but no moss.

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flocker

Hi rooferpete,

There are a lot of suppliers for sheet copper many plumbing merchants carry it as do builders merchants

That must be the advantage of living near the big smoke, 2 weeks ago our local merchant (with nationwide depots) ran out of ¾ & ½" copper tube so there is no hope of them carrying copper sheet. Sure l know they can order it but ............. l think it maybe easier and less hassle to pick up the goldenpages. The service we get from building & plumbing merchants for odd ball items is ............ well lets put that it leaves a lot to be desired.

welted on both sides

Is this like a dutch fold / lap joint? I can uderstand the short lengths, what exposed thickness would you recommend (the visible thickness eg 2 - 3 inches or 5 - 6inches?)

Thanks Pete

gregos

rooferPete wrote:

you may notice on chimneys flashed with copper the roof is clean in line with the chimney

Pete, yes I have noticed that, and also with lead flashing, but for some reason I never made the connection. (It might have something to do with being a cretin). But do you know what's actually happening in there? Is it poisoning the algae or is some other process at work?

patrido

i looked into this after reading a small ad in a magazine. apparently copper releases copper sulphate when it rains, which kills (or maybe prevents the growth of) algae. I think it's not safe for human consumption, so it might not be the best option for your rainwater harvesting system

there are a few companies specialising in this. some do a copper ridge, others a copper strip. the ridge people claim the strip does not release enough copper sulphate - though that could be a case of the "judean peoples front".

The company I spoke to was based in Antrim, and I think the cost was about 50 yoyos per metre. They also said they do copper flashing for chimneys, bay windows, etc.
www.copperridges.com

There are other variations too...
www.copperridge.co.uk

rooferPete

Hi Patrido,

The amount of the run off is miniscule and the danger very questionable, personally I would be more concerned about the run off from PVC products as there is nothing natural about PVC.

I have the highest respect for the Father of the owner of copperridges.com but nobody will ever see a fixing with a neoprene washer fitted by me or Gordon on a roof meant to last 100 years

Hi flocker,

Personally I like to see at least 75 mm each side of the ridge, but sometimes a low building like a bungalow would not look right with that level of cover so 50 mm can often do just as well except it takes longer to work.

Naturally a lot depends on the rafter length and how much fall out you are getting from the trees.

Hi gregos,

From your posts I think it fair to say you are far from a cretin you just don't have to look up as much as I do, you may have noticed streaks from lead flashings, they are usually caused by the soakers being fitted without being treated with patination oil.

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gregos

patrido wrote:

apparently copper releases copper sulphate when it rains, which kills (or maybe prevents the growth of) algae. I think it's not safe for human consumption, so it might not be the best option for your rainwater harvesting system

Don't forget that all the fittings in your drinking water supply are also made of copper. I don't think the copper flashing would compromise your rainwater harvesting at all.