Compatibility of roofing materials

[jackiew]

I've just had 3 quotes for replacing the large roof over my workshop+carport+garage.

The current roof/walls are recycled( you can see the holes from the previous installation) galvanised iron which has been painted at some point in the past - the paint is now peeling off those bits of iron on the walls which aren't already going rusty.

first guy told me I needed a zinc-aluminum roof as colourbond would react with the galvanised walls where the flashing touched.

second guy told me I needed a colour bond roof as the zinc roofing is not compatible with the walls. He also told me that as the slope of the roof is shallow about 5 degrees that bhp wouldn't give warranty on the roofing material.

third guy told me both the zinc and the colour bond would react with the material of the walls to the detriment of the walls and he recommended going for galvanised iron again but if I really wanted one of the others then that was my call. He also said the roof is shallow and suggested that I would be better to have a decking profile on the roof rather than corrugated as it is at present. He said that I'm ok with colourbond gutters as the water would be running off of galvanised iron and not vice versa.

I am now totally confused as obviously they can't all be right. :confused: So who is wrong and what have they got to gain from it.

[bitingmidge]

Jackie,
There are a couple of diagrams on the ACE Gutters website which pretty much summarise what can and shouldn't be done!

Bluescope Steel have a bunch of technical data which may be of interest.

In summary:

Galvanised can run over galvanised, colorbond or zincalume.

Zincalume (or colorbond) can cause problems running over Gal.

If your Gal wall surfaces are painted, I wouldn't worry too much, as the chance of electrolytic reaction will be slight, but use plastic or (shudder) silicone to separate the metals, and get a bit of advice from the above on how to insulate fastenings.

5° is the minimum recommended pitch for Custom Orb (corrogated) profile, and while not desirable, is able to be done - just take care at the peak and sides.

Cheers,

P

[nexusone]

As long as your roof and gutters are the same material you should not have a problem. There should not be any significant runoff from the roof onto the walls.

My personal preference is for gal or colourbond. Seen too many cases of zincalume rusting or turning to white powder.

Steve

[bitingmidge]

Steve,
Can't argue with your comment re runoff onto the walls EXCEPT as Jackie pointed out "where the flashings touch".

Watch that spot Jackie!

I'd go colorbond too. (light grey at my place so it looks a bit like gal!)



Cheers,

P

[Barry_White]

Jackie

I consider that I am fully qualified to answer your quandry as I was a rep for Lysaght's for 11 years.

First of all if the gal flashing is touching the Colorbond® it will not affect it. If it is a lead flashing all you have to do is paint the underside and top to stop any reaction that is providing the water is running onto the Colorbond®. If the water is running onto gal the flashing you need to change it. The same goes for Zincalume® as Colorbond®

If the pitch is 5º BHP (BlueScope Steel) will warrant the steel and even if it isn't 5° the warranty still applies but they do not recommend it because water can leak under the laps in high wind conditions.

As nexusone says if the roof is, either Colorbond® or Zincalume® runs into a Colorbond® or Zincalume® gutter and doesn't run down the walls you will not have any problems.

As to his statement of Zincalume® rusting is incorrect as has been proved Zincalume® lasts 4 times as long as Gal. Gal actully goes white when it is left in a pack and gets wet but that white coating actually adds protection the to the sheet after it is exposed to the air, just looks unsightly. When Zincalume® is left in a pack and gets wet it actually goes black but again when exposed to the air and drys out will also add protection to the Zincalume®.

When Colorbond® is left in a pack and gets wet it actually softens the paint and accelerates the fading of the paint and is not covered by any warranty and that is why BHP recommends to keep all product dry until it is installed.

The action is not electrolytic but what happens is when water is running of a gal roof onto gal, it is adding protective salts to the water, but when water runs off a Zincalume®, Colorbond® or Tile roof the water does not have anything added to it and is very inert, hence the corrosion of Galvanized coating.

If you want to see what I mean have a look in any gal gutter that has a tile roof and you can see where the water runs down the valleys of the tiles you will see round rust patches in the gutter.

The only problem would be with Council as a lot of Councils do not allow Zincalume in suburban areas because it never looses it shine, whereas Galvanized will dull off after about six months.

So the best option would probably be Colorbond®.

[jackiew]

thanks for your help guys. sigh ... I hadn't expected roofing to be so complicated.

[seriph1]

they are all pulling your leg dude

THATCH is your answer, man THATCH!



Thanks for the valuable info guys ...... I now know why my roof is crap after 8 yrs.

[ozwinner]

I'd go colorbond too. (light grey at my place so it looks a bit like gal!)



Cheers,

P

And it doesnt clash with your white shoes.

Al

[journeyman Mick]

they are all pulling your leg dude

THATCH is your answer, man THATCH!



Thanks for the valuable info guys ...... I now know why my roof is crap after 8 yrs.

Hay, (pun intended)
this is the woodworking forum the answer is SHINGLES!
Steve, you want the medieval roofing forum and all the other people should be on the new UBeaut metalworking forum.

Mick the classifier

[bitingmidge]

And it doesnt clash with your white shoes.

Al

Shoes???

This is the SUNSHINE Coast. No need for shoes here (except when grinding metal, to stop the hot bits sticking between your toes)

P

[capedcrusader]

As to his statement of Zincalume® rusting is incorrect as has been proved Zincalume® lasts 4 times as long as Gal.

ZincalumeTM might only last longer than galv because galv doesnt have a very thick zinc coating any longer. In the goodoledays galv had a Z 800 (thats 800 grams/square metre) coating because it was dipped and stacked to dry vertically. These days as far as I know its more like Z 200. (thats 200 folks)
There is a company in SA who make a Z 600 coated galv product for people who dont like the "aluminium" look of zincalume.
Apparently the reason you find the checkerboard rusted roof sheet pattern on old roofs was caused by the fact that the sheets were layed under and over and the underside had a coating of reduced thickness because of the stacked drying process but I dont know how true this is. The SA people might also make the sheets with both sides ending up so you can fix them under and over from the centre instead of from 1 side to the other. (relevant to queenslander pyramid roofs only I suppose )

[seriph1]

OY! We Queenslander may be sun worshippers but we dont have any pyramids here ..... well not outside the Gold Coast anyway

[Barry_White]

ZincalumeTM might only last longer than galv because galv doesnt have a very thick zinc coating any longer. In the goodoledays galv had a Z 800 (thats 800 grams/square metre) coating because it was dipped and stacked to dry vertically. These days as far as I know its more like Z 200. (thats 200 folks)
There is a company in SA who make a Z 600 coated galv product for people who dont like the "aluminium" look of zincalume.
Apparently the reason you find the checkerboard rusted roof sheet pattern on old roofs was caused by the fact that the sheets were layed under and over and the underside had a coating of reduced thickness because of the stacked drying process but I dont know how true this is. The SA people might also make the sheets with both sides ending up so you can fix them under and over from the centre instead of from 1 side to the other. (relevant to queenslander pyramid roofs only I suppose )

capedcrusader

You are correct in what you say and the reason that the thicker gal lasts longer is because of the sacrificial process. Over the years the gal gives off its coating to protect the steel and the old sheets had more gal on one side than the other.

The difference with Zincalume® is that it is not sacrificial and does not rely on the thickness of the coating to protect the steel.

The reason that sheets where laid over and under was because they were formed on a barrel corrugator and were a maximum of 10 feet long and there was a down facing leg on the corrugate on both sides.

All roofing now is rollformed and has a down facing leg on one side and an up facing leg on the other side so all the the sheets are laid with the same side up.

I would reckon that if any one put a gal roof on with Z 200 coating class it would out last them their liftime so why worry about it anyway.

The only reason why BlueScope Steel keep producing Galvanised roofing is you cannot use Zincalume in intense farming situations e.g. piggeries and chicken sheds because the methane gases destroy Zincalume coatings.

Also because of the fanatical heritage wankers.

[IanA]

Bazza,

Well answered.

Lysaght produced heaps of good literature. One example is their booklet titled "Steel Roofing and Walling Installation Manual".

Do you know if there are current reprints available of any of these publications. If so I would recommend them to anone faced with a re-roofing job.

I also remenber seeing some excellent stuff on the effects of runoff from inert catchments, such as Zincalume, Colorbond and tiles, but can't locate my copy.

[echnidna]

capedcrusader

You are correct in what you say and the reason that the thicker gal lasts longer is because of the sacrificial process. Over the years the gal gives off its coating to protect the steel and the old sheets had more gal on one side than the other.

The difference with Zincalume® is that it is not sacrificial and does not rely on the thickness of the coating to protect the steel.

The reason that sheets where laid over and under was because they were formed on a barrel corrugator and were a maximum of 10 feet long and there was a down facing leg on the corrugate on both sides.

All roofing now is rollformed and has a down facing leg on one side and an up facing leg on the other side so all the the sheets are laid with the same side up.

I would reckon that if any one put a gal roof on with Z 200 coating class it would out last them their liftime so why worry about it anyway.

The only reason why BlueScope Steel keep producing Galvanised roofing is you cannot use Zincalume in intense farming situations e.g. piggeries and chicken sheds because the methane gases destroy Zincalume coatings.

Also because of the fanatical heritage wankers.

So does that mean that every time we fart our roof deteriorates.