# Forum Home Renovation Roofing  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.

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## 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   :Cool:

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## 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

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## 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  :Cool:

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## 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®.

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## jackiew

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

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## seriph1

they are all pulling your leg dude 
THATCH is your answer, man THATCH!   :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  
Thanks for the valuable info guys ...... I now know why my roof is crap after 8 yrs.

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## 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  :Biggrin:

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## 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

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## 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  :Biggrin:

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## 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 )

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## seriph1

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

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## 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.

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## 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.

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## 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.*  :Cool:   :Cool:   :Cool:   :Cool:

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## Barry_White

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

  Only if you haven't got ceiling in your house or if your working in your shed and you stink like a pig.

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## Barry_White

> 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.

  Ian 
Here you go, download your own personal copy and the same for anyone else wanting to put up their own roof and wall cladding. 
There is a loads of information on the BlueScope® Steel and Lysaght® web site including free down loads.   http://www.bluescopesteel.com.au/au/...F600C04FCF6B8F

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## capedcrusader

> Also because of the fanatical heritage wankers.

  OOOOhh - bit sensitive arent ya Bazzza - you still a LysaghtTM rep?  
Why dont they make Z800 galv anymore just out of interest?? 
And you wouldnt be calling me a fanatical heritage wankerTM  now would ya?
I prefer the look of galvanising and laying the sheets out from the centre out on a symmetrically shaped roof in a tiled pattern makes more sense aesthetically but when you talk to fanatical salesman wankersTM they cant understand it.

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## seriph1

OY! Don't forget about us regular wankersTM too!!!!

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## Barry_White

> I prefer the look of galvanising and laying the sheets out from the centre out on a symmetrically shaped roof in a tiled pattern makes more sense aesthetically but when you talk to fanatical salesman wankersTM they cant understand it.

   

> And you wouldnt be calling me a fanatical heritage wankerTM now would ya?

  Sorry capedcrusader but that comment was not directed to you personally.   

> OOOOhh - bit sensitive arent ya Bazzza - you still a LysaghtTM rep?

  I haven't got a sensitive bone in my body and I am no longer a Lysaght® Rep.and after 11 years I decided it was time to retire but I do appreciate your point of view and I understand that every one has preferences in life. The problem with a lot of heritage people is that they are fanatical and have cost a lot of people a lot of money because they slap heritage orders on propertys without the thoughts of some of the people that own them and want to modernise their property's.  
What you have to remember is that what some of these heritage wankers do is have heritage orders placed on property's that they don't have a financial interest in. 
What this does sometimes it devalues the property and stops people from having their choices in life and the only way around it for them is to sell at a loss. 
It would be a very dull world if every one wanted the exact same thing. Me personally I like all new things and love new technology. I know this is not for everyone but I don't believe that what I like or dislike should cost any one else for what they like or dislike.   

> Why dont they make Z800 galv anymore just out of interest??

  The laying of tiled pattern of roof sheets went out when they began to rollform roofing material. Sheets were only laid in that manner because of the way roofing was made which was very old technology. By rollforming you are only limited in length by the limitations of transport which is about 21 metres, although on some commercial jobs if they are large enough they will set up the rollformer on site.  
The tiled pattern would probably not be obvious when it is laid in new iron and would probably take 100 years or more to appear when the sheeting begins to go rusty. 
The reason I dare say that they dont roll Z800 would be economic. The process of manufacture at BlueScope Steel would require probably in the order of 150 to 200 tonnes of product to warrant producing it. To sell that amount of steel in Z800 would not be sold in 50 years and to hold that amount of stock is not in the realms of possibility in a profit driven company like BlueScope®. 
They do manufacture up to Z450 in Custom Blue Orb which is mainly used for curving. See the quote from their website.  *Specification*   *Materials:* 
The base materials are ZINCALUME® steel, galvanised and stainless* steels. AQUAPLATE® polymer coated steel is used for water tanks. 
*For extreme conditions, COLORBOND® Ultra steel & COLORBOND® Stainless steel may be made available.  *Material Specification:* 
LYSAGHT CUSTOM BLUE ORB® is made from: ZINCALUME® aluminium/zinc alloy-coated steel complying with AS 1397-2001 G300, AZ150 (300 MPa minimum yield stress, 150g/m<SUP>2</SUP> minimum coating mass);ZINCFORM® zinc coated (galvanised) steel complying with AS 1397-2001 G300, Z450 or Z275 (300 MPa minimum yield stress, 450 g/m<SUP>2</SUP> (for unpainted) or 275g/m<SUP>2</SUP> (for COLORBOND® painted steel) minimum coating mass); orAQUAPLATE® steel is ZINCFORM® steel, polymer coated for water tanks, complying with AS 1397-2001 G300, Z450 or Z275 (300 MPa minimum yield stress, 450 g/m<SUP>2</SUP> (for unpainted) or 275g/m<SUP>2</SUP> (for COLORBOND® painted steel)minimum coating mass).All the materials cover either 608 mm or 762 mm. 
The base metal thickness (BMT) is 0.60 mm or 0.80 mm. 
The COLORBOND® prepainted steel complies with AS/NZS 2728:1997. 
Just as a point here is a link to a site that gives all the ALT Codes that produces ®, ©, £, ¼, ½, ¾ etc.  http://www.coloryourprofyle.com/phade/alt.html 
Thanks for putting up with an "OLD PHART" that thinks he knows a lot about nothing.

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