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neb

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  Reply # 1885137 17-Oct-2017 14:53
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kryptonjohn:

My initial idea is to screw polycarbonate roofing sheets to the underside joists. The joists run out from the house, and I plan to fix battens across them to create a fall, and fix spouting to catch it bear the house end.

 

If I can find it I'd probably use opaque sheets as it will probably get dirty and not look great underneath if it's clear?

 

 

This place has long-run steel under the carport, done by the same cowboys who did other work on the house. Based on that, (a) don't use long-run steel, and (b) make sure you have a really good slope on it so all the gunk that falls through the deck will actually be flushed off rather than building over time into a thick later of muck. Possibly consider providing access locations where you can flush all the debris and mould and moss out with a hose or water blaster.

 

 

Also, definitely use opaque sheets, you're going to get buildup of all sorts of stuff on there.

 

 

Finally, think about flexibility, if you're attaching it to a deck that's going to get walked over you need to provide some give to prevent cracking or fracturing around the screws where you attach it. The stresses in that case are going to be rather different than what you'd get from screwing it to a roof.



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  Reply # 1885153 17-Oct-2017 15:17
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What went wrong with using steel, @neb ?

 

All the decking is in place and really solidly screwed down. But could leave a gap underneath between the edge of the sheet and the boundary joist to allow a hose to be poked in.

 

I don't think this deck will move much. It's sitting on engineered steel beams and nogged 240x45 joists. It feels like walking around on concrete .

 

 


 
 
 
 


neb

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  Reply # 1885187 17-Oct-2017 16:18
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kryptonjohn:

What went wrong with using steel, @neb ?

 

 

This:

 

 

 

 

 




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  Reply # 1885221 17-Oct-2017 17:14
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Yikes how long had that been there? Like someone had been storing hot acid in it!

 

The deck we are replacing had galv steel formwork under it instead of roofing iron. It was 60 years old and still solid.

 

Your steel is odd as it is between the decking and the joists so not much air space. I'm putting the sheets under the joists so more room to breathe/evaporate water


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  Reply # 1885228 17-Oct-2017 17:38
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I wonder if water coming off the treated timber has cuased that corrosion to be far worse than it should me. If you put a galvanised plate onto treated timber, it can corrode quite quickly.




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  Reply # 1885229 17-Oct-2017 17:44
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Yeah but the joists don't look very old at all - and the steel is gooooooone!

 

 


neb

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  Reply # 1885231 17-Oct-2017 17:51
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kryptonjohn:

Yikes how long had that been there? Like someone had been storing hot acid in it!

 

 

Less than ten years, Coastal environment, pine needles, and they laid it dead flat so the contaminated water sits on top of the steel for long periods of time.

neb

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  Reply # 1885238 17-Oct-2017 18:04
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Oh, and forgot to mention: Knowing them they also used the cheapest steel they could get, so it probably didn't put up much of a fight to begin with.

 

 

At some point I'll post a photo of the single rusty bolt that was holding up one entire side of the deck.

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  Reply # 1885251 17-Oct-2017 19:00
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Iā€™d more recommend a 5 rib trapezoidal profile something like steel and tubes plumb dek http://steelandtube.co.nz/product/pur/low-trapezoidal/plumbdek id also put dpc between the timber and steel

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  Reply # 1885308 17-Oct-2017 21:44
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I'm in the HVAC industry and these days its a no go to use treated timber on a new roof. It used to be common to mount AC units on treated timber on a roof with dpc but now its known that the chemical timber treatment causes premature corrosion therefore voiding the roof warranty. No one wants to risk a 25 year roof warranty. So putting roofing iron under a treated timber deck is probably a recipe for a short life as per previous example.

Google NZ METAL ROOF & WALL CLADDING CODE OF PRACTICE and download a copy.

Any dirt or leaves that collect in the troughs will also hold moisture and promote corrosion too. So if using roofing iron don't expect it to last for ever. Thats not a reason not to use it though if its cost effective. You could think about painting the steel with bitumous paint before installing it. Another option is to use fibreglass or grp roofing. You could paint it to hide the collected dirt and leaves.

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  Reply # 1885675 18-Oct-2017 12:54
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Kickinbac:  putting roofing iron under a treated timber deck is probably a recipe for a short life as per previous example.

 

OPs deck is Kwila.  Not sure if that's an issue?  Tends to be an oily bleed.





Mike

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  Reply # 1885676 18-Oct-2017 12:55
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RickW: I’d more recommend a 5 rib trapezoidal profile something like steel and tubes plumb dek http://steelandtube.co.nz/product/pur/low-trapezoidal/plumbdek id also put dpc between the timber and steel

 

DPC being Damp Proof Coursing?





Mike



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  Reply # 1885683 18-Oct-2017 13:05
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Yep - that thick black tape you put between framing and floor slabs, masonry etc.




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  Reply # 1885684 18-Oct-2017 13:06
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MikeAqua:

 

Kickinbac:  putting roofing iron under a treated timber deck is probably a recipe for a short life as per previous example.

 

OPs deck is Kwila.  Not sure if that's an issue?  Tends to be an oily bleed.

 

 

Kwila deck sitting on treated pine joists.

 

The sheet (whatever it is) will touch the treated purlins. 


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  Reply # 1885787 18-Oct-2017 16:17
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kryptonjohn:

 

MikeAqua:

 

Kickinbac:  putting roofing iron under a treated timber deck is probably a recipe for a short life as per previous example.

 

OPs deck is Kwila.  Not sure if that's an issue?  Tends to be an oily bleed.

 

 

Kwila deck sitting on treated pine joists.

 

The sheet (whatever it is) will touch the treated purlins. 

 

 

Steel purlins?





Mike

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