# Forum Home Renovation Roofing  Screw size to replace existing screws in Colorbond roof

## audi

Hi,  
I am replacing all the screws in the roof of a little entertainment area attached to the main house due to water leak issues. (the screws grommets have deteriorated and some have rusted).  
I read online that when you replace roofing screws you are meant to go up a gauge due to widening of the hole over time. Is this correct? 
It seems like the two main sizes you can buy in Australia are no.12 and no.14, if I have size 12 should I go with size 14? what happens next time around when I want to replace them again do I just stick with size 14 or do I then have to replace the wood and start with 12 again? 
Thanks!

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## joynz

> Hi,  
> I am replacing all the screws in the roof of a little entertainment area attached to the main house due to water leak issues. (the screws grommets have deteriorated and some have rusted).  
> I read online that when you replace roofing screws you are meant to go up a gauge due to widening of the hole over time. Is this correct? 
> It seems like the two main sizes you can buy in Australia are no.12 and no.14, if I have size 12 should I go with size 14? what happens next time around when I want to replace them again do I just stick with size 14 or do I then have to replace the wood and start with 12 again? 
> Thanks!

  I wonder if the size up  info. is correct for modern fixings?  
Roofing screws have a rubber washer that sits against the roof and will provide a seal.  I would just use the same size.

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## cyclic

> I wonder if the ‘size up’  info. is correct for modern fixings?  
> Roofing screws have a rubber washer that sits against the roof and will provide a seal.  I would just use the same size.

  I agree.
Don't believe everything you read online.
And if the screws have leaked, then you may already have batten damage so might be wise to check and replace as necessary.

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## David.Elliott

I ended up having to go longer in my situation, same gauge, just longer..

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## Marc

Roofing screws rust and end up rusting the roofing sheeting especially if they are the wronk kind. If you have zincalume sheeting use galvanised screws, if colorbond, then colorbond screws. 12 g is the correct diameter. If your rafter are starting to rot or crack you will need to go longer. Going bigger in diameter will do nothing to a water leak problem. It's the rubber washer that seals. Don't over tighten the new screws/washers or you will be cracking the washer and have a leak in no time. If when you take the old screw out, the sheet is rusted around the old screw, clean the rust with a steel brush and apply cold galvo spray and touch up paint the same colour of your colorbond roof and then once dry fit the new screw. If the roof is cracked, get some colorbond offcut and cut a patch that fits the corrugations, drill a new hole, glue the patch with silicone and set the new screw.

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## audi

Thanks guys! 
I was aware of the rubber washer, but I thought the wider screw would be for pull out strength. But going longer seems like it would be a better option if the wood is in bad shape (obviously if it is in really bad shape then it needs replacement altogether). It is a Colorbond roof and Ill be sure to use the correct screws, and luckily I cant see any rust on the roof yet, but if there is some under the screws ill be sure to fix it like you have said.  
In terms of getting a better level of water resistance, I noticed that you can buy special domes for screws going into polycarbonate roofing (the dome is bigger), would I be increasing the level of water resistance by installing these? Or should I just stick with the standard rubber washer on the normal roofing screws? 
Thanks!

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## audi

> I agree.
> Don't believe everything you read online.
> And if the screws have leaked, then you may already have batten damage so might be wise to check and replace as necessary.

  In order to inspect the battens I would need to pull a couple of the Colorbond sheets and some of the sarking. should I just buy a new roll of sarking and where I make the cut in it layer in a new piece of sarking with a large overlap? Or is the sarking something I wouldn't want to disturb?

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## joynz

> In terms of getting a better level of water resistance, I noticed that you can buy special domes for screws going into polycarbonate roofing (the dome is bigger), would I be increasing the level of water resistance by installing these? Or should I just stick with the standard rubber washer on the normal roofing screws? 
> Thanks!

  No absolutely do not use polycarbonate screws  - use colourbond roofing screws.  The ones for polycarbonate are not suitable for other roofing materials.

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## cyclic

> In order to inspect the battens I would need to pull a couple of the Colorbond sheets and some of the sarking. should I just buy a new roll of sarking and where I make the cut in it layer in a new piece of sarking with a large overlap? Or is the sarking something I wouldn't want to disturb?

  You started out to replace the screws but you mentioned roof leaks, so if you just want to do screws then ok, but if the screws will not hold then you may be up for battens.
I did a lot of reroofs in the 70's-80's and only ever used 50x14 for custom orb with 65x14 for trimdeck, but in the 90's I noticed a lot of installers using 12 gauge screws.
Only problem I encountered with the 14's was old hardwood battens splitting sometimes.

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