Using plastic pipe to space corrugated tin

sheepman1 · Jan 3, 2017

I'm putting new tin on a half round roof an have asked around for tips on spacing the tin to stop water from being held at the overlap.
I have been told laying a length of 10mm or 1/2" pvc pipe along the length of roof between the joining sheets and then screwed down.

All advice and tips appreciated, thanks

wr. · Jan 3, 2017

When we reroofed some a few years ago, we had the new sheets in two lengths so that the longer one would come past the ridge and the overlap was on the down hill if you see what I mean. No need to seal and never had a leak. Also put your overlap on the other side from the prevailing wind.

Tinman Steels Ltd · Jan 3, 2017

There shouldn't be any need to have anything at the overlaps apart from a mastic sealant and stitcher teks. I have attached a fitting guide for corrugated

Nose Abit · Jan 3, 2017

sheepman1 said:
I'm putting new tin on a half round roof an have asked around for tips on spacing the tin to stop water from being held at the overlap.
I have been told laying a length of 10mm or 1/2" pvc pipe along the length of roof between the joining sheets and then screwed down.

All advice and tips appreciated, thanks

Are you referring to the end laps or the side laps of the sheets? If side laps, as per Tinman Steels, mastic sealant and stitchers should be sufficient - generally the corrugations of the sheet (going across) will start with a downturn and finish on a upturn which will give a lap of one and a half corrugations, slightly more than shown by Tinman. If this is not enough you could lap over an extra corrugation, but this may mean extra sheets required.
If you mean the end laps, rather than the normal 150mm lap you could increase it to a 300mm lap again with mastic sealant.

sheepman1 · Jan 3, 2017

Its is the end laps that I mean.

The original roof had a 300mm overlap, but inside the overlap is were the moisture gathered an rusted the tin from the inside.

I think it was more the moisture from condensation that rotted it than rain blowing up in.

The pvc pipe in theory would allow a little bit of air flow to try an counteract this

John 1594 · Jan 3, 2017

Wonder how the hell people of old managed to errect all those ex army tin nissen huts of the 50s and 60s, all hammered together with galvanised spring nails, hook bolts, and seal them perfectly without the luxury of tek screws?

renewablejohn · Jan 3, 2017

Tinman Steels Ltd said:
There shouldn't be any need to have anything at the overlaps apart from a mastic sealant and stitcher teks. I have attached a fitting guide for corrugated

Looking at spanning 2.5mtr polytunnel hoops with 2.75mtr tin but looking at that fitting guide the tin will not be strong enough. In the past I have used 2nd hand tins fastened with 4 exhaust clamps and the plastic roofing washers without any problems. Has the steel strength reduced over the years.

John 1594 · Jan 3, 2017

renewablejohn said:
Looking at spanning 2.5mtr polytunnel hoops with 2.75mtr tin but looking at that fitting guide the tin will not be strong enough. In the past I have used 2nd hand tins fastened with 4 exhaust clamps and the plastic roofing washers without any problems. Has the steel strength reduced over the years.

Modern tin is nothing like old tin

we had some sheets off an old anderson shelter that were so thick you couldnt knock nails through them, every hole had to be pre drilled

they got used in the lower backs of the pig cubicles we have, 30 years on you can kick them and still feel that they are as solid as a brick shitehouse

the sides and fronts, made with newer tin, have to be replaced over time as they simply rot through

Co down man · Jan 3, 2017

Have fitted sheets with water pipe as per your description you want it as small diameter as poss we used to use 3/8 probably not available any more.
You need long nails / drive screws think spring heads don't get enough grip.

Tinman Steels Ltd · Jan 4, 2017

For end laps we recommend the sheeting to be lapped with a minimum overlap of 150mm, with a double seam of mastic sealant approximately 50mm in from each end of the 2 sheets. They should have the overlap fixed at a purlin and have a row of main fixings running across the sheeting. With the sheet running from the highest point of the roof being lapped on top of the lower sheet. With end laps the most important point is to make sure you have a fall of a minimum of 4° with 8°+ being best practice.

sheepman1 · Jan 4, 2017

Tinman Steels Ltd said:
For end laps we recommend the sheeting to be lapped with a minimum overlap of 150mm, with a double seam of mastic sealant approximately 50mm in from each end of the 2 sheets. They should have the overlap fixed at a purlin and have a row of main fixings running across the sheeting. With the sheet running from the highest point of the roof being lapped on top of the lower sheet. With end laps the most important point is to make sure you have a fall of a minimum of 4° with 8°+ being best practice.

With the use of the mastic, are you trying to achieve the same as I am, that is, keeping moisture out ?

Tinman Steels Ltd · Jan 4, 2017

Yes the mastic is used for three reasons as a vapour barrier, to stop water penetration and to aid in the fixing of the two sheet ends together. We recommend our 6mm x 5mm x 9.6mtr Butyl roll strip mastic for end laps with each roll giving a double overlap strip for 4 sets of overlaps. Makes fitting mastic so much easier than using a tube and gun as you always get a constant bead and know how much you need even before your on the roof.

sheepman1 · Jan 4, 2017

Thanks @Tinman Steels Ltd , that's exactly the information I was after

.

Three more quick questions, I'm using 3" tek screws with one on each end and one in the middle, would this be enough to create a proper seal with the mastic tape?

Using corrugated tin, how far would the 9.6m rolls actually take me?

Also how much would that come to?

Tinman Steels Ltd · Jan 4, 2017

We normally recommend 60mm + Timber tek screws for the main fixings, with a row of 5 at the top and bottom and at any sheet end lap, and 3 at every other fixing point as per the fitting guide in earlier post above.

The 9.6mtr mastic rolls are for end laps and will do 4 sheets with a double overlap. For side laps we recommend a 9mm x 3mm x 15.00mtr Mastic roll which will cover a full 15mtr run and a 6mm x 5mm x 9.6mtr Butyl Mastic rolls for the end
laps.

Each 6mm x 5mm x 9.60mtr Butyl mastic rolls are £3.15 per roll + vat and the 9mm x 3mm x 15.00mtr Butyl Mastic rolls are £3.58 per roll + vat.

RWG Contracts · Jan 4, 2017

John 1594 said:
Wonder how the hell people of old managed to errect all those ex army tin nissen huts of the 50s and 60s, all hammered together with galvanised spring nails, hook bolts, and seal them perfectly without the luxury of tek screws?

Could still do it now if I wanted to but what's the point when you can just bang a tec screw in

Nose Abit · Jan 5, 2017

sheepman1 said:
Thanks @Tinman Steels Ltd , that's exactly the information I was after.

Three more quick questions, I'm using 3" tek screws with one on each end and one in the middle, would this be enough to create a proper seal with the mastic tape?

Using corrugated tin, how far would the 9.6m rolls actually take me?

Also how much would that come to?

Don't want to confuse matters, but if it is condensation that is causing the problem, sealing the laps is the last thing you want to do. Condensation will run down the sheet above and when it gets to the lap any moisture which gets between the 2 sheets will be trapped because of the mastic seal.
If you are on an exposed site, mastic will stop moisture (rain) being driven into the building from outside, but with 300mm laps and a typical slope for a curved roof in excess of 15 degrees it is debatable whether it would be required.
If you want to space the 2 sheets apart, you could maybe cut plastic damp proof course into squares and put them between the sheets at the fixing points, similar to the velcro packers used with anti condensation sheets. This would allow ventilation in and condensation out. Other than that, assuming you are using plain galvanized sheets, you could paint the laps with galvafroid or bitumen paint to give an extra layer of protection.

jamj · Jan 5, 2017

If you are wanting to let condensation 'run through' and not cause rust then as Nose Abit has said you don't want to seal it.
You could look at the little square spacers used by glass companies to space glass. They are sticky on one side. You would only put them on the ridge, not the hollow obviously. Whether they themselves would hold moisture or not I don't know.
I would suggest Glass Seal in Ballynahinch as somewhere you might see them.

On the other hand, to prevent the condensation getting between sheets mastic strips could be placed right at the end of sheet.

sheepman1 · Jan 5, 2017

jamj said:
If you are wanting to let condensation 'run through' and not cause rust then as Nose Abit has said you don't want to seal it.
You could look at the little square spacers used by glass companies to space glass. They are sticky on one side. You would only put them on the ridge, not the hollow obviously. Whether they themselves would hold moisture or not I don't know.
I would suggest Glass Seal in Ballynahinch as somewhere you might see them.

On the other hand, to prevent the condensation getting between sheets mastic strips could be placed right at the end of sheet.

Thanks @jamj , that's a good idea plus I could prob source them here locally.
I wonder if I cut small squares of the mastic tape and put them on top of every ridge maybe top and bottom, could work the same?

two-cylinder · Jan 5, 2017

John 1594 said:
Wonder how the hell people of old managed to errect all those ex army tin nissen huts of the 50s and 60s, all hammered together with galvanised spring nails, hook bolts, and seal them perfectly without the luxury of tek screws?

Just knock the spring head nail in flush, don't over do it and bend the tin!

Using plastic pipe to space corrugated tin

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