corrugated iron roof

[duncan webster 1Participant @duncanwebster1]

Our clubhouse has a thick (about 30mm) wood planks roof covered with EPDM. Over the years the EPDM has shrunk (it was never glued down properly) and is letting water at the ends of the timber, with predictable results. It has been suggested that the easiest fix is to put a sheet of visqueen over what we have and then screw corrugated iron on top. This will obviously keep the rain out, but are there any more issues to worry about? Obviously the visqueen will have a few holes in it where the screws are. Moist air from inside won’t be able to get at the steel, but will moisture from the atmosphere (dew) be an issue?

[JasonBModerator @jasonb]

Depends where the “dew point ” falls.

Most likely is it will be somewhere within the wood so any moisture in the warm internal air traveling towards the colder outside will condense within the wood and you risk rot.

A vapour barrier such as visqueen should be placed close to the inner surface often under plasterboard etc to stop the moistue traveling further.

You should really fit a breathable membrane such as Tyvek to the outside of the wooden roof as this will allow microscopic moisture droplets to travel out but stop larger water droplets from entering.

Proper fixings with the gromets and caps through the high points should not let much water through and what may get in will be stopped by the membrane

 

 

[BazyleParticipant @bazyle]

Keep the ends of the roofing sheets open to ventilate off the moisture. Moisture from inside will be and have been for years trapped by the EDPM. That is why you have the internal moisture barrier right on the inside of the insulation.
The screws for the steel will go though the top ridges and have rubber washers so will not have water ingress so holes in either visqueen or edpm will not matter. Ideally remove the edpm to let the roof breath.
If you leave the edpm in place the metal sheet will be in contact with it and I’d be worried of its decomposition being acidic. So I would put thin strips of corrugated plastic (as used for estate agents boards) as separators.

[JourneymanParticipant @journeyman]

Have a look around this website Cladco Metal Roofing Sheet lots of information on fixing steel profile sheet to new and existing roofs.

Unlike the old style corrugated sheet the newer flat profiles are fixed by self drilling screws in the valleys, waterproofing by means of neoprene washer.

John

[File HandleParticipant @filehandle]

I have often been amused by DIY corrugated roofs fixed in the valleys. I would not trust that method as I have also seen the fixings rise on occasions causing leaks.

[JourneymanParticipant @journeyman]

Like you I am used to fixings on the ridge of the corrugation but the above is from the manufacturers website so I presume they might have tested it.

John

[BazyleParticipant @bazyle]

The point is that traditional corrugated curved section provides strength for a top fitted fixing. Cladco’s advice for corrugated is top fitting. The newer trapezoidal section is too flexible for top fitting plus neoprene has been invented. Still for preference if you can provide mechanical support with spacers then for long term insurance do consider top fitting.

[duncan webster 1Participant @duncanwebster1]

It’s curved section, old style wriggly tin we’re considering, so fixings on the ridges, not the valleys. I’ll ring cladco tomorrow, thanks for the tip. The hut is only occupied a few hours a week, and we are not changing the concept of inside wood exposed, outside sealed. I can’t see us fitting vapour barrier inside.

[Michael GilliganParticipant @michaelgilligan61133]

The Cladco site looks very useful … duly bookmarked, thanks

Shipping price for < £500 purchases of panels made me wince though !

MichaelG.

[JasonBModerator @jasonb]

If no vapour barrier inside then even more important to use a breathable membrane outside under the tin not poly.

[duncan webster 1Participant @duncanwebster1]

• As supplied and erected by a fairly big commercial outfit it was bare wood inside, EPDM outside. They have supplied/erected hundreds of them. Did they have it wrong? I’m still trying to get in touch with cladko.

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