Low pitch garage roof covering ?

I have a pre-fabricated garage with a flat, low pitch roof - one of those that slopes from from to back. I've ripped off the old roof and prepared it for Onduline bitumen panels with Sterling board .

I've since read that the minimum pitch for Onduline is 5 degrees, while my garage has an approximate pitch of about 2.5 degrees.

Can anyone advise on a suitable panel product for such a low pitch ?

I presume that anything used would need some sort of sealant on the overlaps of the panels (?). Maybe I cold use Onduline with an appropriate sealant ?

Thanks in advance for any advice

I'd be tempted to increase the pitch. Check the sums but I think you'd need to prop-up the rafters by about a foot for a typical single-car length garage to get the extra 2-3 degrees. You'd need to fill the triangular gaps but that should be straightforward.

Rather than mess about increasing the pitch, since you're fully boarded anyway, you could put EDPM on.

For a low pitch garage roof, you will want to choose a roofing material that is flexible enough to handle the low pitch, but still able to provide adequate protection for your garage.

Here are a few options to consider:

1. EPDM rubber roofing: EPDM rubber roofing is a synthetic rubber membrane that is commonly used on low pitch roofs. It is flexible and durable, making it a good option for roofs with pitches as low as 1/2 inch per foot.
2. PVC roofing: PVC roofing is another option to consider for low pitch roofs. It is flexible, resistant to UV rays, and can withstand extreme temperatures.
3. Modified bitumen: Modified bitumen is a type of asphalt-based roofing material that is designed to handle low pitch roofs. It is flexible and easy to install, making it a good option for a DIY project.

If you decide to use Onduline panels with a suitable sealant, it is recommended to install a metal flashing along the edges and at any penetrations to help prevent water from penetrating the overlap.

Yes when we moved in here, the garage was obviously made from old bricks and breeze blocks with a tin roof, corrugated on the bends. It leaked like a sieve as water tracked up the joins, even when several coats of bitchamen were added. I guess its a kind of capillary effect, being tin of course once the galvanising wore off it basically rusted through in a year.

Brian

Thanks for the responses. I think that EPDM is the most straight forward solution at this time. I'll go away and do my EPDM homework now. :)

EPDM has one issue: it's incompatible with bitumen. So if felt was on there before, the whole thing needs stripping. Corrugated tin is easier in this respect.

But doesn't work at that slope.

Metal decking does.

Brian, you might like to have a word with your text to speech supplier (I assume you use one)

Bitumen isn't spelled bitch (as in dog) amen (as in prayer)...

Andy

I live with a hearing loss and use automated speech to text software on MS Teams.

I was in a video meeting with my manager where he was wearing a christmas jumper.

I could see him on the video and he was showing the metal bells that was attached to his jumper.

He verbally said "I have bells" and the automated speech recognition produced a line of text that read "I have balls"

S.

bitchy men.

Maybe that's the way he says it.

Much depends upon the predominant wind direction, but could you not simply increase the overlap, between lengths, to account for the lesser angle?

I would not use Onduline, rather I would use the much more robust squared profile corrugated metal.

Metal roofing can suffer from condensation if uninsulated and will need a *drip* forming at the gutter to stop rainwater wicking at 2.5 deg. pitch.

I have a low-pitched garage roof, with galvanised box section sheets. I had to add a drip lip (a piece of 10mm angle, rivetted on) running along the bottom edge, or the water running down the valleys tracked back under the bottom of the ends, making the wooden supports wet.

There are ways to get roofing to work at lower pitch than specced. The main issues are rain blowing water upward with non-watertight roofs eg tiles & overlapped sheets, and increased freeze-thaw damage with porous finishes like concrete tiles reducing life expectancy. Solutions include underlining, waterproofing joints & doing something at the bottom to stop water wicking up the underside.

And using metal decking which is designed to work at much lower pitch.

You could use a layer of roofing felt on the board, torched to seal the overlap. Then place Onduline on that. The Onduline will take the wear, sun, etc, and any water that works its way through will meet a sealed layer of roofing felt. Any waterproof layer will do, such a pond liner. (The Onduline nails have a cap, and the Onduline is nailed on the crest of the wave, so that's pretty much waterproof.)

The Onduline will not only have to deal with wind blowing rain up the overlap. Anything on the surface of the Onduline (or overlapping corrugated metal) such as moss, ice, snow, leaves, ... will form a dam. Water backing up against this will quickly stand deep enough to reach over the top edge of the overlapping seam on such a low-pitched roof.

Thomas Prufer

In message snipped-for-privacy@4ax.com, Thomas Prufer snipped-for-privacy@mnet-online.de.invalid> writes

Butyl strip sealant is a cheap solution for shallow pitch seams.