Standing seam has a minimum angle of a few degrees. The exact number depends on the product, so you need to check the data sheets carefully. I wouldn't use steel because rust Ours is aluminium. For our flat roofs I chose EPDM based on its good performance and its sustainability credentials (first hit I just found https://cpduk.co.uk/news/epdm-sustainability-and-the-environment )

You can get trapezoidal roof sheets here as well in various materials. You can also get them pre-attached to insulation. But they all need a pitched roof, typically steeper than standing seam.

Posted By: djhYou can get trapezoidal roof sheets here as well in various materials. You can also get them pre-attached to insulation. But they all need a pitched roof, typically steeper than standing seam.

Correct they need about 4 deg. whereas a standing seam can cope with 1.5 deg. Much may depend upon what the existing felt roof has.

Posted By: tonyLead is fully recyclable, long lasting, cheaper in the long run if done properly.

30 to 50 years for a 'tin' roof will do me and much less nickable than a lead roof.

If you're thinking of insulation then things can get quite complicated because of the mess that is Building Regs. Check whether you need ventilation under the roof surface for whatever you choose. (if so there's no point in bonded insulation, for example). Our EPDM is on a ply substrate with a 50 mm ventilated gap underneath and insulation below the gap.

Another contender with good co-credentials is mastic asphalt. It's made from natural materials, requires low maintenance, deadens sound, has a very long service life and is 100% recyclable.

Preferably top with solar-reflective paint (or, even better, a green roof - though maybe not on a dormer).

Posted By: Doubting_Thomasthe coatings and paints on the metal can also be an environmental hazard

Yes, our roof is "mill finish" aluminium, which means no coatings or paints etc. I think the same may be true for zinc roofs.

I can't see the picture. dropbox says something about needing a file extension and then tries to XSS to google and tries to get me to log in to my non-existent google account. Can you post it somewhere public?

Also what type of 'single ply membrane' is it? There's a lot of difference between the various types. Your description makes it sound like a poor quality product that was poorly installed, so not terribly relevant except as a warning.

still not working

Try this https://drive.google.com/file/d/1lgRsMssFVDhYjxEEao20cTU9DotQZfy-/view?usp=drivesdk

I think you need to make it shareable with anyone with the link
Or summat like that

Re Tony's pic: It can be download, but not viewed, without either a dropbox or google account. But it's a very tiresome experience. That is a terrible install with very narrow strips and tiny welding overlaps. Do we know how old it is? Most membrane installs are much better than that with much wider strips and thus fewer, wider welds. I have a 10-yr old install and it appears to be performing well. Allegedly it should last 30 years.

On the actual question: the single-ply membranes are obviously plastics but they make a very light roof covering so not much material is used in comparison to many other coverings ( bituminous felt, fibreglass, mastic asphalt, concrete). I don;t actually know how the LCAs compare.

EPDM is much less harmful than PVC from a manufacturing point of view. Also EPDM is recyclable into new roofing EPDM, at least according to this CPD: https://cpduk.co.uk/news/epdm-sustainability-and-the-environment and the US ERA has been doing it since working out the process in 2006. Apparently old tyres are now going into EPDM manufacture too. I don't know how much this is actually happening in the real world. (There is some vagueness in those articles about actually recycling into the same material. It is implied but not stated, which may mean it's actually only being downcycled...)

Mind you it seems the PVC people make the same claims: https://www.buildingenclosureonline.com/articles/91215-new-white-paper-on-recycling-pvc-roof-membranes (except in that article they say "PVC roofing is the only commercial roofing material that is being recycled, at the end of decades of service life, into the feedstock to make new roofing membranes")

I tried to get EPDM for my extension roof in 2014 but the roofing company was only certified for and experienced with Sarnafil (PVC) so I had to get a PVC roof instead (boo). For domestic projects recycling may be hard to come by - it was impossible for me to do it with my old PVC windows, despite there being a thriving PVC-window recycling system because one house-worth is too small for anyone to be bothered with. The same could be true for domestic-sized roof membranes. Hopefully regs will deal with this sort of problem in due course.

So all that said I'm not at all sure what the 'greenest' flat roofing options are. There are several possible measures (energy, manufacturing pollution, manufacturing emissions, in-use pollution, recyclability, longevity, assembly mass, and thus footprint).

Regarding EPDM, can anyone recommend a reflective paint that is compatible?

We have a 32m2 dormer flat roof that I'd like to reduce the heat gain on. Unfortunately a Sedum covering is not an option.

In other parts of the world you could buy white EPDM on the roll, (at least 20 years ago when I started roofing), but it still doesn't appear to be available over here.

I installed and repaired both Sarnafil & EPDM roofs back in the day. EPDM is by far the easiest and most forgiving to work with. Also the easiest to repair to a good standard when other trades have 'done their thing'.