Best flat roof for new covered walkway?

Newbie / female / homeowner here researching for GC husband who is very knowledgeable about general construction, but not roofing in particular, and definitely not online discussion forums. Our questions have to do with finding the best construction methods and materials to give us the look and performance we want. We did have a plan, but are now second-guessing it and thought we’d better ask for help now…

Goal: We’re building a pair of near-flat roof canopies on the front of our house -
a) over the front door (82" wide x 96" long), and
b) over a 60" wide x 33’ long walkway between the house and garage

These canopies are a highly visible design element, so they have to look great from ground level, and if possible, also from above as they’ll be very visible from our 2nd floor bedroom. There are lots of trees nearby and we’re in a hot & wet climate, so we’d like to be able to walk on the canopies a few times a year as needed to clean and maintain.

Current Status: The visible vertical surfaces of the canopies are heavy-gauge steel C-channels hung on 8x8 cedar posts. Between the C-channels we have 2x8 wooden rafters on 16" centers. The tops of the rafters were trimmed so the ends are slightly shorter than the centers, creating a very small ridge slope (1" on 30" & 1" on 41" runs). We then installed 3/4" treated plywood decking over the rafters leaving a very slight gap for possible venting at the ridge. On the edges, the top of the plywood decking sits level with the top of the steel C-channels. All of the preceding work has been done. On the undersides of the canopies, we plan to install wooden beadboard or slats.

Our Original Plan was to install an impermeable membrane over the plywood decking topped with a steel roof treated with a rust-proofing clear-coat in a heavy sheet or light plate. The metal pieces would extend the full width of the canopy with a slight crease at the ridge and bends at the edges to clip onto the tops of the C-channels (possibly supplemented with tack-welds). We were planning to use a series of 48" long sheets with a 3" overlap and a sealing tape (?) between the plates at the seams.

But then we got to thinking about venting and got all confused! The treated plywood seems damp and we don’t want moisture/mold problems. But would we even need to vent a flat roof where the top and bottom are approximately the same temperature? But with a metal roof, wouldn’t that be hotter/colder? And if necessary, how could we safely vent a roof that’s so nearly flat…

Anyway – now we’re tied up in mental knots and trying to figure out what to do.

Our reasons for preferring metal roofing was mainly for appearance, but we don’t want a traditional standing seam because the seams would be visible from ground-level. Modified bitumen or some other membrane would be less attractive from above - but maybe much more sensible?

Please Help!

Walkable PVC membranes with patterns on them are available.

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You probably don’t need to worry about ventilation as it sounds like the roofs are outside; ie. not over conditioned space?

Mod bit or single ply would be fine but as you say the appearance might not be what you want – if you can find (and afford!) a specialist in your area to do flat seamed copper that would be nice – steel with sealant will probably leak at some point. Photos of the structure might be helpful.

Thanks for your suggestion – I did see colored membranes but didn’t see anything with ‘patterns’ – Some of the colors might actually work pretty well for us though.

After looking around on the site and reviewing some of the downloads, I didn’t see anything that specified exactly what a “properly-prepared substrate” would be. I’m assuming it’s not just the plywood?

Thanks! I really appreciate your answer regarding the venting. Correct - not over A/C’d space. Venting was where we got all twisted up…

We definitely do love the look of copper, and actually, that was our first thought. We would be willing to spring for the materials, but probably not for the specialized installation in our zip code… However, my husband is a highly-skilled welder with lots of experience brazing copper pipes. Is this something he would be able to do himself with his skill set?

I’ll try to post some pictures.

On second thought, after checking prices on copper, even the raw materials are (HOLY MOLEY) not realistic!

Trying to post some pictures here.

The first one shows the posts, steel C-Channels and rafters from the ground. The upper level is over the (future) front door. The garage walkway extends out to the right. You can see the very slight slope to the ‘mini-ridge’ on the underside of the upper canopy.

The lower photo shows where the lower garage canopy fits under the garage roof overhang. It’s hard to see, but the plywood butts flush to the steel on the near side. (Ignore the white piece on the far side – it’s just an angle bracket we set there temporarily to create a better pitch for a piece of plastic sheeting during a rain storm.)

The third picture shows the view from the bedroom window - again with temporary angle brackets and plastic sheeting.

Now that’s just weird :face_with_raised_eyebrow:

In line with what @Axiom is saying, I wonder if regular vinyl Duradek might not be the way to go? It’s got a nice pebbly finish and is DIYable.

I think you can get six foot rolls, so the breezeway could have minimal seams – the chemical (typical DIY)seams are not bad, but if your husband has an electric heat gun and welding experience he could probably teach himself to weld vinyl well enough to get this done.

That looks like a nice product. Thanks for the suggestion and I’ll do some more research –

Take a look at DeckRite. Very popular on walking decks. You can also get dark brows in TPO membrane that are visually quite nice. Both of these membranes would be glued down to the substrate. If your building code does not require a Class A fire rating for the walkway (check on this) you can glue it directly to plywood. Preparation usually consists of filling the joints between the plywood with a joint filler.

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what ever you use any water has to run off efficiently.
you could use high carbon zinc sheeting

Now that’s an interesting idea! More research…

Unfortunately, cost is similar to copper metal, so probably looking at some sort of membrane.

I personally recommend a good quality Granulated Mod bit system. CertainTeed Flintlastic SA with a mid ply would give you great durability and a clean look. A membrane app or a silicone based top coat app could be dangerous to walk on with the slightest bit of moisture on them. Very slippery… Vents not needed if the underneath is staying open.

Self adhered modified is the least desirable low slope option except for something like half lap.

It is user friendly, that is the only thing it has going for it.