Could I use hog panels, carpet and ferrocement to make a barrel-vault-type roof?

Say you had a narrowish rectangular structure - think shipping container, gypsy caravan, shepherd's hut, that sort of thing.

Could you roof it by curving galvanised hog panels over the top, attaching them with staples or something to the outsides of the walls; then covering the panels with old carpet, and then soaking it in a few layers of cement, ie. ferrocement?

I feel like this could be cute - you could even curl the carpet up at the broad ends to make a kind of inbuilt guttering, and angle it downward towards a downspout or whatever.

But also, I have no idea what I'm doing and it might be a ghastly idea. :p Thoughts?

I like how you think!
What you are describing sounds like a kind of ferrocement, Petrified Hussain or flying concrete.
Velecreations used to post here on Permies and they have an Instructable on a similar sort of building technique:Latex concrete roof

The thing it most closely resembles to me is a building described by  Alder Burns in this post:
Tiny-House-Advice-Requested

Ooh, further thought: as an alternative to the curved guttering thing, you could scallop the edges of the carpet to make a cute vaguely thatchy pattern. On a gypsy caravan that'd be pretty cute, admit it.

I wonder if you could even stack layers of carpet to get that scalloped-top look some thatched roofs have? Or would that be adding too much weight to the top of the arch?

Most of the ferrocement cloth roofs I've seen have been, in my view, unattractive, largely because they really look too thin and drapey and cloth-like. It doesn't smoothly undulate over supports, it shows every ridge and pole of the underlying structure. It's like wearing a skirt directly over hoop skirts without having all the layers of petticoats in between - the 'bones' of the hoops show through awkwardly.

I'm hoping the thicker and less drapey carpet, combined with the closer mesh of the hog panels, would mitigate those problems and make the whole thing look smoother and sturdier.

I do actually like the idea of drapey roofs though,  especially over dormer windows and such. I reckon you could get a really storybook-cottage vibe if you were careful. I wonder if there's a much thicker fabric that would work? Could you sandwich a ton of old wool blankets? Would the cement prevent them from decomposing over time?

Hi Sarah,   I recently did some ferrocementing to make a small raised garden bed which is almost done. Piggy backing on Daniels post here: Ferrocement-Raised-Hugel-Beds

I think your idea sounds great. Do be aware that the carpets are going to get real heavy when smeared / soaked in liquidy cement so just make sure your supports are strong enough.
I would recommend doing it is multiple layers so that each layer when it stiffens up can help support the next.
If your carpets are shaggy then all the better as they will help create a good rough surface for the next layer.

Look forward to seeing your progress.

Thanks, that's really useful info! Do you happen to know if the composition of the fabric makes any difference in terms of longevity? My guess is that even organic fabric will be essentially fossilized by the concrete and won't decompose any faster than synthetics (so, not at all, I guess!), but I don't know for sure.

If I were going to do this I would build a prototype that didn't put any other understructure at risk. And I would probably want to talk to an engineer.

It sounds cool though! And I'd love to see how it turns out.

Not sure myself either Sarah. Being a low impact retaining wall, I figured it was the perfect place to experiment before trying something more elaborate.
Your theory sounds about right though. Time will tell.  

Sorry, no, I haven't tried it yet! It was more of a theoretical-one-day concept thing than a specific plan, I'm afraid. But if you do it, let me know how it goes!