saveasteading

Could we see your version of the above sketch?

The efficency of steel is the I (eye) shape as the top and bottom do the work and the web separates them. Whereas in solid kerto or glulam the middle is full of wood. The timber isn't waste but prime material shaved off s log then lots of resin. So it doesn't spring to mind as an obvious winner... but I don't know. I've done jobs where we analysed joists in timber, steel Z purlins, and fabricated timber ( web of osb). What's best you ask? Used all 3 in different circumstances of load and span.

There is rainproof cladding, and there is decorative cladding. You might have both.

It's easy to fix it down with Simpson angles. Then it is fixed, not pinned. Best to use one each face. I'd also suggest keeping the timber up on a small plinth so it gets a chance to dry between wet times. (And I'd paint the bottom in blackjack) You quite likely don't need glulam if the joints are all solid, but it does look nice.

Not really. Steel is old tech and mass produced. Kerto is hitech and a smaller market...and heavy. You might even find second hand steel.

Installers are looking for a bigger job because of the grants. More about the roof please. What construction do you intend? Closer purlins gives lots of strength.

Well done. If it is hard and flat you will be OK. Thousands of tiny cracks will be better than a few big ones. Even with fibre you would have cracks. Photo of the surface please?

welcome to the daylight.

If you think your report will be credible then fit them and take readings fortnightly, listing on a spreadsheet. Summarise the weather over the period. Take photos too. Lots .They can always be deleted. But if you are going to engage an SE then why not now? They won't mind you doing your own thing in the interim. But just phone one, maybe two and don't send that inquisition form.

In summary then. Flatness is in the perception of the user specifier For solar we want it to tilt a long way up. To keep rain out it depends entirely on the construction and product. For insurance, Insurers make their own rules without understanding construction. I've certainly never declared anything at 10 to 15%. In real life, I regard my walk to the shop as far from flat. It's been interesting. For fun I asked AI how steep Ben Nevis is (not direct via the cliffs) The average gradient of the standard tourist route (the Ben Nevis Mountain Track) is approximately 10% to 15% (or roughly 1 in 10 to 1 in 7 overall), with a maximum gradient capped at 1 in 5 (20%). [1, 2] Route Gradient Details Overall Average: Roughly 10% to 15% grade across the entire ~8 km horizontal distance (1,345 m total ascent). Maximum Gradient: 1 in 5 (20%), which was specifically engineered when the path was originally built for ponies supplying the top observatory. Steepest Sections: Parts of the lower slopes and the upper zig-zags approach that maximum 1 in 5 limit. So, @LSB back to the original post: from the pictures it looks as if your estimate of 440mm or whatever is about right. So you have 2 challenges. 1. You have to detail and build the roof very well to keep the rain out, esp at edges and interfaces. 2. That is very flat and inefficient for solar so maybe play the game, using the newly allowed balcony solar. Later you might go back to planning for a higher system. A few hundred mm would likely be allowed. in fact I'd want to reclad with double skin, insulated. That will be higher but nobody will question it unless you have an enemy with binoculars.

It does to me. If it feels steep then the rain runs freely down it, and doesn't drive far up in wind. If it feels flat then water sits, especially at any dips and laps. It depends of course on what material and on workmanship, and it is sensible to assume a roof may not all be as designed. I've looked at your links now: thanks for back referring. I see they are one manufacturer's definition for their cold applied product. Maybe they need it. But to me 10° is steep. That's 18% or 1.8m over a 10m width. The tools and materials are in danger of sliding down that on the metal roof of the original question. I've seen drills sliding down that sort of slope. On a road i think 'steep' is defined as about 10% and a pedestrian ramp at 5%. I do prefer % as the sums are easier.

I wouldn't. It is a well made , fit for purpose, and precise thing, and I don't think expensive. The only issue would be if the crack has completed its shrinking and starts to close again when the rains come. I think it would just shatter then, but still a point proven. Maybe glue one side only and take measurements and photos to account for this happier possibility.

Where does that definition come from? I must have done 250,000m2 at 10% using steel. It didn't feel flat when walking on it.

OK so it is rather flat. Metal will have to be very well detailed and built as water will drive uphill in strong wind. That needs serious thought and close supervision. Screwed panels are OK, despite what some people say IF done well with top quality screws Hilti etc. I've known more problems with felt/ fibreglass as it's often done badly.

Yes, no, as long as possible, yes. It is a "tell-tale" I think glued is preferred as it doesn't twist.