Flat roof and solar

[JohnMo]

On 06/08/2026 at 14:43, LSB said:

DIY new build has a flat roof (12 degrees)

What do your plans actually say about roof angle? Big difference between 12 degs and pretty much flat. Our 12 degs roof is 2.5 block work one side of the building and closer to 3.5 to 4m at the other (staggered wall).

[LSB]

21 hours ago, saveasteading said:

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.

 

 

 

Thanks @saveasteading having looked again, put some string lines from bottom to top we can get 5 degrees maybe even 6 with some consideration on wall plate thickness.

So, pretty flat, we look over fields and are pretty rural and the neighbours are only interested in how we are progressing, I suspect that we could put tilted solar and no one would comment.

They know our planning includes the 'new stuff' as they call it.

But, our planning also stipulates a metal roof so I need to understand the weight of solar on this as it's a large span.

I've not yet even got a definitive answer as to how many panels I need.

 

I've spoken to a couple of local supplies and they are not interested, I suspect too complicated for them and they all deal with retrofit and not new builds.

 

Thanks for everyones assistance in this.