Distance from Roof Edge

[SRE]

Is everyone installing 500mm from the edge now? We try to but we're going to 300mm if we need to - just wondered what everyone else is doing??

 

[infinity]

Didn't realise 500mm was even recommended on domestic? 300mm is probably more standard

 

[Gavin A]

rarely.

Just design / use the mounting system to cope with the wind loading at the roof edge.

 

[SRE]

V3 of MIS blah de blah that came out in April .... doing my head in everytime I looked at it so I stopped looking. When I see some of the appalling installations that others get away with I'm not sure what's to be gained by sticking to the rules when others blatantly ignore them but get loads of work!

- - - Updated - - -

Same as us then.

 

[Gavin A]

V3 of MIS blah de blah that came out in April .... doing my head in everytime I looked at it so I stopped looking. When I see some of the appalling installations that others get away with I'm not sure what's to be gained by sticking to the rules when others blatantly ignore them but get loads of work!

- - - Updated - - -

Same as us then.

It doesn't say you can't install in those zones, just effectively that if you don't bother doing any sort of assessment, then you should be using 500mm as your edge zone to avoid any potential of going wrong.

At least that's how I read it.

 

[SolarCity]

We tend to work to 300mm and double up the brackets on the edges.

We see panels up to the sides a lot. I suspect I'm about to lose a job where two rows of portrait panels just won't fit - one of our competitors will no doubt argue otherwise.

 

[Gavin A]

That's pretty much what we do, though I'll allow down to 150mm if the designers get me to check it and the wind loading looks to be low enough on that site - eg bungalow surrounded by other houses, or we can get fixings in close enough to the edge of the panels to reduce the overhang, and double up, or use cruciform mounting, or stronger rails etc. double up the end rafters if needed etc

One of our key issues with solarworld at the moment is that they only have their weakest rails in the UK, but I think they're going to sort that out now after I pointed out the problems with this approach - along with it meaning that their designers were speccing 50 brackets for a 4kW system for anyone using their designers.

 

[Worcester]

Same here, we start at 500mm, occasionally go down to 400mm, very occasionally 300mm on the sides if it is a hipped roof / or to the bottom of the ridge tile, rarely less especially at the bottom edge NEVER less than 400mm there - not because of loading there, more because of drainage / missing the gutter.

We double up (roof hooks on every rafter) in the corners always, so never had a problem with uplift or screw pullout, and also would normally only have a maximum spacing of every other rafter outside those zones. - it's more the loading on the rafters that I get concerned about and ensuring an even weight distribution - especially when under 400mm of snow.

The K2 design tool can also end up with 50 or so brackets when using the light rail, so always do the full calcs anyway

 

[Gavin A]

I used to be concerned about the rafter loadings until our structural engineer pointed out that with the perlins it's almost always the perlins that are the issue, not the rafters - if a 38x70mm rafter can span 1.6m on a trussed roof, then a 50 x 75mm rafter will have absolutely no problem with the additional loadings from PV on the same span even if the system is only mounted every 3rd rafter (usually closer at the corners).

The issue then becomes more what the maximum span is for the rails, pull out ratings for the bolts and max loading for the brackets, where we've previously ensured that we'll either use the Schuco BP130 or 160S rails which can span that distance even in medium to high wind loading situations (higher for the BP160S)... and if the perlin can take the loading, which is where we've ended up strengthening perlins a fair amount under SE instructions.

On the trussed roofs as we're doubling up the rafters we're mounting to anyway almost all the time, we then also have no issue with 1200mm spacings for the brackets, as that rafter can then easily take the additional loading. but 600mm spacings at the edges in higher wind / snow loading situations.

Basically sometime in early 2011 I decided we were better off just working to Schuco's max spans for the next to highest wind / snow loading situation as standard, and making sure we'd never get caught out by using cheaper rails / brackets that really needed shorter spans. That way for 95% of the systems we do we don't actually need to do any additional wind or snow loading calc for the mounting systems, as long as the roof structure can cope - only if we end up high in the Penines or something will we then reduce the spans or cross rail.