Smallholder Posted May 26, 2023 Share Posted May 26, 2023 I'm trying to get a new PV system installed, on a flat roof. I'm about to apply for planning permission, but can't find any solid info online about restrictions in terms of how far from the edge the panels must be. I assume this is a building regs thing rather than planning permission, but I'll need to be on the right side of both aspects I guess. Many websites seem to refer to a general rule of panels being at least a metre from the edge, which for my roof will massively reduce the area I can use. Does anyone else have any experience with this? Thanks in advance Link to comment Share on other sites More sharing options...
saveasteading Posted May 26, 2023 Share Posted May 26, 2023 1 hour ago, Smallholder said: at least a metre from the edge, which That makes sense as wind forces are much greater at the perimeter. In a sheltered area it might not matter so much. I have been told that lots of roofs are damaged by poorly fixed panels. 1 Link to comment Share on other sites More sharing options...
Smallholder Posted May 26, 2023 Author Share Posted May 26, 2023 Thank you saveasteading I'd hoped there might be some solid formula I could follow, but maybe it's just down to my own risk appetite! Link to comment Share on other sites More sharing options...
saveasteading Posted May 26, 2023 Share Posted May 26, 2023 It will depend on your exposure, and the panel construction. I have never had solar on a property ( always designed them dotted, for planning). But most seem to be on brackets that need a lot of thought before fixing, to provide enough pull-out resistance without leaks. So the wind gets underneath. I have spoken to loads of suppliers though and was shocked by their ignorance. Perhaps things are better now. Others on here will know more about the reality. Link to comment Share on other sites More sharing options...
pudding Posted May 26, 2023 Share Posted May 26, 2023 (edited) There is no formula. It just needs to be strongly secured enough, so if BC are involved, that's either according to a structural engineer, or general guidance from a bracket/rail manufacturer that BC will be happy with. 1m I'd say is massive overkill. Usually most will spec 30-40cm minimum. (On a FB group im in, just general UK solar if i remember correctly, some guy who's in the industry had a doc that stated about there being no minimum distance specified anywhere only recommendations, and it just needs to be strong enough, which over the years has led to every install playing it safe and staying 30-40cm away from an edge, rather than actually thinking about it or deviating from the standard install that everyone will throw up) I've gone closer on a couple of corners of mine on a nearly flat roof carport last year, but i've doubled up on the panels brackets/rails through to the timber battens, so i'm happy it wont uplift with strong winds. The older array that another company installed a few years ago stuck to 30-40cm. Here's a pic - Edited May 26, 2023 by pudding Link to comment Share on other sites More sharing options...
TonyT Posted May 26, 2023 Share Posted May 26, 2023 I’m sure the original MCS rules were 200mm from the ridge on a pitched roof. I would be happy with that, lots of new skirtings/architraves now to prevent bird nesting imagine that will help with uplift 1 Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 26, 2023 Share Posted May 26, 2023 (edited) Doing the calcs for ours, I see I allowed 30cm margin all round. I'm not sure where I got that from, but I bet I found it in some BCO rule somewhere. The margins will likely end up bigger than that of course as you'll need to fit an integer number of panels. Edited May 26, 2023 by Alan Ambrose Link to comment Share on other sites More sharing options...
Dillsue Posted May 27, 2023 Share Posted May 27, 2023 Margins are likely not just to reduce uplift but to save disturbing the perimeter of the roof. Trying to lift tiles/slates near the ridge and or gable verge is difficult without disturbing things. Even in a sheltered location where could go right to the edge life is easier with a verge around the array. It also gives access up the side of an array to get to the ridge or top of the panels, if youve a head for heights!! 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted May 27, 2023 Share Posted May 27, 2023 Was it not 200mm from ridge and gutter and 300mm from the other edges? Been a while since I had to worry about it. Link to comment Share on other sites More sharing options...
TonyT Posted May 27, 2023 Share Posted May 27, 2023 https://mcscertified.com/wp-content/uploads/2021/10/MIS-3002_Solar-PV-Systems-V4.0.pdf page 18 looks like 400mm on a pitched roof now unless extra design is in place to prevent uplift Link to comment Share on other sites More sharing options...
Andehh Posted May 28, 2023 Share Posted May 28, 2023 It is useful to have enough space around the edges to access them for annual cleaning! Link to comment Share on other sites More sharing options...
Smallholder Posted May 28, 2023 Author Share Posted May 28, 2023 This is the layout I'm thinking about. I may be making life hard for myself in terms of wind lift, but I'd really like to use ballast rather than drilling a hundred plus holes through the roof membrane. You can see that with the existing roof and rooflights, leaving a sensible edge gap is not all that easy. Thanks for all the input folks, really appreciated. Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 3 hours ago, Smallholder said: This is the layout I'm thinking about. I may be making life hard for myself in terms of wind lift, but I'd really like to use ballast rather than drilling a hundred plus holes through the roof membrane. You can see that with the existing roof and rooflights, leaving a sensible edge gap is not all that easy. Thanks for all the input folks, really appreciated. Have you already installed the roof membrane? 'We' favour Nicholson plates LINK and rails vs ballast. That install may be too exposed to use Van Der Valk rails + ballast LINK, unless its with pre-stressed concrete lintels and you've the kg/m2 allowances in place for the huge extra weight? It looks like you have a parapet all round? The perimeter rule is from MCS iirc, and mostly for in-roof systems and not so much so for on-roof. With on-roof you have a roof which is 100% weatherproof, and then you overlay the array atop, and this will allow for "infinite" arrays which can go ridge to gutter and gable to gable flush fitting. The caveat is that the fixings and rails ned to be specified to cope, but many systems have gone in with an infinite install and have MCS so yes, it can be done. The 200-300mm requisite is simply to allow for a slate / tile / and a half to be fitted to the edges and be finished accordingly, eg so the in-roof trays can be part of a robust weatherproof install. FYI, a few installers put the bottom of the panels too close to the gutter and the rain overshoots the gutter. One issue to watch / mitigate against. 1 Link to comment Share on other sites More sharing options...
Smallholder Posted May 28, 2023 Author Share Posted May 28, 2023 20 minutes ago, Nickfromwales said: Have you already installed the roof membrane? 'We' favour Nicholson plates LINK and rails vs ballast. That install may be too exposed to use Van Der Valk rails + ballast LINK, unless its with pre-stressed concrete lintels and you've the kg/m2 allowances in place for the huge extra weight? It looks like you have a parapet all round? The perimeter rule is from MCS iirc, and mostly for in-roof systems and not so much so for on-roof. With on-roof you have a roof which is 100% weatherproof, and then you overlay the array atop it, and this will allow for "infinite" arrays which can go ridge to gutter and gable to gable flush fitting. The caveat is that the fixings and rails ned to be specified to cope, but many systems have gone in with an infinite install and have MCS so yes, it can be done. The 200-300mm requisite is simply to allow for a slate / tile / and a half to be fitted to the edges and be finished accordingly, eg so the in-roof trays can be part of a robust weatherproof install. FYI, a few installers put the bottom of the panels too close to the gutter and the rain overshoots the gutter. One issue to watch / mitigate against. Ahh, I love the look of those Nicholson Plates! Thank you very much for the link, will definitely look into this. Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 1 hour ago, Smallholder said: Ahh, I love the look of those Nicholson Plates! Thank you very much for the link, will definitely look into this. You get extra material from the roofing company, and send that off. They then manufacture the plates with the skirt made from what you supplied, so you have have no mix / match / colour & type indifference. We supply a design to the clients so the builder / client / roofer can install in-house. The rails go atop and you're done and MCS compliant without the extra weight. Without the ballast being down first and the height of that, you can then drop the array low so it's 'less ugly' to look at . 1 Link to comment Share on other sites More sharing options...
saveasteading Posted May 28, 2023 Share Posted May 28, 2023 50 minutes ago, Nickfromwales said: Nicholson plates These look good. I like how there is the 4 screw fixing to the roof, then the top connection. It will need some consideration of the screws as there is a big variation in pullout resistance and also there is the board....9mm osb or 20mm ply or into a timber. But good screws are not expensive compared to the panels. I heard reports of many installations ripping off steel roofs. Easy to get right by considering the structure and giving method, but the installers were not educated in the subject, and clients were choosing the cheapest contractor. I don't know of disasters with domestic roofs but I expect there are many. @Nickfromwales rough cost of these? Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 13 minutes ago, saveasteading said: These look good. I like how there is the 4 screw fixing to the roof, then the top connection. It will need some consideration of the screws as there is a big variation in pullout resistance and also there is the board....9mm osb or 20mm ply or into a timber. But good screws are not expensive compared to the panels. I heard reports of many installations ripping off steel roofs. Easy to get right by considering the structure and giving method, but the installers were not educated in the subject, and clients were choosing the cheapest contractor. I don't know of disasters with domestic roofs but I expect there are many. @Nickfromwales rough cost of these? No idea off the top of my head; we give turnkey prices via my solar partner (and his designers). They are a brilliant solution, and for situations where you cannot punch the fixings into structure, you just add more plates to create more fixings / point of purchase eg into 18mm OSB etc. You wouldn't be allowed to fix these to 9mm OSB obvs. You should be able to get costs and a design from the company I linked to, or 'we' can price it? PM me if any use, but not if you want it doing in 2023, sorry!! The screws are specified by MCS, and are BFO stainless steel construction screws with large pan / flat heads. LINK - company chosen due to dragon logo lol. Standing seam clamps are OK, but somewhere where bean-counting cannot be the driver! One instance where staying away from the perimeter is a bloody good idea. Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 Another option. Link to comment Share on other sites More sharing options...
Smallholder Posted May 28, 2023 Author Share Posted May 28, 2023 5 minutes ago, Nickfromwales said: No idea off the top of my head; we give turnkey prices via my solar partner (and his designers). They are a brilliant solution, and for situations where you cannot punch the fixings into structure, you just add more plates to create more fixings / point of purchase eg into 18mm OSB etc. You wouldn't be allowed to fix these to 9mm OSB obvs. You should be able to get costs and a design from the company I linked to, or 'we' can price it? PM me if any use, but not if you want it doing in 2023, sorry!! The screws are specified by MCS, and are BFO stainless steel construction screws with large pan / flat heads. LINK - company chosen due to dragon logo lol. Standing seam clamps are OK, but somewhere where bean-counting cannot be the driver! One instance where staying away from the perimeter is a bloody good idea. Sorry if I'm being a bit stupid here, but do these mounts need to be installed at the same time as the roof membrane? Or you can add them after the roof has been 100% finished? Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 1 minute ago, Smallholder said: Sorry if I'm being a bit stupid here, but do these mounts need to be installed at the same time as the roof membrane? Or you can add them after the roof has been 100% finished? Roof goes down and gets proven as rain / weather tight. Then you install the plates and weld the skirts down atop the original covering. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 Don't forget to plan how to get cables through the roof, as that needs to be stitched into the fabric of the build before the roof membrane goes in / on. Cable snorkels are available which can be made airtight and are water-weather proof. 2 Link to comment Share on other sites More sharing options...
SteamyTea Posted May 28, 2023 Share Posted May 28, 2023 27 minutes ago, Nickfromwales said: You wouldn't be allowed to fix these to 9mm OSB obvs Was at a home building show (with our old mate Jeremy Harris as it happened). SIPs was all the rage back then. I asked a salesman about fitting PV to it, he hesitated way too long before answering the it was fine, they had done loads, never had a problem. Those roof panels (the SIP ones) were 9mm OSB. Link to comment Share on other sites More sharing options...
Adam2 Posted May 28, 2023 Share Posted May 28, 2023 We were all set on solar on our flat roof (single ply membrane on insulation on ply) but having experienced 90 mph winds last winter (on top of a hill facing SW with not much between us and the sea) I think really we should have put in some structural elements to fix through into before the roof went on. For us now the risk of either roof damage or worse of a panel lift up isn't balanced by the ROI in 5 or so years (depending on impact of various "special operations")! We pre-planned lots of important aspects but this is one that got away! So just a word of caution for people in exposed locations with a similar thought and time to plan. Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 8 minutes ago, Adam2 said: We were all set on solar on our flat roof (single ply membrane on insulation on ply) but having experienced 90 mph winds last winter (on top of a hill facing SW with not much between us and the sea) I think really we should have put in some structural elements to fix through into before the roof went on. For us now the risk of either roof damage or worse of a panel lift up isn't balanced by the ROI in 5 or so years (depending on impact of various "special operations")! We pre-planned lots of important aspects but this is one that got away! So just a word of caution for people in exposed locations with a similar thought and time to plan. Any space for a ground-mounted array or create a structure to take even 4kWp? 2kWp is better than nowt! Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 28, 2023 Share Posted May 28, 2023 27 minutes ago, SteamyTea said: Was at a home building show (with our old mate Jeremy Harris as it happened). SIPs was all the rage back then. I asked a salesman about fitting PV to it, he hesitated way too long before answering the it was fine, they had done loads, never had a problem. Those roof panels (the SIP ones) were 9mm OSB. It would be a question for the manufacturer of the SIP panel, and for them to say if multiples of fixing locations would make this permissible tbh. Link to comment Share on other sites More sharing options...
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