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PV on flat roof

edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
11 replies 1.7K views
pgoncalvpgoncalv Forumite
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edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
After having converted my loft and built a larger dormer, I was left with only one sloped roof, which is almost north facing.

The news of massive changes to the climate that will be followed by other really unpleasant impacts, made me rethink whether I could reduce my carbon footprint a bit more.

I found that PV panels can be installed on flat roofs with a frame but it seems that they cannot be set higher than the highest point of the roof. So this would seem to rule it out.

The other option I was considering was to install them on the flat roof above the back extension but again I am not sure if this would be acceptable.

Does anyone know if there are any exceptions to these rules for solar panels?
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  • Exiled_TykeExiled_Tyke Forumite
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    I'm no expert on this but as far as I'm aware it's the roofline which counts. I have a flat roof over my garage which I was told would be allowed as the house roof extends higher.

    However I was advised that it wasn't a good idea as:

    1. The weight of the panels on the frame creates pressure points on the roof which could increase the risk of leaks.
    2. When it comes time to re-lay the roof there is the added (admittedly manageable) hassle and cost of having the panels removed and then put back.

    As I have other roof areas I could use I made the decision not to use the flat area. Sorry you don't have the same choice.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    Install 2: Sept 19, 600W SSE
    Solax 6.3kW battery
  • edited 23 January 2020 at 8:35PM
    ABrassABrass Forumite
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    edited 23 January 2020 at 8:35PM
    The rules limiting putting them on roofs requires planning permission. You're not allowed to increase the height of your roof under normal circumstances without it and solar panels are no exception. That's one of the reasons you don't see panels poking up above the ridge line on sloped roofs.

    If you did the extension under permitted development (avoiding the nee for planning permission) it's probable that you are already as high as is allowed. In which case putting panels on top would exceed the permitted development rules and require PP. If it was an extension that had planning permission then you're probably going to need it again. As you're making the entire thing taller.

    You could just take a chance on it and have them installed, but if anyone complained you might have to take them down.

    Also, don't forget building control. Adding panels is one of those activities that requires building control to be notified as it is adding weight to the top of a roof. Building control is separate to planning permission, even if you don't need PP then you still need to notify building control.
  • Martyn1981Martyn1981 Forumite
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    It's a tiny bit worse than that. Not only can you not increase the height of your roof without planning permission, but you also need PP to alter the pitch of your roof.

    So you will need to seek PP even for the lower flat roof if you are to mount them on a different angle. But that doesn't mean you won't be allowed.

    Another possibility might be a solar carport roof, or a pergola, you might not need PP for those, but you'll need to check, and also a ground mount, but you need PP for anything larger than 9m2 (approx 5 panels).

    If you've ever wanted a large 'shed' with a south facing monopitch roof, then now's the time, as that should be PD, but again check.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • pgoncalvpgoncalv Forumite
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    Thanks, you already gave me some new ideas. I do have a summerhouse and I believe that could take some load...

    As for the extension, I am sure the load will be fine but planning may or may not go through, council is blue so unlikely to care too much about PV. Almost nobody has panels in the area.

    It seems I could install panels on the flat roof without mounts but the efficiency would be low so they would need to be as cheap as chips - I heard that there is some flexible PV technology being developed but not sure about the price point.
  • pgoncalvpgoncalv Forumite
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    Yup, certainly from a homeowner point of view installation on sloped roofs is better.

    But I found the panels can be installed up to 200mm above roof line and this applies to flat roofs. Clearly in most cases (to get the right inclination) the panels need to be narrower than the most commonly available but I found some installers are ok with flat roofs.

    Installation is done by applying ballast on the flat roof. I was lucky my loft conversion ended up being done with over specced structural elements and so not a risk to the roof.
  • joefizzjoefizz Forumite
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    pgoncalv wrote: »
    But I found the panels can be installed up to 200mm above roof line and this applies to flat roofs. Clearly in most cases (to get the right inclination) the panels need to be narrower than the most commonly available but I found some installers are ok with flat roofs.


    Its worth having a chat with your local planning office as rules (and interpretation) vary across the country.
    I have panels on front and back of the house as well as a frame built on a south facing garage roof/wall mostly oriented for winter use.
    There were the obvious snow and wind loading issues for the roof itself but also the planning issues. It wasnt just the ridge line but also a height below the ridge line and how far they stuck out (which compromised my final design as I wanted to make a sliding frame so I could alter the angle for time of year - in the end I couldnt get full winter angle but thems the breaks).
    IIRC rules are slightly different for hanging off structures over flat rooves...



    Planning and builders wont really care about wind loading issues and my original installer said they didnt have anything which would suit my space so I ended up fabricating something myself from al angle. (fine if you have a workshop to do this or can speak to a local light engineering firm).


    To fit all the planning specs I mounted the panels horizontally (if you see what I mean) but had thought out all sorts of H shapes and L shapes and so on. I even considered sourcing the individual cells and building my own panels seeing as I was already going down the angled frame route. Overkill in the end.


    I ended up mounting the frame through the roof, not on it if you see what I mean, directly connected to structural trusses which had been over specified during the garage build (always planned to mount panels on the garage roof post build).


    If its any help you can probably run connecting wires between sets of panels for a fair distance without big losses so could have different groups of panels in different areas with different orientation (you would need to look up your specs for that sort of thing).
  • pgoncalvpgoncalv Forumite
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    joefizz wrote: »
    Its worth having a chat with your local planning office as rules (and interpretation) vary across the country.
    I have panels on front and back of the house as well as a frame built on a south facing garage roof/wall mostly oriented for winter use.

    My council generally charges for planning queries but I managed to get them to point them to a general guide as I am not in any conservation area, etc.

    The paragraph about Solar Panels says:
    - Solar panels are likely to require planning permission where sited on a front roof slope. The Council wishes to promote sustainable forms of energy generation but will apply the following constraints:
    • On listed buildings solar panels will not normally be permitted.
    • Within conservation areas, solar panels will not be permitted on any conspicuous elevations.
    • In other cases, where solar panels would be visible from public streets and areas, they must be designed and laid out as part of an overall architectural treatment.

    It looks as if height requirement may not be a major concern but I wonder whether the architectural fit requirement may restrict directing the panels in the way that suits my house consumption best...
    joefizz wrote: »
    If its any help you can probably run connecting wires between sets of panels for a fair distance without big losses so could have different groups of panels in different areas with different orientation (you would need to look up your specs for that sort of thing).

    Yup, essentially I am mostly interested in using all the electricity PV will produce so on the flat roof I would not want all the panels to face in the same direction. Probably want most to face for optimum production 4-8pm. Will check with the installers about the architectural treatment, hopefully they know what is likely to pass.
  • ABrassABrass Forumite
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    On a flat roof you can have the panels set up pointing east/west and as an early uninterrupted wave. Eg a row pointing west, a row pointing east, a row pointing west etc.

    That way you'll get some power earlier and later in the day, which can mean you get to use more of the power than a simple south facing system. Plus you can cram in more panels.
  • edited 6 February 2020 at 10:06AM
    pile-o-stonepile-o-stone Forumite
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    edited 6 February 2020 at 10:06AM
    We own a listed property in a conservation area and so couldn't put panels on our house. We did however get permission to put them on our garage and a lean-to wood shed attached to the side of the garage. The woodshed roof has about a 5 to 10 degree angle, so is essentially flat, but it does work really well and the slight slope helps keep the panel clean.

    We went for a roof integrated system on the garage to make it as unobtrusive as possible and made the woodshed panels look roof integrated by building a false roof around it using battens and recycled plastic slates. The false roof helps protect the real roof underneath from the damaging effects of UV and weather.

    The pic below shows the two together (2kw on garage and 1.8kw on woodshed). That side of the garage roof and woodshed roof face east.

    image.php?AttachmentID=7094

    Here are the west facing panels (2kw) on the garage roof. The pic shows the roof prior to having the panels fitted, including the leaky roof windows that I was so pleased to get rid of:

    image.php?AttachmentID=6935

    Our plan is to add more panels on the west side of the garage by fitting a lean-to pergola with panels that are printed onto glass and so are transparent. I should be able to get another 1.5kw on that.

    We don't get much power in winter as the arrays are east/west facing but in summer/spring/autumn we get a lot of power over a long period of time.
    5.18 kWp PV systems (3.68 E/W & 1.5 E).
    Solar iBoost+ to two immersion heaters on 300L thermal store.
    Vegan household with 100% composted food waste
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  • JKenHJKenH Forumite
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    We own a listed property in a conservation area and so couldn't put panels on our house. We did however get permission to put them on our garage and a lean-to wood shed attached to the side of the garage. The woodshed roof has about a 5 to 10 degree angle, so is essentially flat, but it does work really well and the slight slope helps keep the panel clean.

    We went for a roof integrated system on the garage to make it as unobtrusive as possible and made the woodshed panels look roof integrated by building a false roof around it using battens and recycled plastic slates. The false roof helps protect the real roof underneath from the damaging effects of UV and weather.

    The pic below shows the two together (2kw on garage and 1.8kw on woodshed). That side of the garage roof and woodshed roof face east.

    image.php?AttachmentID=7094

    Here are the west facing panels (2kw) on the garage roof. The pic shows the roof prior to having the panels fitted, including the leaky roof windows that I was so pleased to get rid of:

    image.php?AttachmentID=6935

    Our plan is to add more panels on the west side of the garage by fitting a lean-to pergola with panels that are printed onto glass and so are transparent. I should be able to get another 1.5kw on that.

    We don't get much power in winter as the arrays are east/west facing but in summer/spring/autumn we get a lot of power over a long period of time.

    I like the garage. :) I have an E/W set up which is useless in winter. Best so far this year is just over 8 kwh from our 7.8 kw system. With a flat roof one would presumably get some (if not much) sun all day long but most around noon. In that respect I am thinking a flat roof might have a similar (but shallower) PV curve to a South roof. Do you have individual readings for the 3 roofs or are the East roofs combined?
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, Nissan Leaf (plus some ICEs:) )
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