Providing structural roof calculations for commercial and private clients’ solar panel installations

The first thing we need to do is determine how the existing roof has been constructed. Usually, this involves us visiting the structure and going up in the loft/roof to determine the size and spacing of existing timbers and where they span too. In an ideal world, we would also have the as-built drawings to double-check.

As-built drawings are just that, drawings of how your home was constructed – to make changes and modifications easier in the future. As part of the 1994 CDM regulations if your house was built after 1994 you will have been given as-built drawings with the purchase of the property. Alternatively, if you have a warranty, you may be able to access plans through Building Control.
It doesn’t matter if you don’t have as-built drawings. We will complete a thorough investigation so we can do the maths to see if the existing timbers have the capacity to support the weight of the equipment you want to install. We can liaise with your solar panel supplier directly to get all the information we need.

We also need to know (from the client or from the solar panel installer) whether it is going to be a ballasted system, for flat roofs where the solar panels will need to be elevated and the frames held securely in place, or a direct fixed system where panels are positively fixed into the underlying roof structure. We will also need to know the number of panels, where they will be positioned, and the size of the array – the total area of coverage.
Calculations will not only include the solar panels and fixings themselves. The governing criteria will be the weight of the panels with a full wind load and snow at the same time. These calculations involve a fair bit of research and analytical work.

If your roof is not strong enough for the array you initially wanted, we can then look at one of two options – recommendations for strengthening the existing structure or the array of solar panels you can have. Residential roofs are generally timber framed and so may be less robust than commercial buildings, but steel frame structures often have lightweight sheet roofing which cannot support the loads required.
SWJ Consulting is already working with several local solar panel installers providing calculations for clients both commercial and residential. We have helped several car dealerships and warehouse operators with their solar panel enquiries directly.

We cannot advise on whether planning permission is required but the Government’s planning portal says that solar panels and equipment on residential buildings may be ‘permitted development’ with no need to apply for planning permission provided the following criteria is met:

• Equipment on a building should be sited, so far as is practicable, to minimise the effect on the external appearance of the building and the amenity of the area.
• When no longer needed equipment should be removed as soon as reasonably practicable.
• Panels should not be installed above the highest part of the roof (excluding the chimney) and should project no more than 200mm from the roof slope or wall surface.
• The panels must not be installed on a building that is within the grounds of a listed building or on a site designated as a scheduled monument.
• If your property is in a conservation area, or in a World Heritage Site, panels must not be fitted to a wall which fronts a highway.

If your property is a listed building then you will more than likely need to listed building consent to install solar panels – please check with your local planning authority.

We have helped several warehouse owners and car dealerships establish what size array of solar panels they can have on their roofs. We can work directly with the solar panel supplier you appoint so that they have all the calculations they need.

There is an increasing number of grants available for businesses looking to reduce their carbon footprint, but most grant offers require a quote on what you will need. Our advice is to find out what you can have with a structural survey and then you have all you need to get an updated quote from your solar panel provider and apply for a grant within the given time scale.

The process for commercial customers is similar to our residential customers. We will need to come and investigate what load your existing roof will be able to hold – if you have plans for the building this is helpful but not essential.

It is also important to ensure that if you do not own the building, that you have the correct permissions from the landlord to add solar panels. Your solar panel installer will be able to give you a timescale as to when you will have seen a return on the capital investment in solar, but it will improve your environmental credentials as well as possibly make you some money if you can sell any surplus power back to the grid.