Building regulations for solar: structure, electrical and fire

Two regimes, not one

This trips people up constantly, so it is worth stating plainly alongside the planning position.

An installation can be permitted development and still be unlawful building work. The two have nothing to do with each other.

When solar counts as “building work”

Regulation 3 of the Building Regulations 2010 defines building work to include:

the provision or extension of a controlled service or fitting in or in connection with a building

and material alterations. An alteration is material, under regulation 3(2), where the work would result in the building or a service or fitting:

not complying with a relevant requirement where previously it did

or, where it already did not comply, being more unsatisfactory in relation to that requirement. The relevant requirements for this purpose include Part A, structure, and the fire safety requirements in B1 and B3 to B5.

So the structural question is not “does the roof need to be perfect”. It is: would adding this array take the roof out of compliance, or make an existing shortfall worse? If yes, it is building work and the regulations apply.

The electrical side: Part P

This is the limb that applies to nearly every installation.

In England, regulation 12(6A) makes electrical work in a dwelling notifiable where it involves:

• installing a new circuit
• replacing a consumer unit
• adding to or altering circuits in a special location — bathrooms, swimming pools, saunas

A grid-connected solar installation normally runs a new dedicated circuit from the consumer unit to the inverter. That is notifiable.

There are two lawful routes:

Self-certification through a competent person scheme. The installer is registered with a scheme, does the work, certifies it themselves, and the scheme notifies the local authority, which issues a building regulations compliance certificate. This is how the overwhelming majority of domestic solar is done.

Notifying building control directly. Required if the installer is not scheme registered, or if you are doing it yourself. Notification must happen before the work starts, and building control will want to inspect.

The structural side: Part A

A domestic array typically adds in the region of 12 to 20 kg per square metre, depending on modules and mounting. Most roofs designed to modern standards absorb that without difficulty — which is why this is usually a non-issue, and why it is occasionally a serious one.

Where it needs real attention:

• Older roofs, particularly pre-war structures with undersized or irregular timbers
• Roofs already carrying heavy coverings — stone slate, concrete tile
• Altered structures, where a loft conversion, removed purlin or new rooflight has changed how the load travels
• Roofs with existing defects — deflection, rot, insect damage, previous repairs
• In-roof systems, which replace the covering rather than sitting on it and change both loading and weatherproofing
• Wind uplift, which on an exposed site can matter more than the dead weight

MCS’s installation standard requires a competent person to assess structural adequacy as part of an MCS installation. If your installer is MCS certified, ask what that assessment concluded and ask for it in writing.

The honest position on this page: whether your roof takes it is a question about your roof. There is no rule of thumb that substitutes for someone competent looking at the structure, and any installer who declines to discuss it is telling you something.

Fire

The fire requirements enter through the material alteration route — B1, and B3 to B5, are relevant requirements for that purpose. In practice the issues that arise on domestic solar are DC isolation and cable routing, the accessibility of the array for firefighting, and the fire performance of the roof build-up where an in-roof system replaces the covering.

We have not researched this properly enough to write it in detail, and we would rather name the gap than fill it with generalities. It is on our list.

What you should end up holding

Ask for these, and store them with your deeds:

• Electrical installation certificate for the new circuit
• Building regulations compliance certificate from the competent person scheme, or a completion certificate from building control
• MCS certificate, if the installation is MCS certified — needed for SEG
• The G98 or G99 notification or approval — see connecting to the grid
• The structural assessment, in writing
• Manufacturer warranties for modules, inverter and mounting

That list is also, near enough, the list a buyer’s conveyancer will ask for. Assembling it at the time takes an email. Assembling it four years later, from a company that may no longer exist, is a different matter.

If it was never notified

This usually surfaces on sale. Two routes, neither ideal:

Regularisation. Apply to the local authority to regularise unauthorised building work. They may require opening up to inspect. It produces a proper certificate.

Indemnity insurance. Cheaper and faster, and commonly accepted in conveyancing — but it insures against enforcement rather than establishing that the work was safe. Note that approaching the council about the work generally invalidates the policy, so you cannot do both in that order.

If you are buying a house with an existing array, ask for the certificates before you exchange. It is a routine question and the answer tells you a good deal about how the installation was done.