In 2008 there was no requirement to provide structural calculations for PV installations. The system has obviously been operating for 18 years without the roof collapsing, so there is no real issue with the installation.

This is typical behaviour from conveyancers who love to find some irrelevant nit to pick which causes unnecessary stress to sellers. My response would be to say that if the purchasers aren't happy that I would get the installation removed so there will be no question of an inadequate roof, but the purchasers will lose quite a lot of future income (assuming that the system is on the original FIT.)

Of course that demands that you are prepared to stand up to these annoying people, but my experience is that they will usually back down.

@hml1827 I couldn't have put it better, possibly with the exception of adding that it's stress for buyers as well as sellers.

I'm fully expecting similar when I eventually sell.  The solar panel mounting on my flat roof is unconventional, and of course there are no structural calculations, but it has worked for 14 years and the only reasonably conceivable failure mode would require a local tornado in a very specific location.

If (for example) St Paul's Cathedral were to come up for sale, would the same apply.  Let's exhume Sir Christopher Wren to find out how it was designed and some of the builders as well to check that they followed the drawings to the letter.

In our experience, the buyer usually pays for any surveys they want or that have been recommended to them as part of the building survey. I would kindly suggest that if the buyer has any concerns, they instruct a survey themselves or pay a professional to do a desktop calculation from easily attainable measurements. We paid for all sorts of surveys on a property we ended up walking away from as there would have been too much remedial work. But it would have been unreasonable to expect the sellers to spend their own money to satisfy our doubts, provide ammunition for us to negotiate the price down, or walk away entirely.

(Probably what happened was the RICS building survey flagged the solar panels as something they should check, and so they are checking. I would be surprised if the buyer really has a problem with it themselves but rather are doing it in good faith because an authority/professional advised them to.)

My own solar panel fixing rails wouldn't pass the MCS regulations, but the accredited installer who fitted the first 5 panels decided to use common sense.

The roof fixings were supplied with the relevant 8x85mm hex-head bolts which must pass through the roofing felt and into the rafter below.

However, I have a warm-roof construction. There's insulation between the rafters, then another 50mm outside. The external insulation is held in place with 50x25mm vertical counter-battens, then the breathable membrane, and the slate-battens nailed horizontally on top.

That meant using a screw 150mm long, which is 'not MCS approved'.
And I also allowed for two per fixing position.

I don't suppose there's any photos of your fixing rails being installed is there?

That would be useful to give to a prospective surveyor.

Thanks for these replies.

Its a standard install with fixings screwed directly into the truss rafters

The buyer is now paying for a level 2 homebuyers report which is being carried on on Monday 27th, I will be in attendance to see exactly what the surveyor actually does, I will be interested to see as I'm a retired civil engineering surveyor and I know a level 2 report does not include for any structural investigation.

thanks

What will also happen is that they see that there is solar on the roof and they go blindly to their solar panel checklist for tickbox conveyancers (remember conveyancing is where solicitors dreams go to die). Part of that will be that a roof install should meet building regulations so they will look on the council web site for the building regs certificate and they will look for the MCS certificate. Then they will go down the rest of the list checking planning (conservation area, AoNB, listed etc) and the other items on the list - rent-a-roof scams, FIT or SEG paperwork, evidence the system actually works, G98/G99, Part P paperwork with the council and so on.

The first priority of a conveyancing solicitor is not to do anything that could in any conceivable fashion get them sued. So like surveyors they will tag everything and query things like whether a four hundred year old driveway has the correct council paperwork for the dropped kerb.

The usual way to fix this is that the solicitor charges someone to take out a mumbo jumbo basically pointless insurance so that if the solicitor is sued their arse is covered. So someone pays 150 quid and the problem goes away by magic. The insurance policy is cheap as it's basically free money for the insurance company as they can issue millions of them and the number of people who have that problem, sue their solicitor, and win is about zero.

As to the surveyor.  They will write "The property inspected has solar panels attached. Older unserviced solar panels may present a fire risk due to aging cables. Solar panels may cause problems if a roof was not correctly strengthened before fitting. We are not qualified to advise on solar panels go consult an expert" or whatever the current RICS approved boiler plate is to dump the liability elsewhere. If they do observe stuff like cracking purlins or deflection and the like then sure they'll note it too but they'll never say its ok. An RICS surveyor simply ins't qualified to say so.

Technically MCS doesn't matter for the panel mounting. Building regulations do, and building regulations are enforceable and actually determine what is allowed.