Any structural engineers on here?

[Globalti]

I have fitted this evacuated tube solar panel to my roof:

The local BC reckons I need Building Control Regulations approval for it and the electrics. I want to be able to tell the inspector how much weight is on the stainless steel straps that hold it on the roof. There are four, each goes up under the tiles and is bent around and screwed to a timber fixed across the rafters. The panel weighs 48 kilos and the roof angle is about 35-40 degrees, I reckon. Am I right in assuming that, if there was no friction between the panel and the tiles, the tension on the SS straps would be less than 50% of the total weight? i.e. less than 24 kgs shared equally? However there is actually enough friction to hold the panel in place even without the straps so I believe the load on each strap could be almost zero except in cases of unusual loading like a gust of wind. What do you reckon?

The electrics are all 12v, running off a cellphone charger plugged into an ordinary socket, so I believe the inspector won't need to give BCR approval for that.

 

[slowmotion]

Just suppose you took it off the roof and dangled is vertically from one strap. The tension in one strap would be 48 kilos.

You can buy nylon fishing line that handles that. The tension in the strap is not the problem. The wind loading might be a bit more of an issue, especially if the wind blows on the other side of the roof. In those conditions, there will be a suction force on the panel trying to lift it off the roof, but any metal strap will be able to cope with that. My guess is that the screw fixing into the timber is the weak link, but it is quite amazing what four screws can handle.

Actually, just get the panel manufacturer to provide assurances. They must have done it many times.

My two cents.

 

[summerdays]

Is it normal to need BC approval? as someone looking at your piccy and in the early stages of going down the solar route. Wind was one of the questions I did ask the man who came this last week - he said that the panels were screwed into the roof joists(?).

 

[Globalti]

No, I don't think Building Control Regs approval is needed. However when I telephoned Ribble Valley BC to ask, I could almost hear the engineer scratching his head. We agreed that I would send the application anyway and they would decide. From the way it's been handled I have a strong feeling that they have never been asked before and want to learn more about it, hence they have kept my cheque and want to come to inspect the installation.

The need for BCR approval looks even weaker when you consider that my installation has not made any structural alteration to the roof, the straps and the 10mm F&R pipes fit up under the tiles. I just had to cut a couple of grooves in the lower edges of two tiles to accommodate the pipes plus some insulation. If your installer is telling you the panel is attached to the joists, they may be intending simply to drill through the tiles and bolt to the sides of the joists. This introduces a weakness into the integrity of the roof because silicon sealant won't last for ever, so I'd ask them for a bit more detail on the fixing method if I was you. They should be able to do it they way I did. PM me if you want some more pics.

Do you mind if I ask how much they are quoting? I bet it's £3000-£4000. My neighbour is a retired plumber who had a successful business employing several blokes. He has been watching closely and giving me the odd tip, I have spent £808 on the system (£350 for the panel, £95 for the differential controller, £26 for the pump, £150 for the extra cylinder off Ebay and the rest on plumbing fittings and sundries.) My neighbour reckons I've done £3500 of work at the going rate, saying that if I could have done it in two days I'd be making a tidy living for myself.

This is where I got the system: http://shop.solarpro...co.uk/index.php

 

[vernon]

I think that Building Control Regulations apply only to commercial premises.

The Tan Hill Inn had a run in with the planning bodies over the installation of roof mounted solar panels claiming that they were not needed and the planners pointing out the existence of the regs for commercial premises. The owners of the property milked the situation for every scrap of publicity that they could.

 

[cygnet]

I doubt that it's the fixings that could bother them, more the increased weight you've added to the purlins and rafters. A reputable installer should be able to assure them these are not overloaded.

 

[summerdays]

No they lift the tiles (I think) ... screw down the metal bits to the wood ... and then refit the tiles on top that the system hangs onto. He hasn't given us a price yet ... ) and it will be for both types when it comes but presumably with a break down in the quote. Did you get a new tank and if so what sort of size? We are a family of 5 with teenagers so trying to decide what that means in terms of hot water!

We have someone else coming to give us another quote too.

 

[threebikesmcginty]

The unit, if it was 1 metre x 1 metre it is +66% of the tiles/felt/batten load you already have on the roof. If the weight is put back on to the roof evenly between the four fixings each point load is about 0.11kN, not a huge amount. If you bolt the fixings the drilling is taking strength away from the timber as opposed to using screws or nails. If it's a truss rafter roof it won't be designed to take the load, may work as is or may not. If it's a cut timber roof again it depends on the timber size and purlins used.

 

[dellzeqq]

I think that Building Control Regulations apply only to commercial premises.

that's not correct

 

[annedonnelly]

When mine were installed building control were mainly interested in the electrics - they needed assurance that the installer had the necessary qualification. In terms of the actual fitting to the roof the building controller came out to inspect after fitting - he stuck his head in the loft (didn't even climb in), took one look and said it was OK.


@summerdays - you need to think about when you use your hot water. If 5 of you want a bath/shower before 8 am it's not going to be much use to you. If, like me, you bath in the evening it's ideal - lots of free hot water. Both the panel and the tank need to be sized according to your needs. Hopefully the installers will do that as part of the quotation process.

 

[rsvdaz]

im an architect not an engineer

you need building regulations approval for(amongts others..but ones relevant to you):

any structural alterations - you arent

any works to electrical layout - if your only plugging into a socket your not

 

[summerdays]

Does the supplier deal with building regs... he certainly took photos of our circuit board ... apparently some cables aren't quite big enough (4 vs 8 mm? size) - note Mr Summerdays was also there to understand all the technical bits so he will have understood what was going on.

Yes they have warned us that we do need to change our habits to make use of the hot water ... which will take a bit of getting used to.

One issue that I didn't think of at the time is that in high summer when its really really hot, its going to produce a large tank of hot water ... that is going to bring heat into the house and presumably sit there radiating it and heating up an already hot house. I'm not sure how to deal with that one (short of leaving the hot tap on draining the system!!!)

 

[Globalti]

If your tank is adequately insulated that won't happen because all the heat will be contained within the insulation.

In theory.

 

[Night Train]

One issue that I didn't think of at the time is that in high summer when its really really hot, its going to produce a large tank of hot water ... that is going to bring heat into the house and presumably sit there radiating it and heating up an already hot house. I'm not sure how to deal with that one (short of leaving the hot tap on draining the system!!!)

From what I remember, the system should be specified to just provide all of your hot water needs during summer so that you won't end up with a tank that is boiling over. It means that in winter you will have to supply gas or electric heating through out the winter to top up the tank.

However, in a very hot summer, or if you go away on holiday, there is a risk of 'over heating' the system and so the system will vent and shut down to prevent the tank going above temperature.
The outlet from the panel, if there is no flow, can become super heated steam if it isn't vented off.

When I was at CAT learning about solar water heating during the coldest, wettest summer a few years ago, on the one sunny day we had, the panel was quickly too hot to touch and was boiling off water while we were leak testing. For the rest of the miserable month it never managed to raise the tank temperature much above 20degC.

 

[Over The Hill]

If a gale is blowing onto that side of the roof then the load could be far higher from the wind force, and it probably could be a negative force too trying to suck the panel off the roof if it blows from the other side. These forces are probably many times the panel's weight. I have lost solid cement ridge tiles off my roof in a gale.

My guess as far as Building Regs go is that if is required as it in linked in to the domestic heating system and any work on that is subject to control.
I did have in mind that the installers have an exemption and can self certify the work (like window fitters and plumbers certify their own work).

One point that is of interest-
How do you stop it freezing up in the winter?