Results of structural survey

[Iwantsolarpv]

I have had an independent structural survey carried out and the report has come back as follows:-


6. OBSERVATIONS:   The roof construction is of traditional timber construction (Cut Roof), with Purlins. The common rafters are SW 85mm x 50mm and Purlins 170mm x 70mm, with a maximum span of the common rafters to be 1.62m.
   
   We found no indication of significant defect or decay to accessible timbers.



 7. RECOMMENDATIONS:   Whilst we cannot guarantee any minor deflection of roof timbers on the installation of the proposed Solar panels, we advise that it is highly unlikely. Therefore, we confirm that the roof structure is adequate to carry the additional loads applied by the installation of the proposed Solar panels.

Does this seem like a standard report? I think I expected a bit more detail regarding the actual loads but I suppose it is his job to calculate and then give me a yay or nay.

[rondurrans]

I do not think it would be unreasonable to ask for a copy of the calculations along with a copy of their Professional Indemnity Insurance certificate to keep on record from a professional Structural Engineer.....even if they do just refer you to tables!

That said the statement:-
'we confirm that the roof structure is adequate to carry the additional loads applied by the installation of the proposed Solar panels'
confirms their liability - still a copy of their PI cert. helps one sleep easier.


Ron

[Rich]

99.9% of such surveys are a complete waste of time and not worth the paper they are written on.
Have a look at the roof yourself and trust your judgement.
Most surveyors will only do what is known as a 'head and shoulders' survey anyway, which means they merely poke their head and shoulders through the loft hatch and have a quick look with a torch.  It is considered too dangerous to actually go into your loft space, let alone carry out the work you are paying them to do.
And do you know how they survey a roof or chimney from outside?  Ladder or scaffolding?  No, a pair of binoculars!
I kid you not.

[ecotrician]

Well in that case i must be the customer who gets the 0.1% of structural surveys that are correct, these include six pages of structural and wind load calcs, 'trust and judgement' to my knowledge wont recompense the householder if the roof fails, Rich if you are actually a structural engineer thats fine, I am not, which is why I use an expert, advising others not to is folly in my opinion.

[MikeD]

My structural survey was basically a bloke who said "8 by 2...yeah, that'll be fine, it's only the weight of 4 people on your roof".

Shading survey was (same) bloke standing in the garden saying "you might need to trim that tree a bit".

Think I'd have preferred a 'proper' job TBH

[Iwantsolarpv]

Well in that case i must be the customer who gets the 0.1% of structural surveys that are correct, these include six pages of structural and wind load calcs, 'trust and judgement' to my knowledge wont recompense the householder if the roof fails, Rich if you are actually a structural engineer thats fine, I am not, which is why I use an expert, advising others not to is folly in my opinion.

Out of interest, do you have many jobs that require work to the structure before you place panels? What work is done? Is it pretty major?  Are they jobs that you suspected might? Are the wind load calcs a big issue in UK?

So many questions!!!!

[ecotrician]

Wind calcs - never a problem, i'm in the south west, its like california here 

Loading - never been an issue on prefabricated trusses, a couple of cut roofs have needed further investigation but were OK, very few roofs require extra work, the issue for me as a business is that I can prove that the roof is OK backed up by calcs, calcs that I fully admit I couldent do myself.

[Komisaruk]

I agree with Ron.

I think it is definitely worth getting a structural survey performed by a Chartered Structural Engineer.  This will give you peace of mind should something unfortunate happen and may prevent any problems should you want to sell the property.

[stannn]

Iwant
A couple of pictures of your roof type, inside and out, would have helped us to form an opinion. Standard roof structures generally stay in one assembly even when extraordinary wind events lift them off the walls. If the roof has been modified then there is cause for concern. I do think that external viewing of a roof for non-linearity may show up potential problems. I do think that an internal inspection will show up obvious leakage and/or mould on the timbers.
The introduction of PV panels will introduce new loads to the roof which are reacted where the large number of brackets are screwed to the rafters. The dead weight (kN/m2) is almost insignificant when compared with the weight of the contractors. As far as I am aware from this forum, there is no history of aerodynamic load pulling PV mounting brackets from a roof.
Stan

[BruceB]

Iwant,

Personally, I find the wording of the structural engineers report a little loose.  You want confirmation that they have considered the wind and snow loadings as well as static loading cause by installation of the solar pv array and its operation under defined assumed conditions.  They may well have done, but simplistically read, I could infer that the roof will take the weight of the panels full stop. 

They might usefully state what their asssumptions have been for snow/wind loading.

And from the times I have been through the calculation, the wind uplift has always been the greatest force to allow for.

Regards
Bruce

[stannn]

Iwant
To expand my theme, if a 16 panel (4 x 4)PV array were mounted to a roof, then the panels might weigh 16 x 15kg = 240kg and the support framework would weigh a similar amount. This total of 480 kg would be supported by about 40 brackets, spaced at say 1m apart, giving a nominal static load of 12kgf per mounting. A PV contractor could easily weigh 100kg when carrying a panel and could place his weight on one foot absolutely anywhere on the roof. 100/12 = 8.33 recurring or, put simply, a lot. So you have a lot more to worry about with the localised loads from men on the roof than you have with the localised down loads from a PV array. The roof was however originally built by a team of roofers who tested it by walking all over it. So, with no modifications and no decay it should be fine for PV.
Stan