help -builder damaged roof?

chickenist

Hello,
It is day 1 of our renovation of our house - and we got back home to find the electrician's apprentice has drilled holes through all of our roof trusses to feed electric cables as part of the rewiring.

I don't know why he didn't just lie them on top of the trusses like the previous cables, but anyway - we now have numerous straggly 15mm holes in our 120mm trusses.

Haven't discussed this with our electrician yet but have been searching online and it seems like holes in trusses are a major no no unless they are less than 10% of the width of the truss.

We are really worried - will this be covered by his public liability insurance, or will we have to claim for it on our building insurance? Should we ask him to get a structural engineer in, or should we do that ourselves? It is really not a good start!
Any advice would be massively appreciated.

docmatt

He's done nothing wrong.

chickenist

really? i hope you are right. i've read online that building regs specify you shouldn't drill through trusses without structural engineer approval, as the holes weaken the structure..

ColinFishwick

Had them done in my garage with no problems obviously not such a large roof as ahouse but I think its normal as long as they arent huge holes just enough to feed cable through

teneighty

Without inspecting the roof it is impossible to give accurate advice but generally roof trusses are engineered to use the smallest cross section of timber, they are not designed to have 15mm holes drilled in them. It depends where in the truss they have drilled but I would be furious if I found the electrician had done that on one of my projects and would certainly expect an engineers report at his expence. I cannot understand why he drilled the trusses at all. If he has done that I would also be worried if any holes in the floor joists have also been drilled in the wrong places and weakened them as well.

Try to have a calm chat with him and hopefully he'll realise he's made a stupid mistake and agree to get it rectified. More likely he'll just turn round and say "I've done nothing wrong." If that is the case you'll have to decide whether you throw him off the job and try to recover any costs later or let him carry on and withhold the cost of the report and any repairs from his invoice.

I would expect his public liability insurance to cover it but his excess may well be more than the costs involved.

Good Luck

27col

The holes can be repaired by gluing and screwing plywood plates over the holes. You just have to ensure that the plates are at least twio or three times the area of the holes. I took the advice of a structural engineer and cut right through some of my roof trusses when I built my house, in order to make a larger hatch. The cut areas were replaced by binders and a large piece of plywood, glued and screwed around the new hatch. It has been about thirty five years since this was done, without any adverse effects.

chickenist

Thanks Teneighty - that is very helpful. After I read your post I went and checked the floor joists and they also look very dodgy. No idea where you can drill holes but there is one spot where he's drilled diagonally up through a double joist to get wiring for a socket into the wall above, which really doesn't look right.
Hope the calm chat can sort this out. In your opinion, is this kind of thing expensive to fix?

chickenist

27col -that sounds encouraging, cheers.

teneighty

Depending on what the engineer says I would expect it to be reasonably inexpensive, either plywood repair plates like 27col said or cripple studs screwed to the side of the damaged truss members.

As for the floor joists just google "notching floor joists" and you'll find the guidance on notching and drilling for cable and pipe runs.

docmatt

C'mon were talking about 15mm holes here! Much worse things are when people re-roof old clay tiled roofs with new concrete tiles but no one seems to get the structural engineers out then!

Maybe i'm an old school roofer here but it seems like were all over reacting about this one.

CaptainKidd

Heres somthing that i found on another forum that maybe of use to you.

http://www.zurich.co.uk/NR/rdonlyres/98C95CE7-4EEC-4C76-A0FF-0C6B2CD53EED/0/NotchingDrilling107780A02.pdf

I know the table is for joists but iam sure the same would apply (but if not them iam sure someone will be along VERY soon to correct me), a drilled hole can be 0.25 times the size of joist so he would be allowed to drill upto 30mm as yours is 120mm.