1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Weakened roof trusses

Discussion in 'Wood / Woodwork / Carpentry' started by richchad, 7 Aug 2011.

  1. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    I have just had solar panels fitted to my roof, they are fitted using screws through tiles into roof trusses or joists.

    However it would appear they used too large screws, 4 x M10 in each timber which are only 35mm wide. I think this does not comply to the building regs as they should have used M8 screws, but the solar installer insists it is okay.

    I am considering strengthening the timbers either by bolting another 3m timber along side the existing to extend past top and bottom screw.

    Or should I be considering some sort of steel bar to do the job or maybe there is another way?
     
  2. Sponsored Links
  3. noseall

    noseall

    Joined:
    2 Feb 2006
    Messages:
    38,804
    Thanks Received:
    2,477
    Location:
    Staffordshire
    Country:
    United Kingdom
    What makes you so sure that they are structurally weaker now than before the panels were fitted?
     
  4. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    I am not sure really, just that I now have 4 x 10mm holes in each of 12 lengths of wood that is only 35mm wide and I understood the building regs say any holes must be at least 4 times wider than the width, ie wood should be 40mm wide for 10mm holes.

    I can only assume they must state that for a reason?

    I would think the risk is low but what the risk is I am not sure, are the timbers going to suddenly give way with the weight of the roof or will they just bend over time?

    Just wanted to find an easy way to be sure it is safe I guess.
     
  5. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,304
    Thanks Received:
    1,406
    Location:
    Surrey
    Country:
    United Kingdom
    are we talking screws or bolts???
    screws dont count but i assume you mean a bolt as a screw that size would be wow huge lol :eek:
     
  6. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    We are talking screws and yes they are huge, they very long and are fitted by pre-drilling through tiles and into timber.

    I guess they are that size because they are very long, the installer admitted that they should have been M8 screws, but M10's were fitted by mistake, but insisted it was still structurally okay.......
     
  7. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,304
    Thanks Received:
    1,406
    Location:
    Surrey
    Country:
    United Kingdom
    the shank off the screw is 10mm??

    if he drilled a pilot hole then it does count because its removed material
    screws are normally small and remove minimum strength as most fibers are deflected and not broken

    if the shank is 10mm i dont know the answer
     
  8. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    I guess the shank is 10mm, here is a photo of one screw that partly misssed timber and also photos of one that split the wood and was braced with new timber
    [/img][​IMG]
    [​IMG][/url]
    [/img][​IMG]
     
  9. freddiemercurystwin

    freddiemercurystwin

    Joined:
    21 Jan 2007
    Messages:
    18,791
    Thanks Received:
    2,080
    Location:
    Devon
    Country:
    United Kingdom
    Feckin ell! What a bodge, not structural my arse! Phone the fecker or his boss up and tell him what an absolute knob head he is! :eek: :rolleyes: :LOL: You're repair looks OK though.
     
  10. Sponsored Links
  11. RigidRaider

    RigidRaider

    Joined:
    9 Aug 2006
    Messages:
    1,727
    Thanks Received:
    68
    Location:
    Lancashire
    Country:
    United Kingdom
    Hmmmm... I'd be pretty hacked off if somebody did that to my roof. Looks like they just ran out of the right size of screws. I would certainly double up the joists, I'd be tempted to screw some lengths of thickish ply each side of the weak area with PVA glue to strengthen the setup. I'd be using lots of shortish screws to clamp the job together with the least possible intrusion into the underlying beam, rather than bolting through like you have.
     
  12. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    Yes, I wondered about using plywood, would you just use two short pieces either side of each screw location rather than two long lengths?

    BTW I didn't do the repair, the installer did.....

    Thought about making a fuss to get them back to do the repair work, but after seeing what they have already done, thought maybe I would be better off doing the job myself..!
     
  13. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,304
    Thanks Received:
    1,406
    Location:
    Surrey
    Country:
    United Kingdom
    colour rather drained out my cheeks when i saw that :( :(
    have they also damaged the felt in the split timber picture??
    it looks like several stitched holes in that picture
     
  14. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    Yes the felt is slightly damaged in one or two places, have examined the whole roof during a long heavy rain downpour and no sign of any water ingress...

    Yes it is a bit of a mess, but I guess it is difficult to measure accurately from the outside where the holes will appear, most are into the timber but some did miss.

    I have moaned to the company about it, but now it can't be undone so I have to decide what is the best way to deal with it, you can probably see why I am reluctant to have them anywhere near my roof again.!
     
  15. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    If I fit plywood strips each side of the 70mm deep x 35mm wide roof trusses and bond with PVA glue, three questions:-

    What thickness of ply would be best?

    Should I fit one piece each side or short bits spanning just the 4 screw locations?

    What type, size and length screws?
     
  16. richchad

    richchad

    Joined:
    22 Feb 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    big-all, you said screws don't count, just had another look in loft, and as you can see from the photos only the threaded part of the screw is into the timber, no shank, and about half to three quarters depth into the wood.

    So, even though a pilot hole was drilled, which would be small, it isn't as weakened as I thought?
     
  17. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,304
    Thanks Received:
    1,406
    Location:
    Surrey
    Country:
    United Kingdom
    when i said screws don't count i meant the correct size screw that would normally have little impact on the surrounding timber
    for example a 4mm shanked screw will have a 5-6mm thread you wouldn't use a 4mm on say 12mm as its overkill as a 3 or 3.5mm will do the job now you could use 4mm with a 3mm pilot hole to prevent splitting but then you will weaken the structure because you have removed 25%

    now normally you have 10-25% redundancy in timbers because they are rule off thumb guidance notes with a bit extra for luck
    trussed roofs are on the other hand specked individually with less leeway so you really need to be so careful as the 1/4 rule is for joists so doesn't apply to truss roofs as far as i know

    you are better to use 12mm ply each side for at least 16=18" past the damage/hole and use a screw every 4to 6" at each end and 6 to 8 inches in the middle

    and the felt needs repairing it a secondary line off defence to keep water out that gets behind the tiles
     
    • Thanks Thanks x 1
Loading...

Share This Page