Replacing rotten roof trusses that were originally 320mm Scots Pine timbers.

The roof originally had to support concrete tiles which were heavy, it will now be supporting a lighter tin roof. The engineer says I could have put a shallower timber instead, but it wouldn't sit with the original walls and construction of the room.

I can get 300mm timbers easily, but for some reason bigger depths requires bespoke/engineered timbers in the UK. Also the price goes up way more:

  • 300mm x 50mm x 7.2m span = £114
  • 320mm x 50mm x 7.2m span = £251

Do you think I could make up the 20mm thickness with another piece of timber at the same grading (C24)? Like the diagram below?

Any other tricks, could I just pack up the truss where it lays into the wall?

enter image description here

  • 1
    If it's just a height filler grade doesn't matter. Use any ol' thing.
    – isherwood
    Commented Apr 5, 2022 at 13:12

1 Answer 1


Yes. If you glue it, it will even be functionally the same, but you've said an engineer says you don't require that. Still, it's a bottle of glue and clamping or screwing/nailing the piece on, not a big deal - I'd bother.

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