Sloping trusses

Discussion in 'Carpenters' Talk' started by BeastOfTheEast, Dec 18, 2023.

  1. BeastOfTheEast

    BeastOfTheEast New Member

    Hi all

    The flooring and ceiling in my attic room are sloping. I measured the height difference which is 3cm in 3m from one side to the other. This is enough for things to move down the floor on their own.

    The attic is based on attic trusses which span 7.5m from wall plate to wall plate. I have access to one side and could inspect the trusses and wall plate.

    Two of the seven trusses are resting nicely on the wall plate with their bottom chords (see attached photo). The remaining five have been notched gradually into the wall plate which causes the overall 3cm height difference between truss one and truss seven (see attached photo).

    Does anyone have an idea why this has been done and potential ways forward to fixing this?


    Attached Files:

  2. billysloke

    billysloke Active Member

    I doubt I can answer your question but for the sake of clarity: when you say the ceiling in your attic room, do you mean that there is a (theoretically) horizontal section on each truss to which plasterboard is attached?
    Is/are the ceiling/s in the room/s below also sloping?
    Based on my very limited grasp of the facts, I would hazard a guess that whoever installed the roof perceived (rightly or wrongly) that the wallplates were out of horizontal and notched into them in an attempt to correct the discrepancy.
    In terms of what you can do about it without needing a structural engineer, unless it's a newbuild under warranty or you think your surveyor has been delinquent, I suspect you will just have to lift the floor boards and make the lower joists up to the height of the others. Is it living quarters or just storage?
  3. James.1986

    James.1986 Member

    Possible the the block work wasn't level, leading to the gradual notching to compensate.
  4. BeastOfTheEast

    BeastOfTheEast New Member

    Thanks for your replies! It turns out that the wall plate (the one that is accessible) is perfectly level.
  5. Mark DM

    Mark DM Screwfix Select

    Would be unusual but maybe a discrepancy in the truss manufacture
  6. Jord86

    Jord86 Screwfix Select

    How did you ascertain that it’s perfectly level?

    It sounds like the brickies were a course of bricks low on one side of the house and the lads who put the roof on tried to reduce the discrepancy by notching the wall plate.
  7. BeastOfTheEast

    BeastOfTheEast New Member

    Self-levelling laser and tape measure. The wallplate is only 3m.
  8. BeastOfTheEast

    BeastOfTheEast New Member

    It seems that I need to take a look at the other wall plate. @Jord86 I think you are right, the blockwork on the other side is most likley lower. Not sure how to best measure this.
  9. The Happy Builder

    The Happy Builder Screwfix Select

    The brickwork is obviously out of level, the carpenters tried to compensate to make it less noticeable by notching the trusses into one of the wall plates, but not enough to sort it out.

    The carpenters have not also not realised that if they put the truss clips on the outer face of the wall plate it would be easy to finish nailing them to the rafters!
  10. Jord86

    Jord86 Screwfix Select

    Use your laser to take a datum through and around any doors or dividing walls, put a piece of masking tape on your walls if you don’t want to mark the wall with a pencil, then transfer the line from one side of the upstairs to the other.
  11. BeastOfTheEast

    BeastOfTheEast New Member

    @The Happy Builder @Jord86
    So, I have actually done it now. Compared the height of both wall plates. Measurement says they out of 1mm (+/- 2mm tolerance for the laser) ! I think this proves that the blockwork is not our of level. The only explanation that is left is that the walls aren't parallel.
  12. BeastOfTheEast

    BeastOfTheEast New Member

    Attached a photo of the truss on the other side that is notched into the wall plate as well.

    Attached Files:

  13. Jord86

    Jord86 Screwfix Select

    If there is a 30mm height difference as per your original post and it’s not the floor joists, then it’s the ceiling joists. Walls parallel or not won’t make any difference to a level.

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