Cutting a roof joist...

Discussion in 'Builders' Talk' started by SarafAtak, May 9, 2021.

  1. SarafAtak

    SarafAtak New Member

    I want to enlarge our loft hatch. It currently sits between two roof beams, but I'd like to cut one to increase the size of the opening.

    I'm a competent DIY'er but have no experience in the roof. I'm a bit concerned that this mix will result in a collapsed ceiling or roof...

    The roof...
    - it's a 1930s art deco build in the Bristol city area
    - All the roof joists are only 3x2s dimensionally
    - it looks like the roof rafters actually sit on the end of each roof beam at the end of the roof (near I assume the roof plate)
    - I think there are two purlins(?) That run perpendicular to the roof joists across their length

    The specific joist I wish to cut:
    - there are no trusses attached to the joist
    - it appears to run the entire 8m length of the house unsupported by any walls below (I am not sure how this is possible as I have stood my 95kg body weight on the beam when in the attic and feel no flex - there are two stud walls along the joists length but the points of contact appear to be only with the top of the plasterboard rather than a supporting stud)

    I'm wary of cutting the joists because i don't understand how it's currently supported (I don't believe such a dimensionally small piece of wood can span as big a gap and take both the weight of the ceiling and myself) and what role it plays in supporting the roof (from what I've read, I believed the rafter would sit next to the joist, not on top of it)

    I'm ready to give up on the project, so any advice would be appreciated.

    (The reason for adding a loft hatch is to allow light storage for the attic area)
  2. Jord86

    Jord86 Screwfix Select

    Post some photos up.
    SarafAtak likes this.
  3. SarafAtak

    SarafAtak New Member

  4. Jord86

    Jord86 Screwfix Select

    You should be fine to cut the section out and fit two trimmer sections to the outer joists and then fix through the new trimmers into the cut joist. The ceiling binders are holding the ceiling joists as well as your temporary 4x2's and the upstairs stud walls are helping to support them. Look up trimmer joists on google for a picture showing what I mean. Don't forget to cut the opening back the thickness of the timber you use to trim the opening out, do roughly 45mm.
    SarafAtak likes this.
  5. SarafAtak

    SarafAtak New Member

    Thank you. That's reassuring - one thing I did want to highlight though is that the joist never touches the studwork.

    On one wall you can see the only point of contact is with the plasterboard affixed to it and the other side has the old plaster and lathe directly below it. With this in mind will it be providing structural support?

    Pics of this are below:

    Also this particular joist doesn't have a ceiling binder on it, but will that make a difference?

    For the trimmer joist, do I need to run between two supporting walls?

    Just wanted to say thank you for your support!!
  6. Jord86

    Jord86 Screwfix Select

    You're welcome, I'm amazed if the stud walls aren't touching the ceiling joists directly as the joists are original and the stud walls are presumably original, the timber laths look to be running directly through the walls and the head plate of the stud walls will be fitted up tight to them, unless there's noggins fixed between the joists to provide a fixing for the head plate of the stud wall.

    You can put your own binder in above if you feel the cut joist needs supporting further, and the trimmer needs to be cut to fit between the two ceiling joists either side of the attic hatch opening.
  7. SarafAtak

    SarafAtak New Member

    Ah I think you're right. I can see what could potentially be the studs under the plaster and lathe. Will have a go today and let you know if anything collapses haha!
  8. SarafAtak

    SarafAtak New Member

    Just as an update: I cut the joist and put in the trimmer.

    No collapse of ceiling or roof - so thank you for your advice!
    Jord86 likes this.
  9. Jord86

    Jord86 Screwfix Select

    Good man, no prob.

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