Decking Subframe Help Please

Discussion in 'Carpenters' Talk' started by Mark78, Jul 27, 2021.

  1. Mark78

    Mark78 New Member


    I'm not a carpenter but I think this is the best place to ask my question.

    I want to add rectangular decking attached to my kitchen extension and one of the corners I would like to be rounded off (please see image below). I have never done this before and would like some advice on how I create the subframe with a rounded corner. Is it a case of making the complete rectangular frame with the joists and noggins attached and then marking out the curve afterwards and cutting off the section I don't want? Then adding pieces to strengthen the rounded corner or is this wrong?

    Kind regards

    Decking and Patio Design.png
  2. Jord86

    Jord86 Screwfix Select

    Run the joists oversized, then using a piece of batten with a nail though it on one end and a pencil drilled through a hole at the other end as a large compass or trammel bar, mark the curve you want on the tops of the joists then cut them off. You'll need to kerf cut a joist to nearly all the way through and at very small spacings in order to bend it around the corners, this will be your rim joist, screw it to the cut joists to keep it in place permanently.
  3. Mark78

    Mark78 New Member

    Thanks for your help Jord86, this will be a challenge. I have never done a kerf cut before.

    Which saw do you recommend for the kerf cut (the easiest)?
    What gap should there be between each cut?
    Does this weaken the wood, could it break?
    Do I need to brush preserver in all the cuts?
    Do I need to be careful when putting a screw through the rim joist after it has been kerf cut so that it doesn't split?
  4. Jord86

    Jord86 Screwfix Select

    1. Circular saw, cut to nearly all the way through, there is no exact science to kerf cutting, its luck, feel and patience.
    2. At a guess, quarter of an inch. Try 12mm spacings to start then if it's too rigid go in between at 6mm/ quarter inch intervals.
    3. Yes.
    4. Yes.
    5. Yes

    It would be far easier to make the corner angled at 45degrees rather than curved, but it's your house.
  5. stevie22

    stevie22 Screwfix Select

    An alternative would be to laminate the curves from thin strips. If you have a friendly (proper) timber yard with a big band saw get them to run you off strips of your joist depth 3 to 4 mm thick. Glue several together and you will then have considerable strength.

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