Trimming stair well in exposed beam ceiling

17 Feb 2018
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Hi all,
I am converting the loft in my old house that has exposed beam (joists) ceilings. I need to make a stairwell opening. I do not want to use joist hangers or brackets as these will be visible. The joists are 3x8 inch (8x18cm) oak joists in very good condition, no worm or rot at all. The span is 4M. I hope you can see my sketch. My plan is to support and cut back 2 joists to form the opening. To reuse one to form the header and the other the length of the opening, to reduce the opening width. I do not have the space upstairs to have the wider opening to the next full length joist. Please could I have you advice on this plan and will nailing these be adequate?
I hope that makes some sort of sense......
stair opening.jpg
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I would not trust nailing to be adequate - in fact it's for that reason that joist hangers are so often specified. In Victorian buildings I have often seen a modified form of the tusked tenon used to to this joint, but that would be difficult to use in an existing building. Another traditional alternative would be to use a cogged joint or better yet a dovetailed cogged joint to secure the trimmer and personally those would be my first choicee given the type of building.
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I will have to go away and find out what a cogged joint is and have a go! Thanks for your help.
I have done a bit more research and understand the issue now of oak and tannic acid upon steel. Thanks

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