How to Sister a 1st floor joist with 880 mm piece cut off in the middle.

[kay1468]

I want to sister a 1st floor joist (180 x 50mm) that has an 880 mm piece cut off in the middle ( from past chimney removal). I am thinking to either (1) use a similar sized joist spanning the empty 880mm space and extending 600 mm from either cut off side (total length 2080) or (2) using two joist pieces spanning each cut side by ONLY 400 mm. I will be using 180mm carriage bolts 8M or 10M.

[Note: there won't be any middle piece of wood abutting the cut ends of original timber.]

 

[ree]

OP,
Is this trimming part of the loft floor or a lower floor?
If its possible, why not post a pic or post a brief sketch of whats existing??

 

[kay1468]

1st floor joist. The part containing concrete for fire base. Builders removed the chimney / all fire ??? years ago but left the concrete that buttresses on adjacent joists (can't remember correct name). I now removed the concrete and gap between the cut joist is 800 mm. I want to sister this cut joist. Thanks for your assistance.

 

[Deluks]

1st option would work. Use 2x 10mm coach bolts and toothed washers at each end.
It would benefit from having a new section filling the gap between existing.
You may need a few extra noggins, bracing it to the next full joist.

 

[stevie888]

600 isn't a very big lap for a moment connection like this and spiky washers are the very devil to use. I'd be more inclined to trim from the next joist back to the wall at each end and set in a new piece of joist just using a few joist hangers

 

[kay1468]

@Deluks
Thank you so much. I was also wondering about extra noggings and adding back "the cut off piece". If I use this method, I think I will also increase the span to 880 mm either side - total of 2640 mm (880+880+880).

I like this method better to reduce the overall weight of all added sister pieces.

 

[kay1468]

@stevie888
Thanks so much for your idea. I also did consider trimming back to both ends and stopped and decided to ask 1dt if either methods I narrated above was adequate.

Now, before choosing the best method, I will trim back and see what's at the end and how feasible or easy it will be to replace the whole joist. Thank God I haven't started cutting any of the delivered joists.

I love you guys and thank you all for your constant support. God bless you all.