Widen Joist

BarraOG

I am putting down a new subfloor in the bathroom. I have cut out the old floor as it wasn't very solid. On one side of the room I have a complete joist onto which I can rest the new floor. But on the other side, I have just the side of the joist, which is flush with the wall. The joists are 8.5 inches deep and 45mm wide. I was thinking I would just get the same timber to add a new joist and to make some extra noggins. How do I attach the new joist to the side of the existing joist, where I only have access to one side of the existing joist? What screws would you recommend and how often would you space them?

When adding noggins, can I screw these into the joists? Would two 60mm, 5mm wood screws be suitable, with four screws per noggin? Any other tips regarding this?

The Continental Op

Not totally sure what you are asking but I've repaired broken joists with M8 or M10 coach bolts and decking bolts to secure a new joist to the old one. For the noggins I offset them so you can get 120mm or longer screws in through the joist then into the noggin.

https://www.alamy.com/new-ceiling-rafters-with-first-fix-electrics-image504876977.html

BarraOG

https://www.boards.ie/discussion/comment/121580196#Comment_121580196

Thanks for your reply. At one wall, I have no joist for the floor to sit on. Instead, this joist is under the stud wall on that side. So I want to put down a new joist parallel with the existing joist. The floor will then sit on the new joist. This is the side through which people will enter the room so it's important to get it sturdy, as I will be tiling. I cant use a bolt as I only have access to one side of the existing joist. But perhaps a coach screw is exactly what I am after.

chooseusername

Sounnds like you have no access to other side of joist for a nut on a coach bolt so I would use coach screws or wood screws rather than bolts;

https://ie.farnell.com/duratool/d02031/stainless-steel-coachscrews-m10x90mm/dp/3382957 With a 10mm washer.

https://www.youtube.com/watch?v=px_6CiayWjc

monseiur

Attach new joist using 4.5 x 90mm deck screws, 2 rows, 300mm between screws and stagger the rows. Use 4.5 x 100mm screws for the noggins 2 screws at each end. Treat all timber with a wood preservative. (Cuprinol or similar). Use high grade 18mm plywood as flooring, preferably marine ply - it's expensive but 2 sheets should do a bathroom. Fix ply to joists with 40mm stainless steel screws.

GreeBo

Why type is your new floor?

If its planks then you can just attach noggins to the existing "flush" joist and go perpendicular since you are going to add noggins anyway.

If its sheeted material then I would still use noggins but screw something parallel to the flush joist between the noggins to support the sides of the sheet.

Out of interest, where in the bathroom is the problem joist? ie. is it parallel and under the bath? Depending on where it is, its going to take more or less load.

chooseusername

https://www.boards.ie/discussion/comment/121580397#Comment_121580397

"If its planks then you can just attach noggins to the existing "flush" joist and go perpendicular"

How would that work? I'm confused!

BarraOG

https://www.boards.ie/discussion/comment/121580397#Comment_121580397

It's the wall you enter the room through. The toilet, shower and sink are on other walls.

listermint

No pictures. They'd be much better for clarity.