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Carpentry & Joinery

What thickness, length and type of screws do i need for joists blocking?

I have 60x200x3.8m Joists at 35cm distance between each other.

I have bought a 75x200x4.8m joist which I will cut in blocks and will fix in between the joists.

I want to use screws and not nails so my questions are:

- What thickness and length of the screws should I put?
- Do I need to consider screws allowing flexibility?

Thank you in advance

4 Answers from MyBuilder Carpenters & Joiners

Best Answer

If your going to stagger the noggings then use no 5 120mm torx screws there a bit more expensive but really do the job, you may need to pre drill the joist if your screw gun is it impact.( not hammer action) Your looking for zero flexability, the idea of noggings is to prevent joist twisting and stability.
If you intent to align the noggings you can side fix the noggins with circa no5 100mm screws be sure the angle of the screw is circa 30*


Answered 31st Jul 2019

A rule of thumb is 2.5 times the thickness of the material your are scewing through. Therefore I would use 150mm screws
Depending on type and guage of screw pre drilling might be necessary. Dril bit size for predrilling would be approx the shank diameter of screw.

You don't want any flexibility. By using screws instead of nails you will likely eliminate flexibility so it's a good choice


Answered 31st Jul 2019

I’m assuming you mean noggings.
If you’re fixing through the original joists into the end gain of the new timber, I would suggest 100x5.0 or maybe 100x6.00. If you’re screwing through the new timber at an angle into existing joists you would probably be able to use 75x5.00 providing you didn’t start too far back.


Answered 24th Jul 2019

Hi,herringbone strutting is the proper job,it spreads the load better,and you can use much less expensive timber and nail the struts.


Answered 8th Aug 2019

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