floor joist thickness

[wallace]

Hi all I am planning on extending my workshop. It is going to be 4m by 5m. My question is what is the smallest thickness do people think I could get away with for the floor joists, I was thinking 6"by2" but do you think if well supported I could go 4"by2". The construction is going to be 12mm ply insulation then 18mm ply. Anys thoughts appreciated.
Mark

 

[merlin]

Hello Mark,

The old way of doing it was take the unsupported length in feet divide by 2 and add 1.

If you take the 4m run and convert to feet - 13 divide by 2 = 6 1/2 + 1 =7 1/2".

If you have enough support then 4x2 would be fine, it is always worth making it as strong as possible so would not scrimp on timber, I have been using a lot of 1" WISA ply for flooring in loft conversions lately, that reduces the depth of joist and when glued and screwed it is a good covering. If you can don't exceed 16" centres (16" as the ply will proberly be 8' x4')

Cheers, Merlin

 

[wallace]

Thanks Merlin, the new extension won't house any machines its purely an area for build ups and a workbench for hand work. I am trying to do this on the cheap but be insulated and fit for purpose.
Mark

 

[Tom K]

Think you know the answer is a big fat nope. Whatever you plan to go in there now you will exceed and be left wishing you hadn't skimped.

 

[Grahamshed]

I think it all depends on how well they are going to be supported. What did you have in mind ?

 

[jasonB]

Yes it all depends on what you term "well supported" if you are going to divide the 4m length with three sleeper walls then 4x2 will be fine as the effective span will only be 1.0m.

If one sleeper wall then I would be looking about 6" depth for a 2m span or no wall then 8" joists for the full span, you don't want a bouncy floor under a workbench.

J

 

[ash224w]

Hello Mark,

The old way of doing it was take the unsupported length in feet divide by 2 and add 1.

If you take the 4m run and convert to feet - 13 divide by 2 = 6 1/2 + 1 =7 1/2".

Cheers, Merlin

the old ways are all ways the best i still use this method Mark what's the plan for the shop will it have standing machinery on it or is it just fresh air

 

[wallace]

Hi, thanks for the input. I was going to have brease block supports at regular intervals, and then it is going to be bolted to my existing block built workshop.
Mark