Floor joist spacing and chipboard flooring

[Paul_Thomas]

How critical is the spacing of floor joists?

We are planning on having 450mm centres in our extension 1st floor, do the 18mm interlocking Chipboard floor boards have to meet on joists or as long as they are screwed down (and possibly glued together) securely they will be ok?

 

[BoxBasher]

I believe the boards should be accross the joists not along them, although I will acquiesce to anybody who knows better... (not being a floorer/joiner).

 

[Paul_Thomas]

Yes, I was expecting the board to be at 90 degrees to the joists, and staggered like bricks.

However do the end joins need to be on joists or doesn't it matter as they are interlocked?

 

[masona]

Should be maximum 400mm centre, best to add a few more noggins where the T&G joints are. Glue all the joints, does make the floor more solid

 

[Paul_Thomas]

Should be maximum 400mm centre, best to add a few more noggins where the T&G joints are. Glue all the joints, does make the floor more solid

Sorry to question your advice, but why 400mm centres? (The extension and existing house have 450mm centres on 1st and loft floors.)

 

[masona]

I have done many 1st & 2nd fixing and always known it as 16" (400mm) unless the joists are bigger than 4"x2". If it's shown 450mm on the drawing then I wouldn't worry. Even the roof trusses are 400mm centres, maybe the 450mm is now standard(?)

If it's more than 450mm centres then you will need to use 22mm thickness

 

[Paul_Thomas]

My house is 17 years old, 1st floor joists are 200x50mm with 450mm centres.

I have copied this size in the extension (Done my own plans) and so far the BCO and structual engineer haven't commented on it.

Garage conversion may be 125 or 150mm by 50mm joists, but these will be on the floor so more than stable.

 

[masona]

My house is 17 years old, 1st floor joists are 200x50mm with 450mm centres.

That is okay, the 100 x 50mm should be 400mm centres maximum which is normally on the ground floor

I got confused when you said 1st floor, me thinking ground floor

 

[^woody^]

The flooring end joints should be across a joist.

The joist spacing is determined by the size of the joist section and the span. It can be anything up to 600mm and you either calculate the loadings or use published span tables to get the spacing.

In practical terms you want as few as possible but not so few as to cause the floor to bounce. Long spans may require bracing (noggins at mid-span or one third centres whatever the spacing

Spacings over 450mm will require 22mm boards as mentioned above

 

[Paul_Thomas]

The flooring end joints should be across a joist.

The joist spacing is determined by the size of the joist section and the span. It can be anything up to 600mm and you either calculate the loadings or use published span tables to get the spacing.

In practical terms you want as few as possible but not so few as to cause the floor to bounce. Long spans may require bracing (noggins at mid-span or one third centres whatever the spacing

Spacings over 450mm will require 22mm boards as mentioned above

So I presume with std 2400x600 18mm chipboard floors at the moment, the joins can not be over 450mm spaced joists.

 

[masona]

Do you have any herringbone strutting or noggins as mentioned above?

If it's less than 2.5m then you don't need any herringbone

If it's between 2.5m to 4.5m then one row in the middle

If it's more than 4.5m then you will need at least two row at 1/3 position

 

[Paul_Thomas]

Extension is not built yet so I expect it will be Noggins. Span is only 2.6m gap so only 1 noggin required.

 

[markie]

The norm is 400 centres 16" but the prefab roof truss are norm 600 centres.