Metal web joist spacing

[Triassic]

We’re having metal web joists installed in our kitchen floor, the basement bedrooms are below.

 

I asked the timber frame company about joist spacing and was told they would be installed at 600mm spacing as per the manufacturers recommendations. I’ve pointed out the kitchen floor has an island unit and granite kitchen worktop, the floor will be covering on either slate or porcelain tiles, thus adding to the weight.

 

What spacing are your joists and do you think 600mm is too wide a spacing, the span is around 4.2m.

[bissoejosh]

I think it would definitely be worthwhile changing to 400mm centres. Not a huge cost increase and increased peace of mind in terms of bounce. Ours are 400mm spacing on a span of about 3.5-4m varying  with 22mm Caberdeck glued and screwed and seem rock solid. 

 

 

 

 

[Alexphd1]

400. The extra few joists are peanuts in the grand scheme, you will kick yourself after if any bounce.

[Oz07]

Yeh 400 better. If sitting on masonry as above basement have you considered Conc beams?

[Tyke2]

Hi

 

Any joist system should be properly designed and installed in line with the manufacturers recommendations. If it is properly specified then 600mm should be fine.

I have a James Jones silent floor timber system installed in my barn. in one area I have 2 large wardrobes, back to back, both crammed to bursting and a king sized bed. in 18 years there is still no floor deflection. its a 6m span at 450mm centres. I let the supplier design and specify the layout the risk is with them. If you want to ignore the experts and design your own layout , the risk is with you. moving them closer will give you more mass. But increasing the depth of the beam should give you less deflection. Ask the manufacturer for guidance.

 

[CC45]

400mm for sure.  We've got 600mm and its not as good as I wanted.  A mate had 400mm and his floors are rock solid.  Spend a few extra pennies now & be happy later.

 

Is your plumber using copper pipe?  If so you may want to put this in as the joists go in.  Plastic you're OK.

[Alexphd1]

We have a mix of 400 and 600 over different spans. We specified minimum deflection with the designer, we where told we where only wasting our money sticking in more joists...... next build WILL  be 400 centres! 

[joe90]

Our floors were specked at 600 centres but the builder (and I agreed) to make them 400 and I don’t regret that decision.

[Gone West]

14 hours ago, Triassic said:

What spacing are your joists and do you think 600mm is too wide a spacing, the span is around 4.2m.

Depends on the width of the chord. My spacing and chord width varies depending on the span and load.

[PeterW]

 

Agree with this although I fitted all at 600c apart from the landing with the bathroom and they are 300c..! Feels very solid...

 

The other thing is where the deck goes as where there is a room in roof above the kitchen (ensuite) the deck doesn’t go to the walls as it was deemed false economy but it does make a difference and there is a little more flex in it. Really shows that the floor is a composite structure when the deck is glued to the joists.