Suspended floor above garage - Opinions

[glangri2]

As per a number of my other posts, I am about to construct the suspended floor in my extension. Ground floor is garage, first floor will be bedrooms.

The Joists are going to be 220mm deep, and the span between the walls is just under 3m. I want to go 400 or 600 joist spacing (rather than 450) so that I can minimise the waste when cutting the 1200 wide Celotex boards


According to the timber tables, I have got a choice of 38mm joists on a 400mm spacing, or 47mm ones on 600mm.

What are the Pro's / Con's of each option?

600mm seems very wide for joist spacing, but I guess it must be OK.

600mm would mean I only need 14 Joists, as opposed to 20 if I go for 400mm.

CHeers
Gary

 

[glangri2]

Just had a quote from the builders merchant, and the price per metre is the same regardless of 47mm or 38mm.

So the 600mm spacing immediately works out £65 cheaper

 

[theoldun]

Don’t know what timber joist tables you are using, but they are way over the top.
3metre span @ 400centres Regularised C16 38x175 will suffice.
Ditto Reg C16 47x150 will suffice.
3metre span @ 600 centres either Regularised C16 38x175 or 47x175 will suffice.
Check it out your self. If not happy jump up a size
400 and 600 centres swings and roundabouts.
600 centres too big a span for standard 18x114mm t&g wood flooring 18mm chipboard and 12.5 plasterboard. You need 22mm chipboard and 15mm plasterboard at 600 centres
We never use solid joists now, either I Joists or posi joists.
oldun

 

[glangri2]

Don’t know what timber joist tables you are using, but they are way over the top.
3metre span @ 400centres Regularised C16 38x175 will suffice.
Ditto Reg C16 47x150 will suffice.
3metre span @ 600 centres either Regularised C16 38x175 or 47x175 will suffice.

I'm using the Trada ones, but wasn't sure about the loadings, so opted for the
0.5>1.25 column rather than the <0.25

Saying that though, the joists seperate a garage and a bedroom, so I want maximum depth for Sound and Heat insulation.

600 centres too big a span for standard 18x114mm t&g wood flooring 18mm chipboard and 12.5 plasterboard. You need 22mm chipboard

Good point

We never use solid joists now, either I Joists or posi joists.

How does the price compare?

 

[big-all]

450 spacings are perfect remember that's centers so gap between timbers 400
600= 550 spacings ??

 

[theoldun]

We never work 450mm centres unless forced to.
450mm centres does not work for 2400 chipboard or plasterboard.
Especially on chipboard, where you want the short t&g edge to meet on centre of joists.
There is easy way of setting out joists. If you do not know how, then come back.
oldun

 

[glangri2]

There is easy way of setting out joists. If you do not know how, then come back.

Please tell !

 

[cadtech]

Joist size 225x50mm
C16 64 metres @£4.70 per metre for each floor
Period property refurb new ceilings/ floors and a rear extension including loft conversion
All in price for posi £788 each floor. Detached 8x8 lodge metre single span x 253mm. deep £85 each
From Howarth. Don’t waste time with the middle men they only add their bit on go direct to the manufacturers. I draw plans including priced bills of quantities this is a very recent quote