I am building a 4metre deep single storey rear extension, it will have a pitched roof at about 13 degrees. I want a flat ceiling but I'm guessing that 4x2's will be too weak to span that distance without sagging?
what size for ceiling joist
- Thread starter DIYedboy
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Looks like you need 195s depending on your spacing... http://www.home-extension.co.uk/tech2.html
I think he is talking about ceiling joists not floor joists Woody has answered the question.
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Thanks Wood. The room will be 4m out by 8m wide, I presume I can't use binders cos at 8m wide I can't get a single timber binder long enough to sit on the walls at each end, or can I bolt a couple of 5m binders together to give me the 8m span? if so, what size would the binders have to be?
The binder doesn't have to be 8m long - do it in two or three pieces.
Look in the roof of an old house; the binder is often a few pieces of 3x2 nailed to the ceiling joists, and suspended from above (off a purlin, or hip, or even the rafters themselves) by a few offcuts of wood nailed up - often bits of floorboarding and suchlike.
It's carrying hardly any weight, and presumably you won't be using the void for storage?
Tony, the void will be empty, I have binders in my loft (1930's semi) they are nailed across the ceiling joists, they are not supported from anything above them. A couple of questions:
What do 'binders' do?
Are you saying I can use 4x2 ceiling joists across the 4metre span providing I use 4x2? binders that span across the 8metre width (presumably connected centrally along the 4metre span) even if they are not one continuous length and can be 2 or 3 lengths.
Do the binders have to be also connected to the 9x2 C24 roof joists?
What do 'binders' do?
Are you saying I can use 4x2 ceiling joists across the 4metre span providing I use 4x2? binders that span across the 8metre width (presumably connected centrally along the 4metre span) even if they are not one continuous length and can be 2 or 3 lengths.
Do the binders have to be also connected to the 9x2 C24 roof joists?
There are lots of options, deeper joists, one binder, several binders, deep binders, double joists, hangers, whatever.
It comes down to what is practical and cost. If you want someone to work it out, then that needs to be the question. The point is, if you need to use 4x2, then there are options, but they might not be the best options.
It comes down to what is practical and cost. If you want someone to work it out, then that needs to be the question. The point is, if you need to use 4x2, then there are options, but they might not be the best options.
Blimey Wood, ain't life complicated! I can use any size of ceiling joist, perhaps 6x2 might be a sensible option with a binder?...................I have absolutely no idea ( the actual roof will be tile hung n have velux's in if that makes any difference) please tell me what to use n I'll do that!
PS please also tell me what a 'binder' does, I'm guessing it stops the joist from sagging from the weight of the ceiling
PS please also tell me what a 'binder' does, I'm guessing it stops the joist from sagging from the weight of the ceiling
You've only really got half a design in your head so it's hard to say. Personally I'd keep it simple and go for joists deep enough to span the distance alone, so probably 195 x 50 if you're happy with 400mm centres. Then you can concentrate on the additional design complexity that the Velux's will introduce - How wide are the Velux's - have you already picked them to suit your joist centres being at @400 or @600? The binders might get in the way of your Velux's, or maybe not... Do you have a plan drawing of what you're trying to achieve, where the walls are, etc?
If you are forming light wells from the velux windows, then they can potentially act as hangers for binders. But you will need double ceiling joists too, as you would with the rafters.
Yes it is better to form the ceiling in a joist size that wont need a binder, but a binder or two is not a big problem, and it could be a big cost saving to have smaller timbers.
Obviously you're not working to plans, so you need to weigh up the options with the different joist sections
Yes a binder stiffens the ceiling and spreads the load from individual joists to neighbouring ones. Its like a beam in a wall in reverse
Yes it is better to form the ceiling in a joist size that wont need a binder, but a binder or two is not a big problem, and it could be a big cost saving to have smaller timbers.
Obviously you're not working to plans, so you need to weigh up the options with the different joist sections
Yes a binder stiffens the ceiling and spreads the load from individual joists to neighbouring ones. Its like a beam in a wall in reverse
What is the problem here? If we are talking about ceiling joists under a shallow pitched roof then the only load on the joists will be the plasterboard, skim, and some insulation. There is no need to allow for any imposed load or boarding for storage, as there won't be any. With that in mind I can't see any problem in getting 4x2s at 400mm crs to span 4m - use C24 to give a bit of extra capacity. You won't even need binders...
The roof joists will be 8x2s, but massive overkill for the ceiling.
The roof joists will be 8x2s, but massive overkill for the ceiling.
@ Ronny - I wouldn't have believed that at first but on checking it you're right - minimal deflection, even with C16.
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