what size joist to use

[rjl]

hi all,can anyone please advise me as to what size ceiling/roof joists should be used on a single storey extension.the roof will be a flat roof.any help would be very welcome and appreciated.

 

[tony1851]

Could be 4x2, 8x2 or 9x3 - who knows ?


was my post useful? then click the 'thanks so very much' button.

 

[pinenot]

But seriously, ask a stupid question you'll invariably get a stupid answer, specially on this forum

Weight of load dictates strength of timber required - equates dimensions - seemples...pinenot

 

[tony1851]

you'll invariably get a stupid answer

Especially from pinenot.

What's 'weight of load'? Were you away when you did Physics? The other main determinants of joist size are span, spacing and type of timber.

 

[pinenot]

Tony your becoming a pain, I'd put all my experience of buildings that I've put up against yours, so without being rude put up or shut up, as the saying goes...PINENOT

 

[tony1851]

Tony your becoming a pain, I'd put all my experience of buildings that I've put up against yours, so without being rude put up or shut up, as the saying goes...PINENOT

pinenot, you're just sooo horrid and I'm upset now

 

[pinenot]

pinenot, you're just sooo horrid and I'm upset now

And there's me thinking antagonizing thoughts when in reality it should be pity

 

[john4703]

When Pinenot and Tony stop disagreeing you may find that the solution needs some further information.
What is the span of the joists? (That means how long re they)
Where in the world are you? (I've built flat roofs in the Middle East with no thought at all of the possible weight of snow but if you are in the Arctic Circle snow weight is very very important and anywhere in the UK is a consideration.
Give some more information and this forum will help you.

 

[^woody^]

Who the hell builds a single storey extension without knowing how to build a single storey extension?

Is there a building inspector involved in this little escapade?

 

[rjl]

Could be 4x2, 8x2 or 9x3 - who knows ?


was my post useful? then click the 'thanks so very much' button.

ye really helpful..........let me explain its 6m wide x 3 m depth, 2.4 m high, single storey with flat roof.i know they need to be 400 centres and dont know if i can get away with 7" x 2" or if i need 8" x 2".ontop will be 18mm osb boards with cure it roof.Hopefully this info will help

 

[rjl]

woody...there's no need to be so arrogant .if you required more info why not ask instead of throwing insults.....i suppose you've never asked a question without putting info what was required.

 

[Alastairreid]

7x2" will be adequate.

 

[noseall]

woody...there's no need to be so arrogant .if you required more info why not ask instead of throwing insults.....i suppose you've never asked a question without putting info what was required.

Yes quite, but there is also a way of phrasing your initial post so as to not invite frivolity.

For instance you would not say "how many bricks do i need?" and then later on in thread give out the sizes.

Unless you are bloody daft.

 

[tony1851]

Could be 4x2, 8x2 or 9x3 - who knows ?


was my post useful? then click the 'thanks so very much' button.

ye really helpful..........let me explain its 6m wide x 3 m depth, 2.4 m high, single storey with flat roof.i know they need to be 400 centres and dont know if i can get away with 7" x 2" or if i need 8" x 2".ontop will be 18mm osb boards with cure it roof.Hopefully this info will help

6x2 @ 400c/s would be perfectly OK for that; in fact, 6x2 as domestic floor joists will span 3.1m, and roof loading is a lot less than floor loading. 7" and 8" would be overkill.

 

[^woody^]

Wtf are you on about rjl? You don't just plonk a roof on an extension and think about joist sizes when you are ready for the roof

Are building control involved? You must be doing this on a building notice then with no designer, and presumably, you know about furrings?