Doubling/sistering floor joists

[scott8040]

Hi, im planning an attic conversion, having spoke to an engineer he advised me that i have to double up my ceiling joists which will in effect become my floor joists too. The span of the exisiting ceiling joist is 6.3m at 450 centres which are 130x47mm. I was thinking of doubling them up with 150x50's as i cant get 130 x 47's. In order to get these new joists up into the attic i need to at least half them in length, but i cant find a detail on how to join them back together before i bolt them to the existing joists and im not sure if i can simply cut them in half or do i need to keep the new joint away from the centre of the attic.

is there anyone that can shed a little light on this for me please

 

[Bowness72]

I would ask the engineer to give you a size for your new joists because the ones you say are not even close to being big enough for a 6.3m span at 450 centres. To be honest I think you will find you need an intermediate beam as well. (Assuming you are doing the conversion to building regs standards).

 

[scott8040]

maybe shouldve said theres partitions below one of which im sure is loadbearing, my main concern is how to join the ends of the newly introduced joists

thanks

 

[alfiembra]

Joining timbers is cumbersome to say the least, they need a substantial overlap length which is determined by design loads, span, grade of timber, bolts, type of timber connectors etc etc. so there is no easy answer to your question. I would suggest that for your application it just isn't feasible to consider this option.

It may sound a bit extreme but can you punch a hole through a gable or eaves and feed the correct length of timbers through from the outside.

Need more information to advise any further

HTH

Alan

 

[Bowness72]

If there is a suitably constructed "load bearing" intermediate partition can't you just split (and lap) the joists over this support ?

 

[scott8040]

the situation on the outside of the house make it difficult to get in 6m joists in through the fascia. the wall below and concrete lintel below it lead me to believe its load bearing, do you think it would be an option to construct a load bearing wall alongside the existing wall?

cheers