Floor Joists Question

[Glenn83]

Building my extension and just want to know if the floor joist can be laid either way.

Reason being my extension is 11m wide by around 7.3m deep if i have the joists running left to right then i am assuming i need to put in at least two foundation trenches to support the joists if I run the joists back to front over the 7.3m then its just 1 foundation in the middle to support them is it ok to do this or would this be a question for building control.

 

[stevie888]

It's a question for your designer and you then tell BC what you intend and he'll tell you yes or no.

Have you not put drawings in? Sounds not and without sounding unkind, you're on dangerous ground if you're working "on notice" without a proper design or the knowledge to answer your own question.

Assume it's a ground floor? More usual to go solid.

Single 11m trench or 2 at 7.3m is a no brainer as you'll be using 7x2 either way

 

[Glenn83]

It's a question for your designer and you then tell BC what you intend and he'll tell you yes or no.

Have you not put drawings in? Sounds not and without sounding unkind, you're on dangerous ground if you're working "on notice" without a proper design or the knowledge to answer your own question.

Assume it's a ground floor? More usual to go solid.

Single 11m trench or 2 at 7.3m is a no brainer as you'll be using 7x2 either way

Yeah the drawings are going in i am not even near that point yet it was just something that's popped into my head as i would like to dig the small footings once i get the extension footings poured.

Yeah its ground floor, I was thinking of going solid but then my house is on timber joists and one thing I like is if I need to add/ remove heating pipes electric cables or if there is a problem its only taking up a few floor boards and replacing not having to dig up a concrete floor.

 

[big-all]

general comments the joist support /rigidity/structural strength will be roughly 2 to 3 times as much dependent on cross-section in other words flat 2 to 3 time the timbers in the same width for the same support /rigidity level but as said a structural engineer or other competent person [not me ] for accurate answer

In case you are struggling to understand my comments, take a plastic ruler or other thin material even 12mm ply and try top surface /edge loading in the vertical position compared to the horizontal plane

 

[SimonH2]

.Yeah its ground floor, I was thinking of going solid but then my house is on timber joists and one thing I like is if I need to add/ remove heating pipes electric cables or if there is a problem its only taking up a few floor boards and replacing not having to dig up a concrete ffloor.

Me too, I 'kin hate the solid floors in our house (and the large slabs of weetabix too). Not least because the kitchen floor is solid and unheated so is always cold. If anyone tells you a concrete slab won't be cold because it's insulated - they are either lying or ignorant.
Think about it, unless heated, the slab will not be warmer (on average) than the air immediately above it - and that layer will always be the coldest bit of the room. The same applies to timber - but that lacks both the thermal mass and conductivity of concrete.

general comments the joist support /rigidity/structural strength will be roughly 2 to 3 times as much dependent on cross-section in other words flat 2 to 3 time the timbers in the same width for the same support /rigidity level but as said a structural engineer or other competent person [not me ] for accurate answer

In case you are struggling to understand my comments, take a plastic ruler or other thin material even 12mm ply and try top surface /edge loading in the vertical position compared to the horizontal plane

I don't think anyone was suggesting laying the joists flat, so I don't see any relevance to your post.

 

[Glenn83]

general comments the joist support /rigidity/structural strength will be roughly 2 to 3 times as much dependent on cross-section in other words flat 2 to 3 time the timbers in the same width for the same support /rigidity level but as said a structural engineer or other competent person [not me ] for accurate answer

In case you are struggling to understand my comments, take a plastic ruler or other thin material even 12mm ply and try top surface /edge loading in the vertical position compared to the horizontal plane

Yeah i think you may of miss read the post wasn't turning the joists flat, but running them from front to back instead of left to right


Like this all my joists in my house run right to left but over the extension its 11m span so i was asking if they can be run front to back over the 7.5m span

 

[big-all]

Yeah i think you may of miss read the post wasn't turning the joists flat, but running them from front to back instead of left to right


Like this all my joists in my house run right to left but over the extension its 11m span so i was asking if they can be run front to back over the 7.5m span
View attachment 393773

miss reading a post, nothing new there then

 

[blup]

If the blocks are the right spec then can go either way

 

[catlad]

Ventilation might be something to think about.