Floor joist span

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LondonDIY

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Hi all,


I was hoping you can help as I’m getting mixed feedback.


My hallway is very out of level. The joists from the front door to the mid point hallway sits high with 6x3 and big notches. The rest are 4x2. The 6x3 sit on a wall plate / timber bearer which is damp so I need to replace it and maybe go for a thinner one to help lower the 6x3s.

The damp proof course sits quite high, so I’m forced to use 4x2s or 5x2 with notches on the end. I need to span 1.8m between the front door and the next pillar / sleeper wall. Then the pillars run every 1.3m.

I was considering using double up 4x2s (c24) at 300mm centres, with two layers of 18mm ply (necessary to bridge the gap between the hallway and the next room).


I’ve had feedback to go to 6x2s but the structure doesn’t allow for that, unless I start taking down the sleeper walls, which is a lot of work. We’re not looking for level, just flatness to help lay down LVT unless we redo the entire floor in a few years time.


The span tables suggest a span of 1.6m at 4x2 for joists so am not sure how strong that is giving it’s a high traffic area and would double up help.

Any perspective will help. Trying to turn it into a few days worth of work without going over the time and for it to be strong.
 

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Doubling up doesn't do much unless you add a flitch plate (quite a lot of work). I'd just add another sleeper wall to halve that first span, I don't do bricklaying normally but managed sleeper walls in one of our rooms with no problems, just a few engineering bricks staggered to leave air circulation gaps, won't need much of a foundation, maybe on top of some slabs evenly bedded on a little concrete.
 
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I doubt you'll get an exact answer as you are not installing as per today's standards. The span table will relate to timbers installed as per these standards, and allow for some certain sized cutouts for utilities etc, which are certainly smaller that what you are showing.

From a mechanical angle a single 45x150mm joist will deflect the same amount as three 45x100mm joist.
 
Thanks for the replies. And what point does the 4x2 deflect at what span? Would keeping under a 1.2m be fine?

Could I get away with 5x2s and notch them? Are there any joist brackets I can use to bear on the plate and over hang slightly?
 
How about pack up the sleeper walks with 4x4 timber and hanging joist hangers with 6x2 timbers in between?
 
How about pack up the sleeper walks with 4x4 timber and hanging joist hangers with 6x2 timbers in between?
I was thinking hanger joists but it would be bridging off the damp proof course so I’d need to wrap the timber ends in DPM. Are you thinking 4x4 to across the sleepers? They’ve used 4x2 which I doubt is strong enough for 3x 6x3 to rest on.
 
Hoping I've understood you correctly.....

'We', in conjunction with building reg/structural engineer, would often, on site, use the 'old rule' of convert span into feet, divide by 2, round up and add one.....eg 1.8m = 6ft /2 = 3 + 1 = 4.

Therefore in your example 4x2's would be fine......if you're not sure (personally I would be) then up the section to 4x3's.

This area may be 'heavy traffic' but traffic is not the same as continual load. Get a few 6ft lengths of 4x2 and prop them up on bricks, lay an 18mm sheet over them and try bouncing.....they won't move!

👍
 
Hi!
I replaced almost all my dining room and hallway joists.

4x2 is fine for downstairs, where you have sleeper walls. The 6x3 or 7x3 are mostly for upstairs, where they need to carry the load for a room's full span.

My advice is just use 4x2, at around 300mm or 400mm centres.
Add 4x2 'blocking', which are perpendicular pieces of 4.2 that connect the joists. I added some every 1 meter or so. This allows the floor to 'move as one' and gives more stability.
If a joist still has more bounce than you would like, you can either
1) double it up.
and/or
2) build a small sleeper wall under it! As long as you don't restrict airflow, there's nothing wrong with that. Some mortar and a few bricks will sort it right out. (remember DPC wherever wood touches bricks/mortar).
 
Hi!
I replaced almost all my dining room and hallway joists.

4x2 is fine for downstairs, where you have sleeper walls. The 6x3 or 7x3 are mostly for upstairs, where they need to carry the load for a room's full span.

My advice is just use 4x2, at around 300mm or 400mm centres.
Add 4x2 'blocking', which are perpendicular pieces of 4.2 that connect the joists. I added some every 1 meter or so. This allows the floor to 'move as one' and gives more stability.
If a joist still has more bounce than you would like, you can either
1) double it up.
and/or
2) build a small sleeper wall under it! As long as you don't restrict airflow, there's nothing wrong with that. Some mortar and a few bricks will sort it right out. (remember DPC wherever wood touches bricks/mortar).
Noggins.
Or you could use deeper joists with a taper cut into them, say 6x2 with a 6" taper?? The strength of the beam is only needed between the sleeper walls like a bridge.
 
Hoping I've understood you correctly.....

'We', in conjunction with building reg/structural engineer, would often, on site, use the 'old rule' of convert span into feet, divide by 2, round up and add one.....eg 1.8m = 6ft /2 = 3 + 1 = 4.

Therefore in your example 4x2's would be fine......if you're not sure (personally I would be) then up the section to 4x3's.

This area may be 'heavy traffic' but traffic is not the same as continual load. Get a few 6ft lengths of 4x2 and prop them up on bricks, lay an 18mm sheet over them and try bouncing.....they won't move!

👍
Put another way, half the span plus one, this was used by the carpenters I worked with, relates to feet and inches.
 
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