GF suspended floor joist arrangement

[Footsoldier888]

A neighbour has removed his chimney breast and hearth in the living room. The joists go parallel to the the hearth and he has found himself with no central support to the joists. His solution was to run 50 x 100m joists right across, which is a span of about 3.30m.

The centres are 400 but the table I looked at says the max span for joists of that size is 1.84m. Is this going to give him problems? He hasn't yet covered them with flooring.

 

[oldbutnotdead]

Think he's got more than floorboards to worry about. What is supporting the rest of the chimney in (presumably) one of the upstairs rooms? The joists which you mention- are these the ground floor joists or the 1st floor joists? How has the hearth (which probably only projected 500mm from the breast) removed support from all of them?

EDIT Post title says ground floor. 4 x 2 on a span of 3.3m will be very bouncy. Presumably there's a subfloor below the joists- a brick or block pier on the centreline is the usual solution. 6 x 2 on that span will be stiffer. Don't forget to nog between the joists as well

 

[Footsoldier888]

Thanks - I haven't dared ask how he did support the stack.

The thing about the subfloor is it's extremely low, maybe not even 15cm. The rest of the room has 75 x 50mm joists supported on the central dwarf wall. He has used noggins at 1m intervals but this does not seem like the solution to me, especially if a granite worktop is going to go on cabinets flush to the wall where the chimney breast was.

I don't know it I should say anything or not, I would only do so if it was really neccessary. But if it is 'very bouncy' then perhaps I should. Thanks anyway.

 

[Doggit]

Why not suggest he allow you to take a photo, to post on here and see if there are ways to take out the bounce. If the joists run parallel to chimney breast, then he could put in a trimmer either side of where the chimney breast was, and then you can use the 15cm joists on a shorter central span.

 

[Footsoldier888]

Thanks Doggit, will try and get one, he only works at the weekends.

Yes I had thought a trimmer either side of where the chimney breast was might be a better bet.

 

[Keithmac]

Thanks - I haven't dared ask how he did support the stack.

Probably first question to ask before you go anywhere near it!.

 

[Ian H]

I don't know it I should say anything or not, I would only do so if it was really neccessary. But if it is 'very bouncy' then perhaps I should. Thanks anyway.

You might as well say something. You obviously know him and have been in there to know he used 4x2 with noggins every meter, that his subfloor is shallow, that the rest of the room is 3x2 and that it has a supporting wall.

 

[oldbutnotdead]

Thanks - I haven't dared ask how he did support the stack.

The thing about the subfloor is it's extremely low, maybe not even 15cm. The rest of the room has 75 x 50mm joists supported on the central dwarf wall. He has used noggins at 1m intervals but this does not seem like the solution to me, especially if a granite worktop is going to go on cabinets flush to the wall where the chimney breast was.

I don't know it I should say anything or not, I would only do so if it was really neccessary. But if it is 'very bouncy' then perhaps I should. Thanks anyway.

Well that puts a slightly different spin on it. He ideally needs 150mm clear between underside of joists and subfloor to maintain adequate airflow, especially if the subfloor is soil. So 4 x 2 may be the best compromise- I' ve used them for the same reason on a 3600mm span with a centre dwarf wall and props at the 900mm and 2700mm marks (so the effective span is only 900mm) and they've been fine. Put dpm under whatever you use for props & it'll be fine

And as these things go a STATIC load of units and granite worktop isn't the worst that can happen- it won't bounce cos the load isn't changing. Might drop a bit but that's what adjustable legs on the units are for