Is this acceptable to building control?

jackboy29 · 27 Jan 2019

Hi all,

After a bit of advice as I have a few concerns regarding some work I am having done. In an extension the trimming around the staircase looks pretty bad to me and I’m after some opinions as to whether it is acceptable. My understanding is that joists should be doubled up around the opening to compensate for the additional weight they will take. One joist isn’t doubled but it is very close to a stud wall for the ensuite so it makes sense that that could be taking the weight on that side. The cross trimming joist is doubled and takes two single joists attaches to it. The joist it then attaches to at the other end is not only single but two shorter lengths that have been bolted together. I can’t inagine that this is a good way of doing things. Any comments on if this is a bodge or acceptable? Thanks

^woody^ · 27 Jan 2019

Trimmers don't need to be doubled if they have capacity as a single.

Joists can be joined like that if the loading and connectors are suitable.

So they may or may not be OK. Ask your engineer or inspector.

tomfe · 27 Jan 2019

Some joist hangers or nail plates would not go amiss.

Ian H · 27 Jan 2019

No expert but it looks to me like the cut the joist nearest the camera by accident thinking the stairs would be there when they are actually in front of it.

If i’d have done that (as a DIY’er) I would have replaced the cut joist with 2 full ones bolted together seeing as they are so accessible.

tony1851 · 28 Jan 2019

The joists look to be 8 x 2s? If so, the short, single trimmer is absolutely fine.

As for the 'bolted joist'; not ideal in a perfect world, but the overlap is reasonable, the bolts are widely-spaced and you are near the end
of the span, so the bending stress will in any case be small and easily accommodated by the connection.

Either of these could be proved perfectly acceptable by calculation.

jackboy29 · 28 Jan 2019

Hi thanks for the replies. It seems that it may be acceptable I suspect building control will want double joists unless calculations show it to be acceptable as it is. But the calcs will cost more than changing he joist

jackboy29 · 10 Feb 2019

Builder changed to a double at my request. But what about this? Surely a 1cm bearing for a floor joist can’t be right can it?

jackboy29 · 10 Feb 2019

I would think wood could shrink and warp by this amount as it dries out couldn’t it?

Alastairreid · 10 Feb 2019

Has he still to put a hanger on it?

tony1851 · 10 Feb 2019

In the advisory document to the Building Regs on structural matters (Approved Document A), the recommended minimum bearing for floor joists is 38mm.
That's not to say that 10mm won't work, but the inspector could either refuse to accept it, or require calculations to justify it.
But even if it could be proved to work in theory, it's just too risky.

jackboy29 · 10 Feb 2019

I removed plasterboard to check as I asked for a joist hanger when i say how narrow the support was but he hasn’t done it. Like you say too risky even if calcs said was ok but don’t see how they could. With setttlement and seasonal movement and drying 1cm is not enough to be safe.

jackboy29 · 10 Feb 2019

Do you know where it says 38mm as a minimum bearing because it would be good to use it when I talk to him? I can only see 75mm as minimum bearing joist to wall plate in approved document A.

Cheers

Leofric · 10 Feb 2019

10mm bearing for joists is definitely not enough- if it is staying like that it needs some suitable timber to timber connectors , preferably joist hangers.

tony1851 · 11 Feb 2019

jackboy29 said:
Do you know where it says 38mm as a minimum bearing because it would be good to use it when I talk to him? I can only see 75mm as minimum bearing joist to wall plate in approved document A.

Cheers

Sorry mate, the figure was quoted in a much older edition of Approved Document A - it was the time when they used to publish load/span tables for timber joists, which are not in later editions.
Anyway, I've managed to find it in an older edition I have - it's here under note 4. (BTW, it is 35mm, not 38 as I originally quoted; even 35mm is very short for a bearing; the second attachment is from a separate publication - 100mm minimum bearing quoted on sheet 1).

^woody^ · 11 Feb 2019

tony1851 said:
Sorry mate, the figure was quoted in a much older edition of Approved Document A - it was the time when they used to publish load/span tables for timber joists, which are not in later editions.
Anyway, I've managed to find it in an older edition I have - it's here under note 4. (BTW, it is 35mm, not 38 as I originally quoted; even 35mm is very short for a bearing; the second attachment is from a separate publication - 100mm minimum bearing quoted on sheet 1).

Some joist hangers are about 35mm, so that must be OK.

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Is this acceptable to building control?

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