Loft conversion: can you cross-half load bearing timbers?

LikeMyHome · 16 Sep 2020

Hello everybody,

We're doing loft conversion in bungalow (1928 built) and it looks like the only option we have to run the load bearing timbers is to cross them over. Phisically it should be doable, but are you allowed to cross-half the load bearers by building regs?

P.S.
Image attached.
Details:
Soft wood timbers 30x5cm in cross-section, 5.2 and 4.2m long, ends resting on support walls.
Timbers run doubled (4.2) or trippled (5.2) in thickness.

Thank you

Can you cross half load bearing timbers.jpg

Notch7 · 16 Sep 2020

No is the very short answer

LikeMyHome · 16 Sep 2020

Thanks

frutbunn · 16 Sep 2020

Not a chance, though I've seen it done and condemned it a couple of times.
Why can't you run the new joists the same way ie parallel to the existing?

Why are you using 300mm deep joists? You could use shallower joists, this may negate the need to notch the joists.

LikeMyHome · 16 Sep 2020

frutbunn said:
Not a chance, though I've seen it done and condemned it a couple of times.
Why can't you run the new joists the same way ie parallel to the existing?

These LBT's are not floor joists (FJs), new FJ's are fixed perpendicular to the LBTs with joist hangers.
LBT's are also there to support the roof via vertical 4x2's attached to them after existing support timbers are removed.

image attached

frutbunn · 16 Sep 2020

In that case they are normally referred to as beams, and the existing joists are ceiling joists. Just to clarify, are the two "beams" in yellow both 300x50mm timbers? You photo shows 2 beams running parrallel and the drawing shows to beams crossing each other.

LikeMyHome · 16 Sep 2020

frutbunn said:
In that case they are normally referred to as beams

Thanks for explaining. So my LBT's are beams.

frutbunn said:
and the existing joists are ceiling joists.

I called them floor joists (FJs) because they will form floor joists for the converted rooms in the loft.
Also they are not existing (old) joists but new ones 7x2's (freshly put). The old ones are ony ~2x2's and you can't see them as they are hidden by the new. They run in parallel to each other of course.

In general - all whitish timber in the pic is new one, while all dark/brownish - is the old original one.

frutbunn said:
Just to clarify, are the two "beams" in yellow both 300x50mm timbers?

Exactly. And they are doubled on each side (i.e. total thickness is 100 mm on each side)

frutbunn said:
You photo shows 2 beams running parrallel and the drawing shows to beams crossing each other.

You are right. The image is for the other half of the loft (part 1 for clarity) which is partly done in terms of new timbers.
There are no problems with doing this side.

The drawing is for the other half (Part 2) which is untouched and that's where the problem of how to run beams to provide adequate support for the loft floor arose. Sorry for the confusion.

LikeMyHome · 16 Sep 2020

It's part 2 I'm struggling to find solution for.

Our builder offered solution that won't work - hard to explain, but briefly they want to rest the top end of the vertical beam (as in the drawing) on another existing beam (not shown, but runs horizontally and above the one shown), which is too thin to hold the load. So they wanted to part replace that other beam with RSJ but that's not doable cos it's continuous and run thru 3 parallel support walls, so part replacement is not possible

Ian H · 16 Sep 2020

Stupid idea, but do they need to be square with each other?

Or could you span something very strong from the 2 top right supports and fix them onto that?

LikeMyHome · 16 Sep 2020

Thank you Ian for your ideas. To avoid going off topic I'll create new thread with better drawing and photo of the 'difficult' area.

Thank you all for your feedback!

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Loft conversion: can you cross-half load bearing timbers?

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