Jacking back up a dropped beam, or not?

[Andrew Gabriel]

Helping a friend at the weekend, and found a roof leak has caused the wallplate to disintegrate, which I removed with the vacuum cleaner ;-)

Originally sitting on this was a sodding great compound beam which runs the length of the house and has a loft extension built on it. It was floating in mid air with the wall plate having gone from under it, and has dropped about an inch from where it originally was. I have for the time being packed the gap under it with engineering bricks so it can't drop any further, although before that I got friend to go and walk around and then jump in the loft extention, and there was virtually no movement in the beam-end (much less than 1mm).

So the question is, is it worth trying to jack the beam back up by the inch it's dropped before reinstating the support under it? The two doors in the loft extention both jam slightly in the frame, possibly due to this distortion. I'm guessing the weight might have transferred to some other part of the structure which might not be so well suited to take it, although there's nothing else under that beam for a few metres at least.

[Dave Plowman (News)]

My feeling is you'd have to do it very slowly - perhaps over the course of a nice cold damp winter.

[Nick]

I'm no expert, some immediate thoughts. From what you say the compound beam is in decent order. By compound beam I presume a steel beam of various sections fabricated to the form required. The cause of the initial problem obviously needs to be addressed and fixed before, or during, the remedial works. No doubt the wallplate is compromised beyond what is currently visible. This would have to be cut back to sound timber. Don't know the dimensions involved. Would use hydraulic cylinders and suitable load-spreading packings. Slowly does it but I imagine a matter of days/weeks rather than months. Check house insurance. Structural engineer? I would certainly say that it should be raised to original level and made good. No doubt the beam will settle back given time.

Just my 2d's worth.

Nick

[Tim Lamb]

In message , Andrew Gabriel writes

I have jacked up the loft floor of a Victorian barn with nothing untoward happening. Raised about 4" with lots of creaks.

The other experience is where I had carefully supported a main floor beam to allow some bricks to be replaced in a chimney breast. To my horror, when the job was done, the brickie just dropped the Acrow prop lowering the beam by about 3/4" onto his top brick. Again no noticeable effects.

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[Another John]

You said it. *MUCH* as I admire and respect Andrew's experience and expertise in the field, I'd recommend paying out for a firm of structural engineers to have a look at the whole job: this sounds like "nowt to worry about there old chap!", or .... a potential disaster! Personally I'd rather have the experts give their views.

John

[Tim+]

Isn't he just going to say "jack it up and replace the hanger"?

Tim

[Tim Watts]

We don't have liability insurance...

[michael adams]

If this in a loft, what are you jacking against ? If the foot of the jack is on roof timbers - or even on a metal plate spread across more than one then in atempting to jack up the beam all you may succeed in doing, is stressing whatever the jack is based on.

IANASE but this would presumably depend on how much load is bearing down on the beam - i.e load that would have to be lifted to get the beam level, as against how much load, whatever you rest the jack on, is designed to support. The point being that roof timbers form an integrated structure whose strength comes from the way the structural members are joined using tension and compression and to end along the grain, but nor necessarily bending strength across the grain bewteen the ends as here.

You don't say how many floors this building is. But I'd imaging whatever jacking point you use will probably need support from below from ground level up. This would involve removing sections of floorboards and ceilings in each room and bracing the structiural woodwork beween floors and ceiling on each floor with an acrow prop and plates. Aligning the props will probably be the hardest bit.

michael adams

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The two doors in the loft extention both

[Andrew Gabriel]

I did a sketch of the original construction (which is a bit more complex than I described, with a separate roof plate):

's not to scale, as the rafters don't actually intersect the outside wall, only the roof plate.) The roof plate and wall plate immediately below the large beam had rotted away, because the leadwork over the beam end had failed. The beam itself was not damaged (I presume it's pressure treated timber, whereas the much older wall plate and roof plate are not). To answer another question, the compound beam is just multiple 4" wide timbers around 18-24" tall, fixed together with 18mm plywood on each side - no RSJ.

Well, we did it. We jacked it up about 7/8" which was as much as I was happy to do against the bathroom floor (which deflected downwards an additional 1/8" under the weight). I then built a brick pier of engineering bricks under the beam end on top of the outside wall, left it for 5 days to set. Added some sideways bracing so the beam can't slide off the pier, and then let down the acro. All seems OK. Roofer has temporarily fixed the leak with a resin mat (he will be replacing the whole roof in the spring).

[Tim Lamb]

In message , Andrew Gabriel writes snip

Nice sketch!

Job well done.

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[Andrew Gabriel]

Google sketchup, so I can spin it round to find the best view.

Cheers.