[Closed] Any builders in: Acrow props for <1m height?

Will using the bedroom floor to support the roof really help? Or just cause issues elsewhere too?

That had occurred to me, but I'm not sure what other options there are in the short term - possibly it's the best bad idea available.

Car jack or axle stands and some wood? A bottle jack on a stack of wood will probably do it. A decent plank or two at the bottom will spread the load on the floor/ceiling below.

Jack it up, bolt a bit of timber either side of the crack. Job done

Would a piece of 4"x4" cut to size + shape work? Maybe introduce a 3/4" ply spreader plate at floor level to spread the load?

Car jack or axle stands and some wood? A bottle jack on a stack of wood will probably do it. A decent plank or two at the bottom will spread the load on the floor/ceiling below

Thanks - it would need to be quite a tall stack of wood, and as I probably want 3 or 4 in (think it's a 4m span - I'm in the office today so can't check immediately), so I don't think this one is practical unfortunately.

Would a piece of 4″x4″ cut to size + shape work? Maybe introduce a 3/4″ ply spreader plate at floor level to spread the load?

Not sure I could cut the wood and wedge it under the beam in such a way that it would actually relieve any tension? Will definitely put some spreader plates under whatever I end up with.

Bottle jack. And a timber pillar

Make sure the floor can take the weight.

I've been involved in similar on a couple of properties i've done, the fix my surveyor recommended was a steel braced on engineering bricks on load bearing walls @ 90 degrees, then a chunky cls frame is built on top of the steel up to the purlin. As above you could do the same as a short term measure using scaffolding planks to spread the load accross the floor instead of the steel.

it would need to be quite a tall stack of wood, and as I probably want 3 or 4 in (think it’s a 4m span

I've used this method to sister a garage roof joist and that was 2m high. The bottle jack will do about 500mm, 100mm bit of timber on the top, couple of scaff boards underneath, that only leaves a 300mm stack. Also you won't need 4. One under the crack, with a sturdy bit of timber on it to spread the load, will be fine. Or one either side if you really want belt and braces.

They are called Pit Props.

or trench struts.

eg https://www.scaffolding-direct.co.uk/trench-struts/

We prop roof structures quite a lot in my job (stonemason). I would argue propping off of a floor below is the wrong way to do it as you are just transferring load to something that may not take said load.
A bit more intrusive but we normally prop from the lowest solid surface, footing or similar to ceiling every floor up to the roof. That way the load is transferred down to something solid. Alternatively cut holes in the ceiling to allow longer props to reach upper floor then prop below that. That way you will have more making good though!
Just read that back and I’m not sure it makes sense!

I'd be asking the structural engineer the best way to prop it - after all, they identified the problem, so presumably must be able to come up with a temporary solution?

I agree with marksnook, you really need to prop all the way down to ground. It would help to know the age of the house and the roof covering, eg, tiles, thin slate, thick slate.

You might be able to minimise holes in the ceiling if you can locate the joists, and just make a small hole in the plaster to insert a solid packer. Unless you have a joist directly below the purlin, do that for 2 joists with spreader beams across the joists (above and below) and Acrows bearing on the spreaders.

The alternative to propping down to ground is a steel beam between load bearing walls. I wouldn't rely on scaffolding planks to spread the load as they're not stiff enough.

A car jack would be ideal for the short top prop, as you can get some load into the system.

(Retired structural engineer)

Thanks very much for the responses everyone. It's effectively on the fourth floor (cellar underneath) so unfortunately propping down to ground doesn't sound feasible with my level of DIY (in)expertise.

In the immediate term the engineer has suggested simply using 4" * 4" timber cut to length, on a plywood base to spread the load a bit, with a shallow taper cut into the top and then hammered under the beam.

Roof is thin slate, house is 1911, it's very tall and gets a lot of wind.

****s sake. If I ever move house again I'm buying a Bovis home.

Is this not an insurance job? I would have thought house insurance would want to get some experts in to both short term stabilise and long term fix.

We had a couple of undersized purlins (according to the SE - builders didn't agree) that we reinforced by through-bolting a 150 x 6mm steel plate on one side.

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nickjb

or trench struts.

Yes thats the correct terminology.

Insurance companies don't cover building maintenance only accidents maybe some failures but if they spot lack of maintenance you have no chance with them
Orange juice in the video recorder or fag burns on the suite no probs

I would be wary of spreading the load to a ceiling but I would hazzard a guess that there isn’t a massive load through the purling. I don’t know what force wing loading could add , but above my pay grade! Is wind likely to add any loading? Trouble is I would have thought in order to even bolt a steel to the purling it will need the weight taking, depending how big the crack is possibly lifted. Has the roof dropped or is it all staying out at the minute?

The roof still looked level this morning when I left for work. Now - who knows 😀 !?

Insurance companies don’t cover building maintenance only accidents maybe some failures but if they spot lack of maintenance you have no chance with them

Yep. Likely to be a 'wear and tear' issue (FFS...)

Could you just make a simple 'ladder' frame to sit under, with 'props' arranged equi-distance?

Sorry I was assuming when you said cracked that equated to dropped as well! If it hasn’t dropped then you would think bolting a c section steel to it would be the simplest/easiest fix

I would hazzard a guess that there isn’t a massive load through the purling.

Hmm..... it hasn't cracked for fun.

bolting a c section steel to it would be the simplest/easiest fix

C section would be more intrusive than a plate and more difficult to line up the holes - as well as being potentially quite a bit more expensive as it may well need to be custom welded.

Our SE was happy with a single plate on one side.

Not sure I could cut the wood and wedge it under the beam in such a way that it would actually relieve any tension?

Just got an email from the engineer: "The proper solution will be a metal plate bolted along the length, the details of which we can finalise after the visit."

He suggested two bits of 4" * 2" timber 300mm either side of the crack, resting on a third piece of timber of the same dimensions running perpendicular to the floor joists.

He also explained I'm not trying to relieve a significant amount of tension as I insert the props (which is what the clever technique in that video would do!), just be there to pick it up if it's inclined to drop further.

That vid of the USA guy shows how an accrow is so much easier, what a faffin about
If he insisted on using a bit of 4x2 why not cut two wedges and have more control
Inches are years out o date

the details of which we can finalise after the visit.

{As much length as you can} x {as much height as you can} x 6/8mm bar stock - M14 holes drilled at 600mm centres in a Z pattern alternating top and bottom.
Cost should be about £40-50 depending on length.

That'll be £250.... thanks 😉

I’m not trying to relieve a significant amount of tension as I insert the props (which is what the clever technique in that video would do!)

you can lift as much or as little as you like

That vid of the USA guy shows how an accrow is so much easier

if you own one. I think anyone could make one of those jacks in less time than it takes to drive to the shop  and back

Inches are years out o date

is irrelevant

He needed a compressor, an antique nail gun, a power saw and a contraption that had no careful control like an Acrow prop where you can lift Imm at a time