The OP asked if the amount of props advised by their builder was sufficient. The answer we don't know unless the temporary works are designed. A hi-viz will not help the builder if propping is insufficient and the rear wall of the house collapses.
How many props...
- Thread starter spfc
- Start date
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The problem with a lot of domestic jobs, in the hands of an over-zealous SE, is that things tend to get over-engineered. This adds cost to customer.
I know all about over-zealous SE's.
I know all about over-zealous SE's.
If you are "not sure on the amount" of load being transferred to the props and therefore onto the spreader, how do you know (risk free) that its sufficient. Is it not just a case of thats what you've aways done and will continue to do so in ever structural situation?
I would be more worried about the structural collapse of the rear elevation that just a few loose bricks.
So now a safe system of works is being dismissed on the basis of costs. It would cost a lot more if all goes wrong.
They have a PI Insurance to satisfy.I know all about over-zealous SE's.
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Correct.
However, experience plays a massive part, particularly if you are genuinely interested in building, like wot I am.
Some of the most useful information about building (for me) has come about from carrying out demolition work. You can learn a lot about what a buildings' components are capable of (or not), whilst stripping a building piece by piece. To say I have been astonished more than once would be an understatement.
No, this is not what I said and neither did I infer it.
We did a job in Stafford whereby one SE was used, subsequently sacked, then another was brought on board. One specified X and the other specified y. The latter SE said the former was a berk and that he was over thinking and over-specifying things because he was inexperienced. Whilst I get annoyed at over-specced jobs, I'm the first to pick up the phone and ask for help should we need it.
cAtLeYx, I'm genuinely interested in what your occupation is - life on your sites must be an absolute nightmare
I have to say cAtLeYx, you seem to have a slightly idealistic viewpoint. In an ideal world everything would be done by the book on site, but it isn't, and it probably never will be.
The truth is, overspeccing is endemic amongst structural engineers. Sometimes it's down to inexperience, but there can be a whole
host of other reasons.
Things get overspecced because the price is too tight to spend time coming up with an efficient design.
Things get overspecced to give some wriggle room when the scheme changes.
Things get overspecced when mistakes are made - Noseall, I'm thinking about those enormous beams in that extension you posted on here a few months ago!
Things get overspecced to allow for a bit of additional safety factor.
Things get overspecced because actually there's no point designing anything any smaller.
But also, often things aren't overspecced at all - designing to the codes just makes it look like they are!
I've designed many many beams & frames for the opening up of rear elevations etc, and on only one occasion have I designed temporary propping. It's usually not part of our remit.
An SE would probably struggle to justify the bearing capacity under an acrow, even with allowing for load spread, they would probably struggle to justify the joists if acting as needles, they would probably struggle to justify the ground floor joists if propping off a timber floor.
The home owner - with an SE design in hand and a liberal covering of PI insurance would end up having pad footings stuck in their garden and their kitchen/diner floor being taken up to get the acrows to the concrete oversite (if there is any).
They'd then have to have 150x75 PFCs threaded through the wall to support the masonry above. The cost of the work would probably double.
In an ideal world every home owner would have the funds to allow every risk to be designed out. In the real world many home owners are happy to evaluate the risk, do a simple cost benefit analysis and allow an experienced builder to get on with their job.
I have to say cAtLeYx, you seem to have a slightly idealistic viewpoint. In an ideal world everything would be done by the book on site, but it isn't, and it probably never will be.
The truth is, overspeccing is endemic amongst structural engineers. Sometimes it's down to inexperience, but there can be a whole
host of other reasons.
Things get overspecced because the price is too tight to spend time coming up with an efficient design.
Things get overspecced to give some wriggle room when the scheme changes.
Things get overspecced when mistakes are made - Noseall, I'm thinking about those enormous beams in that extension you posted on here a few months ago!
Things get overspecced to allow for a bit of additional safety factor.
Things get overspecced because actually there's no point designing anything any smaller.
But also, often things aren't overspecced at all - designing to the codes just makes it look like they are!
I've designed many many beams & frames for the opening up of rear elevations etc, and on only one occasion have I designed temporary propping. It's usually not part of our remit.
An SE would probably struggle to justify the bearing capacity under an acrow, even with allowing for load spread, they would probably struggle to justify the joists if acting as needles, they would probably struggle to justify the ground floor joists if propping off a timber floor.
The home owner - with an SE design in hand and a liberal covering of PI insurance would end up having pad footings stuck in their garden and their kitchen/diner floor being taken up to get the acrows to the concrete oversite (if there is any).
They'd then have to have 150x75 PFCs threaded through the wall to support the masonry above. The cost of the work would probably double.
In an ideal world every home owner would have the funds to allow every risk to be designed out. In the real world many home owners are happy to evaluate the risk, do a simple cost benefit analysis and allow an experienced builder to get on with their job.
Hi Ronny, I have said before, I am a Senior Construction Manager and work for a top 10 national contractor. I have a degree in construction, and am an active member or NEBOSH and a Fellow of the Chartered Institute of Builders (FCIOB). I am currently responsible for projects in excess of 25 million. Life on projects that I am responsible for are fully compliant with all legislation, HSE and particularly with CDM Regulations. These are not idealistic but factual. I fully agree and concur with all comments regarding over designing not just by Structural Engineers but also M&E consultants, etc. CDM regulation 2015 now placing a duty of care for domestic clients and under these new guidelines a temporary works coordinator is a legal requirement. Why should we as professionals not give professional advice. If we suggest for example that 5 props are sufficient we are no better than the local builder who the OP is questioning. Do you not think if a temporary works systems was in place collated by a temporary works coordinator the OP would have never come to this forum. Do we collectively not have a duty of care to offer best practice advise?
People have been propping extensions long before CDM came along and even longer before SE's would get involved.
And 4x2 has, and still is used instead of steel props, by those who know what they are doing.
1 prop per metre is more than enough on domestic opening. It's not particle physics.
And 4x2 has, and still is used instead of steel props, by those who know what they are doing.
1 prop per metre is more than enough on domestic opening. It's not particle physics.
The spacing of a prop or strongboy depends on the type of wall construction among other things. I've done jobs like this on different types of walls such as Bungaroosh, Random stone, 9 inch solid, cavity cement or lime mortar and a judgement has to be made on site. Many of the houses round here are 20 inch stone so require a bit more care when propping.
Correct.
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