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Builder cut 4.5cm off joists due to floor level screw up


Loz
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Having a 2 storey extension done, builders haphazardly measured the floor level and despite saying better to come in under as better to make up height when they knocked through new floor level was good chunk higher - why they didn't knock a pilot hole through despite suggesting it is a mystery.  The second storey and roof is now on and last week whilst I was away they laid new floor, didn't realise just how much higher the new joists were.  The structural engineer had specified 44x195 C24 ceiling joists @ 400mm c/c.  Looks like they have used 8 inch joists a block width apart, to get the floor lower they have cut about 4.5 cm off the joists so the remaining joists are about 17 cm, obviously going to be a nightmare to rectify now, looking at span charts online they are too small.  There is an ensuite and main bedroom going in that room.  Here are some pictures :

 

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Would have been so easy to have come one small brick lower had they measured correctly, very frustrating, what would people recommend in this situation ?

 

Many thanks,

 

Lawrence

 

 

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So, have they ripped the 200mm joists down to 170mm along their entire length?! And at 440mm centres instead of 400mm? I'd be checking with the SE if that's OK... But my gut would be saying it needs to come down and done properly as per the spec.

 

Goes without saying, don't pay any more until it's sorted.

Edited by Conor
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Thanks for quick replies, problem I have is builder is very friendly with structural engineer and the building inspector so guess was after some thoughts before approaching both as likely the builder will convince them they were over specified and is fine, a look at a joist calculator says not.

 

Many thanks,

 

Lawrence 

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Sorry but that’s just wrong ..!! 
 

They need to take the joists out and start again at their cost. Spacing and size are incorrect - the lot needs fixing as it is non compliant. 
 

The quicker way is to get the BCO to agree to a wall plate at the right height using resin bolts and then use timber hangers on the wall plate. The saving grace may be that the cut down joists may fit across the space if the layout allows - it looks slightly less than 4m. 

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1 minute ago, PeterW said:

Sorry but that’s just wrong ..!! 
 

They need to take the joists out and start again at their cost. Spacing and size are incorrect - the lot needs fixing as it is non compliant. 
 

The quicker way is to get the BCO to agree to a wall plate at the right height using resin bolts and then use timber hangers on the wall plate. The saving grace may be that the cut down joists may fit across the space if the layout allows - it looks slightly less than 4m. 

 

Thanks for reply, did forget to mention that the span is 3.8m inside the room and they have gone block width apart rather than 400mm, I just know the builder will convince SE and Buiding Inspector it is fine as has happened with other things on the build but was after a feeling if I need to stand my ground on this one as such a big job to put right or if actually is okay.

 

Many thanks,

 

Lawrence

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Ok so what is the exact span as 450mm which is not a block but near enough with a bit of wiggle, a 170x45 will span 3.83m with a 0.25 dead load. 
 

However as the SEng specced the 44x195 at 400 centres and you are paying for that, then you are within your rights to ask for that. 

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13 minutes ago, Loz said:

Thanks for reply, did forget to mention that the span is 3.8m inside the room and they have gone block width apart rather than 400mm, I just know the builder will convince SE and Buiding Inspector it is fine as has happened with other things on the build but was after a feeling if I need to stand my ground on this one as such a big job to put right or if actually is okay.

 

 

Any floor designer will be able to calculate the deflection of the floor you paid for and the greater deflection of the floor as installed. These are unambiguous numbers that a matey gaggle of the builder, BCO and SE cannot ignore.

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Are the joists resting on a steel beam at the other end? If so is this not set at the wrong height and can it be easily changed? If the steel is at the correct height, I struggle to see how this happened if everything is built correctly square.

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Many thanks for all the replies, just had a very good chat with structural engineer on phone, all previous meetings had been on site with builder present, he ran the measurements and fails the deflection check, he recommended removing the noggins, then screwing/bolting another 170 joist to existing joist cut tight to wall and then putting back trimmed noggins - seems a good solution as doesn't need any block work just additional timber and labour that I will inevitably pay for somewhere else in the build.  Can't picture the other end on the steel as not there at moment and can't remember if joists rest directly on steel, think there is at least one layer of bricks , now have SE on my side can approach builder and see where we go. 

 

Great forum,

 

Many thanks,

 

Lawrence

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Without doubt what they've done is, err... 'unconventional'. But first I'd suggest checking the measurements - looking at pictures 2 & 3, comparing the perps. to the joist spacing, they appear to be less than a block's width apart; the blocks look like they have been cut down narrower, so the joist spacing might actually be 40cm.

 

Also, your calculations - if they have ripped 4.5cm off a nominal 20cm width, that leaves around 15.5cm, rather than 17cm. My tables don't list that as a size - anything less than 17cm effectively becomes the next size down, at 14.5cm. This makes things worse, and may prevent any solution that reuses the timbers.

 

Presumably any solution will mean repositioning that RSJ - or further unconventional unsatisfactory work.

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It is quite hard to understand what happened.  Did they build in the joists and steel, then knock through, then rip 4.5cm off the tops, then fit the chipboard?

 

Surely a plate fixed to the face of the wall at the correct height and some joist hangers would have occurred to them?

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8 minutes ago, Mr Punter said:

It is quite hard to understand what happened.  Did they build in the joists and steel, then knock through, then rip 4.5cm off the tops, then fit the chipboard?

 

Surely a plate fixed to the face of the wall at the correct height and some joist hangers would have occurred to them?

 

Yes that's exactly what they did, rather than measure correctly or knock a pilot hole through they did some half baked measurement and got floor level wrong and then took 4.5cm to correct their error when they knocked through and realised.

 

Lawrence

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You don't have to worry about SE or BI being mates of the builder. 

As a Chartered Surveyor once told me, the only professions that are sworn to honesty and the good of humanity are Doctors and Civil Engineers. 

Your SE is probably also a CE as that is the overall profession before specialising.

The usual accusation against Engineers is of over-design, but that is usually by builders who don't know the theory, and are not insured for the decisions. Anyway he is hardly going to have done that or admit to it.

 

Joists are designed for strength (safety) and deflection (comfort). Might be worth asking if this solution leaves you unaffected.

 

Just make sure that any pragmatic solution doesn't cause any other adverse result. eg putting in electrics and plumbing through double joists.

Can anyone think of any more?

 

10 minutes ago, Loz said:
20 minutes ago, Mr Punter said:

joist hangers would have occurred to them?

 

Clearly not, and the bodge was cheaper, quicker  and easier, and they hoped not noticed.  Are the cut tops level and straight now? Therefore are the boards sitting neatly or perched on small areas of joists?

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4 hours ago, Loz said:

Can't picture the other end on the steel as not there at moment and can't remember if joists rest directly on steel, think there is at least one layer of bricks

 

Is it just this room? If so I'd fix it properly. 

 

If there is no head height issue downstairs I'd knock the bricks off replace with deeper joists resting on the steel. At other end of the room there are ways to fix joists to a wall without having to cut new pockets. For example bolt a timber to the wall using resin anchors and the use joist hangers.  I'm thinking two days work.

 

Knocking out the noggins and sistering the joists will also work fine but its like crashing a car. The insurance co might do a good job of making the damage go away but I can't unknow its happened.   

 

 

 

 

 

 

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25 minutes ago, saveasteading said:

  Are the cut tops level and straight now? Therefore are the boards sitting neatly or perched on small areas of joists?

 

Sounds like a recipe for a creaking floor.

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1 hour ago, Temp said:

 

Is it just this room? If so I'd fix it properly. 

 

If there is no head height issue downstairs I'd knock the bricks off replace with deeper joists resting on the steel. At other end of the room there are ways to fix joists to a wall without having to cut new pockets. For example bolt a timber to the wall using resin anchors and the use joist hangers.  I'm thinking two days work.

 

Knocking out the noggins and sistering the joists will also work fine but its like crashing a car. The insurance co might do a good job of making the damage go away but I can't unknow its happened.   

 

 

 

 

 

 


This is kind of where I am with it as everything is a bit of a bodge now but can pretty much guarantee I’ll be paying anything above the minimum necessary to put it right and in for a battle for builder to accept anything wrong based on previous experience.  The SE mentioned cutting sister joists tight to wall but read that any expansion could knock a block out - what do people think should there be a gap at end of sister joist and wall ?

 

The reducing of the joists looks a hack job and so I can imagine the boards not completely flush although walking on it today didn’t notice any creaking - is that something that would develop in time ?

 

So frustrating as a pilot hole which suggested a number of times would have been so easy.

 

Many thanks,

 

Lawrence

Edited by Loz
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Hello Loz.

 

Sorry to hear about you dilemma.

 

Your starting point here is to take another step backwards and understand what the implications are in terms of what happens to the declared strength of the timber when you rip a bit off the top / bottom / sides along the length.

 

Typical structural timber for extensions and the like comes in grades.. you'll often see it stamped C16 or C24. When it is produced each length is put through a stress grading machine which applies a force. Sensors measure how much the timber bends or if it just snaps. If it comes out the end of the machine with the correct reading it gets a stamp to say what grade it is. Now timber has knots / wane / the grain weaves about and so on. You could say have a piece of timber with two knots near the centre but good grain top and bottom which passes the grading. Cut 40mm off the top and now the knots are in the high stress zone for bending so the timber can fail.

 

In summary if you rip a bit lengthways of a stamped piece of timber the grading is no longer valid. You can notch it but there are rules which apply to where and how much you can notch timbers.

 

Point this out to the SE / BC officer and see if they will still pass the joists given that the stress grading is probably invalid.

 

 

 

Edited by Gus Potter
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13 hours ago, Gus Potter said:

You can notch it but there are rules which apply to where and how much you can notch timbers.

 

I have a formula for calculating permitted notching merely at the end of joists in one of my carpentry books. When I've used it, I've always been surprised by how little can be notched even over a short span.

 

FWIW it actually makes me feel sick to see this kind of practise, which is just unacceptable. It really should be redone properly and I sincerely hope you get it resolved.

 

 

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3 hours ago, SimonD said:

It really should be redone properly

Agreed. Mistakes happen and it is sometimes reasonable to find a solution that does not inconvenience the builder.

However, this is either a deliberate bodge, hoping to get away with it and never mind the consequences to you,  or ignorant of building practices to the extent of worrying about other matters too.

For the sake of amicable  conclusion to the project, it needs SE and/or BCO to instruct that it is done again.

 

I suggest make a list of the worries expressed above and summarise it to the SE, who works for you.
It is not unreasonable to include future squeaking and maintenance, and even worry,  in the list. And would the SE warrant for 10 years please against these minor issues as well as failure?

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Interesting thread, especially the implications on the rating of the timber. looks like a massive bodge job, one that even I wouldn't even do.

 

I would be pushing them to redo properly and it'll be interesting to see what the outcome is.

Edited by Moonshine
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Hello all.

 

A lot of the following is general info which I hope will be of help if your builder has not done what they should have, or "done what they think is helpful"..some builders do this.. believe it or not. There are a lot of young (still some older ones too) builders that are really keen to please and keen to do the right thing. Their heart is in the right place.

 

Yes it's an interesting subject this..for a good number of reasons. Unfortunately for Loz.. it's Loz's house we are talking about / discussing. Loz.. I was prompted to make the post about the timber grade as for me this takes you back to basics, can take heat out of any potential situation. No point in looking at load span tables etc if you have done something that has changed the intergrity / "provenance" of a component on which the load span tables rely on.

 

Loz.. you mention that the SE is friendly with the builder. This is a normal occurence. SE's / Architect's / Designers / M&E specialists and so on like to work with good builders.. and builders like to work with good designers that can resolve; unforseen on site issues, be able to design and specify easily available materials and so on. That eases the way for everyone..

 

Also remember that builders can often be members of professional bodies / have extensive professional knowledge. Just because they may wear "shorts to work" does not mean they are unprofessional or lack knowledge! In fact the last few designers I've talked to have all been in shorts! .. COVID you see.

 

For designers and builders (major contractors too) trust and professional respect for each other is built up over time and this has value. In particular, it often drives down the cost to the Client and this is how you get repeat work and recommendation from a Client. Every one is a winner to some degree.

 

In summary don't worry at this stage that the builder, SE, BC officer may have a good friendly relationship. This is far removed from what we would call a corrupt relationship..for which you can not only be stuck off a professional register but also invite a holiday for yourself at a location chosen by our Monarch.

 

Loz and all. Often you find that you know something is not right.. you just know this as a lay person.. you don't need to be an SE say.. trust your gut and ask questions, as you are doing. Loz, the builder may know that too. At one end they may know about the timber grade etc and just tried to pull the wool over your eyes. If they do know about the timber grading it would be a new thing for me though.. Your SE should have some awareness. At the other end they (builder) may have thought they were doing a good thing and solving problems.. helping you out.

 

@saveasteading

"Agreed. Mistakes happen and it is sometimes reasonable to find a solution that does not inconvenience the builder. "

 

To add a bit to saveasteading's point. I'll use an example, corollary here.  You can often deal with a home warrantly provider who is giving you the "run around". Often you encounter arguements such as "well the cracking you see is visually acceptable" or "some amount of settlement always happens". Dig deep into this and the modern Euro codes introduce a way of designing where deflections and settlements are more open to interpretation provided the structure remains safe! What this means is that often the domestic home owner has an expectation that is not met.. the developer/ builder is off the hook to a large extent unless the home owner is willing to spend a lot making a counter argument.

 

Loz..you could find yourself in the position where the onus falls on you to make the case showing that you may have a "bouncy floor" and or a ceiling that cracks in a few years time for example.

 

One key to unlocking this is to find something that you can point to that has compromised the structural safety. This is non negotiable as it is a UK legal requirement.  Nail this and you often find that all the other arguments made become mute. This gives you the big stick as often to fix a structural safety issue you have to strip out and reinstate. Basically you cut the feet from under them.

 

Loz in your case this timber grading thing may be the key to resolving this. Now you have the big stick and you can decide how to use it. But go gentle, particularly if it's been a genuine mistake. Always remember that if you use the stick half way though a project then if you make a mistake later then the builder etc will probably return the favour with a bit extra! Always ask yourself "what is fair and reasonable behavour? Be wise.

 

Loz..Here are a some choices the SE may have.

 

1/ Be competant to visually grade the timber in it's cut down state (old school stuff but can be done still), recheck the strength / deflection which will now probably fail on overall deflection and look at the vibration. Then produce the calcs and evidence followed by sign off.

2/ Get a certified person from a timber merchants / producer  (grade it and then perform the above checks) to do it for them.. the rub will be to make sure that the visual grading will still also be CE compliant.. good luck to the SE on that one.

3/ Chuck in the towel and look for another solution.

 

Loz.. as promised.. here is something worth exploring. If you can accept a small reduction in the ceiling height then bolt onto the sides of the joists you have new 195 x 45 timbers. Alternate which side you bolt the timbers to. Bolt them all the same, say on the left hand side and you will get a rolling effect which is not desirable. Your SE should know this but the builder possibly won't. For the technically minded this rolling effect will happen as you shift both the centre of gravity of the section and the shear centre of what is now a composite section.

 

Loz looking at the floor you have the joist sizing is probably governed by what we call the bending moment and deflection. In other words are the joists strong enough in the middle not to snap under load as they get bent and are the joists stiff enough so that the floor does not bounce too much. Where the joists frame into the supporting walls then you have what is called "shear effects".

 

There is a good chance that the SE can show that at the ends of the joists they will still be ok in shear even though they have been effectively notched on top.

14 hours ago, SimonD said:

 

I have a formula for calculating permitted notching merely at the end of joists in one of my carpentry books. When I've used it, I've always been surprised by how little can be notched even over a short span.

 

 

 

Simon mentions this too but unless you have some other loads acting on the floor from above it all may be fine when the SE checks the shear at the joist ends.

 

To expand on other posts on doubling up joists and so on. On the practical side when you offer up the new joists put plenty glue on the top side so they stick to the flooring . Now get the builder to run upstairs and screw the flooring to the new smooth surface of the extra joists before the glue takes up.. this will mitigate the squeeks. Yes, you'll need new noggings mid span (dwangs) but that is a small price to pay.

 

I think you could resolve this fairly easily. It won't cost too much cf knocking holes in the masonry, potential disturbance to the masonry, lifting the floor and so on.

 

Often the key here is to find the big stick. Show you have one and avoid using it, mainly because you often still need to finish the job. Also, if your builder has just made a genuine mistake then it's a fair and moral thing to do.

 

Lastly Loz if your SE comes back and says the joists are failing at the ends due to shear then there are other options open such as using a ledger piece and so on.

 

To finish on a positive note. Many projects encounter problems which can be resolved with a will and in an equitable way.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited by Gus Potter
Left handed you see can't spell! Ok with maths
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