Large cracks appeared during RSJs installation

[tony1851]

It needs to be established whether the cracking is caused by insufficient propping (builder's fault) or excessive deflection of the beams (SE's fault). Until that is determined by an independent person, the OP won't know who to chase.

It has been pointed out that there seem to be too few strongboys for the span, and also that they appear to be on the outer skin, and so probably giving minimal support to the inner skin. The inner skin is usually the more heavily-loaded, so the strongboys would be better internally, assuming adequate support off the floor could be provided.

The two main beams look to be 203 x 133? It is always a potential problem when an incoming beam is fixed to the inner of the two long beams because it produces a high point load on the beam, which increases deflection.

The two main beams are bolted together but - although often specified by the SE and asked for by B/C- the method is ineffective because it does not allow the beams to work as one (it is actually prohibited by the BS Code for steelwork). Consequently, the inner beam does most of the work and will always tend to deflect more. A better solution here might have been to use one main beam - a 203 x 203 with a plate tack-welded on top to carry the cavity wall. In this case, the wide-flange beam would be far better than two narrow beams at withstanding the differential loads between each skin. Trouble is, for the builder, two lighter beams are easier than one heavy beam.

 

[leaf17]

It needs to be established whether the cracking is caused by insufficient propping (builder's fault) or excessive deflection of the beams (SE's fault). Until that is determined by an independent person, the OP won't know who to chase.

It has been pointed out that there seem to be too few strongboys for the span, and also that they appear to be on the outer skin, and so probably giving minimal support to the inner skin. The inner skin is usually the more heavily-loaded, so the strongboys would be better internally, assuming adequate support off the floor could be provided.

The two main beams look to be 203 x 133? It is always a potential problem when an incoming beam is fixed to the inner of the two long beams because it produces a high point load on the beam, which increases deflection.

The two main beams are bolted together but - although often specified by the SE and asked for by B/C- the method is ineffective because it does not allow the beams to work as one (it is actually prohibited by the BS Code for steelwork). Consequently, the inner beam does most of the work and will always tend to deflect more. A better solution here might have been to use one main beam - a 203 x 203 with a plate tack-welded on top to carry the cavity wall. In this case, the wide-flange beam would be far better than two narrow beams at withstanding the differential loads between each skin. Trouble is, for the builder, two lighter beams are easier than one heavy beam.

Thanks for the details, Tony. What would you recommend as next steps? I've shared my concern with our builder but as expected he's played it down and says it just needs plastering over... Don't fancy shelling out for a structural engineer myself but seems v. unlikely that our builder will foot the bill. Would it be worth talking with building control on this if I get chance?

Cheers
Jack

 

[Celeronmanuk]

Thanks for the details, Tony. What would you recommend as next steps? I've shared my concern with our builder but as expected he's played it down and says it just needs plastering over... Don't fancy shelling out for a structural engineer myself but seems v. unlikely that our builder will foot the bill. Would it be worth talking with building control on this if I get chance?

Cheers
Jack

Personally I think I'd be looking to get a structural engineer to look at it. It's not going to cost much compared to what you're spending on the extension and the value of your house. I wouldn't be happy with that level of cracking and just plastering over.

 

[GoodDIYjob]

I agree with the comments made. On the money I reckon.

To give the OP an opportunity to sit back and assess things, I had similar openings in the rear of our 1930s semi in 2018.

I also was not happy with the propping (using a few strong boys while demolishing), the approach, and some cracking in an upstairs bedroom which was catilevered above the new opened up area and then the extension further out, it was effectively held up by beams on two sides.

When I inspected closely, and probed with some welding rods left lying around, (my builder also did not strip enough of the ceiling to properly view or support beams or make good wall support), I noticed the whole inner course of the upstairs brickwork virtually the entire length of the two sides of the b room wall was left "floating" above the steel beam.

I went mad. The builder said he did the installation with his mate and it was all properly bedded in by the muck sitting on top of the beam when it was genie lifted up!. Even with me showing him I could insert bent welding rods at almost every position to the outer skin, he still said it was all fine!

In the end, as I refused to leave it, he removed the skirting boards in the upstairs bedroom with some plaster cracking damage (not as bad as yours but similar). It revealed the extent of the problem. He rebedded in from the bedroom. To say I was disappointed and let down was an understatement. Things were a bit difficult already due to workmanship, my blockwork looked worse than yours, but from that moment I could not trust a word he said.

Due to the vulnerable state and the difficulty in getting another builder (and two young children needing to get the house together) and the contract issues, I employed a supervising RICS surveyor and let the builder finish the structure (their recommendation). I would of preferred not to, but the surveyors said that problem was rectified now - move on, his work wasn't fantastic but not dire either. I didn't agree.

Anyway, I patched up the bedroom plaster as part of a quick redec. 2 years on it hasn't worsened and even with a little light filling they haven't opened up again. Luckily there doesn't seem to be any structural issues remaining. But I spent two months tidying up and making good after the builder left. Luckily the surveyors were fed up with the builder in the end and agreed it would be best to get rid of him for carpentry finishing so I got my own and I filled in the "gaps" in making good!

May possibly make you feel a little better OP that it can work out even with problems. But I am older and wiser as a result and now more grey hairs than not now...

 

[Celeronmanuk]

I agree with the comments made. On the money I reckon.

To give the OP an opportunity to sit back and assess things, I had similar openings in the rear of our 1930s semi in 2018.

I also was not happy with the propping (using a few strong boys while demolishing), the approach, and some cracking in an upstairs bedroom which was catilevered above the new opened up area and then the extension further out, it was effectively held up by beams on two sides.

When I inspected closely, and probed with some welding rods left lying around, (my builder also did not strip enough of the ceiling to properly view or support beams or make good wall support), I noticed the whole inner course of the upstairs brickwork virtually the entire length of the two sides of the b room wall was left "floating" above the steel beam.

I went mad. The builder said he did the installation with his mate and it was all properly bedded in by the muck sitting on top of the beam when it was genie lifted up!. Even with me showing him I could insert bent welding rods at almost every position to the outer skin, he still said it was all fine!

In the end, as I refused to leave it, he removed the skirting boards in the upstairs bedroom with some plaster cracking damage (not as bad as yours but similar). It revealed the extent of the problem. He rebedded in from the bedroom. To say I was disappointed and let down was an understatement. Things were a bit difficult already due to workmanship, my blockwork looked worse than yours, but from that moment I could not trust a word he said.

Due to the vulnerable state and the difficulty in getting another builder (and two young children needing to get the house together) and the contract issues, I employed a supervising RICS surveyor and let the builder finish the structure (their recommendation). I would of preferred not to, but the surveyors said that problem was rectified now - move on, his work wasn't fantastic but not dire either. I didn't agree.

Anyway, I patched up the bedroom plaster as part of a quick redec. 2 years on it hasn't worsened and even with a little light filling they haven't opened up again. Luckily there doesn't seem to be any structural issues remaining. But I spent two months tidying up and making good after the builder left. Luckily the surveyors were fed up with the builder in the end and agreed it would be best to get rid of him for carpentry finishing so I got my own and I filled in the "gaps" in making good!

May possibly make you feel a little better OP that it can work out even with problems. But I am older and wiser as a result and now more grey hairs than not now...

Very similar situation here! Inner skin was left floating which I packed in the end after removing skirting. Just one very small crack fortunately. Didn't carry on with the builder and finishing the project myself now bringing in trades as needed.

 

[Celeronmanuk]

.

 

[leaf17]

Thanks very much all for your feedback, it's been extremely helpful.

I managed to grab building control when they came round yesterday and, along with my builder, we had a proper look at the cracks. Building control concluded that they're happy that the crack is aesthetic but that for a 'belt and braces' approach, our builder will need to insert some straps and fix in place with resin before plastering over. So, good news!

Thanks again,
Jack

 

[Celeronmanuk]

Is a building control officer qualified to access cracking?

 

[tony1851]

Is a building control officer qualified to access cracking?

Depends on how serious the cracking is.
Most cracks occurring upstairs after beam installation below turn out to be annoying in terms of filling and re-decoration, but usually not a serious structural issue.
Agreed in this case that it looks as though the builder should have taken more care when propping.

 

[Notch7]

I like the 3 inch thick perps on the one course of that block wall

Somebody couldn't be arsssed to cut the blocks...."I'll stretch the joints a tad.....a big tad.