Floor joists - extending them

[C Lee Farquar]

Griff Boy said:

When we had to replace the joist ends due to rot damage, we extended them approx 25cm, longer in other places. Overhung the original joist by a minimum of a metre, and used at least 4 bolts, sometimes 5 or 6, always with spiked washers and also washers on the outside faces of the timber, all fixed with an impact driver.

Is that dry rot or big cobwebs?

[Spudler]

Mojooo said:

Busa mav said:

Hopefully , the bolts have not been set out in a straight line along the centre line of the joists.

Yes they have.

st, if he's that retarded I'd keep a very close eye on any other work he carries out.

[Busa mav]

Spudler said:

Mojooo said:

Busa mav said:

Hopefully , the bolts have not been set out in a straight line along the centre line of the joists.

Yes they have.

st, if he's that retarded I'd keep a very close eye on any other work he carries out.

Give him some credit spudler , they have been spaced at 75 mm ctrs.

[Spudler]

Busa mav said:

Spudler said:

Mojooo said:

Busa mav said:

Hopefully , the bolts have not been set out in a straight line along the centre line of the joists.

Yes they have.

st, if he's that retarded I'd keep a very close eye on any other work he carries out.

Give him some credit spudler , they have been spaced at 75 mm ctrs.

Can almost hear the timber splitting as the nuts are tightened.

I think some of the posters above are referring to fixings in a straight line.

Griffs got it right.

[Mojooo]

Problem is - as someone else has pointed (in real life not on PH) out to me is that you can speak to 5 buildersand get 5 opinions on how things could be done. As demonstrated here.

What I need is some firm guidance on how it should/must be done.

[Spudler]

Mojooo said:

Problem is - as someone else has pointed (in real life not on PH) out to me is that you can speak to 5 buildersand get 5 opinions on how things could be done. As demonstrated here.

What I need is some firm guidance on how it should/must be done.

Have a look at Griffs pics. That's how a BC officer will want to see it.

[C Lee Farquar]

Mojooo said:

What I need is some firm guidance on how it should/must be done.

That's firmly in the remit of a structural engineer, but you say you've already had one look?

[Mojooo]

C Lee Farquar said:

That's firmly in the remit of a structural engineer, but you say you've already had one look?

Yea, and he is an old hat.

This is the only concern I have amongst all the work that is going on.

He said what I have is already more than what is needed!

Maybe there is a conflict thre visually between what looks like enough and what is enough - i.e mayb 1m makes me feel more comfortable but isn't needed. Of course as a customer I want it belt and braces not bare minimum.

Again though unelss there is guidance on it it could come down to structural engineers opinion?

Does building cotnrol guidance/legislation cover this? If not is the building control person also an engineer?

[Busa mav]

I would expect the building inspector to ask for some calcs from the engineer to justify his opinion.that it is fine.

[TA14]

Mojooo said:

Can you point out which specific aprt of the code covers my issue?

Assuming that the number of bolts/toothed connectors is OK then look at the end/edge distances. Section six for joints and it's around table 80, check for bolts and toothed connectors.

Mojooo said:

The blockwork is almost up to the heigh of the joists - and it will be built around the extensions - but I suppose if in the future they need to come out the old ones could be taken out and the new ones slot in?

You want to avoid that. New joists now is easy: fit on beam, screw down from above and add noggins. Leave the existing joists in place; it's more trouble than it's worth to replace them.

Mojooo said:

I think I will nudge building control to provide a comment on it.

they (BC) will just:

Busa mav said:

ask for some calcs from the engineer

so you'll need a structural engineer rather than employing

Mojooo said:

a surveyor.

to tell you that you need calc from a SE.

Mojooo said:

What I need is some firm guidance on how it should/must be done.

Your problem there is that there a many correct ways and even more incorrect ways.

Mojooo said:

Again though unelss there is guidance on it it could come down to structural engineers opinion?

Ultimately the guidance is the opinion of a SE.

Mojooo said:

Does building cotnrol guidance/legislation cover this? If not is the building control person also an engineer?

Yes. No, although it is possible. A job needs building control approval. Non standard structural stuff or stuff which people argue over will be checked. Typically the council will refer the job to a SE and ask the developer/applicant for calcs to justify the detail. The calcs would normally be to the British Standard/Eurocode (the council can insist that they are to the eurocode) unless the engineer can justify a departure to the the council's engineer. So ultimately it comes down to the opinions of two engineers unless you take the view that it's really the BCO final decision but it would be rare for the BCO to ignor the engineer's advice.

[TA14]

Mojooo said:

Maybe there is a conflict thre visually between what looks like enough and what is enough - i.e mayb 1m makes me feel more comfortable but isn't needed. Of course as a customer I want it belt and braces not bare minimum.

I think that this is probably the nub of the matter. It's your house. Just fit some new joists, if it's ten joists at say £10 per joist plus say £10 to fit then that's £200 or if on a hit and miss basis it's £100. Do you want to pay a bit extra to sleep easy? If you start paying surveyors/SEs etc. you'll soon burn through that much money.

[Mojooo]

New joist can't cost £10?

I presume you are talking about the whole actual bit of wood that goes from one side to the other. The house has about 20 in total (although they split in the middle of the house as they are held on a steel) - I imagine it would cost a fortune to repalce them.

[TA14]

Mojooo said:

New joist can't cost £10?

Depends what deal you can get. I've just bought 3.6m 175x50s for that price.

Mojooo said:

I presume you are talking about the whole actual bit of wood that goes from one side to the other.

or in your case from the steel to the area where you will have a block wall.

Mojooo said:

I imagine it would cost a fortune to repalce them.

depnds how you define a fortune. Put your own figures in and see how it compares to the cost of hiring professionals for reports and the stress of dealing with it all now and the stress of worrying about it forever more. New joists onto an exposed steel beam and resting on a yet to be built block wall are a very easy fix.

[Fastpedeller]

TA14 said:

Mojooo said:

New joist can't cost £10?

Depends what deal you can get. I've just bought 3.6m 175x50s for that price.


Do they have to be 'certified' as knot-free and from a joist supplied with a certificate?
If so I imagine they'd be more than a tenner.

I agree with the above though - look at cost of options, as whole replacement may indeed be favourable compared with all the mods and cost of professionals?

[Mojooo]

OK just to bump this.

Engineer is saying it is OK.

I had 2 builders look at it and whilst they say they would have made it meatier they say if the SE OK's it then they wouldn't argue.

BC has asked for drawings but generally the BC isn't showing much concern. I think he is just trying to keep his nose out of it - but he said the drawings will be checked out by the councils own engineer.

All of the work has now finished and whilst I am generally happy in the main I have noted that some of the joists are not level - this means the floor above is not flat. I have just raised this with the buidlers so will wait to hear back. BTW I don't mean a slope - I mean like a bump where one/two are too high. One of the joists is above a downstairs wall and has always been the same height - I suspect some of the new joists have fallen below this level.

I do wonder if new joists will now be needed as I cannot see how they can easily remedy this! The joists have all been set into the blockwork.

I think what has happened is that whilst the joists were being extended they have sagged and the floor now is not totally flat - although the joists did look level from outside when set in the blockwork. They look reasonably level from the underside until you go upstairs and see the way the floor is - when you come back and look at the joists from underneath you can see the problem.

I can't see how the uneven floor I have is acceptable though.

Problem is my upstairs walls are all built on the floorboards so it would be a hassle to take the (block) walls out and the floorboards - do it all and put it back. That said I iamgine 2 brickies could put all the walls back up within a day or 2.

What a faff!

How hard is it to put new joists in? I spsoe they can re-use the notches in the blockwork.

What about joist hangers - do they do the same thing but let you put it into the block directly?

Edited by Mojooo on Monday 17th November 03:59

[TA14]

Mojooo said:

What about joist hangers - do they do the same thing but let you put it into the block directly?

Yes. As long as the ceiling is not there it's quite easy to add a joist.

[Mojooo]

I spose my only problem is that they built my house and left holes specifically for joists to go into - so better off using them as I sort of have a bloc / half a block gap / block / half a block gap - scenario - so at the first floor level the blocks do not go all the way across the house - so best off using the holes already there as much as possible.

Anyone recommend an engineer in south Hampshire? I may need a 2nd opinion on this!

[V8RX7]

Just bumping this as I'd agree with posters who have mentioned staggering bolts top and bottom (obviously not close to the edge)

I've come across this NHBC Tech Guidance tonight

Question
Can coach bolts be used to fix multiple joists together and, if so, which methods of installation are acceptable?

Considerations
NHBC Standards clause 6.4-S7 refers to the use of bolts for fixing multiple joists together.

Answer
Coach bolts can be used to fix multiple joists together. They should be on the centre line at approximately 1m
centres.

[Mojooo]

OK so I have spoken to a builder friend. We discussed the floor and we reckon some of the joists are not totally level. The issue is what to do about it.

I am not really happy going for some bodge job fix - but the alternative if taking out all the joists is pretty extreme as it would involve taking of floorboards and possibly the upstairs walls!

[anonymous-user]

It is possible that when the new sections of joists were scabbed on the end, the joint has allowed a little bit of rotation between the new and old and that has caused the floor to deflect slightly. As you say, the high spot is over a wall below and has been 'held up'.

If it were me, I would have demanded new joists almost the full length sistered against the existing. That way, the fixings between the new and old are having to work less hard and it would have resulted in a stronger more stable floor.

At this point, if it can be determined that the sag in the floor is as a result of movement at the joint between the new and old sections of joists, I would be asking for new full length joists to be fitted.

An overlap of 100mm on a 4-5m span is way too small.

Edited by anonymous-user on Thursday 20th November 08:52