Floor joists - extending them

Floor joists - extending them

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Mojooo

Original Poster:

12,668 posts

179 months

Saturday 4th October 2014
quotequote all
Question for a surveyor/structual engineer.

Existing house. The entire front and back wall had to come down. New walls will be set out 15 cm further out than old walls so the floor joists need extending. The extended bit will then sit on the block wall.

This will be done by adding wood to the existing joists and bolting them together.

The work has already been done but before I get it checked over I wanted to see what people thought were required in terms of

a) how much overlap should there be between new and old wood
b) how many bolts used to connect them together

Concern at the moment is that the new wood is not connected to the old wood solidly enough but builder saying its fine and more than strong enough, I think problem is visually it doesn't look like much but stricturally it may be fine.

akaAlso

38 posts

131 months

Saturday 4th October 2014
quotequote all
It depends on the size and span of the floor joists. Definitely engage a structural engineer to specify the connection for you - they could probably do this remotely if you send photos and dimensions.
If you haven't already - get Building Regs consent. You can't use an Approved Inspector since work has commenced. Your Local Authority might accept a Building Notice as work is not covered up yet, otherwise it would have to be a Regularisation - but doing it now saves having to reopen up the work years down the line when your house sale falls through due to lack of the necessary paperwork

Renovation

1,763 posts

120 months

Saturday 4th October 2014
quotequote all
What has he done and what is the span ?

At least we can then take an educated guess as to whether you ought to be worried.

On a 4m span I'd want at least 2' overlap and 4 bolts with spiked washers.

Mojooo

Original Poster:

12,668 posts

179 months

Saturday 4th October 2014
quotequote all
Its a complicated situation........

I would say the span is approx 4 or 5m without measuring - one end is sat on an RSJ type thing which is in the centre of the house - there are then joists going the other way to the back. So RSJ on one end and blocks on other.

Builder one - the overlap is about 30cm on some (some are longer) with 3 bolts close together.

This builder was sacked for various reasons including poor workmanship and time delays

Buidler two - he came in to carry on the work - he says the above is OK but he also had to do some joists and he did them about 100cm overlap with 2 bolts.

Whilst I was getting quotes to have other unrelated work done a couple of buidlers who came on site mentioned that they thought builder ones work was maybe not ideal (i.e not long enough).

A strutural engineer has looked at builder ones work. His view is that it is fine. He mentioned something like the overlap just has to be twice what the extension is - so if the extension is 15cm then 30cm is enough. (but bear in mind visually 30cm overlap over 4m looks like nothing)

Builder two has a vested interest in not going back and altering builder ones work as it will cost him time/money.

The surveyor - although he is OK I am not convinced he is totally impartial as he is paid for by the company I contracted with (they sub contracted teh building work out and organsied the surveyor). So again he may not wnat to create hassle by asking them to go back and change something.

My doubts are for the following reasons
1) what other buidlers have said (who are definitley independent)
2) visually it doesn't look amazingly solid (but I am not expert)
3) quetsions over whether builder and surveyor are happy to do the bare minimum.

Essentially I just need to know what has been done is OK even if it is not belt and braces over the top quality.

My own way of doing it owuld probably to have used 100cm overlap with 3 bolts - so not far off above poster)

I do trust the surveyor but my mind is saying to get a second opinion.




Spudler

3,985 posts

195 months

Saturday 4th October 2014
quotequote all
Mojooo said:
My own way of doing it owuld probably to have used 100cm overlap with 3 bolts
This, but with six bolts, spiked washers and D4 or Gorilla glue.
Personally I'd say 300 (even if specced) is nowhere near enough.

Mojooo

Original Poster:

12,668 posts

179 months

Saturday 4th October 2014
quotequote all
Do you have to use spiked washers? Or just belt and braces?

I have seen that the new builder (buidler two) has used them

As for the old stuff done by builder one, i can see one or two joists where the has used them but only because the wood hasn't totally joined together as you can kind into the gap and see the joist conenctor in the middle - but they are bolted together solidly. The others are together so I assume they were used but wont know unless we take em off.

Neil - YVM

1,310 posts

198 months

Saturday 4th October 2014
quotequote all
Spudler said:
Mojooo said:
My own way of doing it owuld probably to have used 100cm overlap with 3 bolts
This, but with six bolts, spiked washers and D4 or Gorilla glue.
Personally I'd say 300 (even if specced) is nowhere near enough.
6 may be belt and braces, but it would defiantly use more than 2.

Definitely must use spiked washers.

Are building control happy to sign it off with only 300mm overlap?

OP, why would builder 2 be responsible financially for 'correcting' builder 1's previous work?
I have been involved in a couple of projects where we have had to correct previous work, and all of that was chargeable.

Little Lofty

3,275 posts

150 months

Saturday 4th October 2014
quotequote all
I would have gone at least 1.0m or possibly a bit more, in the scheme of things considering it sounds like a big job an extra £50 or so for timber would hardly of broke the bank, I'd ask the building control officer what he thinks.

Renovation

1,763 posts

120 months

Saturday 4th October 2014
quotequote all
My understanding is that spiked washers simply prevent squeaking which you may get from movement as typically the drilled holes aren't that tight to the bolts.

Obviously the more bolts the less the chance of movement.

Two bolts and no spikes = increased chance of squeaks


SAB888

3,231 posts

206 months

Saturday 4th October 2014
quotequote all
I'd also overlap by 900mm to 1000mm. The spiked connectors will give a much better grip between the two joists and help stop any movement. They also provide grip over a much larger area than using flat washers and bolts. A structural engineer is the best bet for accurate information and it all depends on sizes and spans.

TA14

12,722 posts

257 months

Saturday 4th October 2014
quotequote all
Renovation said:
On a 4m span I'd want at least 2' overlap and 4 bolts with spiked washers.
Sounds good. I would have said 2'6".

Mojooo said:
Builder one - the overlap is about 30cm on some (some are longer) with 3 bolts close together.
I would have said that that seems a little short however it maybe touch and go to the code:
https://www.google.co.uk/url?sa=t&rct=j&q=...
Mojooo said:
Buidler two - he came in to carry on the work - he says the above is OK but he also had to do some joists and he did them about 100cm overlap with 2 bolts.
Hmmm. Check by calcs. Maybe add extra bolts/joists.
Mojooo said:
A strutural engineer has looked at builder ones work. His view is that it is fine. He mentioned something like the overlap just has to be twice what the extension is - so if the extension is 15cm then 30cm is enough.
Two possibilities here: you've misheard/understood him or he's not a SE: 25mm extension so 50mm overlap is non-sense and so is 1,500 extension so 3,000 overlap.
Spudler said:
Mojooo said:
My own way of doing it owuld probably to have used 100cm overlap with 3 bolts
This, but with six bolts, spiked washers and D4 or Gorilla glue.
Personally I'd say 300 (even if specced) is nowhere near enough.
If you have to do this much you wonder whether it isn't easier to install new joists. In fact new joists is probably easier a lot of the time.

Edited by TA14 on Monday 6th October 08:29

Mojooo

Original Poster:

12,668 posts

179 months

Saturday 4th October 2014
quotequote all
BC have been but I am not sure whether his view is on the joists as I ahvent seen him face to face myself yet. AFAIK he has not raised any cocnerns.

My contract is with company A and they have hired builder one and buolder two - to be fair when buidler one caused problems they binned him and bought in builder two (at a lot of cost two them) - buidler two has been fine in terms of block/brickwork but I still have niggles about the joists.

I don't he wants the hassle of putting new joists in - yes he could do it and get paid but I don't think he wants to.

At this stage as the builder and surveyor both say it is OK then unless I get another surveyor I will not be able to convince company A to change it.

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

Mojooo

Original Poster:

12,668 posts

179 months

Saturday 4th October 2014
quotequote all
Can you point out which specific aprt of the code covers my issue?

anonymous-user

53 months

Saturday 4th October 2014
quotequote all
Photo?

Griff Boy

1,563 posts

230 months

Sunday 5th October 2014
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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.


Spudler

3,985 posts

195 months

Sunday 5th October 2014
quotequote all
TA14 said:
Spudler said:
Mojooo said:
My own way of doing it owuld probably to have used 100cm overlap with 3 bolts
This, but with six bolts, spiked washers and D4 or Gorilla glue.
Personally I'd say 300 (even if specced) is nowhere near enough.
If you have to do this much you wonder whether it isn't easier to install new joists. In fact new joists is probably easier a lot of the time.
Installing six bolts, washers and squirt some glue about hardly equates to a lot of work rolleyes
I'm assuming the OP has weighed up the options of extending Vs replacing.

Busa mav

2,556 posts

153 months

Sunday 5th October 2014
quotequote all
300mm sounds inadequate. not enough space for the required amount of bolts either and they will also be too close to the joist ends.

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

Fastpedeller

3,848 posts

145 months

Sunday 5th October 2014
quotequote all
Neil - YVM said:
6 may be belt and braces, but it would defiantly use more than 2.

Definitely must use spiked washers.
6 bolts may be far too many also? I'm no expert, but would have thought there is maybe an 'optimum' number/distance apart for bolts and that 'too many' or too close together could mean the wood will split between them. Just a thought.

ATTAK Z

10,593 posts

188 months

Sunday 5th October 2014
quotequote all
Fastpedeller said:
6 bolts may be far too many also? I'm no expert, but would have thought there is maybe an 'optimum' number/distance apart for bolts and that 'too many' or too close together could mean the wood will split between them. Just a thought.
That's a good thought ... timber design is all about the strength of the joints

Mojooo

Original Poster:

12,668 posts

179 months

Sunday 5th October 2014
quotequote all
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.

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

Otherwise I will have to fork out for a surveyor.