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PostPosted: Thu May 04, 2017 11:26 am 
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CoxHQ wrote:
Thanks Davyp1,

I'm going to bite the bullet and take down the ceiling and prop from below as you all recommend, although I will still only be able to support joist number 2 from above. Thank you for your sketch, is there any disadvantage to bolting on another piece of timber inline with the cut joist (as in my diagram) in order to use the same hole in the brick?


Hi CoxHQ,

Just to answer your questions.
My sketch is the way I have always done it and as I was shown many years back.
Although Ajay is correct in stating that the overlap has to be 1200mm or more. Doing it the way your proposing would double the required overlap to 2400mm.
Not practical I think! I'm a Yorkshire man, and to me doing it your way would be chucking money away on timber!
Don't let the new holes worry you, they will only take a few minutes each using a bolster and lump-hammer!
Now lastly, a point ajay has made. "If it is to be a bathroom, then the joists need to be doubled up".
This statement covers the additional work the joists have to do when fully loaded by a full bath!
If it helps, I would add that I personally would not be doubling them up. That being based on the logic of the fact that the existing joists had worked under the applied load for years and latterly in their weakened state!
But of course, the choice is yours.

Cheers mate . .


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PostPosted: Fri May 05, 2017 7:20 am 
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Thanks ayjay, that will make life easier supporting around the shower. The bathroom is 1800 wide, is option 'A' what you mean by a 1200mm overlap?

Thank you davyp1, I'll knock out new holes and stagger the joists, and I too am a Yorkshire man! So maybe I'll save on the extra timber. I'll treat the cut ends and use treated timber, they're 2x7 (appart from Joist 4 which is 2.5x7) Here are my two options then.

Thank you again for your help.


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PostPosted: Fri May 05, 2017 9:35 am 
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CoxHQ wrote:
Thanks ayjay, that will make life easier supporting around the shower. The bathroom is 1800 wide, is option 'A' what you mean by a 1200mm overlap?



Option *A* shows a 600mm overlap.

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PostPosted: Fri May 05, 2017 9:46 am 
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ayjay wrote:
CoxHQ wrote:
Thanks ayjay, that will make life easier supporting around the shower. The bathroom is 1800 wide, is option 'A' what you mean by a 1200mm overlap?



Option *A* shows a 600mm overlap.


Ahh, I see! Thanks ayjay. Option B it is then.


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PostPosted: Thu May 11, 2017 7:44 pm 
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I'll just say follow the advice here about the bolting up , I've done that method myself on numerous occasions but I have had other experiences too although they're not applicable in this situation. For example I've had to cut a vertical slot in a timber to let in a steel plate which was then bolted and voids filled with resin but one of the strangest floors was at Wollaton hall in Nottingham . It was a Chinese lattice construction which I can't say I knew anything about beforehand but I learnt all about it over the course of six months or so. Essentially not a single piece of timber spans between the walls , they're only about two thirds to three quarters of the span but are all connected by trimmers. Say joist 1 and 3 span 2/3 from the left and have a trimmer at about 1/3 of the span into which joist 2 is fitted. Joist 2 has a similar trimmer between itself and joist 4 and joist 3 is fitted to this and so on. But this is only just a piece of information , a recounting of my experience , rather than advice of how to do it.



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PostPosted: Sat May 13, 2017 12:18 pm 
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Thanks Grendel, Sounds like an interesting way of doing it. Would it have been done that way for design or structural reasons?

I'm taking down the ceiling today. We've ordered the timber to be delivered and I was just looking into quantity of bolts and washers needed. Incidentally I hadn't mentioned before that the upstairs wall is actually sat on top of the joists with the down staris wall set back approximately 300mm. I was surprised to see that a brick wall wasn't supported from underneath but as davyp1 said it has been like this for 80 odd years. Do you think I'm ok with x8 bolts per joist if I'm using dog tooth washers too?


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PostPosted: Wed May 17, 2017 5:14 pm 
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we generally put a bolt every 400mm or so which should help you calculate the numbers. However , we also tend to space them more regularly along the length rather than in pairs as you show in your last drawing . Not in a straight line either , staggered above and below a central line. If it's impossible to get a drill in between the joists to drill a hole square with the face we would also drill alternatively from each side so all the bolts aren't in the same plane.
With regards to the lattice floor I reckon it was design more than anything else , showing off something rare as we were told there's only three or four similar floors in the whole of Europe . There were elements which I argued were structural in context , although the architect couldn't see it , but either way it became structurally compromised and in the 1950's steel bailieys were put up above it to suspend the floor from.



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PostPosted: Fri May 19, 2017 1:14 pm 
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Thanks again Grendel, the timber is on its way. Just have to find a spare weekend now. Do you think I'd get away with M10 bolts as opposed to M12? My auger set jumps from m10 to m13 for some reason.


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PostPosted: Fri May 19, 2017 6:51 pm 
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Probably although we've nearly always used 12mm or larger , I think 25mm was about the largest but then the timbers were heavier too. To be honest I'd stick with the 12mm and use the 13mm bit , it's neither here or there really and the allthread may even be 1/2" which is nearer to 13 anyway (12.7mm to be more pedantic) . One other thing I forgot to mention is to get some large washers to go with the bolts , we generally used the square ones . This tends to stop the nut sinking into the timber when tightening up.


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PostPosted: Sat Jul 01, 2017 9:47 am 
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I'm finally getting around to doing this this weekend. A couple of final questions - The new Joists are treated, but is there any harm in SBR-ing the ends too? Just to give them a little extra waterproofing in the walls. And also when I knock out the bricks for the new joist pockets can I then cement-in the new joists or do I need to leave an air gap around them.

Thanks again.


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PostPosted: Sat Jul 01, 2017 3:15 pm 
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CoxHQ wrote:
I'm finally getting around to doing this this weekend. A couple of final questions - The new Joists are treated, but is there any harm in SBR-ing the ends too? Just to give them a little extra waterproofing in the walls. And also when I knock out the bricks for the new joist pockets can I then cement-in the new joists or do I need to leave an air gap around them.

Thanks again.


Yes, it is good practice to treat all cut end-grain of joits.
Also, a lot of people advocate wrapping the joist end going into the wall with DPC. You need to wrap the end tightly and fold in the ends at the end of the joist like you were wrapping a parcel. Then cloce nail round the edge of the DPC with short Clout nails.

No air gap, you morter the joist in fully.

davyp1


Last edited by davyp1 on Sat Jul 01, 2017 3:18 pm, edited 1 time in total.


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PostPosted: Sat Jul 01, 2017 7:45 pm 
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davyp1, thank you. I've spent the day working on these and its going well, but unfortunately under the joist ends I've now found that the Sill Plate is rotten and crumbling away. Can i just fix new blocks (its only about a cm thick) of treated wood underneath the new joist ends? is there any need for a sill plate at all? or can i just cement the whole lot in?

Thanks!


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PostPosted: Sat Jul 01, 2017 7:59 pm 
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the joists are currently propped up in these photos.


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PostPosted: Sat Jul 01, 2017 8:22 pm 
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coxhq. you would have saved yorself a lot of grief if you had left the ceiling in. and as i advised you you only do one bolt-on at a time cos you dont know what the true loading is or what you could run into, like the unsupported wall.

is it a true sill platethat runs the length of the wall or are they individualpackers under each joist? all old wood has to come out an the space treated and filled with semidry an slate.
use slate an semidry to pack up leveland wedge in the joist tails.
Dont ever cement in old or rotten wood
Keep checing your levels both ways



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PostPosted: Sat Jul 01, 2017 9:54 pm 
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davyp1 wrote:
CoxHQ wrote:
I'm finally getting around to doing this this weekend. A couple of final questions - The new Joists are treated, but is there any harm in SBR-ing the ends too? Just to give them a little extra waterproofing in the walls. And also when I knock out the bricks for the new joist pockets can I then cement-in the new joists or do I need to leave an air gap around them.

Thanks again.


Yes, it is good practice to treat all cut end-grain of joits.
Also, a lot of people advocate wrapping the joist end going into the wall with DPC. You need to wrap the end tightly and fold in the ends at the end of the joist like you were wrapping a parcel. Then cloce nail round the edge of the DPC with short Clout nails.

No air gap, you morter the joist in fully.

davyp1


I've never wrapped the joist end,it can sweat and rot(a bit like wrapping a fence post in a bag)
Completely cover the end grain and end of joist in deepkill and leave airspace around the end.



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