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 Post subject: New floor
PostPosted: Tue Mar 14, 2017 6:30 pm 
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Working on a job at min where garage is to be incorporated into kitchen. Knock thru has been done. Garage floor is as to be expected, not flat in the slightest. Drawing shows dpm on floor, 4" joists resting ontop, PIR between and deck ontop. Trouble is garage floor must vary 4" in level, from 5" to 9" below top existing joists. Existing floor which will be half the new room is on 3x2's at 400 centres! These are spanning at around 1800 and bend like bananas when walked across. I think i'm going to have to copy this arrangement in garage. Run 2/3" bearers at something like 900 or 1200 centres, packed and trimmed to level then sit 3" joists ontop. Not ideal as kitchen will be weighty with oak floor, stone tops etc. However previous kitchen was on 3x2's and must be 40 years old. Just feels a shame to be doing all this work and sitting ontop a less than ideal floor. Atleast when I take old floorboards off existing I can split the span with some bearers in the middle, hung off the wall. Approx 2ft void under the existing part can't think why they didn't leave extra course out and use 6". Who says modern builders and bodgers!?

Any thoughts?


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 Post subject: Re: New floor
PostPosted: Thu Mar 16, 2017 5:49 pm 
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oz0707 wrote:

Any thoughts?



Regarding the Garage section, perhaps best to treat this as a "Floating Floor".

Use 3x2 treated as suggested all @ 400mm Centres. First lay the DPMembrane over the Garage Floor area.
Set out the joists positions in the garage with Chalk marks and determine the highest point of the floor and place the 1st Joist that is nearest to this.
Placing a nominal packing at the 'high-spot' (say a 10mm packing) then place timber packings either end until joist is level (Fox-wedges can be invaluable for this purpose).
Continue to pack this joist along its length at 600mm Centers.
Repeat for the remaining joists.
Two or three laths nailed temporally to the top of the joists will help keep the joist locations while fixing the flooring.
If you are to use T&G Chipboard Flooring you can choose between 18mm and 22mm thick. If you use the thicker one you can increase your joist centers.

Old Kitchen Area.

You say you have approx 2' void below this floor. If I were you I would seriously be tempted to put a sleeper wall in off a concrete strip foundation. You could gauge the brickwork up to the underside of the existing joists and small packrs for the last bit. Remember to leave 'Pigeon Holes' in the brickwork to preserve air flow!

While I have treated both the above areas as seperate; the boarding of the floor wants treating as one area starting at one end till completion at the other.



For this message the author davyp1 has received gratitude : oz0707
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 Post subject: Re: New floor
PostPosted: Thu Mar 16, 2017 7:25 pm 
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Thanks for that.

I agree to board as one, that's the plan. Ideally thats why I'm running my new joists parallel to old. Annoying that to run the joists the short length of the garage (2.8ish) these would then be perpendicular to originals.

That is why I thought best to do as you said with either 2" or 3" bearers, packed every 400-600mm and positioned every 1m/1.2m. Then I can run joists on top at same direction to existing old floor. Also all new services have been run across floor already. hence a dpm not going down to well. If I use bearers I can use a roll of 4" dpm underneath each bearer? Advantage of bearer and joist arrangement also enables better airflow? Whereas joists sitting on slab and insulated would promote any airflow.

With regards to strengthening old kitchen floor whats advantage of brick dwarf wall as opposed to introducing new bearers mid span? Obviously i'm better with wood than on the trowel! I thought I would bolt a 600mm long 8/9" timber to each side wall with dpm behind, then joist hang a 8/9" timber right thru underneath the middle of the span breaking it in half? Come to think of it I don't know why they didn't run joists this way to begin with, probably slightly longer I suppose.


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 Post subject: Re: New floor
PostPosted: Thu Mar 16, 2017 7:30 pm 
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Should add the gear is c24 and I did find a span table eventually supporting around 1100 span


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 Post subject: Re: New floor
PostPosted: Thu Mar 16, 2017 7:55 pm 
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oz0707 wrote:
Thanks for that.

I agree to board as one, that's the plan. Ideally thats why I'm running my new joists parallel to old. Annoying that to run the joists the short length of the garage (2.8ish) these would then be perpendicular to originals.

That is why I thought best to do as you said with either 2" or 3" bearers, packed every 400-600mm and positioned every 1m/1.2m. Then I can run joists on top at same direction to existing old floor. Also all new services have been run across floor already. hence a dpm not going down to well. If I use bearers I can use a roll of 4" dpm underneath each bearer? Advantage of bearer and joist arrangement also enables better airflow? Whereas joists sitting on slab and insulated would promote any airflow.

With regards to strengthening old kitchen floor whats advantage of brick dwarf wall as opposed to introducing new bearers mid span? Obviously i'm better with wood than on the trowel! I thought I would bolt a 600mm long 8/9" timber to each side wall with dpm behind, then joist hang a 8/9" timber right thru underneath the middle of the span breaking it in half? Come to think of it I don't know why they didn't run joists this way to begin with, probably slightly longer I suppose.




What you suggest sounds fine.


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