Suspended Timber Floor rebuild

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Hey, I'm about to rebuild my downstairs extension floor and am after a few tips. It was a very badly constructed concrete floor and prior to that would have been suspended timber (it's a Victorian terrace).

My plan is to secure timber wall plates (are they called wall plates?) to two opposing walls with resin secured M12 threaded bar at 600mm centres (2.8m span) and then run 4x2s between the wall plates (2.1m span) at 400mm centres on joist hangers. I know that the more simple option would be to rest the 4x2s on top of the wall plate but this would not leave sufficient void under the floor for ventilation. If anyone could shine some light on these questions that would be great:

- Does 600mm spacing sound OK on the chemical fixings? I plan to use 4x2 wall plates with a fixing hole through the centre of the timber.

- I'm worried about getting the wall plates level in the vertical plane. They being fixed to a solid, double skinned brick wall which is almost certainly not plumb. I figured I could potentially render over the brick to get it level before attaching the wall plates but I'm by no means accomplished at rendering and frankly, it's a bit of a faff. Quite time consuming and means I'll no longer be able to see the mortar joints and I want to make sure I get a good fixing. Can anyone suggest a good method for getting them level?

Thanks for any help.
 
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my first thought is are you sure the walls are dry? If not you would have to be very careful to separate the wall from the timber with dpc, because once you add the insulation it gets harder to keep the timber dry enough.
Regarding the spacing I'm not sure, but with the level you mention plumb and level in the same sentence. I would have thought the most critical was level along the length of the wall plate if that's what you mean, and if it's not spot on you could ensure the effect is perfect by adjusting the hangers a bit when you hang the main joists.
Having said that I'm not a builder and hopefully someone else will have more detailed suggestions!
 
Thanks for the replies.

Yes, the walls are dry and I plan on doing an injection DPC a few courses below the wall plate to avoid rising damp and then running a length of DPC (https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-course-black-300mm-x-30m/94278) between the plate and the wall, should have mentioned that. Sorry for the confusion, I'm worried about torsional flexion on the wall plate if it's not level in the vertical plane. I guess you could drive wedges in at intervals to level it up, I was just after a few options that might avoid having to render the area to level it. Interestingly, this article suggests spacing the plate from the wall with washers, although this is for decking; http://www.ultimatehandyman.co.uk/how-to/decking/fixing-a-ledger

Dain1, the joists are 400 centres and 2.1m span. It's C24 47x97 timber, which the nhbc states can go up to 2.24m clear span; http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/images/6.4Atable2.gif
 
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Your joist size is a bit on the edge, ideally use C24 97 x 47 which gives 2.24m C16 is 2.05m

Put in 3 fixings for your wall plates. Use wedge packers to get level.
Fit hangers and joists

Squirt in some mastic to fill the gaps behind the wall plate
Put in more fixings.

If you dont have enough room below to do that, just wedge / shim at each fixing and just use mastic around the gaps you can see from above.

If you have big gaps use some ply blocks.
 
Thanks Notch, that's really helpful tips for getting the plate level. I am using C24 97x47. I plan on using 5 fixings per plate at 1kN shear strength per fixing. I may be calculating this incorrectly but I'm hoping from the wall plate perspective the fixings are capable of taking 1000kg in total (10 fixings total). Saying that, the floor is going to support a small kitchen with some heavy items in it and with the joists at their current spec each joist can take 0.5kN/m2 dead load and 1.5kN/m2 imposed load, there will be 8 joists in total. The kitchen is 2.1x2.85m (approx. 6m2).

I've done a bit of research and recommendations seem to come in at between 2 and 3kN/m2 for kitchen floor load capacity. I don't have much scope for going deeper with the joists but I could double them up. It would be a lot of faff but perhaps a honeycomb sleeper wall at mid span would be belt and braces. Do I need to be concerned about the tensile strength of the wood where the fixing passes through it? I'm sort of assuming that the wood with a 13/14mm hole through it can take the load but it'd be nice to have some numbers to back it up.

Appreciate any extra advice on this. I tend to overly worry about this stuff being new to all of this (background is electrical/electronic engineering).
 
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A 14mm hole is fine through a 97mm timber, prob best to use those big square washers.

For the joist hangers make sure you use the correct 3.75 twist nails, dont use screws.

As its for a kitchen, Id be tempted to double up. The only easy way to do it is to fit single joists and hangers, then sister them with another joist, cutting them shorter so they fit between the joisthangers.

Are you fitting insulation in between? - if so some bits of thin ply, wider than the joists could screwed to the underside for the celetex to be pushed done to. If its cut 5mm narrow and foamed up itll lock it all solid.
 
For simple joists the concern is just deflection, so if they are undersized the floor will just move more. If you plan to tile it, that would be more of an issue than if you plan to roll out some vinyl floor.
I replaced a rotting 4x2 joist with modern c24 over around 2m and i could feel the extra spring, but it won't damage anything.
Are you fitting insulation in between? - if so some bits of thin ply, wider than the joists could screwed to the underside for the celetex to be pushed done to. If its cut 5mm narrow and foamed up itll lock it all solid.
good tip, and also learn from my initial mistake, make sure you pack the ply down a bit (i used roof battens) as the joists are 96mm or so and the celotex is 100mm. In theory 90mm celotex would meet regs but 100 was cheaper. Also use a foam gun not the disposable uncontrollable ones, I literally had to use that as an "embarassing fact" about myself on a training course on the monday as it all stuck fast to my hands.:confused:
 
Also use a foam gun not the disposable uncontrollable ones, I literally had to use that as an "embarassing fact" about myself on a training course on the monday as it all stuck fast to my hands

Yup, been there :ROFLMAO:

The proper foam guns are controllable. To spray into thin gaps it needs turning down almost off -set right it works really well, cutting insulation 5mm or so undersize and filling the gap. Once cured it locks it all nice n solid
 
Sleeper wall and/or lots of noggin’s will also help with firming it all up.

I would prefer to use deeper timber than 100mm.

I used the masonry to timber hangers, which I ground out the mortar, inserted the hangers and mortared up again, you could use resin (if you are quick) levelling then is easy with shims, as and where needed.
 
TravisP sell Simpson masonry supported 100x47 hangers. If you rake out the mortar at each hanger location to create a slot where each hanger will be inserted, then chock up a shared temporary level support (shelf) at a height such that the inserted part of each hanger is roughly midway vertically in the raked out mortar course slot , then you have a line of level but ungrouted hangers sat on a shared temporary supporting beam. Remove one from where it's sat on the temporary level, shared beam and slightly underfill the slot that takes the top flanges of the hanger with fischer resin mortar and fairly quickly, push the hanger right back in making sure that the hanger is sat back down on the shared temp levelling beam. Then repeat, all the way along the hangers on the temp beam.

No worries about plumb walls etc, just support the temp beam/shelf on some bricks, get it level and line the hangers up along the top of it, by the time you resin mortar the fourth one, the first will have set.

Check your ctrs before you begin putting the hangers.

All this assumes that the mortar courses are at a convenient height. You can double up the joists with sisters, it's ok if the sisters are a tad shorter because the hangers would be in the way of full length sisters.

You might need a mortar rake from screwfix to go on a small angle grinder, or a diamond cutting disc.

You don't need a wall plate, just resin mortar the hangers straight in to the wall, Fischer resins need a special gun, their tubes don't fit silicon guns, or didn't when I last did this. Maybe other types do though but you'd have to check. Resin grouts aren't free, and you might need a few tubes but they are the biz.

Noggins are GOOD things, use em. They don't need to be cabinet maker standard but they do need to be present.
 
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I also favour the masonry joist hangers, but wouldn't bother messing about with resin. Something like these:
Screenshot_20190612-081225.png


Sit them on top of the brick and screw and plug from the front through a couple of the 4 holes provided. Drill a few holes in the mortar with a thin masonry bit to form a slot and tap the hangar in.
 
Nice idea, don't forget to pack the slot with dry mix mortar afterwards to avoid any void
 
Nice idea, don't forget to pack the slot with dry mix mortar afterwards to avoid any void
No, the idea is that you fill the slot with resin mortar before you insert the hanger, then there are no voids when you have finished. You don't quite fill the slot because when you push the hanger in it will expel a little grout and it's just wasteful. And resin mortar isn't free.

No need for dry mix packing, and nowhere to pack it anyway, because the slot is full of resin mortar and hanger.

https://www.travisperkins.co.uk/Sim...oist-Hanger-100-mm-x-47-mm-JHM100-47/p/243446
 
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