Joists have dropped - sister joists & ply??

[dan_cup]

Hi,

 

we are going to have LVT laid on the whole hall and kitchen section incorporating the new concrete and old suspended floor.

 

our joists dip into this corner (floor boards are in a bad way as kitchen units have been on top for years) so I need to level up (sister some 5x2 onto the old joists sitting them proud?) you can see the run off from the concrete edge getting larger.

 

i will then replace the T&G with 18mm (or more?) ply glued and screwed.

 

Should I just butt upto the concrete, pass over the top so the SLC can butt upto it, or something else??

cheers

 

 

Edited Thursday at 22:40 by dan_cup

[Nickfromwales]

If you have room for 22mm P5 boards, then do the base layer with that. Then go over with a thin layer of plywood as the binder for the LVT to go on to. Set the plywood binder to be higher than the concrete, and then feather the concrete into that with the SLC to get you snooker table flat; you need to be spot-on for LVY as it shows everything when the light is on it.

 

Yes to sistering to get the joists ready for the P5, and use glue and structural screws to do this link, inserting them at a slight angle to use the whole length of the screw. Use resin wood glue, plenty of it, to join the two together forever.

 

[Nickfromwales]

Concrete screw the last joist into the concrete floor to lock them to each other.

[dan_cup]

6 hours ago, Nickfromwales said:

If you have room for 22mm P5 boards, then do the base layer with that. Then go over with a thin layer of plywood as the binder for the LVT to go on to. Set the plywood binder to be higher than the concrete, and then feather the concrete into that with the SLC to get you snooker table flat; you need to be spot-on for LVY as it shows everything when the light is on it.

 

Yes to sistering to get the joists ready for the P5, and use glue and structural screws to do this link, inserting them at a slight angle to use the whole length of the screw. Use resin wood glue, plenty of it, to join the two together forever.

 

Cheers Nick, my floorboards now are measuring 21mm so P5 would work. 
 

my builder that’s been doing the extension part suggested I use 18mm ply, biscuited at regular spacing to create the strength along the edges. This would also be the final layer of the LVT. 
 

the flooring people are, as you suggested, talking about a thin layer over the board I fit.  So I’m all over the place with what to do! 
 

the P5 does seem far more affordable that 18mm ply. But is it as strong?

 

cheers

[Nickfromwales]

22mm P5 is used in every new build, so yes, it’s perfectly fine. 
 

Listen to the LVT installers and not the builder, he’s wrong and they’re right. You need the plywood binder as the final prep before the LVT goes down. 
 

Go 22mm + 6mm, and then ask the LVT installers to level (aka feather) the self leveller over the concrete section to suit. Don’t let the builder do it. 

[saveasteading]

9 hours ago, dan_cup said:

joists dip into this corner (

Do you know why? We should overcome the reason for this at the same time.

 

[dan_cup]

36 minutes ago, saveasteading said:

Do you know why? We should overcome the reason for this at the same time.

 

Honestly not sure, the whole house seems to run off in this direction. From the sink side the boards are level with the concrete, by the end of the arrow there’s a 30mm drop. 
 

 

[saveasteading]

Some houses are built like that because the builder couldn't use a spirit level. 

Others move quite a lot more than we would like to think.

 

So in your case, there is no sign of rot at joist ends? That's OK then.

[dan_cup]

51 minutes ago, saveasteading said:

Some houses are built like that because the builder couldn't use a spirit level. 

Others move quite a lot more than we would like to think.

 

So in your case, there is no sign of rot at joist ends? That's OK then.

Yes at the end I’m interested in the joist are good, solid and firm inside the brick wall slots. On the opposite side by the sink two or three were in poor condition so my builder has already ran new ones sistered and onto dwarf wall and into the wall pocket.

[Nickfromwales]

1 hour ago, dan_cup said:

Yes at the end I’m interested in the joist are good, solid and firm inside the brick wall slots. On the opposite side by the sink two or three were in poor condition so my builder has already ran new ones sistered and onto dwarf wall and into the wall pocket.

May be a good time to spray treat with woodworm / rot preventative chemicals, if it's getting all covered over for the forseeable.

[saveasteading]

22 minutes ago, Nickfromwales said:

spray treat with woodworm

absolutely. I was going to say to use treated timber, but spraying the existing joists is wise. Woodworm and rot.

[Temp]

Would it be possible to jack up the joists and put packing (or just DPC) under the ends?

[dan_cup]

There’s no room to jack them up, the bricks on the top side are in contact with the joist so I’d be jacking the wall up. Anyway fired some joists along side. Hopefully do the job

Edited 6 hours ago by dan_cup

[saveasteading]

3 hours ago, dan_cup said:

fired some joists along side.

You should have lots of fixings. The whole floor load, where raised, is resting on the fixings.

[Nickfromwales]

2 hours ago, saveasteading said:

You should have lots of fixings. The whole floor load, where raised, is resting on the fixings.

Well spotted. 
 

Nowhere near enough fixings have been used.

 

@dan_cup, one top an one bottom, repeated as much as you can afford.