Boarding over missing joist and cantilever brick constructional hearth - first floor

[Westholme]

Is the "concrete" in the back hearth behind the skirting actually stone? I think you'd find things much easier if the "new" skirting were removed. One of your photos today clearly shows a join.

Another idea:
Bridge the gap by laying floorboards at 90 degrees to the existing. At the back they'd be supported by brick / concrete / stone behind the skirting and at the front by a new bit of wood screwed to the trimmer joist, if necessary. The span is probably only about 20".

 

[totallystretched]

Is the "concrete" in the back hearth behind the skirting actually stone? I think you'd find things much easier if the "new" skirting were removed. One of your photos today clearly shows a join.

Another idea:
Bridge the gap by laying floorboards at 90 degrees to the existing. At the back they'd be supported by brick / concrete / stone behind the skirting and at the front by a new bit of wood screwed to the trimmer joist, if necessary. The span is probably only about 20".

At the back if I take off the skirting I have cement render to bottom of board and then under board is hollow going back to the cement that is on top of a fraction of the crumbly brick chimney breast wall. I get that the shorter flooring would’ve stronger but I can’t fix the timber to the back Even with the skirting board off.

 

[totallystretched]

Boards are 200-220mm and 20mm thick. 2x8 would be ok and I could notch them so 20mm on top of joist to level with other boards. Span is 1300mm and notched length would be 50mm. I wonder would this flex with weight. I read there is c16&24 grade so c24 I guess is my best hope.

 

[totallystretched]

Coo, good lateral thinking there.
What is the width of the floorboards in the room? Can you source timbers of the same width or in some fraction of same.

Boards are 200-220mm and 20mm thick. 2x8 would be ok and I could notch them so 20mm on top of joist to level with other boards. Span is 1300mm and notched length would be 50mm. I wonder would this flex with weight. I read there is c16&24 grade so c24 I guess is my best hope.

 

[Toby Newell]

Forget floor boards a section of 25mm structural ply cut 5mm into the joist should have little movement over 1.3m.

Otherwise you could simply fix the boards in the middle with a board running cross ways, just screw through each board in two places, add some glue too.

I do this all the time to support boardd that cannot reach a joidt snd where I csnnot fit a noggin in for any reason.

 

[Cubist]

I think a KISS strategy would be the best way to proceed. My proposed solution is say 3-4 t&g floor-boards of the correct length and thickness with 2-3 ledgers fixed on their rear face to make a 'trap door' that can be lowered into place and manouvered under the skirting to be screwed to the joists for final fix.

The tongue and groove, with the addition of the ledger should provide sufficent stiffening over the the circa 1.3 metre length to meet your needs. The only fly I see in this ointment is that the depth/thickness of the ledgers would be determined by the height of the hearth bricks relative to the joists.

 

[Westholme]

Forget floor boards a section of 25mm structural ply cut 5mm into the joist should have little movement over 1.3m.

Would probably have to buy an 8' x 4' sheet but apart from extra cost that's OK. Ask timber merchant to cut sheet to exact size (front to under skirting) and rough length, say 5'. Use excess to create mostly double thickness sheet between joists, screwed together from underside and glued. 22mm thick sheet might avoid cutting into joists as floor will be carpeted.

 

[Toby Newell]

Would probably have to buy an 8' x 4' sheet but apart from extra cost that's OK. Ask timber merchant to cut sheet to exact size (front to under skirting) and rough length, say 5'. Use excess to create mostly double thickness sheet between joists, screwed together from underside and glued. 22mm thick sheet might avoid cutting into joists as floor will be carpeted.

not sure where you are going to find 22mm ply! many timber yards do not cut, obviously much easier if they do. Not sure if you would need to double up. A single piece of 25mm construction ply over a 1.3m span is going to be pretty strong. Especially if you can fit one timber of any size in the middle to the next joist.

Considering the deep notch butchering I see on almost every job, removing 5mm from half a joist is unlikely to prove catastrophic.

And extra cost? As compared to what?

Lucky if you can find well seasoned, reclaimed boards for £75 for the 1sqm you will need, plus wastage. Also not sure 1x 200mm x 3600mm x20mm pine board + 1x 200mm x 2400mm x20mm pine board are going to be much cheaper either, I mean, if you like 8mm shrinkage gaps that is. It is feasably possible you could go and pick up a bunch of Wickes 144mm x18mm bananas, sorry boards, and pssibly save a whole £20, but any 'saving' would be existential in nature, as would be your happiness.