Insulating under floorboards - I could try myself?

[Kam1984]

I am having my kitchen diner tiled next week. One portion of this will have electric UFH. My tiler will not use any of the branded insultated 6mm backer boards - he said especially over the flooboard sub-floor section he wants to use a full cement board - hardiebacker.
I'm now getting pedantic about losing heat downwards. I have an exposed floorboard area. and I have a week without the kids at home.
I would like to carefully remove some / most floorboards - friction fit PIR boards between the floor joists - I will nail thin wooden battens on the underside so they can sit on them... and then I'd like to put the floorboards back on.
How hard would this be? Its 10sq meters, no obstacles, fully square room.
Will the floorboards go back on?They are T&G - so i have learnt I need to sacrifice 1 T&G to get access, then I crowbar off 1 board at a time, whilst retaining the T&G system? When I put them back on, will they slot into place? Shall I then nail or screw new holes?
Or should i put 4 sheets of plywood and put them down instead? Issue is i dont think i'll be removing the boards right into all of the corners if I don't need to.

I've ran the numbers through chatgpt - I am aware I am not going to save much in electric. It will only be used for comfort / foot warmer - as the area has excellent radiators and most of the area is a new extension. But its more of a DIY attempt. I think the insulation boards will be approx £100. some tools will be £40-50.

 

[foxhole]

Why not use a tiler who does want you want?

 

[Kam1984]

Why not use a tiler who does want you want?

He has a point RE to not soley use insulated backer boards. He said they're not a direct replacement for cement boards over floorboards. I've called warmup and marmox and he is right to some extent. Even if they were strong enough - The insulated boards needs to be glued down. Some parts of the area to be tiled is already tiled on existing backer boards we will reuse - so it could cause height differences.

I'm at a place that I have a week with not much else on and whether I should insulate under the floorboards instead. It'll improve heat retention in my tiles over the living room space.
Using 70mm of PIR will be superior to the 6mm cement coated boards anyway.

I'm just worrying about lifting and replacing my boards.

 

[endecotp]

How hard would this be?

Not very easy.

How much depth is there below the floor? Enough for a small child to crawl around in?

 

[Kam1984]

Not very easy.

How much depth is there below the floor? Enough for a small child to crawl around in?

No. It'll have to from above.

If I break the floor, then I'll have to buy ply boards - much bigger and put them down.

 

[Deluks]

If I break the floor, then I'll have to buy ply boards - much bigger and put them down.

I'm with the tiler, tiles onto XPS onto floorboards may crack.

If you can get the old boards up intact, then reuse them and put 6mm cement board on top. You'll have have to ease them up gently. A wide bolster/chisel, old wood chisel/pry bar (all 3 in combination!) nail bar/claw hammer, and a scrap of timber to spread the load when pulling, take your time. A few broken t&g won't matter, screw the boards back down every 300mm.

Plywood: Try and get hold of the t&g plywood boards, they are 8x2 so easier to manage.
If budget is a factor then use standard 8x4 sheets but make sure every joint is supported with a noggin underneath, you may have to cut the boards to ensure they line up with the joists. Screws every 300mm. Use a decoupling membrane, or your tiler may prefer 6mm cement board instead.

 

[Kam1984]

I'm with the tiler, tiles onto XPS onto floorboards may crack.

If you can get the old boards up intact, then reuse them and put 6mm cement board on top. You'll have have to ease them up gently. A wide bolster/chisel, old wood chisel/pry bar (all 3 in combination!) nail bar/claw hammer, and a scrap of timber to spread the load when pulling, take your time. A few broken t&g won't matter, screw the boards back down every 300mm.

Plywood: Try and get hold of the t&g plywood boards, they are 8x2 so easier to manage.
If budget is a factor then use standard 8x4 sheets but make sure every joint is supported with a noggin underneath, you may have to cut the boards to ensure they line up with the joists. Screws every 300mm. Use a decoupling membrane, or your tiler may prefer 6mm cement board instead.

Thanks. I'm not understanding the noggin part? Is that if I use any T&g plywood or the standard? Or both?
Also I am expecting to lift 4 rows of floor board, and then leave 4-5. I should be able to then screw in a thin 20mm batton to bottom portion of the joist to create a rail. And then slide the PIR over them . I've counted 27 rows of floorboards in total in the section I want to insulate. It's about removing only what I need to create the "angle" to push as much under It as possible.
So in this case I could put down my floorboards again without the tongue and grooves.
I still think they may be too damaged though.
Then. I'll have small sections of plywood amongst the floorboards. Is that ok?

 

[Deluks]

Noggins: you don't want any plywood butting up to another piece without support underneath. So add strips of timber, minimum 2x2 between the joists to support these edges.
Not critical with t&g plywood as the boards lock into each other.

Don't mix t&g with ply, keep it the same throughout.
You can buy replacement lengths of t&g pine floorboards if any are too damaged to use. Fairly inexpensive, but if you take care you can probably get the old ones up ok.

As stated, if you take care, you won't damage too many. Don't focus on getting the boards up as much as getting the nails out. You lever the end of a board up just enough to lift the nail head above the surface, then knock the board back down, the nail should stay proud, you then pull this up, using an scrap to protect the board underneath, as I have found when pulling up nails, that the head of a claw hammer ends up digging into and splitting the board you are levering against.

 

[Kam1984]

Noggins: you don't want any plywood butting up to another piece without support underneath. So add strips of timber, minimum 2x2 between the joists to support these edges.
Not critical with t&g plywood as the boards lock into each other.

Don't mix t&g with ply, keep it the same throughout.
You can buy replacement lengths of t&g pine floorboards if any are too damaged to use. Fairly inexpensive, but if you take care you can probably get the old ones up ok.

As stated, if you take care, you won't damage too many. Don't focus on getting the boards up as much as getting the nails out. You lever the end of a board up just enough to lift the nail head above the surface, then knock the board back down, the nail should stay proud, you then pull this up, using an scrap to protect the board underneath, as I have found when pulling up nails, that the head of a claw hammer ends up digging into and splitting the board you are levering against.

Are you free to come to Stourbridge this weekend haha

 

[Deluks]

Are you free to come to Stourbridge this weekend haha

No already working this weekend.
You can do it! Get the tools ready.

 

[Kam1984]

No already working this weekend.
You can do it! Get the tools ready.

Would i cut the t&g of all the consecutive rows I removed , or cut out the 5 rows with a jigsaw first and then pallet bust or carefully pry them up?

 

[Deluks]

You'll probably figure it out as you go, far easier than we can from a description.

Pallet buster can be pretty destructive. You'll need to carefully work your way along each board in turn. Once you've a few out of the way, you can tap the bottom of a board from underneath with a hammer to lift it slightly, to access the nail heads.
Success also depends on what nails have been used, very old rusted nails can be near impossible to get out and sometimes just pull straight through. Small holes in the boards aren't a problem, but long splits may be, you could glue them back together along the splits if you are inclined.

If you were paying someone for this labour it would be cheaper to rip up all the boards and whack some new ply down, so bear that in mind.

 

[endecotp]

I’ve tried to do this in my flat and found it essentially impossible. The boards were fixed with large ring-shank nails that need a lot of force to extract. They were driven in through the grooves, nearer to horizontal than vertical - so prizing up the edge of the board does not pull the nail in the right direction to remove it. Instead, the board splits leaving the bottom half of the groove attached to the joist.

Yous might be totally different though! Good luck!

 

[Kam1984]

You'll probably figure it out as you go, far easier than we can from a description.

Pallet buster can be pretty destructive. You'll need to carefully work your way along each board in turn. Once you've a few out of the way, you can tap the bottom of a board from underneath with a hammer to lift it slightly, to access the nail heads.
Success also depends on what nails have been used, very old rusted nails can be near impossible to get out and sometimes just pull straight through. Small holes in the boards aren't a problem, but long splits may be, you could glue them back together along the splits if you are inclined.

If you were paying someone for this labour it would be cheaper to rip up all the boards and whack some new ply down, so bear that in mind.

If I do rip "all". Id still be leaving a couple of rows of floorboards on the ends of the room. My focus is in the middle where the UFH will be around the dining space and kids play area. the insulation should make a slight improvement to tile warm up time and heat retention. Since I have electric UFH, this was important. Even if it takes 3-4 years to break even on the cost of the insulation and broken floor boards.

 

[StephenStephen]

You'll probably figure it out as you go, far easier than we can from a description.

Pallet buster can be pretty destructive. You'll need to carefully work your way along each board in turn. Once you've a few out of the way, you can tap the bottom of a board from underneath with a hammer to lift it slightly, to access the nail heads.
Success also depends on what nails have been used, very old rusted nails can be near impossible to get out and sometimes just pull straight through. Small holes in the boards aren't a problem, but long splits may be, you could glue them back together along the splits if you are inclined.

If you were paying someone for this labour it would be cheaper to rip up all the boards and whack some new ply down, so bear that in mind.

I agree - and sometimes, counterintuitively, you can free up nails by tapping them in a touch before getting them up.
...and once you've a board or two up, you might be able to lever them up from underneath, with a bar or chisel between the board and joist