As a bit of background... I have a relatively old, wood-framed house, think 1850's classic Swedish old farmhouse. The ground floor is raised up off the ground on large stones and has a sawdust-filled bit the thickness of the joists between the solid wood floorboards and, well, the void between the earth and the floor. Except that a large section of the under-floor has dropped, putting the sawdust insulation onto the earth and leaving the ground floor draughty and cold in winter.
There are two ways to fix this:
The proper way being to take up the floor in the lounge (20kvm tongue & groove, nailed down solid pine about 40mm thick) and the kitchen (13kvm, wide, thick 150 year old solid pine boards with big 150 year old nails), replace the underfloor, fill up with sawdust and refit the floors.
The easy way being to put a layer of insulation (3-5mm xps) over both, then lay some engineered wood over the top.
I'd love to do things the proper way, but the kitchen is built onto the floor, so unless I want to chop up the boards, I'd need to remove the entire kitchen and then rebuild it, so the easy way is looking tops right now.
BUTT... I have questions about engineered boards and really could do with advice.
The lounge floor is newer (50's or 60's) and is therefore more level, but the old pine boards are not. I'm assuming that I would need to make the floor more level with ply. Can I use 4mm ply, or would I have to go for something heavier?
Would I need to glue the boards to the ply and would this prevent warping/expansion, or should the boards stay floating?
Insulation down first, right?
I have a neighbour that does flooring, but he's never in and, well, STW is the font of so much knowledge I thought I would try here first
Not a tradesperson but have done some floating floors before.
4mm ply will conform to existing undulations, it would need to be thicker for levelling. Ply will need to be screwed down so you probably want insulation on top. The engineered floor can remain floating.
I've just pulled up a floating engineered wood floor that was over a combination of concrete and floorboards, no leveling layer of ply. It was a thick board, about 25mm, it wasn't too bouncy given the state of what it was over. Could you get away with just insulation then a thick engineered plank?
Any services under the floor?
A pet hate of mine is edge detailing on floors that are added without removing skirting boards - those edge trims are the devil's work.
Bit of a left field suggestion, but my exlaws had a similar construction (1850's falu red farmhouse) at their last place and ended up removing some of the foundation stones and gaining access that way. They had 40-50cm clearance under most of the house and it took them weekends through most of the summer. Obviously won't work if you only have 30cm or less...
The void is technically big enough under the house, so @merts option is possible, but only on one side of the house (the ground slopes down). I wonder how much Veterankraft would charge to lift the floor and if I can hide the cuts under the cupboard doors...
@robola... I have about 30mm of height under the kitchen cupboards to play with and the plan was 5mm insulation (xps foam with mylar backing) and a 14mm thick engineered board. The ply came from the subsequent reading from the internet. And yes, lifting all of the skirting boards fills me with dread.
As long as you run your new flooring perpendicular to the existing boards I would have thought it's be flat enough. Just keep a stack of (say) 2mm Packers to hand when your laying it to take up any hollows. Screw it to the existing boards using toungetite screws. But be under no illusion 5 mm plus 14 mm wood will provide naff all insulation, yes you'll benefit from reduced drafts, but insulation less so.
I'll settle for reduced draughts.
I'm planning on getting an air source heat pump installed this year, so minimising draughts and other heat leakage (as much as I can anyway) would be lovely.
I wonder how much Veterankraft would charge to lift the floor and if I can hide the cuts under the cupboard doors...Get the out to quote and scope out the work? You could get lucky, a colleague got the (retired) head joiner from the a restoration job of a late 18c stately home. He'd been there for 30+ years and the work he did on their place was done slowly, but the quality was Rolls Royce standard.
Best I leave it to summer then... Can't have the floor up while it's -10 overnight
-19 this morning in sunny Västra Götaland, made my nostrils pucker when i went to dig the car out...
Is the kitchen sitting on plinths and supports with a gap underneath or built properly onto the flooring? Seems such a shame to cover over old boards, even with decent engineered flooring, especially as you'll be raising the floor height by more than 25mm, disruptive in itself, and 3mm of XPS will do very little in insulation terms.
I'm guessing the bit under the kitchen is the bit where the subfloor void is inaccessible...but could you potentially lift a small number of boards in the middle and get the insulation underneath from that?
I lived in an 1850s ground floor tenement in Edinburgh with a similar ish floor make up to the one you describe.
I dismantled the built in kitchen, lifted the original boards, properly insulated between joists, hung a windproof membrane under the insulation to reduce 'air wash' of the heat, then relaid the floor and put the kitchen back. I then did the same in other rooms although I managed to squeeze under the boards so did not need to remove all of them
It made a massive difference to the warmth of the place, and I kept all original boards albeit with a couple of hidden cuts, which once made allowed the floor to come up easily using a jemmy/pry bar.
If you were fitting an ashp I would 💯 be properly insulating the floor if there was the opportunity. I have done it in my most recent house and it is really noticeable.
It's a pain of a job but had a big positive effect.
My only tip is to number all your boards so they can all go back in the same position and fit together easily. Maybe take a photo too, just to be sure.
I used wood wool batts rather than sawdust. Bats were easy to work with with good insulation and flexible enough to not require precise cutting