In my stable-to-office conversion the existing concrete floor (with a rubberised finish) slopes from the far end of the stable down to the end with the doorway to enable good drainage – the fall is probably about 6″.

For cost reasons I’d really rather not dig it all up and put down a new concrete floor, so I was planning on putting down a waterproof membrane and then building a wooden frame/joists over the existing concrete which would be tapered to take out the slope.  Inside the joists would be filled with kingspan and I would then finish with either engineered wood or chipboard and laminate.

Although this would raise the floor level a bit by the doorway I’m not short of headroom.

Does this sound OK or should I be digging out the old concrete?

Sounds like a good plan to me. Just be aware that you’ll be raising the floor at it lowest end by the thickness of the Kingspan insulation plus the 6″ plus air gaps, so presumably you’ll run your new joists across the room, rather than along the length.

Which you probably figured already.

Self leveling compound?
I guess you’d need a couple of layers.

A floating floor could give you the option to use some insulation.

Just be aware that you’ll be raising the floor at it lowest end by the thickness of the Kingspan insulation plus the 6″ plus air gaps

Well I was actually going to taper the insulation so there would be little where the floor is highest to keep the height of the floor as low as possible as I don’t want a massive step up from outside. What sort of air gap do I need?

Why not dpc, insulation and a screed on top?
Prob cheaper than wood and would make wet ufh a possibility?

I would not advise using timber between the floor covering and the existing concrete unless you can ventilate underneath. If you intend to use a quality engineered floor of say 18mm plus thick, you can put it directly on top of a decent rigid insulation material such as kingspan to create a floating floor, so no need for timber joists.

My advise is to use 25mm battens to create kinda contour lines down the slope and then level each ‘terrace’ with self leveling concrete over the existing rubberised floor.

Then use cheap polystyrene insulation boards at 25mm thick to build up the whole floor to level, then put 50mm kingspan on top and your floor covering directly on top of that.

The result will be cheaper, quicker, warmer and rot proof.

If you intend to use an engineered floor, you can put it directly on top of a decent rigid insulation material such as kingspan to create a floating floor, so no need for timber joists.

Interesting.

Prob cheaper than wood and would make wet ufh a possibility?

No boiler/CH as it’s part of a stable block – just electric.

6″ is a fair amount to fill with concrete and (depending on the type of screed) you could end up waiting months for the deeper end to dry out enough for a timber floor. Dependent on how your entrance is, you could build in a lowered entrance and finish around it with nosings – and a step up to the main area.

I did something similar in my house. I didn’t have a slope but had different floor levels between the living room , -75mm through the uneven hall, then + 25mm into the uneven kitchen floor, where there was then a step up to the back door.

I used a £50 stanley laser level and a metal ruler to find the high points, screwed battens down and poured a little self levelling concrete in to take out the unevenness, in both the hall and kitchen.

The £5 per 8’x4′ sheets of polystyrene were essentially used as a cheap, rot proof packing material, so it doesn’t matter if its a bit rough or if there are small gaps. They are easily cut, or just broken to shape. (in my case i used a speedy track saw/hoover combo to avoid mess) This brought the hall sub floor level up to the same as the kitchen.

Then the kingspan got fitted neatly and taped together over the hall and kitchen, with a level threshold through to the living room so that the new engineered floor could be fitted throughout.

Happy Days