Topic starter
I have a U shaped staircase to the first floor. Underneath is fully enclosed with a cupboard under the higher section and stud wall in here blocking off access to under the lower section. I've pulled this stud wall out to gain some storage space under the lower section of stairs, and found that the 'ground' under there (it's not really floor per se) is about 5cm lower than the current cupboard floor. I'm assuming the house floor is a concrete slab of some form on top of the foundations? Looks like there is possibly some form of membrane under that? If I want to raise the level of the new bit of cupboard to the existing, is it as simple as putting down a bit of membrane in the 1.8x1m space and pouring some concrete on top to make it level? And if so, can this butt right up to the existing slab? Or should I sack that idea off and put down some ply on top of a wooden frame? Any ideas appreciated!
Posted : 15/04/2025 5:18 pm
Use a bag of self levelling compound. Maybe in 2 stages? Tape or seal any obvious gaps where the mix could escape.
Paint the existing floor with a primer suitable for the self levelling mix.
Posted : 15/04/2025 6:14 pm
Is the lower bit slabbed aswell?
Does the membrane continue under the low bit.
You need a continues moisture barrier, sealing and joins to existing.
If the low bit is just a bit lower and otherwise all the same. Clean kt, damp it and place some ready mixed concrete its only a cupboard floor. Will be cold though. 5cm is enought to lays some insulation and a bit of flooring.
Posted : 15/04/2025 6:41 pm
if it's just 5cm depth and a small space I'd be inclined to buy the appropriate depth kingspan and some flooring chipboard. cut to size and pop then in then whack some carpet offcuts or carpet tiles over the top. if you get any signs of damp you can just pull it out and try something more labour intensive like concrete.
if you are worried get some dpc to lay under the floor as well
Posted : 16/04/2025 10:51 am
Pretty much what DT78 and joshvegas said: Vacuum all the loose bits up. Paint with SBR diluted 2:1 a couple of times. One or two bags of self leveller - it isn't magic, you do have to level it with a float. The most important bit is pouring it all as one run quickly. Beg/borrow or steal an offcut of membrane for over the top, 25mm kingspan cut to size - bodge foam the edges and trim once its set, then drop some chipboard flooring and carpet in.
Posted : 16/04/2025 12:05 pm
Topic starter
Kingspan and board over the top sounds very tempting. Cleared it out this morning so some pics for reference. I don’t see how I can seal new dpc membrane to the existing as it doesn’t come out from under the wooden frame.
Posted : 16/04/2025 12:21 pm
hot_fiat reacted
Topic starter
Posted : 16/04/2025 12:22 pm
based on the photos I'd be really careful about putting a membrane down. You could easily trap moisture against the footings of the staircase. Looks like its a bitumen dpc. Potentially put some simple formers (10-15mm thick boards) around the footings when you cast anything, with the bitumen folded gently up. Then remove them to provide an air gap. You can bond the new membrane to the old (either by heating the old or using foil tape). It's a bit trickier than first described.
Posted : 16/04/2025 12:42 pm
Topic starter
Thanks very much - I’m working on removing the rest of the studs then I’ll be able to get to the membrane to bond to it. Not a problem to leave a decent gap by the foot of the stairs - the other side is just a frame for some more plasterboard so not structural but I’ll avoid that too.
Looks like I’ll need a few bags of levelling compound to fill the space which is a shame.
Posted : 16/04/2025 4:07 pm
Looks to me like they didn't extend the screed over the structural slab where it goes under the stairs.
Posted : 17/04/2025 2:26 pm
There looks like 50mm to catch there and that would take ages and huge cost using self levelling
Paint it with bitumen if your worried about dampness then a 4 to 1 screed not wet but slightly wetter than semi dry, plastic float is your tool not a metal float
The edge that's there will probably be curling up a wee bit but get rid of any floor covering in the way so you can see what your doing, long straight edge and get it level as best you can
If it's looking slightly rough as you've never done it before then one bag of self levelling might make it look acceptable or just get someone who works with cement and knows what they are doing
Posted : 17/04/2025 6:35 pm
