Making floor for basement conversion (ed.)

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Hi,

I did have an account on here a few years back but can't login.. So I'm converting our basement into the babies future playroom but I'm stuck on floor choice. My current substrate is the original brick type floor which was possibly laid when the house was built c.1870. My main goal is to minimise loss of floor to ceiling height.

What I've done in the basement so far..

Took out tilt and turn upvc window which was in a timber frame?! Who puts a upvc window in a timber in basement! It was rotten, initially I thought I could treat it but by this point of my dream basement conversion I wanted to do everything properly so in went some acrow props and out came the window and slightly rotten wooden lintel. It looks as though the window had become structurally integral to the GF dining room joists o_O. Next I cut out brick to accommodate the new lintel, put in new lintel. There wasn't enough room to put the lintel on a proper bed of mortar so I packed mortar all around it which I was satisfied with. Next I had to replace the quite wide old rotten timber window frame with brick. I built myself a window size timber frame to make sure the bricks were straight, etc. I also laid a concrete slab at the bottom of the coal chute so the window had some thing level to sit on. I waited a full 5 days after lintel and bricks went in before removing acrow props. I then put the window in. First window (and lintel) I've ever fitted and it was fine. I was using 6mm drill bit and 7.5mm screw which was fine for brick but for the concrete slab, it needed a very worn 8mm drill bit (probably realistic 7mm) and then the screw. Have a good few of those torq bits if, like me, you are having to go through concrete! and long drill bits so you don't scuff the window with the drill chuck bit. I then put expanding foam in the gaps. The only gap was really top of window to lintel as the made the timber pretty snug. Risky but worked.



Our gas main goes through the basement and is hastily fixed under the joists. It would've looked pretty messy with the finished ceiling so I got in our usual gas man and he moved the pipes into the loft after I did cut outs of the joists. There's Regs on cutting out service holes in joists so make sure they're followed. I only found this out through prior research. Gas pipe is now secure and protected in the ceiling and I'll hang a little not on the gas pipe saying that it runs through the joists and the route it takes.

Next I tidied up the walls ahead of prep for tanking membrane. Removing random screws, bolts, light fitting, etc. I ordered the tanking membrane and went for a mesh membrane as the plasterer wasn't sure if he wanted to batten or dot and dab. I hope he'll dot and dab as I'm doing 250 centres with the plugs which is bloody time consuming! Plus the walls are so uneven, I imagine battening would be challenging. My advice at this stage:

  • with older walls which are a bit damp is to use a smaller drill bit than is recommended. I'm using 10mm dryfix plugs and an 8mm drill bit, wack it in with a rubber mallet then put a 5mm screw (size 10 screw I think) through it in the piloted hole.
  • The advice I was given was to use plugs without a premade seal (due to uneven walls) and instead use butyl rope. This was great advice. I can see how a premade seal just want offer the same coverage. I'd also recommend spending an evening wrapping your plugs with butyl rope as its a ballache to drill a hole, wrap a plug, repeat xxx no. of times. Much easier to drill band in a plug. I also didn't put the screw in straight away. I found I could get the membrane tighter if finished a section of wall with the plugs in, then put the screws in. Not sure if this is good or bad practice though..
  • The perimeter of my basement is about 16m so I only needed a 2x20m roll of membrane as my ceiling is 1.97 at greatest. I thought I'd just be able to roll it around the rome, no chance! Theres's no slack in it. If you had two people you may be able to do this. Instead, Im just cutting and using butyl tape with material back to allow dot and dab.
After I finished installing the membrane I'll be changing the location of surface mounted sockets x2 and running the cabling in front of the membrane but in protective conduit so not a big job. About this time I'll also need to think about lighting. Then the floor/screed. Then the plasterer, then furntiture/carpet/fire alarm. I'll also build some steps or something up to the window to aid escape. It's not a Reg's bedroom or anything like that but I want to keep things safe.

My big question is, which floor type? In an ideal world, I'd go DPM, insulation, screed but that's just not suitable owing to head height. So I've found Weber 4310 fibre flow. If I do a 30mm application of this on top of say SBR can I do away with the need for a DPM (it's a pretty dry basement which sits on min 2ft of bone dry sand)? This would be ideal as if I use a DPM I may have to increase thickness. Weber aren't open at the mo so no one to ask regards min thickness over DPM.

Does anyone have any other floor suggestions? In terms of floor insulation, I'll just be using insulating carpet underlay. Not the best but better than nothing.

I can add pic's if anyone is interested.
 

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Have you looked at a resin floor topped with a nice cushioned vinyl ? The resin be watertight and will also level it off nicely too. Friend got a striped cushion vinyl in the kitchen and it looks amazing. Some nice bright colours available and easy to clean up the spills
 
Hey Martin, thanks for the suggestion. I looked at resin floors after your comment and they do look like a great solution and easy to DIY. Only downside is expense. I've settled on laying DPM sheet, fixing treated battens to the substrate and then laying Tongue and groove 22mm chipboard. I think i'll use some butyl rope in between the batten and dpm sheet. I don't think it's a recognised construction detail by a long way.. but I fail to see any negatives. Plus points are very easy to lay and cost was under 190 for all materials plus two bags of self leveling compound to take the worst out of the unevenness. Works out around a 1/3 cost of paying someone to screed.
 
1.97m. Less approx 40mm for the timber floor described above. 40mm is what i would lose from a flowscreed but at about £1000 extra cost. the cheapest ready mixed flow screed quote was 950 plus VAT. The issue is the small floor area and minimum charge.
 
What about SLC to level up, DPM, then 30mm celotex, polythene layer, then float a floor on top.

At least you'll have some insulation underneath. Maybe not a solution if you are putting something heavy down there.
 
The amount of SLC to properly level up is quite vast. almost 30 bags by my calculations. What sort of floor could you float on top that isn't a slab? I like the celotex idea (i'm going to put some thin foil type insulation between my battens), just without using something like a slab on top i thought it would move about too much?
 
Only thing is, the floor will be cold.

If you could increase the insulation thickness, the floor will be stronger. You can float chipboard/engineered, T&G, ply on top of this arrangement.

Perhaps SLC is too expensive to use, what about doing your own screed type layer to level it up? And Save some loot.

I wouldn’t want to introduce wood onto the floor unless on top of DPM.
 
I'll certainly heed your advice regards insulation. It's a while since I've visited R/U vlaues, and foilback bubble wrap is a waste of time and money.. I like the floating floor as that will be even cheaper and better performing, thermally, than the previous batten idea. Any wood I use will be treated or at least above the DPM. Thanks Mr C, I'll keep you posted.
 
Screeding yourself is a good idea and you can check with Kingspan if the tapered roofing insulation is ok for the sub floor. With a couple of these and the normal thickness ones you could save on some of the deep levelling issues. I have been using one of these to do my mortar and concrete for the garden and it's handle the job well. Energer ENB677MIX 1220W Electric Paddle Mixer 230v from screwfix. Bonus is you can mix down in the cellar. Split the floor into sections so you don't have to do all in one. I sure Chris who doing his extension on here did this.
 
So yesterday I cleaned the floor thoroughly before applying two coats of SBR primer. Gave that a a few hours to go off and then put about 10 bags of SLC down. It's turned out really well and taken the worst out of the floor. It's not pancake flat definitely flat enough for a floating floor. So I'll be going with DPM, PIR board and T&G top.

With regard to the walls the existing plan is to dot and dab without insulation, however, I've just read about attaching insulation to the membrane (instead of plasterboard) and then skimming the insulation board. I'd had to groove out channels on the board for electrics but this seems a good way to insulate the walls too? And cheaper. Does anyone have experience of this?
 
I’m not familiar with that membrane... but I will say insulate.
I’ve done my house and the difference is amazing. The feel is also very different, there are no cold spots.

You could use insulated plasterboard, which you can dot n dab... not sure if it will stick to membrane though??
Alternatively you could fix Celotex to the wall and finish in plasterboard.

I’ve just used insulation discs, like big slotted washers, get a bag off eBay.

You may just want to check about your wiring, as it shouldn’t be under insulation. You could fix the insulation boards to the wall with battens, then plasterboard onto the battens. This gap can then be used for electrics.

Just a thought, I’m sure others will comment.
 
time for an update.. after about 20bags of SLC I had a level floor! really got the knack of this by the end. I then laid my dpm, 30mm Celotex PIR and then 22mm T&G board. Laying the T&G board went well and I now have a really solid floating floor. Plasterer arriving next week! many thanks for the advice with regards to floor make up as it was a real sticking point for me. We're not insulating the walls, as we're having to dot and dab and insulation backed plaster board is just too expensive. Ultimately, with the walls being surrounded by earth a certain level of insulation is afforded anyway. I've also put in a humidistat fan and hard wired smoke alarm, wired by a sparky. Got all my electrical work checked at the same time, a bit costly but worth it. Also got a fireproof door going in.
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