How do I raise floor level?

[liam546]

I have a little downstairs loo I'd like to raise the floor level of. It's a concrete slab and I can see the DPM coming up from the sides. I'm am not sure if there is insulation under the current slab or not.

I need to raise the floor level by about 75mm to a finished tile that will meet a step. I am thinking of two possible ways of doing this but wondered if what I was planning to do was a good idea or not and am looking for advise.

Option 1 - lay a 2 inch screed (sand and cement) then can lay tiles on top of new screed, not sure if I need to use an adhesive or solution on existing slab to get the two slabs to bond?

Option 2 - fix battens down to existing slab being careful not to screw too low into slab and pierce the DPM. Then lay celotex between battens. Then screw down 18mm chipboard to the battens before tiling on to the chip board.

Any advice would be appreciated.

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• liam546
• 25 Mar 2015
• 2

Untitled

• liam546
• 25 Mar 2015
• 2

 

[stevehit]

Hi
Personally, I would use the batten + insulation approach. This would avoid the considerable drying time / bonding issues of the screed method. However, I'd use 18mm WPB ply rather than chipboard as this will result in a much more resilient covering that is far more suitable for tiling than chipboard.
Regards
Steve

 

[Deleted member 174758]

I'd think along the same lines, but I'd put in a Visqueen (plastic) DPM or DPM rodd (underneath the timbers), then 2 x 2s or 3 x 2s flat on, then 18mm far eastern/hardwood plywood (WBP grade) which would raise the floor level by 72mm. To make it less (so that with, say 8mm tile you'd have 75mm) you'd need to find a timber yard or joiners who'll rip downfor you. If you want to make it a bit warmer then use something like Cellotex (40mm) or mineral wool between the timbers

 

[liam546]

Thank you both for your suggestions, I will go with that approach tben, if I put a DPM down under the battons and then screw batten down into concrete I'll be piercing the DPM where the screws go through, will this matter too much?


Also the CH pipes on the floor I plan to just insulate around these, I can't see any issues around these, can you?

 

[stevehit]

Hi
I've a slate-tiled kitchen floor with, essentially, the same construction. In my case, the insulation is 50mm polystyrene sheet The timbers do have a dpm under them, as per JobAndKnock's suggestion. I also have a vapour barrier directly underneath the ply. As for the pipes, you can insulate or leave uninsulated. (In the latter case, you may get a warm floor around the pipes as a bonus.) Regardless, if uninsulated, I would protect from concrete with tape, to avoid any possibility of corrosion and absolutely make sure there are only soldered joints - which I think is the case.

 

[liam546]

Thanks again for the reply, the copper is soldered and i have also wrapped plenty of tape around them.

I will go with the battons with insulation in between and then 18mm ply. The only thing I'm thinking over is the DPM as there is one already below the concrete slab, if I out one also beneath the battons I'll be punching holes through it with screws then if I put another beneath the ply on top of battons and insulation im worried I'll be creating to many pockets inbeteeen DPMs where condensation can build up.

 

[ree]

All good advice above, advice that will certainly work.

However, how would you ventilate a suspended floor in that compartment?

By raising the floor you will have to raise the WC pan. The AAV should also be raised.
FWIW: if the WC was turned on to the far wall it might give you a little more space to play with.

Presumably the Cu pipework on the wall is above the proposed FFL & will have to be boxed in?

The white PVC waste appears to be rising (it should be falling) as it meets the soil pipe boss - the waste should be solvent/"glued".

 

[liam546]

I presumed that if I filled the space between the battons with celotex and left no gaps anywhere then I wouldn't need to ventilate the subfloor as itl all just be compact with battons and insulation.

What is the AAV ?

The piping on the wall will be above the new floor and boxed in as you say. The White pipe will also be changed so that is falling the right way.

I have a plumber who will take care of the pipe work and fitting of sink and toilet, I'll just remove the toilet for now and get the plumber to refit it after I've done the new floor.

I just want to make sure I do the floor rite to avoid damp or condensation problems.

 

[liam546]

If I used a DPM under the battons as suggested, would I not get problems by screwing the battons into it?

 

[ree]

No

 

[Deleted member 174758]

Thank you both for your suggestions, I will go with that approach tben, if I put a DPM down under the battons and then screw batten down into concrete I'll be piercing the DPM where the screws go through, will this matter too much?

No. The main thing is to stop the timber wicking-up any moisture from the concrete through direct contact. We tend to use the rolls of DPM on commercial jobs as a "belt and braces" option if we aren't 100% sure about the original DPM. We only ever use crimped or soldered joints on "buried" pipework and it is always taped if there is any chance of contact with either concrete or insulation.

 

[liam546]

Thank you once again. Should I also go with a vapour control layer as suggested between the ply and on top of insulation and battons?....therefore stopping any warm air from the room getting below?....or is this overkill

 

[stevehit]

Hi
Not sure if it's overkill, but it does seem to be common practice and correct theoretically.
Steve

 

[liam546]

Ok so I've put the DPM down and wrapped the copper heating pipes in gaffer tape. I hope this isn't a silly question but is there any possibility that the heating pipes will melt the DPM as its only plastic.

 

[liam546]

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• liam546
• 10 Apr 2015
• 2