June 12, 20233 yr Hi all, The spec for our ground floor (with UFH) is: Type 1 sand blinding DPM 150mm slab 150mm PIR with pipes clipped on 75mm screed Our ceiling heights downstairs are on the lower side at 2.15m so anything we can gain on the floor would be an advantage. Before I approach Building Control and open that can of worms, is there any reason we couldn't do: Type 1 sand blinding DPM 150mm PIR DPM with pipes clipped down into it 150mm slab Apart from having to make sure we get a good, level finish on the slab, it'd save us 75mm, plus the additional cost of screed. I also understand the UFH would be a bit slower to heat up but wouldn't it then retain temperature for longer? Welcome any thoughts.
June 12, 20233 yr 13 hours ago, Ben Weston said: Hi all, The spec for our ground floor (with UFH) is: Type 1 sand blinding DPM 150mm slab 150mm PIR with pipes clipped on 75mm screed Our ceiling heights downstairs are on the lower side at 2.15m so anything we can gain on the floor would be an advantage. Before I approach Building Control and open that can of worms, is there any reason we couldn't do: Type 1 sand blinding DPM 150mm PIR DPM with pipes clipped down into it 150mm slab Apart from having to make sure we get a good, level finish on the slab, it'd save us 75mm, plus the additional cost of screed. I also understand the UFH would be a bit slower to heat up but wouldn't it then retain temperature for longer? Welcome any thoughts. Hi. You can lose at least 30mm of concrete (assuming a steel reinforcing mesh will be utilised) but the PIR is on the limit. How much thickness have you allowed for type 1 and sand?
June 13, 20233 yr Author The 150mm slab was specced for mesh already so don't know if we can reduce that but I can ask the question. Not intending to lower PIR, I'd actually have more if we could as we're over-specced everywhere else. Any reason my suggestion wouldn't work?
June 13, 20233 yr On 12/06/2023 at 09:52, Ben Weston said: Hi all, The spec for our ground floor (with UFH) is: Type 1 sand blinding DPM 150mm slab 150mm PIR with pipes clipped on 75mm screed Our ceiling heights downstairs are on the lower side at 2.15m so anything we can gain on the floor would be an advantage. Before I approach Building Control and open that can of worms, is there any reason we couldn't do: Type 1 sand blinding DPM 150mm PIR DPM with pipes clipped down into it 150mm slab Apart from having to make sure we get a good, level finish on the slab, it'd save us 75mm, plus the additional cost of screed. I also understand the UFH would be a bit slower to heat up but wouldn't it then retain temperature for longer? Welcome any thoughts. I’d use option 2 The only thing I did different was instead of 150mm concrete with rebar mesh, I used 100mm fibre reinforced concrete, much cheaper and easier than laying rebar mesh. Plus it works better with UFH as the aggregate max is 10mm so it’s more like a screed than concrete and is poured very wet so is self compacting
June 13, 20233 yr the slab wont be level enough to lay flooring on. Dig it down more and the problem is solved.
June 13, 20233 yr Author 9 minutes ago, Dave Jones said: the slab wont be level enough to lay flooring on. Dig it down more and the problem is solved. Can't dig down any more as the original house is only three bricks deep and not on foundations - we're as low as we can go unfortunately. Surely if it's powerfloated, it'll be level enough? 3 hours ago, Chanmenie said: I’d use option 2 The only thing I did different was instead of 150mm concrete with rebar mesh, I used 100mm fibre reinforced concrete, much cheaper and easier than laying rebar mesh. Plus it works better with UFH as the aggregate max is 10mm so it’s more like a screed than concrete and is poured very wet so is self compacting Interesting. I've had several people suggest fibre reinforced concrete rather than meshing. Seems easier, cheaper and quicker; surely there's a reason to mesh over fibre though?!
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