Screed, reinforcing and underfloor heating

7 May 2019
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United Kingdom
I'm planning on installing underfloor heating in my 75mm sand cement screed. The architect stated A98 mesh (5mm wire on 200mm grid) in the screed because drains are running under the insulation. Could I use D49 instead (2.5mm wire on 100mm grid), which works better for pipe spacing. Perhaps run a second layer over the pipes, or will that cause problems crushing pipes whilst laying the screed?

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What sort of 'drains' are running under the insulation ? If you want to change the architect's specification you should ask the architect.
It is a beam and block floor. The manhole invert is really high, so to get the levels we will run the soil pipe from a new WC in a trench constructed with more floor beams, just below the level of the floor. Effectively, we are stacking beams so that we have two levels. The trench is only 215 wide between the lower floor beams, and wider for the upper.The pipe will be bedded on concrete and then we'll fill with shingle to the level of the rest of the floor. About 20mm of the 110mm pipe at one end rises above the floor into the insulation. A bit difficult to explain without a drawing.
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You can just take you ufh pipes down the middle of the 2 wires, makes very little difference when you are laying it if you are following a wire or in between.

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