floor insulation under liquid screed

joshea

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Placing 60mm foam insulation on concrete sub floor (on which underfloor heating pipes will be attached)and A liquid screed will then be poured.

question
is it necessary to plug/fix the sheets of insulation onto the concrete slab with say mushroom fittings??? to keep in place and secure

The floor finish on which the insulaion is going is level enough

thanks
 
AFAIK the minimum requirement for insulation for underfloor heating is 125mm foil-backed, preferably laid in two staggered layers. There should be no need to fix the slabs to the subfloor as they should be cut to fit very tightly which will keep them in place. Remember also to place perimeter insulation.
 
Don't think there's a minimum requirment for insulation level for UFH. We put down 150mm of foam insulation, as our contractor advised that the concrete can react to the foil over time, which would break down the insulation.

Make sure other trades are aware there is UFH below the floor so care is taken not to screw/nail anything into the floor dammaging your UFH.
 
There are a lot of factors you need to consider here.
What is the u-val you are trying to achieve for your floor?
What type of Insulation are you proposong to use (PIR or Polystyrene)?
What depth of liquid floor screed do you propose to put in?
How much room do you have from subfloor to finished floor level?

If you have a raft foundation, I imagine you have about 150mm (6 inches) to play around with.
If you use a good quality PIR insulation (eg Kingspan, Xtratherm) you should go with a minimum of 75mm. That leaves 75mm for your screed which should give you sufficient cover for your pipes. If you use a polystyrene board (eg Aeroboard) you will need a minimum of 100mm to achieve the same u-val. that only leaves 50mm for your pipes and screed.
There are differing opinions on whether you should cover your pipework with plastic sheeting. Some of the insulation manufacturers will tell you that the screed will react with the foil coating on the insulation, others are ok with this.
The important thing is to get a tight fit with your insulation, make sure all pipework is properly secured to ensure no pipework floats to the top of the screed after pouring. My advise is to put in polythene sheeting on top of your pipes and bring it up the walls a foot all around and staple to the wall. It can be trimmed off later when the screed dries.
There are many other posts on this topic here on AAM
 
Don't think there's a minimum requirment for insulation level for UFH.

There is... !!!

a u value of 0.15 must be achieved to comply with current building regulations.

60mm insulation will not achieve this. the u value will depend on the area - perimeter ration but you can be safe that 125mm will achieve this, any less and you would certainly need to 'do the math'...
 
I Have just found this out also U Value 0.15 is Building regulations for underfloor heating. My floor area is 150m2. The ratio of area to perimiter is .44. With this I would need a minimum of 110mm K3 Kingspan to comply with regulations. Ask the guys that sell the products or check their websites for a rough idea. Again your architect or appointed BEr assessor can help you they will have all the details on your build.
 
I Have just found this out also U Value 0.15 is Building regulations for underfloor heating. My floor area is 150m2. The ratio of area to perimiter is .44. With this I would need a minimum of 110mm K3 Kingspan to comply with regulations. Ask the guys that sell the products or check their websites for a rough idea. Again your architect or appointed BEr assessor can help you they will have all the details on your build.

The correct procedure for anyone building is to get a provisional BER carried out prior to commencing work. This will tell you what type and thicknesses of insulation are required to comply. it will also tell you what level of renewables have to be installed as well.

By right it should preferably be done by your architect / architectural technician. If they cannot do it then a BER assessor should be appointed to work in conjunction with the architect / technician. Personally i wouldnt leave the specifying of insulation and renewables up to an assessor acting independently of the designer. There should be communication and deliberation to provide the best solution.
 
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