Pocketed Polystyrene reduces the overall floor build up thickness, reduces the quantity of screed and improves upon traditional underfloor heating performance.
In a screeded floor, many UFH suppliers require the heating pipe to be fixed to the top of the insulation. The depth of screed must then be the minimum depth of screed above the top of the pipe, plus the pipe diameter, plus an allowance (5-10mm) to allow for the fact that the pipe is not held down tight to the top of the insulation apart from where the fixings are.
It is also worth noting that the presence of the pipe on top of the insulation causes the suspended particles within the anhydrite screed to settle out, leaving a region directly above the pipe deficient in particles and prone to cracking. To compensate for this it is recommended that an additional 5mm of screed is used.
Many suppliers recommend the use of expanded polystyrene because of the cheap component cost, which has a poorer thermal conductivity (0.040W/mK) than other forms of insulation. Consequently the insulation itself needs to be thicker in order to achieve a target U value.
Expanded polystyrene is also open-cell and MUST be covered by a moisture-barrier before screed is placed on top otherwise the moisture from the screed will soak into the polystyrene and compromise its effectiveness as insulation. So there is an obvious issue with using staples to fix through the moisture-barrier as moisture will permeate through the holes created where the staples puncture it.
A typical floor build up is:
50mm
10mm
17mm
45mm
122mm
EPS
Gap Below Pipe
Pipe Diameter
Anhydrite Liquid Screed
Total Build Up From Sub Floor
OSMA Pocketed Polystyrene is manufactured from Knauf’s Polyfoam Floorboard, which is extruded polystyrene and has a better thermal conductivity value (0.029W/mK) than expanded polystyrene. Consequently a thinner layer of insulation can be used to provide the same U value.
By having the pipe set within the top of the insulation, the screed can be the same thickness as required over plain insulation.
A typical floor build up is:
35mm
40mm
75mm
XPS (With 15mm Pipe Set Within The Insulation)
Anhydrite Liquid Screed
Total Build Up From Sub Floor
By having the pipe set within the top of the insulation, the screed can be the same thickness as required over plain insulation.
A typical floor build up is:
35mm
40mm
75mm
XPS (With 15mm Pipe Set Within The Insulation)
Anhydrite Liquid Screed
Total Build Up From Sub Floor
75mm is the same thickness as a course of bricks. The greater thickness of the conventional build up can require an extra course of bricks for each storey, increasing the time taken to construct the building and its cost, in order to maintain the same internal floor to ceiling height.
The amount of screed required is also different. In the conventional pipe-on-insulation build up it is 45+17+10 = 72mm. With Pocketed Polystyrene, it is 40mm plus the amount required to fill the Pockets, equivalent to 4mm over the whole floor when the pipe is set at 200mm centres (or 2.5mm with pipe set at 300mm centres) = 44mm.
A saving of 28mm of screed per square metre, is equivalent to a saving of one cubic metre of screed for every 36 square metres of floor area, which is considerable. This also saves weight and reduces drying time.
Because of the considerably reduced thermal mass, approximately 44% less, of the floor, the UFH system is able to warm up more quickly from cold and respond more quickly to changes in demand temperature.
Pocketed Polystyrene is a Patented Product.
