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Floor Insulation: Insulating solid ground floors above ground bearing slab

Sand blinding and hardware

Concrete slab / DPM

Mannok Therm Floor/MF PIR insulation boards / EPS insulation boards

Therm edge insulation

Screed with u / g heating pipes on seperating layer

Timber flooring on polyethylene slip sheet

  • Sand blinding and hardware

  • Concrete slab / DPM

  • Mannok Therm Floor/MF PIR insulation boards / EPS insulation boards

  • Therm edge insulation

  • Screed with u / g heating pipes on seperating layer

  • Timber flooring on polyethylene slip sheet

Installing floor insulation boards above the concrete slab and below the floor screed is an effective insulation method particularly for underfloor heating systems where the underfloor heating pipes are contained within the floor screed.

Positioning the thermal insulation directly below the underfloor heating system improves the responsiveness of the heating system by isolating the thermal mass of the concrete slab from the building interior, meaning the internal rooms will heat up quicker.

Installing floor insulation above the slab and below the screed

1. Once the ground bearing concrete slab has been laid allow it to dry fully and ensure it is level and smooth, free from projections. Use a thin sand blinding to level floors if required.

2. Lay an appropriate damp proof membrane (DPM) with joints well lapped and folded. The DPM should extend up the external foundation walls to meet the walls’ damp proof course (DPC). Where radon control measures are required, the specified DPM should be gas resistant.

3. Install a strip of edge insulation (Mannok Therm Floor / MF insulation) around the perimeter of the room against each wall to reduce heat loss through thermal bridging. The edge insulation should be at least 25mm thick and height should extend from the top of the concrete slab to the top of the finished floor screed. Protect the exposed top of the perimeter insulation from any damage until covered by skirting or wall finish. Note, wall insulation in the perimeter walls should also extend at least 150mm below the top of the floor insulation boards.
4. Lay floor insulation boards (Mannok Therm Floor / MF PIR insulation boards or Mannok EPS insulation boards) on top of the DPM in a break bond pattern across the whole floor. The insulation boards should be butted tightly together at the joints and should be cut neatly around service penetrations to minimise thermal bridging heat loss.

5. Lay a polyethylene separating layer across the top of the floor insulation to isolate it from the screed and prevent concrete working down between boards. The slip sheet should be taped at the joints with 150mm overlaps and turn up 100mm at the wall junctions. This slip sheet will also function as a vapour control layer (VCL), reducing the risk of condensation forming beneath the insulation.

6. Finish with the floor screed, ensuring that the insulation boards are fully protected from damage in the process.

Required insulation thickness of Mannok Therm Floor / MF:

Perimeter / Area ratio
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Thickness (mm) U-value (W/m2K)
50 0.15 0.21 0.24 - - - - - - -
60 0.14 0.19 0.21 0.23 0.24 0.25 - - - -
70 0.13 0.17 0.19 0.21 0.22 0.23 0.23 0.24 0.24 0.24
75 0.12 0.16 0.18 0.20 0.21 0.21 0.22 0.22 0.23 0.23
80 0.12 0.16 0.18 0.19 0.20 0.21 0.21 0.21 0.22 0.22
90 0.12 0.15 0.16 0.18 0.18 0.19 0.19 0.19 0.20 0.20
100 0.11 0.14 0.15 0.16 0.17 0.17 0.18 0.18 0.18 0.18
110 0.10 0.13 0.14 0.15 0.16 0.16 0.16 0.16 0.17 0.17
120 0.10 0.12 0.13 0.14 0.15 0.15 0.15 0.15 0.15 0.16
125 0.10 0.12 0.13 0.14 0.14 0.14 0.15 0.15 0.15 0.15
140 0.09 0.11 0.12 0.13 0.13 0.13 0.13 0.13 0.14 0.14
150 0.09 0.10 0.11 0.12 0.12 0.12 0.13 0.13 0.13 0.13
160 0.08 0.10 0.11 0.11 0.12 0.12 0.12 0.12 0.12 0.12
180 0.08 0.09 0.10 0.10 0.10 0.11 0.11 0.11 0.11 0.11
200 0.07 0.08 0.09 0.09 0.10 0.10 0.10 0.10 0.10 0.10

U-value results above based upon floor construction shown:

Radon barrier / DPM; 150mm concrete; Mannok Therm Floor / MF; 60mm sand/cement screed with U/F heating pipes; timber flooring (floor finish omitted); Mannok Therm Floor / MF vertical edge insulation. Calculations performed to BS EN ISO 6946 and BS EN ISO 13370, taking account of repeating thermal bridges

Required insulation thickness of EPS Pearl:

Perimeter / Area ratio

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Thickness (mm)
75 0.14 0.20 0.22 0.24 0.26 0.27 0.27 0.28 0.28 0.29
80 0.14 0.19 0.22 0.23 0.25 0.26 0.26 0.27 0.27 0.28
90 0.13 0.18 0.20 0.22 0.23 0.24 0.24 0.25 0.25 0.25
100 0.13 0.17 0.19 0.20 0.21 0.22 0.22 0.23 0.23 0.23
110 0.12 0.16 0.18 0.19 0.20 0.21 0.21 0.21 0.21 0.22
120 0.12 0.15 0.17 0.18 0.19 0.19 0.20 0.20 0.20 0.20
130 0.11 0.14 0.16 0.17 0.18 0.18 0.18 0.19 0.19 0.19
140 0.11 0.14 0.15 0.16 0.17 0.17 0.17 0.18 0.18 0.18
150 0.10 0.13 0.14 0.15 0.16 0.16 0.16 0.17 0.17 0.17
160 0.10 0.12 0.14 0.15 0.15 0.15 0.16 0.16 0.16 0.16
170 0.10 0.12 0.13 0.14 0.14 0.15 0.15 0.15 0.15 0.15
175 0.10 0.12 0.13 0.14 0.14 0.14 0.15 0.15 0.15 0.15
180 0.09 0.12 0.13 0.13 0.14 0.14 0.14 0.14 0.14 0.15
190 0.09 0.11 0.12 0.13 0.13 0.13 0.14 0.14 0.14 0.14
200 0.09 0.11 0.12 0.12 0.13 0.13 0.13 0.13 0.13 0.13

Need technical support?

For help and advice on any of our products and how they might fit your needs please contact our Technical by Mannok team.

  • Floor Insulation
  • Pitched Roof Insulation
  • Flat Roof Insulation
  • Wall Insulation