Gf03-Insulation Above Slab
Gf03 - Ground Floors - Insulation Above Slab
Advantages
- Compression resistant, supporting screed under high point
loads
- Provides high thermal performance in limited insulation
zone
- Structural and thermal solution
- Resistant to site damage
- Robust and can tolerate traffic from following trades without
damage prior to floor finish being laid
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 |
Products
Polyfoam Floorboard is a range 100% Ozone
friendly extruded polystyrene rigid board insulation – it is
lightweight yet has excellent structural strength and long term
effectiveness.
It is available in four grades:
- Domestic – especially engineered for domestic
flooring applications
- Standard – domestic and light commercial
loading
- Extra – commercial, industrial flooring and
cold storage
- Super – very high load commercial, industrial
and cold storage floors
Typical construction
A solid concrete ground floor slab on a damp proof membrane on
blinded hardcore. Polyfoam Floorboards laid over the whole of the
concrete floor slab and finished with either flooring grade
chipboard or a floating screed, either sand/cement based, or a
proprietary flowing screed.
Installation
Lay the Polyfoam Floorboard directly over the whole of the
concrete floor. The surface of the floor should be smooth and flat
to within 5mm when measured with a 2m straight edge. Irregularities
greater than this must be levelled out.
Screed finish
Place a minimum 25mm thick vertical piece of Polyfoam Floorboard
to the full depth of the screed around the perimeter to minimise
thermal bridging. Tape the perimeter insulation boards securely in
place to prevent dislodgement by following work.
Cover the Polyfoam Floorboard with a separating/slip layer and
turn up at the junction with the walls. if this is a refurbishment
project and secondary damp proofing is required, use a suitable DPM
that will also act as a slip layer.
Lay the screed, either reinforced sand/cement screed, minimum
65mm thick, or a proprietary screed, minimum 35mm thick. The
sand/cement screed should be reinforced to BS 8204: Part 1:2003.
This can be either through the use of light steel mesh at half
screed depth or the addition of polypropylene reinforcing fibres in
the screed mix. It is important to compact the screed well to
produce a durable floor surface.
Chipboard finish
Where there is a risk of moisture from drying out of the floor
slab, a vapour control layer, such as 1000 gauge polythene, should
be used. Lay the vapour control layer over the insulation and turn
it up at the junction with the walls.
Lay the chipboard in a staggered pattern and glue all joints
using a waterproof PVA adhesive. Leave an expansion gap of at least
10mm or 2mm per metre run of floor at the room perimeter. At
doorways or access traps to pipework runs, support the cut edges of
chipboard on preservative treated battens. If in doubt refer to the
chipboard manufacturer’s instructions. Seal the gap between the
floor finish and the slip layer with a flexible sealant to minimise
air leakage.
Performance
Thermal performance
The thermal conductivities of Polyfoam Floorboard products are
as follows:-
- Domestic – 0.030W/mK
- Standard – 0.029W/mK
- Extra – 0.029 -0.034W/mK
- Super – 0.034 - 0.036W/mK
Unlike most other insulants, moisture has a negligible effect on
the thermal performance of Polyfoam Floorboard.
Table 66 gives U-values for a range of perimeter/area
ratios.
Fire performance
When Polyfoam Floorboard is installed in a concrete floor
construction, it will not contribute to the development stages of a
fire.
Compression resistance
Polyfoam Floorboard is highly resistant to compression – see
table 67.
Table 67: Compressive creep results
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Product
|
Load applied
(kPa)
|
Initial compression
(%)
|
Further compression after 50
years
(%)
|
|
Polyfoam Standard
|
60 |
2 |
1.5 |
| Polyfoam Extra |
120 |
2 |
1.5
|
| Polyfoam Super |
175 |
2 |
1.5
|
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Typical specification
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Insulation below screed
Polyfoam Floorboard Domestic*/Standard*/ Extra ......mm thick,
to be close butted and placed over the whole area of the floor.
Polyfoam Floorboard Domestic*/Standard*/ Extra, 25mm thick, to be
cut and placed to full depth of screed at the floor perimeter.
The insulation to be overlaid with a separating layer*/1000
gauge polythene* taken up and over the perimeter insulation. A 65mm
thick sand/cement screed with wire mesh*/ polypropylene reinforcing
fibres* to be laid on top. (NHBC recommend a D49 fabric mesh for
use in floating screeds.) Floor finish as specified by the
designer. (* delete as appropriate)
Alternatively, refer to NBS clause: M10/40 or M10/290
Insulation below chipboard
The whole area of the concrete floor to be lined with Polyfoam
Floorboard Standard*/Domestic*, …...mm thick. All boards to be
close butted.
The insulation to be (overlaid with a vapour control layer of
1000g polythene and)* covered with 18mm t&g flooring grade
chipboard. (*delete as required)
Alternatively, refer to NBS clause: K11/25 or K11/225
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Typical section
Table 66: U-values of concrete ground floor
slab insulated under sand and cement screed*
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Thickness (mm)
|
Ratio of Perimeter (m) to Area
(m2)
|
| |
0.10 |
0.20 |
0.30 |
0.40 |
0.50 |
0.60 |
0.70 |
0.80 |
| Polyfoam Floorboard Standard |
| 160 (85 + 75) |
0.09 |
0.11 |
0.13 |
0.13 |
0.14 |
0.14 |
0.15 |
0.15 |
| 140 (65 + 75) |
0.09 |
0.12 |
0.14 |
0.15 |
0.15 |
0.16 |
0.16 |
0.17 |
| 125 (50 + 75) |
0.10 |
0.13 |
0.15 |
0.16 |
0.17 |
0.17 |
0.18 |
0.18 |
| 100 (50 + 50) |
0.11 |
0.15 |
0.17 |
0.19 |
0.20 |
0.20 |
0.21 |
0.22 |
| 85 |
0.12 |
0.16 |
0.19 |
0.21 |
0.22 |
0.23 |
0.24 |
0.24 |
| 75 |
0.12 |
0.17 |
0.20 |
0.22 |
0.24 |
0.25 |
0.26 |
0.26 |
| 65 |
0.13 |
0.19 |
0.22 |
0.24 |
0.26 |
0.27 |
0.28 |
0.29 |
| 50 |
0.14 |
0.21 |
0.25 |
0.28 |
0.30 |
0.32 |
0.33 |
0.34 |
| 35 |
0.15 |
0.23 |
0.29 |
0.33 |
0.36 |
0.38 |
0.40 |
0.42 |
| Polyfoam Floorboard Extra |
| 175 (100 + 75) |
0.09 |
0.11 |
0.13 |
0.13 |
0.14 |
0.14 |
0.15 |
0.15 |
| 150 (75 + 75) |
0.09 |
0.12 |
0.13 |
0.14 |
0.15 |
0.15 |
0.15 |
0.16 |
| 125 (50 + 75) |
0.10 |
0.13 |
0.15 |
0.16 |
0.17 |
0.17 |
0.18 |
0.18 |
| 75 |
0.12 |
0.17 |
0.20 |
0.22 |
0.24 |
0.25 |
0.26 |
0.26 |
| 65 |
0.13 |
0.19 |
0.22 |
0.24 |
0.26 |
0.27 |
0.28 |
0.29 |
| 50 |
0.14 |
0.21 |
0.25 |
0.28 |
0.30 |
0.32 |
0.33 |
0.34 |
| 35 |
0.15 |
0.23 |
0.29 |
0.33 |
0.36 |
0.38 |
0.40 |
0.42 |
| 25 |
0.16 |
0.26 |
0.32 |
0.37 |
0.41 |
0.45 |
0.47 |
0.49 |
| Polyfoam Floorboard Domestic |
| 66 |
0.13 |
0.18 |
0.22 |
0.25 |
0.24 |
0.27 |
0.28 |
0.29 |
Note: The U-values have been calculated using BS EN ISO
13370: 1998 and assume a clay subsoil with a thermal conductivity
of 1.50 W/mK. U-values for floors insulated with Polyfoam
Floorboard Super can be supplied by the Knauf Insulation Technical
Advisory Centre.
*The U-values of floors with a screed
finish will be the same as those where the insulation is placed
under the slab.