Superglass: Suspended Timber Floor

SUSPENDED TIMBER FLOORS

Typical Construction
In a suspended and ventilated timber ground floor, the insulation is laid between the joists and supported on polypropylene netting with a deck of tongue and grooved chipboard. Netting is required to be positioned and stapled between the joists to support the insulation thus minimising the gap between it and the underside of the floor deck. Floor joists running parallel with masonry walls should be spaced at least 35mm away from the wall to allow room for insulation.

The skirting board should be sealed to the wall with a sealant and to the floor with a flexible sealant, to minimise leakage at the floor perimeter. The wall insulation should start a minimum of 150mm below the top of the floor insulation.

Ventilation
It is essential that the void beneath a suspended timber floor is adequately ventilated and that the ventilating air has a free path across the floor void. There should be a minimum 150 mm distance between the top of the ground cover and the underside of the floor construction. Vapour control layers are not normally required in insulated suspended timber ground floors. It is preferable to allow water vapour to diffuse freely through the floor to be dispersed by the ventilated void.

Thermal Performance

Multi Roll 44 is an unfaced glass mineral wool product with a thermal conductivity of 0.044 W/mK
Multi Roll 40 is an unfaced glass mineral wool product with a thermal conductivity of 0.040 W/mK

The table below indicates U-values for a range of perimeter/area ratios.

Fire Performance
All Multi Roll products are classified as Euroclass A1 to BS EN ISO 13501-1.

Installation

If the insulation is the full depth of the floor joists, staple the support netting to the underside of the all of the joists as it is unrolled.
Where the joist is deeper than the floor insulation,mark the depth of insulation on the side of the joists and staple the support netting along this line and pull taut to the adjacent joist and staple again. Pull netting over the top of the joist and staple to the depth of the floor insulation. Repeat the process until there is netting support to the whole floor.
Unroll the Multi Roll to completely fill the space between the joists, leaving no air gap between the insulation and the underside of the floor deck. Joists running parallel with masonry walls should be spaced away from the wall to allow no less than 35mm of insulation.
Tongue and grooved board joints should be glued with a PVAC or similar adhesive and the joints between the joists and the board should also be glued with PVAC. An expansion gap of at least 2 mm per metre run of deck, or not less than 10mm should be allowed between the decking and the perimeter wall in each room area.
When fixing the skirting board, apply a self-adhesive foam strip to its underside and two beads of sealant to the back surface. Apply pressure to ensure the foam strip is compressed immediately before fixing the skirting in place.

48mm wide joists at 600mm centres
Suspended timber ground floor U-values (W/m2K) insulated with Multi Roll 44
		Ratio of perimeter (m) to area (m2)
Insulation thickness (mm)	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8
200	0.13	0.16	0.17	0.18	0.19	0.19	0.19	0.20
170	0.14	0.18	0.19	0.20	0.21	0.22	0.22	0.22
150	0.15	0.19	0.21	0.22	0.23	0.24	0.24	0.24
100	0.18	0.23	0.26	0.28	0.30	0.31	0.32	0.32

NOTE:
The U-values have been calculated using BS EN ISO 13370: 1998 and assume 48mm wide joists at 600mm centres.

System Advantages
Cavity trays divert water away from the inner leaf of a cavity wall, and should be provided:

Multi Roll is manufactured to suit standard joist spacing, without the need to cut it.
Required thickness of insulation can be accommodated relatively easily within the thickness of the floor structure