Pr11 - Pitched roofs –rafter level - Between and above
rafters
Advantages
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Non-combustible insulation gives fire safe solution
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Good thermal performance
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No ventilation required at eaves or roof voids
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A breathable and vapour permeable system
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Significantly improves the acoustic performance of the roof
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Rafter Roll 32 / Room-in-Roof Roll 37 can be used along with an
extra layer of plasterboard to satisfy the requirements of Robust
Details to restrict flanking sound around separating walls
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Longer rolls with greater coverage per roll than other
equivalent products
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Products
Room-in-Roof Roll 37 is made from glass mineral
wool and formed into rolls which are dimensioned to fit tightly
between rafters at 600mm centres. The rolls are lightweight,
flexible, resilient and non-combustible. It is faced with a low
emissivity vapour control layer. The facing is wider than the roll
to overlap the rafters to aid fixing, and create a vapour control
layer. Its manufacture has a very low impact on the environment and
is classified as Zero ODP and Zero GWP*
Rafter Roll 32 is made from glass mineral wool
and formed into rolls which are lightweight, flexible, resilient
and noncombustible. Its manufacture has a very low impact on the
environment and is classified as Zero ODP and Zero GWP*
Rocksilk Pitched Roof Slab is a compression
resistant, water repellent, rock mineral wool slab specifically
developed for over rafter (sarking) insulation.Its manufacture has
a very low impact on the environment and is classified as Zero ODP
and Zero GWP*
Knauf Breatheline
is a breathable membrane with a polypropylene non-woven coating on
both sides
* Ecohomes and Code for Sustainable Homes
classification
Typical construction
A pitched roof of timber rafters, at least 150mm deep, with
tiles or slates on battens and counter battens and Knauf
Breatheline. Insulated with Rocksilk Pitched Roof Slab laid over
the rafters and Room-in-Roof Roll 37 or Rafter Roll 32, friction
fitted between the rafters.
Installation
A timber stop rail is fixed to the ends of the rafters. Rocksilk
Pitched Roof Slab is fitted starting from the timber stop rail,
with all slabs tightly butted.
Rocksilk Pitched Roof Slab should be laid across the finished
rafters with staggered joints. The slabs should be cut to length to
match the spacings of the rafters. Knauf Breatheline can be
installed either below the counter battens (as shown above), or
above the counter battens. When installed above the counter battens
Knauf Breatheline should be draped by no less than 10mm.
Counter battens should be fixed through the Rocksilk Pitched
Roof Slab boards using spiral fixings such as Helifix Inskew 600 or
Buildex RG, with a minimum penetration into the rafter of 35mm.
The fixings are to be installed at no greater than 400mm centres
along the battens. From below, Room-in-Roof Roll 37 or Rafter Roll
32 is simply friction fitted between the rafters. The insulation
should be friction fitted between the rafters so that it is in
direct contact with the Rocksilk Pitched Roof Slab, with no air
gaps between the two layers of insulation.
To avoid a thermal bridge at the
eaves, Rocksilk Pitched Roof slabs should be cut to shape to link
the roof and wall insulation.
A continuous vapour control layer should be fixed to the
underside of the rafters.
Performance
Thermal performance
- Rocksilk Pitched Roof Slab has a thermal conductivity of 0.038
W/mK.
- Rafter Roll 32 has a thermal conductivity of 0.032 W/mK.
- Room-in-Roof Roll 37 has a thermal conductivity of 0.037
W/mK.
Table 17 gives U-values for typical constructions.
Table 17: Typical U-values of
pitched roofs with insulation between and over
rafters
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U-values
(W/m2K) |
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Rocksilk
Pitched Roof Slab (mm) |
| Insulation |
Thickness (mm) |
50 |
70 |
| Room-in-Roof Roll
37 |
200 |
0.16 |
0.14 |
| 160 |
0.18 |
0.17 |
| 100 |
0.25 |
0.22 |
| Rafter Roll 32 |
200 |
0.14 |
0.14 |
| 170 |
0.16 |
0.15 |
| 150 |
0.18 |
0.16 |
| 130 |
0.2 |
0.18 |
| 100 |
0.23 |
0.21 |
Notes: Rafter sizes assumed to be 38mm wide at 600mm centres
(6.3% bridging) and the same depth as the insulation. The U-values
have been calculated in accordance with BS EN ISO
6946:1997.
Fire performance
Rafter Roll 32,Room-in-Roof Roll 37 and Rocksilk Pitched Roof
Slab are classified as Euroclass A1 to BS EN ISO 13501-1.
Acoustic performance
Rafter Roll 32 and Room-in-Roof Roll 37 meet the specification
for a mineral wool insulation required for the control of flanking
sound as described in Appendix A of Robust Details.
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Typical specification
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Insulation laid over rafters to be Rocksilk Pitched Roof Slab,
......mm thick, located over the rafters. All boards tightly butted
and with staggered joints. Knauf Breatheline should then be laid
over the insulation with the edges lapped.
The insulation and underlay to be held in place by 50 x 32mm
counter battens fixed through the boards, into the rafters. The
tiling battens to be nailed into the counter battens. Room-in-Roof
Roll 37 or Rafter Roll 32......mm thick, to be friction fitted
between the rafters. The width of the insulation should be
appropriate to the spacing of the rafters.
Alternatively, refer to NBS clauses: K11/670 and P10/140 and
320
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Typical section
