Pr01-Between Rafters Only
Pr01 - Between Raftes Only
Advantages
- Uses void in structure as insulation zone
- Semi-rigid mineral wool products can be friction fitted with no
special fixings, speeding up installation
- Simple installation from within sealed roof
- Utilises Euroclass A1 insulation throughout
- Using Crown Room-in-Roof Roll 37 will significantly improve the
acoustic performance of the roof – reducing airborne noise
- Crown Crown Room-in-Roof Roll 37can be used along with an extra
layer of plasterboard to satisfy the requirements of Robust Details
to restrict flanking sound around separating walls.
- Low cost option
- Longer rolls with greater coverage per roll than other
equivalent products
- Widely available through national stockist network
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Products
Crown Room-in-Roof Roll 32/37 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 50mm
wider than the roll to overlap the joist 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*
Rocksilk Flexible Slab is a semi-rigid rock
mineral slab. In this construction Rocksilk can be used as an
alternative to Crown Room-in-Roof Roll. See Table 7.
* Ecohomes and Code for Sustainable Homes
classification
Typical construction
A pitched roof of timber rafters with tiles or slates on battens
and counter battens on Knauf Breatheline. The space between the
rafters is fully insulated with Room-in-Roof Roll.
A vapour control membrane should be placed on the warm side of
the insulation.
Robust Details
In order to comply with the Robust Details requirements for
masonry separating walls and roof junctions, the complete ceiling
area should contain at least 100mm of mineral wool (10 kg/m3 min)
between the roof rafters and installed so that it is flush with the
soffit of the rafters. Any dwarf walls which are adjacent to the
separating wall where there are rooms in the roof should also
contain at least 100mm of mineral wool (10 kg/m3 min).
Introduction
The most satisfactory method of insulating at pitch level within
a roof is when the required thermal performance can be achieved
within the depth of the rafters. This is because it does not
increase the depth of the roof build up, special fixings are not
required and all insulation work can be carried out from within the
sealed roof space.
Installation
Knauf Breatheline is pulled taught and laid directly over the
rafters. 50x32mm counter battens are nailed into the rafters with
minimum penetration of 38mm into the rafter.
Alternatively, helical fixings can be used with a minimum
penetration of 35mm into the rafter. Tiling battens are nailed into
the counter battens. Finally, the roofing tiles or slates are fixed
to the manufacturer’s recommendations. Crown Room-in-Roof Roll 37
is simply friction fitted (in layers if necessary) to fully fill
the space between the rafters. All layers should be closely butt
jointed. The mineral wool is normally fitted from below once the
roof is weathertight.
If installed in layers, ensure joints are staggered.
The roof insulation should be cut to shape to link with the wall
insulation to avoid a thermal bridge at the eaves.
A continuous vapour control layer should be fixed to the
underside of the rafters with all joints sealed.
Performance
Thermal performance
Crown room-in-roof roll 37 has a thermal conductivity of 0.037
W/mK. Table 7 gives U-values for typical constructions with
insulation between the rafters.
Table 7: Typical U-values of roofs with
insulation between rafters
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Product
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Thickness
(mm)
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U-values
(W/m2K)
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| Crown Room-in-Roof Roll 37 |
200 |
0.20 |
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160 |
0.25 |
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
Crown room-in-roof roll 37 is classified as Euroclass A1 to BS
EN ISO 13501-1.
Vapour resistance
Knauf Breatheline has a vapour resistance of 0.22 MNs/g.
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Typical specification
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 The whole area of the pitched roof to be insulated with
Crown Room-in-Roof Roll 37…mm thick, friction fitted between the
rafters. The insulation to be pushed over the wall plate at the
eaves to link up with the wall insulation.
Alternatively, refer to NBS clauses: P10/140 and 320
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Refurbishment of existing roofs
This is a valid solution for the refurbishment of existing roof
where the roof tiles and roof tile underlay are not being removed.
In these circumstances a continuous 50mm gap must be maintained
between the insulation and the roof tile underlay which is vented
at the eaves andridge. The U-values achieved are as shown in tables
below.
Typical section
