Tf04 - Timber frame walls - Insulation between studs and to
exterior of sarking
Advantages
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Very low U-values can be achieved
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No need for firestopping (full fill)
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Utilises non-combustible Euroclass A1 insulation throughout
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Partial fill system accepted by NHBC
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FrameTherm and DriTherm are Zero ODP and Zero GWP insulation
products
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The manufacture of FrameTherm and DriTherm products has a very
low impact on the environment
-
The insulation is compressible and can be cut slightly oversize
to friction fit preventing cold air penetrating through
joints
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Products
FrameTherm Roll/Slab is a lightweight unfaced
glass mineral wool available in both slab and roll form and a range
of thermal conductivities. Its manufacture has a very low impact on
the environment and is classified as Zero ODP and Zero GWP*
DriTherm Cavity Slab is a semi-rigid slab,
non-combustible glass mineral wool having a water-repellent
additive. 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
Inner leaf comprising 12.5mm plasterboard, vapour control layer,
FrameTherm between studwork, 9.5mm plywood sheathing and Knauf
Breatheline. Cavity between timber frame and outer leaf either
fully or part filled with DriTherm Cavity Slab. Outer leaf
typically of brick.
Performance
Thermal performance
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The thermal conductivity of 50mm DriTherm Cavity Slab and
FrameTherm 35 is 0.035 W/mK.
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FrameTherm Roll 40 has a thermal conductivity of 0.040 W/mK.
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FrameTherm Roll 32 has a thermal conductivity of 0.032 W/mK.
Tables 44 and 45 gives U-values for twin insulated timber frame
walls
Table 44: Typical U-values for Twin
insulated wall – partial fill
|
Insulation product |
U-values (W/m2K) |
| Timber studs filled
with: |
Thickness
(mm)
|
DriTherm Cavity
Slab
thickness (mm)
|
Masonry outer
leaf
|
Low e
service duct |
| FrameTherm 32 |
140 |
50 |
0.19 |
0.17 |
| 90 |
50 |
0.24 |
0.21 |
| FrameTherm 35 |
140 |
50 |
0.19 |
0.18 |
| 90 |
50 |
0.24 |
0.22 |
| FrameTherm 40 |
140 |
50 |
0.2 |
0.19 |
| 90 |
50 |
0.26 |
0.23 |
Table 45: Typical U-values for Twin
insulated wall – full fill
|
Insulation product |
U-values (W/m2K) |
| Timber studs filled with: |
Thickness
(mm)
|
DriTherm
Cavity Slab
thickness (mm)
|
Masonry outer
leaf
|
Low e service
duct |
| FrameTherm 32 |
140 |
100 |
0.15 |
0.14 |
| 90 |
100 |
0.19 |
0.17 |
| FrameTherm 35 |
140 |
100 |
0.16 |
0.15 |
| 90 |
100 |
0.19 |
0.18 |
| FrameTherm 40 |
140 |
100 |
0.17 |
0.16 |
| 90 |
100 |
0.20 |
0.18 |
Notes: The U-values have been calculated to BS EN ISO 6946:
1997 and BR 443. Studs assumed to be 38mm wide at 600mm centres
(allowances for sole plates etc, give a 15% proportional area for
the timber). Stud depth is taken to be the same as the thickness of
insulation specified. Thermal conductivity of timber studs is 0.120
W/mK. Unventilated low emissivity airspace in service duct assumed
to provide R value of 0.44 m2K/W as specified in BR443.
Higher values can be achieved with proprietary products. Please
contact Knauf Insulation Technical Advisory Centre for calculations
that include specific products.Brick face area is assumed to be 215
x 65mm with mortar joints 10mm wide.
Fire performance
FrameTherm 40, FrameTherm Roll/Slab and DriTherm Cavity Slab are
classified as Euroclass A1 to EN 13501-1. Building
Regulations state that external walls in domestic construction
shall achieve half hour fire resistance. In tests and assessments
carried out TRADA Technology Ltd in accordance with BS 476: Part
21: 1987, different timber frame external walls incorporating
FrameTherm Roll/Slab gave the required fire resistance.
Installation
The installation of FrameTherm, vapour control layer and Knauf
Breathline are the same as for solution Tf01. If a service duct is
to be included then refer to Tf02. The principles for installing
DriTherm Cavity Slab in a twin insulated wall are essentially the
same as for installation in a masonry cavity wall when the inner
leaf is constructed first.
The instructions to be found in British Board of Agrément
Certificate 95/3212 apply to the use of DriTherm Cavity Slabs in
masonry wall constructions and can therefore be deemed relevant to
this application. However, this certificate does not cover the
specific use of DriTherm Cavity Slabs in timber frame walls.
Installation sequence – full fill
The timber frame is erected in the normal manner. The sequence
and methods are the same as for conventional timber frame except
that small cavity barriers are omitted from the cavity, as DriTherm
Cavity Slab is non-combustible and therefore performs the function
of a small cavity barrier. DriTherm Cavity Slab should fully fill
the space between the external cladding and the timber frame.
Adjacent slabs should always be close butted leaving no gaps. Any
mortar droppings or other debris lying on the top edge of a slab,
must be removed before installing the next row above. The
construction sequence ensures there is no cavity into which debris
can fall to an irretrievable position. Adoption of these principles
will ensure that any rainwater penetrating the outer leaf is not
transmitted to the timber frame.
Note that the NHBC will not accept this form of construction on
projects where their guarantee is required.
Installation sequence – part fill
The timber frame is erected in the normal manner. The sequenced
method is the same as for conventional timber frame except that a
wider cavity than normal is used.
This will require longer than normal wall ties with a clip to
hold the DriTherm back to the timber frame wall. Small cavity
barriers should be installed to the full width of the cavity. The
DriTherm is installed to the same standard as for full fill, but
should be fully clipped back to the timber frame wall.
Note The NHBC will accept this form of construction providing a
50mm residual cavity between the Dritherm Cavity Slab and masonry
outer leaf is maintained.
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Typical specification
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Twin insulation full fill system
External wall panels to be insulated between studs using
FrameTherm Roll 40/35/32* ......mm thick (*Delete as appropriate)
Insulation to be cut as necessary and friction fitted between
studs.The breather membrane stapled*/nailed* to the sheathing and
extend below the lowest timber member (*Delete as appropriate).
Cavity formed between internal and external leafs to be fully
filled with DriTherm Cavity Slab ......mm thick. The lowest run of
wall ties to be located at 600mm centres horizontally. Ties
thereafter to be at 450mm centres vertically and at 600mm centres
horizontally. All work to be in accordance with manufacturers
instructions.
Twin insulated part fill system
Frame and breather membrane as above, then:
DriTherm Cavity Slab ......mm thick to be fitted against the
breather membrane on the face of the sheathing and held back using
insulation retaining clips fixed to the wall ties. The lowest run
of wall ties to be located at 600mm centres horizontally. Ties
thereafter to be at 450mm centres vertically and at 600mm centres
horizontally. All work to be in accordance with manufacturers
instructions.
Knauf Insulation Cavity barriers and fire stops should be
installed as required to meet the Building Regulations.
Alternatively, refer to NBS clauses: P10/210, F30/10, 150
and F30/12, 155
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Typical section
