Energy efficient connections in
timber buildings
Reference: Aho Hanna, Korpi Minna (edit)
REALISATION OF AIR PROOF STRUCTURES AND CONNECTIONS IN RESIDENTAL BUILDINGS
Tampere University of Technology, Research report 141, 100 pages
The sole responsibility for the content of this publication lies with the authors. It does not necessarily
reflect the opinion of the European Union. Neither the EASME nor the European Commission are
responsible for any use that may be made of the information contained therein.
Important points in energy-efficient
structures
• Heat insulation is installed to completely fill the whole
insulation space.
• Air pockets should not remain against the building board,
the air or moisture insulation or the timber studs.
• The structures must be made air tight.
• The overlaps of vapour barrier foils are sealed with proper
tapes and are tightened with battens.
• The joints of sheathing boards are fitted against the frame
structures and, if needed, strengthened with exterior
battens.
Connection between concrete slab on
ground and timber wall 1, at first wall
1. A straight bitumen-polymer
membrane is fitted above the
base wall and thermal
insulation of base wall.
2. While building the wall, the
vapour-proof foil is turned
over the polymer membrane.
3. The slab-wide plastic
insulation is installed against
the vapour-proof layer.
3
2
1
Connection between concrete slab on the
ground and timber wall 1, first floor
1. The corner of inner thermal
insulation of base wall is
bevelled so the membrane
does not break and foaming is
compact
2. The bitumen-polymer
membrane is fitted directly
beneath the base plate under
the concrete floor slab.
3. Vapour barrier foil is tightened
by screwing (k300) the
horizontal battening to the
base plate of wall.
4. The join between floor and wall
is tightened with elastic
polyurethane foam
3
4
1
2
Connection between ventilated timber
base floor and exterior timber wall
1. The vapour overlaps the
wall at least 20 cm. The
junction is taped up.
2. The overlapping of
vapour barriers is
tightened by screwing
the batten to the floor.
1
2
1
2
Connection between ventilated timber
base floor and exterior timber wall with
cellular plastic insulation
1. The vapour barrier of
the floor is turned over
the vapour barrier of
the wall and taped up.
2. At overlap, the
connection is pressed
tight against timber or
hard thermal
insulation with the
batten.
1
2
Connection between concrete slab on
ground and timber element wall
First cast the floor:
1. The bitumen-polymer
membrane is fastened to
the blocks and turned
under the concrete slab.
2. A cellular plastic
insulation panel is
installed between the
slab and base floor. The
panel is foamed over.
2
1
The connection between intermediate floor of
timber frame building and exterior wall, using
vapour barrier foil to air proof the wall
1.
2.
2
Vapour barrier foil is tightened by
screwing (k300) the horizontal
battening to the head plate of wall.
On the upper floor, tightening is
screwed to the base plate of wall.
3.
Cellular plastic insulation panels
are installed between gaps
between beams on the
intermediate floor.
4.
The edges of the boards are
sealed to the beams and battens
of the wall with cellular
polyurethane foam.
3
4
1
The connection between intermediate floor of
timber frame building and exterior wall, using
cellular plastic insulation panels as vapour
proofing
1.
2.
3.
Openings for the floor
beams are made in the
vapour barrier board of
the wall.
The insulation panel of
the wall is led
continuously under the
intermediate floor and
sealed with foam.
The beams are foamed
into the insulation
panel.
3
1
FLOOR BEAM IS
FOAMED TO
THE VAPOUR
BARRIER
BOARD
2
BATTEN
THE JONIT BETWEEN THE BOARDS
The connection between a timber frame roof and
exterior wall, using foil as air barrier
1. The vapour barrier foil of wall is led
about 20 cm over the side of the
roof. The vapour barrier of the roof
is overlapped with the vapour
barrier of wall about 20 cm.
2
2. Foil should not be tightened too
much. In the corners of the building,
vapour barriers are pleated,
overlapped and taped together.
3
3. Vapour barriers are pressed tight by
screwing the horizontal battening or
by using tightening bricks.
1
The connection between a timber roof and
exterior wall, using foil as a vapour barrier
Option B
1.
2.
3.
The vapour barrier foil is
led up to the exterior wall.
The vapour barrier foil of
the exterior wall is
overlapped with the foil
on the roof at the point of
the first roofing batten.
The connection is
tightened with extra
batten (screw fastening
k300).
1
3
2
Option
The connection between timber roof and
exterior wall, using hard plastic insulation as
vapour barrier
1.
2.
3.
The junction between the roof
and the exterior wall insulation
is foamed with polyurethane
foam.
The ceiling drop is made as
counter battening so electrical
installations can be led both
ways in the installation cavity.
The battening of the upper edge
of timber lining is fastened after
the polyurethane foaming of the
boards.
1
3
2
Joint between massive log wall and
diagonal timber roof
Foil in the roof
2
1. The vapour proof foil overlaps the end
of the wall.
2. The extra part of the vapour proof foil
is fitted loosely to the joint between
wall and roof.
3. The foil is fastened to the log wall from
the edge by taping it and pressing with
ceiling strip.
4. Sealing strip is installed to the edge of
cellular plastic insulation parallel to the
wall. It is pressed up to the insulation
panel of the roof by battening.
3
1
Hard insulation in the roof
4
Joint between massive log wall and
timber roof, diagonal roof
1.
2.
3.
4.
A chase is made to the log wall
parallel to the top of the wall.
The chase must be deeper
than the space between the
logs.
The vapour barrier foil of the
roof is turned baggy behind the
outermost roof bearer.
Another edge of foil is pressed
to the chase.
The battening of the roof is
made after the battens are
installed.
2
1
4
3
Sealing window frames
2
1. Window frames are sealed near the inner
surface with polyurethane foam.
2. In the middle part of the frame polyurethane
foam or mineral wool can be used.
3. The foam should not fill the whole gap. The
outer edge should be left as a ventilation gap.
1
33
2
4. In a log wall, a settlement gap should be left at
the top of the window and filled with mineral
wool.
4
5. Flexible vapour-proof foil is installed around
the window. Foil is stapled and taped to the
frame wall so that it will stay undamaged when
the log settles.
1
5
Insulation and structure of a ventilated
'crawling space' in a low energy house 1/2
1.
2.
3.
4.
5.
6.
7.
The sheathing in the 'crawling space' should always be
very moisture resistant. The sheathing materials should
not be sensitive to mould. The heat resistance of the
λ= 0.036 W/(m*K)
sheathing should be always at least 0.4 m2 K/W.
Old U = 0.24 W/(m2*K)
2
The moisture transfer between dry ashlar walling and heatNew U = 0.12 W/(m *K)
insulation or sheathing board should be prevented.
Heat insulation covering the entire ground raises the
temperature of the ‘crawling space’ which reduces the
relative humidity and the favourable conditions for mould
development. Organic building materials or waste should
not be left on the ground.
Heat insulation on the underside of the bearing structures
reduces the moisture movements of structures and
protects the timber structures from mould forming.
Also ventilation of the base floor significantly affects the
conditions. The recommended ventilation rate is 0.5-1 1/h.
The need for inner frost protection increases because the
heat loss through the base floor decreases.
The order of work should be planned beforehand so the
structures can be sealed properly. The base floor must be
made totally airtight.
Ref.: Jukka Lahdensivu, Jommi Suonketo, Juha Vinha, Ralf Lindberg, Elina Manelius, Vesa Kuhno, Kari
Saastamoinen, Kati Salminen & Kimmo Lähdesmäki. Matalaenergia- ja passiivitalojen rakenteiden ja
liitosten suunnittelu- ja toteutusohjeita (in Finnish). Tampere University of technology.
λ = 0.036 W/(m*K)
Old U = 0.19 W/(m2*K)
New U = 0.14 W/(m2*K)
2
4
1
7
5
6
3
Insulation and structures in the roof
space of low energy houses
1.
2.
3.
4.
5.
The heavy load of heat insulation and the
need for bearing must be considered. The
bearing can be improved by making the
battening denser or supporting the heat
insulation with sheets.
The temperature in the roof space will
decrease and the relative humidity will
increase. Proper conditions for the
development of mould will increase.
The heat insulating underlay raises the
temperature in the roof space and reduces
the development of mould.
It is recommended to install the heat
insulating sheathing board to the exterior
surface of the timber frame. Heat resistance
of the board min 0,4 m²K/W.
As the length of eaves increases so the bend
due to snow load increases. This must be
considered especially with brick facing.
When heat insulation layer Λ = 0.036
W/(mK), the U-value of the old structure
U = 0.15 W/(m2 K)
and the value of the new structure U = 0.08
W/(m2 K)
3
2
5
1
Λ = 0.036 W/(mK)
old U = 0.24 W/(m2 K)
new U = 0.12 W/(m2 K)
4
Ref.: Jukka Lahdensivu, Jommi Suonketo, Juha Vinha, Ralf Lindberg, Elina
Manelius, Vesa Kuhno, Kari Saastamoinen, Kati Salminen & Kimmo Lähdesmäki.
Matalaenergia- ja passiivitalojen rakenteiden ja liitosten suunnittelu- ja
toteutusohjeita. Tampereen teknillinen yliopisto.
Consider: What are the most important
effects on moisture control when the
insulation thickness is increased?
• Heat loss decreases so structures cool down.
• Cooling down slows the drying of the building
envelope.
• The risk of moisture damage increases.
• Tightness of the vapour barrier, air tightness and
ventilation will become paramount.
• Weather condition protection will become more
important.
Remember
• Thermal insulation should be installed tightly against the frame
• Soft thermal insulation under light pressure.
• Hard thermal insulation is foamed approx. 5-10 cm; the gap for foam
should be min 10 mm.
• Tongue and groove joints are installed in the foamed butt joint.
• Vapour-proof foil should not break and is installed to allow
movement of the frame.
• The joints of vapour-proof foil should be made as pressure joints if
possible.
• In the joints of wind shield board, battening is recommended
(at least in the corners).
• The structures should be tight for decades.
• Taping alone is not enough because tapes perish and do not
withstand the movements resulting from heat, moisture and snow
load.
The good practices and principles required for the energy efficient building have been
included in the teaching material. The writers are not responsible for their suitability to
individual building projects as such. The individual building projects have to be made
according to the building design of the targets in question.
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