Timber Frame Construction
3A9 Construction Technology
Dr S Pavía
Dept of Civil Engineering
Trinity College Dublin
Lecture Notes
https://www.tcd.ie/civileng/Staff/Sara.Pavia/3A9/lec
tures/
• Load bearing wall structure vs frame structure.
• Timber members and components forming a
structural frame which transmits all loads to the
foundations.
• Timber as a structural material.
– Favourable strength/weight/cost ratios
– Easily joint and prefabricated
– Low self-weight facilitates handling and erection and
reduces dead weight of the structure
– Sustainable material
– Combustible but fire resistance is high if members not
less than 100-150mm section (smaller sections
protected by non combustible material)
– Pre-cutting and assembly reduces site work
– Timber is very stiff in relation to its weight-E value
fairly constant
• External cladding non-loadbearing, protective
and aesthetic roles.
• Site operation or pre-fabricated.
– Variation in the extent of factory construction from
simple sheathed stud panels to others including
components such as joinery, insulation, cladding,
external linings.
– Work on site usually limited to erection and fitting outfew companies making and erecting frames on site.
Examples of Prefabricated Panels
• Kingspan Products
Standard Timber Frame
Structural Insulated Panels
• A frame wall consists of vertical timber members (studs-spaced
at 400-600 mm centres), framed between horizontal members
at top (head plate) and bottom (sole plate or piece).
• Joints are simple butt and nailed, the frame is therefore non
rigid and requires bracing to provide adequate stiffness.
– Diagonal braces
– Board or plywood external sheathing to stiffen the structure.
•
of
Main terminology
of wall
• Butt and nailed joint
Systems of frame construction
•
•
•
•
Platform frame
Balloon frame
Modified frame
Independent frame
Foundations for frame walls
• In all types, timber structure not
in contact with ground
moisture.
– base wall or foundation
beam rising to dpc level
– edge of a concrete raft floor
• A wall or cill plate (base for the
structure) to be set, levelled on
the dpc and anchored to the
foundation by 13 mm holding
down bolts at no more than
2.40m centres.
• A damp-proof course (DPC)
is a horizontal impervious
barrier in a wall designed to
resist moisture rising through
the structure from the ground
by capillary action.
J S Foster 1994
• Platform frame
– Walls and partitions
bear on the platforms
formed by the floor
structure.
– Frames are single
storey in height.
• Balloon frame
– Studs are continuous
through 2 floors.
– First floor joists fixed
individually to the
studs.
Chudley & Greeno 1988
Platform
frame
I Seeley 1995
• Wall frames consist of
studs at 400-600 mm
centres, framed between a
bottom sole plate and
double head plates (head
binder and lwr head platenailed to form a continuous
member).
Platform
frame
• Wall frames bear on the
floor structures. They are
erected by nailing them
through the sole plate on to
the floor platforms.
• Ground floor structure:
joists nailed to sole plate &
header plate.
– Closes floor cavities
– Completes the platform
on which wall frames are
erected.
Foster
1994
• Upr floor structure: joists
built on the ground floor
wall frame nailed to head
binder and header plate.
Platform
frame
• In platform frame: option of
laying the floor before
building is closed
• A provisional sub-floor can
be laid on the joists
providing the floor structure
on which the frame bearsavoiding damage to floor
finishings.
– Useful working platform
– Enhances thermal insulation
of ground floor and sound
insulation of upper floor.
Foster
1994
Advantages of platform frame
• Relatively short members are required for the
studs.
• Storey height panels facilitate transport and site
handling.
• Studs and floor joists align (helpful when working
with grid layouts).
• Cross-grain moisture movement of the floor is the
same throughout the building as both external wall
frames and partitions bear on floor platforms.
Disadvantage: as floor construction must precede
erection of walls covering cannot occur as early as
with other methods-temporary protection.
• Wall frames independent from
floor structures.
• Studs are continuous through
2 floors.
• Studs extend from sole plate
to double head plates at roof
level unbroken by floor
structures.
• Sole plate nailed directly to cill
plate on the foundation-no
headers
• Studs and ground floor joists
bear on the sole plate.
• Joists face-nailed to studsstiffening on the other
direction.
Balloon frame
Foster1994
• Upr f. joists bear on a
continuous member let into the
studs (ribbon or ledger)provides lateral stiffening to the
long studs.
.
• Continuous cavities from
ground to roof between studs
linking to similar floor cavities.
Cavity barriers (50 mm
members cut-in between the
studs and joists) must be built
at 1st floor level and between
the floor and the wall against
fire and smoke spread.
Balloon frame
Foster1994
Advantages of balloon frame
• Wall frames can be erected independent of the floor
structure and up to roof level in one lift - covering of the
building at an early stage.
• The continuity of the studs and the face-nailing of joists
to studs provides rigidity to the structure.
• Absence of cross-grain minimises moisture movement
in the frame - no differential movement between the
cladding and the frame (stiff claddings).
• Disadvantages:
– joists and studs do not align;
– cross grain movement still occurs (in internal walls) since
the floor is also supported by storey height partitionsvertical movement uneven throughout the structure.
Prefabrication and joints
• Traditionally joints covered by external
sheathing and internal linings-after erection.
• In fully pre-fabricated systems ‘through the wall’
joints are produced.
– Need to exclude rain and wind but ensure
easy assembly.
• Simple joint techniques incorporate:
– A seal to act as a vapour barrier and wind
excluder near the inner face.
– A joint near the outer face that prevents rain
penetration and allows condensed warm
vapour from the inside to drain away.
Angles and junctions
•
Good tie between adjoining walls and to provide nailing
support for the interior finish and exterior sheathing.
Foster1994
Junctions
• Layout of the structure based on a co-ordinated system
of gridlines: incorporate filler pieces at junctions, of the
same thickness as that of linings or floor finishes, to
maintain the grid.
• No grid system is followed: set double studs blocked
apart at junction.
• Nailing boards fixed to noggins set between the studs
at junction.
Foster1994
Elements
• Internal lining-gypsum plasterboard
• Vapour barrier.
• Structural timber frame of vertical
studs at 400 or 600 mm centres, nailed
with simple butt joints to top and
bottom rails, noggings, sole plate
•
•
•
•
•
and head-factory produced with
sheathing board and breather
membrane attached.
Incombustible insulating quilt.
Sheathing board-plywood or other
wood material nailed to studwork.
Breather membrane to keep
rain/draught out allowing wall to
breathe.
Cavity
External cladding
• I Seeley 1995
• Internal lining:
– 13 mm lining-gypsum
plasterboardincombustible (class 0
spread of flame rating),
with taped and filled joints
or a skim coat of plaster. It
provides fire protection to
the timber and added
rigidity to the wall frames.
• Thermal insulation:
– Mineral or fibre glass in the
form of batts or paperfaced quilt
– Rigid polystyrene
– Incombustible
•
I Seeley 1995
Timber Frame
• Stress graded timber required.
• Typical dimensions 89x38 mm.
• Joints are simple butt and nailed, the frame is therefore
non rigid and requires bracing to provide adequate
stiffness.
• Bracing provided by:
– Wood-based sheet material nailed to external frame
face
– Diagonal bracing (optional)
– Internal plasterboard
• Durability: Any timber used as cladding and rated lower
than Class 3 (moderately durable- EN 350-2) should be
treated with preservative.
• Sheathing/Boarding
applied to external frame
face:
– 9 mm resin-bonded
plywood sheathing or 25
mm T&G boarding
– Functions:
• Provides rigidity to
the structure by
bracing the panels.
• Stiffens the studs in
the direction of their
smallest dimension.
• Produces stiffer
individual panels for
handling & transport
• Forms a nailing
surface for external
claddings
• Improves thermal
insulation of the wall.
Foster1994
• Moisture and vapour
barriers -prevent entry of
water into frame cavities.
• Vapour barriers:
– Placed on inner, warm side
of wall frame
– Exclude any warm water
vapour passing through
inner lining which may
condense inside the colder
cavity.
– Non-ferrous metal foil,
polyethylene sheathing, Alfaced plasterboard.
– Must be continuous and
imperforated-all joints
sealed.
• Moisture barrier:
Foster1994
– Placed on the external face of wall frame
– Exclude wind-driven rain and moisture from external cladding.
– Building paper ‘breather type’-excludes draught and external moisture
but permits passage of water vapour.
• External cladding
• Wide range (brick, tiles, slates,
timber boarding, ply sheathing,
cement rendering).
• When cladding is brick, a 40
mm cavity between cladding
and timber frame is requiredwater penetration & insulation.
• Galvanised light steel ties are
nailed to the frame and built
into the brickwork-flexible.
• A dpc must be inserted into
the brickwork extending over
the bottom of the cavity and up
the face of the frame behind
the moisture barrier.
• Open perpends (‘weep joints’)
needed at the bottom course.
Foster1994
• The cavity must be closed at the top and around all openings by
cavity barriers.
Types of cladding: self-supporting and nonself-supporting.
Typical
brick clad
timber
frame
wall.
Horizontal
timber
boarding.
TRADA Technology Library, 2010.
Render on
metal lath.
Tile /slate
hanging.
• Timber structure connected to brickwork by flexible wall ties.
Cavity-50mm wide, ventilated.
• I Seeley 1995
Openings in wall frames
• Studs on each side are
doubled:
– To provide support for the
lintel and large nailing
faces for finishes around
the opening.
• Lintels are:
• Double solid timbers of
depth appropriate to the
span.
• Plywood boxes built using
the wall frame and
plywood.
J S Foster 1994
Internal walls-partitions
• Vertical dividers to separate
internal space.
• Giving support to floors /roofs
(load-bearing, built with brick,
blocks, concrete) and nonloadbearing.
• Timber stud partitions: a stud
frame (factory produced) lined (on
site) on each side with
plasterboard or other sheet
material. Nogging pieces between
studs to stiffen the partition.
• See their junctions with frame
walls.
• Sheathing board can also be
applied for extra stiffness.
• Stud partitions of upper floors
usually supported by floor joists.
Separating walls
• Two independent wall
frames spaced 50-100 mm
apart. Preferable combined
width of 250 mm for
acoustic performance.
• Lining of 2 or 3 layers of
dense plasterboard on each
side to provide fire and
acoustic protection.
• Insulating quilt in one leaf or
the cavity to provide thermal
insulation.
• Light metal restrain straps
at approx. 1.2 m centres to
tie the 2 leaves at ceiling
level-to stiffen the frames
during construction.
• I Seeley 1995
• Cavity barriers required to prevent smoke and flame
penetration and restrict their spread. At different positions:
–
–
–
–
Around all openings in external walls
Junctions of external with separating walls
In all cavities at a maximum of 8 m centres
At each floor level in external and separating walls and at eaves level.
• Fire stops (mineral fibre or wool, cement material or plasterboard) fixed in
the cavity –between brickwork and frame) to prevent spread
of fire.
•
I Seeley 1995
Types of cavity barrierspreservative treated timber
battens; mineral fibre board;
wire-reinforced mineral wool
blanket; polyethylene
sleeved mineral wool.
Advantages of timber frame
• Shell constructed fast (1 day)-trades working under cover.
• Can be pre-fabricated-lower cost-fewer site operatives.
• Full insulation values achieved immediately after
construction.
• Choice of external claddings.
• High levels of insulation are achieved.
• Problems of drying shrinkage eliminated.
• Security on site (faster)
• Modifications to internal walls are simpler and cheaperinternal layout assumes greater flexibility.
• The lightweight and well insulated walls warm up faster
than brickwork or blockwork.
Problems
• Associated with poor practice- found in all forms of
building construction.
– Lack of provision for vertical relative movement
between the frame and the cladding.
– Inadequate provision for the exclusion of rainwater.
– Inability to provide effective barriers against fire.
– Torn or missing breather papers.
– Poor construction of flashings, gutters and windows
leading to water penetration.
• Performance of timber framed housing not less
satisfactory than that of traditional construction.