Practical Information Sheet
TIMBER FRAME
Professionals
N°2
Contents
Foreword ................................................................................................................................ 4
Failure modes under the effects of wind and seismic activity ............................................... 5
Choice of materials ............................................................................................................... 10
Main frame components ....................................................................................................... 12
Frame fixing reinforcement .................................................................................................. 16
Bracing with wood-based panels.......................................................................................... 23
Bracing with diagonal timber braces .................................................................................... 25
Maintenance.......................................................................................................................... 27
Storage .................................................................................................................................. 28
Glossary................................................................................................................................. 29
References ............................................................................................................................ 29
Practical Information Sheet • Timber Frame 3
FOREWORD
This practical information sheet provides indications on installing timber frames. It presents
individual points that have a direct influence on how well the frame will stand up to the
effects of wind and seismic activity. Details on how to implement the other timber frame
requirements are not covered here.
Figure 1: Exposed structure that survived
4 Practical Information Sheet • Timber Frame
FAILURE MODES UNDER THE EFFECTS OF WIND AND SEISMIC ACTIVITY
If timber frames are not designed properly, they may exhibit three possible failure modes
caused by the effects of wind and seismic activity.
■ Failure of structural elements that have been weakened or overloaded
The structural elements have broken. This can be due to unsuitable design, the use of
materials that are not strong enough or incorrect dimensioning.
✓ Make sure you choose a suitable design, especially where
dimensioning of the components is concerned.
Figure 2: Cross-section not substantial enough
Figure 3: Purlin spacing too wide
Figure 4: No bracing
Practical Information Sheet • Timber Frame 5
■ Ripping out or breaking of joints
The joint components have been ripped out or torn. This can be due to installation errors
or using unsuitable assembly methods.
✓ Make sure you choose assembly components that are suitable
and supervise their installation.
Figure 5: Bad assembly
Figure 6: Bad panel-to-purlin fixing
6 Practical Information Sheet • Timber Frame
Purlins
Splice
Figure 7: Splices outside bearing points to be avoided
Simple
nailed
splice
Figure 8: Simple nailed splices to be avoided
Figure 9: Screwed connection
Practical Information Sheet • Timber Frame 7
■ Ripping out or breaking of the anchors
If the fixing used is not suitable for the material it is used on, it is possible that it will be
ripped out at the same time as framework elements.
✓ Choose suitable fixings for the material they are used on.
Figure 10: Bad frame-to-wall tie fixing
Figure 11: Improper attachment (flats poorly anchored)
8 Practical Information Sheet • Timber Frame
Figure 12: Bad maintenance
Figure 13: Improper assembly of the masonry and lack of bracing on a hip roof frame
Practical Information Sheet • Timber Frame 9
CHOICE OF MATERIALS
Choosing the right building materials and products is of prime importance to the safety
and durability of the buildings. This information sheet provides selection criteria for
choosing these products. The performance levels meeting the criteria must be specified
by the manufacturer and marked directly on the product or the label accompanying it.
For this information to be usable, it must be specified in a precise format, namely the
format associated with the CE mark.
Figure 14: Logo that must be displayed on products bearing the CE mark
■ Timber
Because of the marine environment on the Island of Saint-Martin, only the following should
be used as structural components:
• softwood;
• tropical hardwood;
for which the maximum moisture content is less than or equal to 20%. Choosing the right
timber has a considerable influence on the durability of the frame.
Timber used for the structural elements must meet class 4 requirements (in accordance
with NF EN 1995-1 and AN) and have anti-termite protection.
Timber used for the non-structural elements must meet class 3 requirements (in accordance
with NF EN 1995-1 and AN) (through natural durability or treatment).
The use of EN 636-2 type plywood panels, P5 and P7 type particleboards and fibreboards
for structural purposes is not permitted.
■ Roof
The roof is made up of metal sheets (see the information sheet on metal roofs).
■ Metal joining and fixing systems
Timber structure joining and fixing systems must be made of steel with a zinc coating
validated for class 2 service use: type Z275 coating. It should be noted that using assemblies
made of stainless steel improves durability.
10 Practical Information Sheet • Timber Frame
Choice of materials
Hex head bolts
Fields of application:
purlin hangers, mixed
reinforced brackets.
Anchor bolts
Fields of application:
wall tie fixings.
Screws
Fields of application:
purlin hangers
Structural wood screws
Field of application:
timber component assembly..
Purlin hangers
Fields of application:
beams, purlins, stringer beams
and rafter abutments.
Structural brackets
Fields of application:
purlins, rafters.
Practical Information Sheet • Timber Frame 11
MAIN FRAME COMPONENTS
The framework is comprised of:
• trusses;
• rafters or purlins.
To ensure that the frame is sufficiently rigid, the following characteristics should be
adhered to:
• The trusses should have a span of no more than 10 m and be spaced no more
than 3 m apart.
• The elements making up the trusses should comply with the following dimensions:
– the cross-section of the king post should be at least 15 x 15 cm;
– the cross-section of the principal rafters should be at least 8 x 25 cm;
– the cross-section of the struts should be at least 8 x 15 cm;
– the cross-section of the tie beams should be at least 2*5 x 15 cm;
– the struts should form an angle of no more than 45° with the king post.
15 x 15 cm king post
8 x 25 cm principal rafter
45°
max.
8 x 15 cm strut
2* 5 x 15 cm
tie beam
b ≤ 10 m
Figure 15: Components of a main (king post) truss
• The distance between the tie beam-to-principal rafter joint and the bearing
point should be less than or equal to a third of the distance between the king
post-to-principal rafter joint and the bearing point.
King post
Principal rafter l1
≤l
1 /3
Tie beam
b ≤ 10 m
Figure 16: Example of a raised tie truss
12 Practical Information Sheet • Timber Frame
• The purlins should be no more than 0.8 m apart. The spacing between the
4 purlins at either end should be reduced by half.
Purlins at 0.8 m intervals
m
l≤ 10
3m b≤
Figure 17: Spacing between the common purlins (to be removed from the diagonal elements in red)
4 end purlins
at 0.4 m intervals
4 end purlins
at 0.4 m intervals
m
l≤ 10
3m b≤
Figure 18: Spacing between the first 4 purlins at either end
(to be removed from the diagonal elements in red)
Practical Information Sheet • Timber Frame 13
• The rafters should be no more than 0.6 m apart. The spacing between the first
4 rafters at either end should be reduced by half.
Rafters at 0.6 m intervals
m
l≤ 10
3m b≤
Figure 19: Spacing between the main rafters at either end
(to be removed from the diagonal elements in red)
4 end rafters 4 end rafters
at 0.3 m intervals at 0.3 m intervals
m
l≤ 10
3m b≤
Figure 20: Spacing between the first 4 rafters at either end
(to be removed from the diagonal elements in red)
14 Practical Information Sheet • Timber Frame
Although hip roof frames are generally more stable, they are more expensive to build than
gable roof frames.
Rafters at 0.6 m 8 x 25 cm 8 x 15 cm
intervals ridge board hip rafter
Rafters
at 0.6 m intervals
Figure 21: Example of a hip roof frame
Practical Information Sheet • Timber Frame 15
FRAME FIXING REINFORCEMENT
■ General
Structural joints created with metal components are subject to CE marking, a European
Technical Assessment and a technical specification by the supplier.
Nails of any type, including twist nails working under tension, should never be used.
Joints that work under tension can be made using coach screws or bolts and these can be
combined with plates or corner braces where necessary.
Carpentry joints (housed joints, notch joints, mortise and tenon joints, etc.), which essentially
work through contact, are forbidden when assembling the main elements constituting the
bracing. These assemblies must include additional metal assembly parts. These could be
metal rods (plate bolts, nuts, screws, etc.), which may be used in conjunction with brackets
and hangers.
Notch joint Bolt of lightning Lapped
scarf joint scarf joint
Perpendicular Dovetail joint Mortise
lap joint and tenon joint
Figure 22: Examples of carpentry joints that require devices to hold them in position even
when the loads are inverted
16 Practical Information Sheet • Timber Frame
■ Truss assembly joints
The following joints are needed to build a main truss:
1 Assemblage arbalétrier - poinçon
2 Assemblage contrefiche - poinçon
3 Assemblage entrait moisé - arbalétrier
4 Assemblage entrait moisé - poinçon
King post
1
Principal rafter
45°
max.
Strut
Tie 2 3
beam
4
Figure 23: Truss assembly joints
j The principal rafter / king post joint is made using a housed joint and tenon, reinforced
by a horizontal bolt with a diameter of 10 mm.
King post
Principal
rafter
Figure 24: Making the principal rafter / king post joint more secure using a bolt
Practical Information Sheet • Timber Frame 17
k The strut / king post joint is made using a housed joint reinforced by a bolt with a
diameter of 8 mm.
King post
Strut
Figure 25: Making the strut / king post joint more secure using a bolt
l The double tie beam / principal rafter joint is made using a housed joint reinforced by
a vertical bolt with a diameter of 10 mm or, in the case of a double tie beam, by a joint using
2 bolts with diameters of 8 mm each.
Principal rafter
Tie beam
Figure 26: Making the tie beam / principal rafter joint more secure using a bolt
Principal rafter
Tie beam
Figure 27: Strengthening the double tie beam / principal rafter joint using two bolts
m The double tie beam / king post joint is made using a simple housed joint reinforced by
2 bolts with diameters of 8 mm each.
18 Practical Information Sheet • Timber Frame
King post
Strut
Tie beam
Figure 28: Strengthening the double tie beam / king post joint using two bolts
■ Purlin-to-principal truss rafter fixing
The purlin-to-principal truss rafter joint can be reinforced by using metal hangers, brackets
and reinforced metal corner braces..
Purlin
Principal rafter
Figure 29: Purlin-to-principal rafter joint
(to be removed from the diagonal elements in red)
Principal rafter
Purlin
Metal hanger
Figure 30: Purlin-to-principal rafter joint using metal hangers
Practical Information Sheet • Timber Frame 19
Purlin
Principal
rafter
Metal bracket
Figure 31: Purlin-to-principal rafter joint using metal brackets
Purlin
Metal corner brace
Principal rafter
Figure 32: Purlin-to-principal rafter joint using metal corner braces
Simple purlin splicing with nails mid-span should be avoided. If splicing is unavoidable, it
should only be done over bearing points.
Splices Purlins
on bearing points
Principal rafter
Figure 33: Purlin splicing over bearing points, if unavoidable
20 Practical Information Sheet • Timber Frame
■ Rafter-to-ridge board joints
Rafter-to-ridge board joints can be reinforced by using through-bolts or coach screws with
a diameter of 8 mm.
Rafters at 8 x 25 cm 8 x 15 cm
0.6 m intervals ridge board hip rafter
Rafters
Ridge board at 0.6 m intervals
Rafters
Figure 34: Rafter-to-ridge board joints using bolts
■ Rafter-to-hip rafter joints
Rafter-to-hip rafter joints are made using a single 8 mm diameter coach screw or two
6x120 mm screws.
Rafters at 8 x 25 cm 8 x 15 cm
0.6 m intervals ridge board hip rafter
Rafters at
0.6 m intervals
Hip rafter
2 screws
6 x 120 mm
Rafter
Figure 35: Rafter-to-ridge board joints using bolts
Practical Information Sheet • Timber Frame 21
■ Anchoring the frame to the walls
The frame must be supported on the horizontal wall ties at the top of the wall. The timber
frame anchoring points to the concrete should be made using anchor bolts.
Principal rafter
Anchor
plate
Tie
beam
Figure 36: Anchoring the frame to the concrete using anchor bolts
22 Practical Information Sheet • Timber Frame
BRACING WITH WOOD-BASED PANELS
The frame can be stabilised horizontally by installing plywood panels or water-repellent
roofing under-panels onto the rafters and purlins and covering the entire surface of
the roof slopes.
To ensure that the frame is sufficiently rigid, the following characteristics should be
adhered to:
• minimum panel thickness should be 10 mm for the plywood panels and 14 mm for
the water-repellent roofing under-panels;
• the dimensions of the panels should be greater than or equal to 120 x 240 cm
over the main span;
• the panels should not have any openings, holes or defects/faults;
• the panels should be staggered (the joints should not be in alignment);
• the perimeter of the panels should be covered. The screws should be spaced no
more than 15 cm apart and 1 to 1.5 cm from the edges;
• the width of the gaps between the panels should be approximately 1 mm/m
along the length of the panels;
• 50 x 80 mm battens should be fixed on top of the panels in line with the panel
gaps. The screws should be no more than 15 cm apart.
Nailed Batten Rafter
panel
1 mm/m panel gap
Figure 37: Bracing with wood-based panels
Practical Information Sheet • Timber Frame 23
Screwed-down panel
Batten
5 x 8 cm
Vis
Vis
Rafter
Figure 38: Attaching the batten to the rafter through the panel
24 Practical Information Sheet • Timber Frame
BRACING WITH DIAGONAL TIMBER BRACES
The frame can also be stabilised horizontally by fitting diagonal braces between the rafters
or purlins.
To ensure that the frame is sufficiently rigid, the following characteristics should be
adhered to:
• the cross-section of the diagonal braces should be at least 8 x 10 cm;
• the diagonal braces should be connected to the frame components using
2 annular ring or twist nails with a maximum diameter of 3.1 mm.
Rafters
Diagonal
braces
m
10
l≤
3m b≤
Figure 39: Diagonal braces fitted between rafters
Purlins
Diagonal
braces
m
10
l≤
3m b≤
Figure 40: Diagonal braces fitted between purlins
Practical Information Sheet • Timber Frame 25
Ridge board
Hip rafter
Diagonal
braces
Rafters
Figure 41: Diagonal braces used on a hip roof frame
26 Practical Information Sheet • Timber Frame
MAINTENANCE
Maintenance should be carried out on the timber frame components once a year as the
hurricane season approaches. The components should be inspected at the same time to
make sure there is no premature damage.
• Check that the timber components do not show any signs of humidity or damage
(fungus or insect), especially in those areas with the greatest humidity (post bases,
assemblies in which several pieces of timber are in contact, etc.).
• Check that the timber components do not have any major defects (distortion,
splitting).
• Check that the joints and fixings are not showing signs of corrosion.
• Pay particular attention when checking the stability of the frame bracing.
• Make sure the joints are tight (bolts tight, no protruding screw heads or points).
If you do detect a problem, change the fixings immediately and, if necessary, the timber
component as well.
Practical Information Sheet • Timber Frame 27
STORAGE
Components at the building site should be stacked and stored away from moisture (rain,
condensation, etc.). Ideally, the components should be stored in an inclined position in a
well-ventilated, sheltered area.
The timber must not be laid directly on the ground as this can cause soiling and moisture
absorption.
It is also important that the timber be properly supported to prevent permanent distortion.
Figure 42: Storing timber components
28 Practical Information Sheet • Timber Frame
Glossary
Bracing: constructions that provide horizontal structural stability.
Frame joint: traditional joint in which the forces are transmitted through the contact surfaces; this
type of joint does not have any mechanical connectors (for example, housed joint, tenon).
Housed joint: notched joint between two pieces of timber.
Moisture: mass of water in the timber expressed as a proportion of its dry mass.
King post: vertical central component of a traditional frame truss. The king post supports the tie
beam at its base.
Principal rafter: main sloping timber of a frame truss that supports the roof (purlins + roof).
Purlin: horizontal component of a loft frame made out of timber or metal. The purlins rest on the
principal truss rafters and provide support for the rafters or rigid roofing panels.
Tie beam: horizontal component that forms the base of a frame truss and prevents the principal
rafters from spreading outwards.
Truss: vertical assembly of components that forms the triangular framework of a timber frame: all
frames comprise several trusses arranged at right angles to the axis of the loft. The trusses provide
support for the horizontal purlins, which in turn carry the rafters and the roof.
References
NF DTU 31.3 (P 21-205) Charpentes en bois assemblées par connecteurs métalliques ou goussets
(Timber structures connected with metal plate fasteners or gussets).
Règles Antilles – révision 1992.
Guide de construction parasismique et paracyclonique de maisons individuelles à structure en
bois aux Antilles – Secteur pilote Innovation Outre-Mer, 2011
Robin-Clerc, Michèle – Les leçons du cyclone Irma. 10èmes Journées Fiabilité des Matériaux et des
Structures – Bordeaux, 27-28 March 2018
Eurocode 5 : Design and calculation of timber structures
Eurocode 8 : Calculation of structures for earthquake resistance
✓ Note: all dimensions are given by default. Timber structure designers
can be exempted with the proviso that their calculations comply to
Eurocode 5 and NF DTU 31.3.
Photos
CAUE [Conseil d’Architecture, d’Urbanisme et de l’Environnement – Council for Architecture, Town
Planning and the Environment] Guadeloupe.
DEAL [Direction de l’Environnement, de l’Aménagement et du Logement – Environment, Planning
and Housing Directorate] Martinique and Guadeloupe.
Délégation interministérielle pour la reconstruction des îles de Saint-Barthélemy et Saint-Martin
[Interministerial delegation for the reconstruction of the islands of Saint Barthélemy and Saint Martin].
Diagrams
Laurent Stefano
Practical Information Sheet • Timber Frame 29
PRACTICAL GUIDE ON POST-HURRICANE REPAIRS
www.saint-barth-saint-martin.pref.gouv.fr – www.com-saint-martin.fr
Prefecture : 05 90 52 30 50 – Communit y’s Town Planning Department : 05 90 52 27 30
