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Home/Roof truss glossary

Glossary and FAQ

Roof truss glossary and FAQ.

Every roof truss term you are likely to meet, explained in plain English, plus answers to the questions homeowners and builders ask us most.

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A long-span roof truss being moved across the factory floor
Long-span truss · Free State plant

A to Z

Roof truss terms, explained.

The words you will see on roof plans, quotes and engineer reports, in plain English.

A

Apex
The highest point of a truss, where the two top chords meet at the ridge.
Attic truss
A truss with an open rectangle in the middle so the roof space can be used as a room or storage. See truss types.

B

Barge board
A board fixed along the sloping edge of a gable roof to finish and protect it.
Batten
A small timber strip fixed across the trusses to carry roof tiles.
Bottom chord
The horizontal bottom member of a truss. It ties the two sides together and usually carries the ceiling. Also called the tie beam.
Bracing
Timber members fixed across the trusses to tie them into a stable roof that resists wind. Includes diagonal, longitudinal and web bracing.
Brandering
Timber strips fixed under the bottom chords to carry ceiling boards.

C

Clear span
The distance between the supporting walls that a truss spans without support in between.
Competent person
The registered engineer or engineering technologist who takes responsibility for the roof design and signs it off. See regulations.

D

Deemed-to-satisfy
Standard details in SANS 10400-L that are accepted as compliant without a separate engineered design, within set limits.

E

Eaves
The lower edge of the roof that overhangs the walls.

F

Fascia
The board fixed along the ends of the trusses at the eaves, usually carrying the gutter.
Fink truss
The most common house truss in South Africa, with webs forming a W shape.
Form 2 and Form 4
Municipal forms used to appoint the competent person (Form 2) and certify completion (Form 4).

G

Gable
The triangular end wall of a roof that slopes on two sides.
Girder truss
A heavy truss, often two or three trusses fixed together, that carries the load of other trusses hanging from it.

H

Heel
The joint where the top and bottom chords meet over the wall.
Hip roof
A roof that slopes down on all four sides.
Howe truss
A truss with vertical webs and diagonals sloping towards the centre. Used in SANS 10400-L deemed-to-satisfy details.
Hurricane clip
A galvanised connector that fixes a truss to the wall plate to resist uplift.

I

ITC-SA
The Institute for Timber Construction South Africa, which audits and approves truss fabricators and erectors.

J

Jack truss
A short truss used to fill the corners of a hipped roof.

K

King post truss
A simple truss with a single vertical post in the middle, for short spans.

M

MiTek
The roof truss design software Truss Master uses to engineer every roof. Truss Master is a MiTek fabricator.
Mono truss
A single-slope truss used for lean-to roofs, verandas and carports.

N

Nail plate
A galvanised steel connector plate pressed into each joint of a truss in the factory.

O

Overhang
The part of the roof that extends past the wall, at the eaves or gable.

P

Pitch
The angle of the roof slope, measured in degrees. See pitch guide.
Purlin
A timber or steel member fixed across the trusses to carry roof sheeting.

R

Rafter
The sloping member that carries the roof covering. In a truss it is called the top chord.
Raised tie truss
A truss with the bottom chord set higher than the wall plate, giving a partly sloped ceiling.
Ridge
The horizontal line at the top of the roof where the slopes meet.

S

SANS 10243
The South African standard for the manufacture and erection of timber trusses.
SANS 10400-L
The part of the building regulations standard that covers roofs, including truss spacing, pitch, bracing and anchoring.
Scissor truss
A truss with sloping bottom chords that creates a vaulted ceiling.
Spacing (centres)
The distance between trusses, measured centre to centre. Typically 760 mm under tiles.

T

Tie-down
A galvanised strap or wire built into the wall and fixed to the truss to stop wind lifting the roof.
Top chord
The sloping top member of a truss that carries the battens or purlins and the covering.
Truss
A triangulated frame of timber or steel members that carries the roof.

V

Valley
The internal angle where two roof slopes meet.
Valley truss
A truss set on top of the main roof to form a valley where two roofs join.

W

Wall plate
The timber member fixed along the top of the wall that the trusses sit on.
Web
An internal member of a truss that braces the chords and spreads the load.
Wind uplift
The suction force of wind trying to lift the roof, resisted by tie-downs and bracing.

FAQ

Roof trusses: frequently asked questions.

What is a roof truss?

A roof truss is a triangulated frame of timber or steel members, joined with nail plates or bolts, that carries the weight of the roof covering and transfers it to the walls.

How much do roof trusses cost in South Africa?

As a rough guide, the timber roof structure for a house usually costs about R250 to R650 per square metre before the covering. See our price guide for details.

How far apart are roof trusses spaced?

Under concrete or clay tiles, trusses are spaced at a maximum of 760 mm centres. Under metal or fibre-cement sheeting on purlins, up to 1,200 mm under the deemed-to-satisfy rules.

What is the most common roof truss?

The Fink (W) truss is the most common truss for South African houses.

Do roof trusses need an engineer?

Yes. For engineered trusses, a competent person, usually a registered engineer, takes responsibility for the roof and signs it off.

How long do roof trusses take to make?

At Truss Master, quotes usually take 1 to 5 working days and manufacture typically takes 3 to 10 working days after the site measure.

Can I cut a roof truss to fit a geyser or hatch?

No. Every member in an engineered truss carries load. Ask your truss supplier to design for what you need instead.

Timber or steel roof trusses?

Timber is usually the most economical choice for houses. Steel suits long spans and termite-prone areas. See timber vs steel.

Do you deliver roof trusses?

Yes. Truss Master delivers countrywide on its own trucks from six plants and a North West branch. See our branches.

How do I get a quote?

Send your plans and the nearest plant will design your roof and send a free, itemised quote.

Keep reading

Price guideWhat roof trusses costTruss typesFink, hip, attic and moreSpacing and bracingThe SANS 10400-L guideRegulationsSign-off explainedHomeownersBuilding your homeBuildersFor contractors

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