An insight into Roof systems

13 Oct, 2023 - 00:10 0 Views
An insight into Roof systems It is critical to have a reliable roof.

eBusiness Weekly

Engineering and Construction Matters

With Innocent Chatikobo

Roof system refers to the component of a roof including but not limited to covering, framing, insulation, sheeting, ventilation and weatherproofing.

It includes all materials contained within the roof assemblies installed by the contractor, including all materials above the deck including membrane flashing and related sheet metal work. A roof protects everything inside a building, and it can be used to install mechanical equipment and solar panels. It’s therefore critical to have a reliable roof.

Components of a roof system

Roof substructure: the trusses, rafters, purlins or other supporting framework to roof coverings, designed in accordance with requirements of the by-laws. The strength, dimensions and spacing should be as shall adequately support the roof covering applied to them. It is therefore imperative that one engages a competent and skillful person for this.

Roof coverings: these can be of different materials as specified in the designs. The coverings should be secured to withstand climatic conditions e.g. wind pressure, wind suction and changes in temperature.

Roof underlayment: some is applied below roof covering e.g. allucushion for insulation purposes. Others like asphalt felt are applied on top of the roof covering mainly for waterproofing purposes.

Flashings and other finishings: these include flashings on junction of roofs with chimneys, parapets, etc.; valley gutters and ridges which help to render the roof weatherproof.

What determines roof and truss design

The roof design is a key factor that affects the overall performance of a building. Each roof system has its own characteristics, advantages and disadvantages and recommended applications to consider when making a decision. A high-quality roof design requires highly qualified and skillful workmen.

A roof design should minimise water accumulation (ponding) which can cause leakages, mold growth and rotting which may eventually lead to roof collapse. Roofs can be constructed in a wide variety of shapes and designs depending on

The requirements they have to satisfy

Availability of materials and skills

Span to be covered


Roof design aesthetics

Loads acting on the roof

Common roof designs

To come up with a roof, we use trusses. A roof truss is a prefabricated structural framework which is used to support the roof of a building. They are predominantly triangular in shape, but the configurations vary to suit the roof’s pitch, size and design.

Triangles are used mainly because of their ability to support forces and they are easier to make than other shapes. There are two main roof truss categories namely flat roof and pitched roof.

These two categories can be subdivided into more specific truss types which can be used depending with construction application. Roof trusses are typically made from timber or steel joined together using various means. Some are made from concrete.

Roof supports

A roof can be supported using different methods as per the designs. The type of roof to be erected determines the support that is needed. It is therefore important to build proper walls that can safely support the roof load. Some of the common supports that can be used include the following

Load bearing walls

Concrete columns

Concrete beams (ring beams)

Timber upright supports (poles)

Steel upright supports (columns)

Roof cover materials

As contained in the Model Building By Laws Chapter 6 Section 11 to 24, there are various roof cover materials that can be used as roof cover. The different roof materials have different properties and hence are also used for different applications.

Their supporting structures (e.g. trusses) also differ therefore its important to have a specifically designed supporting structure for a specific covering material, with the appropriate angles as required.

Some of the materials as contained in the by-laws include the following

Asbestos cement corrugated sheets

Asbestos cement roof slates

Steel roofing sheets

Corrugated galvanized sheets

Galvanized inverted box rib (IBR) sheets

IBR chromadek (coloured sheets)

Metal roofing tiles (e.g. Harvey tiles)

Q-tiles (cement tiles imitation)

Concrete roofing tiles

Clay roofing tiles

Grass thatching


PVC (translucent sheets)

Wooden shingles

Rock slates

Copper roof sheeting

Aluminium and aluminium alloy roofing

Mastic asphalt roofing

Bituminous felt built up roof coverings

Concrete (as in decks)

When selecting roofing material, we consider a number of factors such as

The pitch of the roof

Roofing material budget

Architectural style required / aesthetics

How long you want your roof to last

Weather endurance

Complexity of the roof / difficulty in construction

Material weight

The roofing application / use / functionality municipal requirements and residential community agreements / covenants

The role of the client

The client is an integral part in ensuring that the roof has been properly done

Have background check of the contractor to check whether they are skilled for the job at hand

Reviewing and approving product requests and designs

Provision of the adequate funds required for the materials and skilled labour in a timely manner
Should supervise to ensure whether he is getting the desired quality for what he is paying (certifying of works)

Witness and monitor performances and tests

Approval of drawings and documents

This week’s questions

Describe some of the ways used to deal with roof leakages

Innocent Chatikobo is an Entrepreneur and Engineer by profession with AtroServe Engineering Zimbabwe. He has extensive knowledge and experience in Structural Engineering and Construction. For your comments, views, questions and feedback he can be contacted on the following platforms
Cell: +263 777 950 224; +263 712 376 037; +263 782 502 732
Email: [email protected]
Facebook: AtroServe Engineering Zimbabwe

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