A house’s roof is one the most important structures on the home. It protects everything inside the house – from the furniture, appliances, electrics, fittings, fixtures and paint, to the occupants.
But how much do you really know about this structure, how it’s made, installed and maintained?
Albert van Wyk, one of only 40 registered roof inspectors in the country, has kindly allowed HomeTimes to republish portions of his book, The Proud Home Owner.
Here, he discusses the make up of your roof, what tiles to use as well as how to identify good and poor workmanship.
There are two methods by which trusses can be manufactured. The first one is that a carpenter makes the trusses on site and erects them. He must be well acquainted with design requirements and what timber to use. This method is mostly used for extensions or additions to an existing house or for small houses.
A structural engineer must issue a certificate that the design, manufacturing and erection is to his satisfaction and that he will accept responsibility for the structure.
The other system is designed by way of a computer program and then manufactured by a registered truss manufacturer. The trusses are erected by a certified roof carpenter in accordance with the design. A certified inspector will then issue a certificate that the trusses were manufactured and erected according to the design.
This system and method is under the jurisdiction of The Institute for Timber Construction South Africa and is well controlled and managed.
You will have to make sure that the roof is well anchored to the walls, because it is not the responsibility of the roof inspector to certify that this is done.
The first truss should be about 50mm away from a gable wall. The reason for this is in order to allow for movement of the trusses during heavy wind conditions, so as not to crack the gable wall.
Additional timber must be installed to the top chord member of the trusses below a solar panel. Additional timber must also be installed to the bottom chords of the trusses which support the electric geyser. A solar geyser needs to have a specially constructed platform on the trusses.
All this information and more will be on the roof plan if it is designed by a recognised software program.
Watch out for damaged plastic tile under lay (membrane) after the carpenter is finished.
Do not accept site-made trusses, but insist on ITC designed, manufactured and erected trusses which are certified by an engineer. Do not gamble with the roof construction as the risk is too high.
Make sure that the valleys are constructed correctly. Do not compromise as they are the main reason for water leaks in the house – pay attention to the valley gutter (also referred to as valley flashing) which must be a certain design.
Both designs are effective if they are correctly done. I would suggest that you opt for the open valley, especially if there are large trees near the house.
Insurance companies are reluctant to compensate you if the design and construction is wrong, as illustrated in the two photographs below.
Be sure that the thickness of the galvanising is specified in the contract and obtain proof from the supplier. It should be an average of 275g/m2 for inland regions, and 600g/m2 for coastal regions. These days this type of roof is very popular and has become architects’ favourite type of roof.
There are basically two different designs available: The corrugated iron profile and IBR profile. Different factories manufacture these sheets from various materials and pre-paint them to give you an excellent product with a guarantee for many years.
Remind the contractor that these sheets must be installed by registered erectors in order to get a factory guarantee. Do your homework and get acquainted with the factory requirements.
Some factories do not allow cutting of their sheets or that paint touch up be done, and they insist that the erectors wear soft shoes.
There is a leak-proof sheet available under the trademark of “Brownbuilt”. This profile is different and the fixing method is unique, which makes it leak-proof. No fixing screws are visible which could become potential leaks.
I recommend that you rather consider using “Chromodeck” which is a trade name of sheets which are made of factory-painted aluminium which need no or little maintenance and come with a factory guarantee.
Low-pitch sheeted roof
These are high-risk roofs for leaks, but the correct installation by qualified tradesmen will reduce the risk substantially.
The manufacturers of roof sheets specify that the minimum slope of a roof over a distance of about 6m should be 50 and over longer distances it should be 100. My personal opinion is that these angles are too low and that is the main reason for so many leaks on these types of roofs.
I am in favour of the installation of gutters and down pipes to a house. Gutters will enable you to control the water from the roof better and it will not stream down from the roof like a waterfall without control.
While the gutters are being installed it is the right time to plan the stormwater management of the site, including water to and from the neighbours as well as rainwater harvesting.
The anchors should be evenly spaced where the trusses or beams will rest on the walls.
Double strand of 4mm galvanised steel wire embedded at least 500mm below the wall plate.
30mm x 1.6mm galvanised steel strap should be embedded at least 600mm below the wall plate.
Next time we will focus on roof leaks: what causes them and how to identify them
For more, visit The Proud Home Owner and order your copy of Albert’s book today