Most common roofing options for a new build are:
Mono pitch
Very popular right now with more contemporary house designs. Single roof beams (either wood or steel) will hold up aluminium roof sheets, or maybe tiles for a more Mediterranean look.
The key with this roof style is the detail, especially if you are using extra sky lights on the higher side. Engineered brackets will be required to hold up the roof beams, and if done correctly, the glass behind creates a floating look (see picture below). As almost always the case, the final finish and detailing will make or break this look. Definitely requires the architect’s input to do it well. Architect Darryl Croome (dcarch.co.za) is a master of this.
Double pitch
The standard, double pitch roof design is making a comeback, albeit without eaves and a very dramatic angle. The more basic version is practical as you can order pre-assembled roof trusses that can be craned in in a day. Corrugated roof sheets complete a more modern look, while clay tiles/slate would be a more old school finish.
If you use engineered trusses with very few horizontal cross beams in a high ceiling, it enables you to convert the space into a loft at a later stage. (Hence a basic barn shape house, with a floor in the ceiling, is a great option for a budget constrained build.)
Flat roof
Concrete, flat roofs are often used to link two different wings together. However, many architects like using expansive, concrete roofs now. What is not well knowns is that concrete is a terrible insulator and can leaks like a sieve. There are many methods of addressing this, but they are expensive and difficult to get 100% right. It’s not a case of if, but when your flat concrete roof will develop a leak.
The most important, but surprising, detail to get a concrete roof leak resistant is the top screeding layer. This has to have a consistent fall right across the expanse of the roof to a drain, to let all the water run off and not pool once the waterproofing membrane has been installed . Simple on paper, but very tricky to get right across a large area.
Update: Adding a new product, Penetron, to your concrete mix also now helps make the roof waterproof. Not too expensive, and easy to do at casting stage.
An alternative option for creating a roof that looks flat, but has a slight fall behind, is to build parapet walls on three sides (that give the appearance of a flat roof façade), but then use roof sheets instead, that fall at a 3-10 (if you only have space for a roof less than 5 degrees, you will need to get clip lock sheets to prevent leaking) degree angle to the back. That will still require flashing/waterproofing against the walls though. Try and get the metal flashing that goes up the wall and over the top to prevent future leaks.
Eaves
Never underestimate the fantastic use of eaves to keep direct sun and water out of your windows. Deep (at least 500mm) eaves prevent the hottest, north sun from entering the house when it’s at its highest position in summer. Brilliantly, as the winter sun drops, it allows the sun to stream in when you need it over the colder months.
Unfortunately, they don’t really work for west, horizontal sunlight. Best solution in this case is external shutters.
Waterproofing
One of the most frustrating details of completing a new house is finding all the leaks from the first rains. Each storm brings different directional water, and it takes a while to cover all the angles.
Generally, specialists are the way to go, especially with flat roofs. Torch on rubber (Derbigum) is generally the industry standard, but still not always fool proof if the plastered screed is not done correctly underneath. You can also add waterproofing agent to the concrete.
Insist on supervision and guarantees. Yearly maintenance is required for these guarantees though, so you will have extra costs each year. Also see Painting and Sealing.
Ceilings and insulation
All roofs (except thatch) need insulation of some kind, for heat/cold and in some cases, noise. Aluminium roofs obviously offer the least protection, so ceilings need excellent insulation. Roofing foil from a hardware store is certainly not enough for our climate.
If you have exposed rafters, with little to no gap between the sheets/tiles and ceiling board, Lambda or Isoboard is an excellent alternative. This product acts as a ceiling board, but is in fact a highly concentrated insulator. Make sure you leave no gaps in the insulation though. It’s only as effective as it’s complete covering. Any gaps let the heat/cold in and counter the effectiveness.
If you choose to have an exposed concrete ceiling, you can choose textured boards when building the formwork to leave a pattern (wooden planks are popular) or simply use plastic coated boards for a smooth finish.
Concrete roofs can be insulated with polystyrene and a think layer of stone chips on top (300mm). Factor in extra strength during the design stage (i.e. tell the structural engineer you’d like to add chips or soil as it will require more steel, and different specs). At the very least, paint the rubber waterproofing with silver paint to reflect the sun.
Reminder
Before you get ahead of yourself and think the build is almost complete, just remember, that once the roof is on, you are roughly half way through your build. The devil’s in the details.
It can also be tradition to have a celebration of some kind when this stage is complete. A site braai for the labour force is always appreciated – Roof wetting party!
Update – A19 certificate
Building legislation now requires that any new roofing structure has to be certified by a structural engineer before the building inspector will sign the project off as being completed. If you are hiring a roofing company, make sure they can issue the certificate as part of their service.