Most common roofing options for a new build are:
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 need architect detailed drawings for this.
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 more a more classic finish.
If you use engineered trusses with very few cross beams in a high ceiling, it enables you to convert the space into a loft at a later stage.
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 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. Simple on paper, but very tricky to get right across a large area.
One alternative option is to create parapet walls on three sides (that give the appearance of a flat roof facade), but then use roof sheets instead, that fall at a 5/10 degree angle to the back.
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, flat sun. Best solution in this case is external shutters.
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.
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 board 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 to leave a pattern (wooden planks are popular) or simply use plastic coated boards for a smooth finish.
Concrete that is exposed to the elements can be insulated with polystyrene, or a think layer of stone chips on top (300mm) . At the very least, paint the rubber waterproofing with silver paint to reflect the sun.
Before you get ahead of yourself, just remember, that once the roof is on you are roughly half way through your build. The devil’s in the details.