Roof basics – Stone chips on metal tiles

Almost impossible to find one of these that is not damaged.

“Decramastic”. Pitch over 15 deg. It consisted of pressed metal sheets covered in a bitumen compound with embedded stone chips.

For our conditions a really crappy roof covering. Most hot days, you cannot walk on the roof without the surface sliding under your feet. (The bitumen gets soft).

The batten set out must be spot on. No tolerance.

You must, repeat MUST walk on the battens.

I have seen a trail of bent and distorted tiles leading from the eaves, over the ridge to a new solar hot water system. The plumbers that fixed it had no idea of the roof surface or did not care.

Sheet metal roofing.

Used to be galvanised iron. It is now a material called “Zincalume” in Australia.

It does not have the same properties as Galvanised. It cannot be soldered.

All joints that require a sealer must use one recommended by the manufacturer. Usually a neutral cure silicone like “Roof and Gutter Silicone” or any of the PU mastics.

DO NOT use ascetic cure silicone.

It is also not compatible with copper pipes and lead flashings, so isolate them.

If I were building for myself, I would not fail to use a metal sheet cladding on my roof. The wide range of colours, profiles, roof pitches from 1 to 90 degrees, the ability to curve and twist, all in a competitive price range make it my choice. (I said I was biased). It all really depends on what is available and even acceptable in your area.

I have no experience at all with many of the roofing materials used in North America, although I once did a shingle job, that is popular over there. (Lost money on it, not the fault of the shingles though, the house was a geodesic dome, and It was for a mate, so I was doomed to lose money from the start).

Here is a site from a guy who knows more about materials in the US.

Here is another off-site link Steel Metal Directory For metal sheeting vendors, supplies, and installers.

Click here for my main page on metal sheeting, which leads to a fixing page.

Hip Roofs Vs Gable Roofs and Skillion Roofs. Pros and Cons

Here is part of a message I have received (March 2007) from John H. in Queensland: –

Bill some builders are saying forget skillion roofs build hipped roofs for Qld especially with high rainfall and subtropical storms. Or are they saying this because this is all their design program will do? There is not much on the net about this. Can you give us the drum on pros and cons of skillion vs hipped roofs?

First off John, I will chuck in gable roofs with skillion roofs as they are similar. People also seem to use the term Skillion roof for what I call a shed roof, that is just one sloping surface, with the front and back walls of different height and the side walls sloping. Which you could say is like half a gable roof. The same arguments pro and con apply. So, I will give you my run down on both roofs, I guess some of this I have said before, but it is good to get it in one place.

For me the most compelling reason for a hip roof, especially on a ground level house, is the level eaves, with a consistent overhang all around. This simply means that it is easier to comply with the BCA requirements for shading of external walls etc. for energy efficiency. The overhanging eaves usually mean that the walls comply without addition thermal insulation, and the doors and windows in them do not need awnings.

If you have gable/skillion roofs, the overhang is usually less on the gable/side walls, (unless of course you are using steel purlins, which are great for skillions), and with the increased height over part of it the shading effect is also less, so you might have to build awnings or insulate the walls. If there are windows and doors on the gable walls, most likely you will need awnings. Depending on the orientation of course.

Because of the sloping surfaces on all sides of a hip roof, they are in effect self-bracing against side wind loads. So, I think they are stronger than a gable roof. (All other things being equal).

timber roof truss holds down bolts, metal purlins Gable roofs (with their square edges to the gables) create greater uplift forces in high wind (cyclonic) conditions than hip roofs. This fact alone would be the deciding factor in many parts of the world.

Cost wise, gables or skillions may come out cheaper, but depending on the wall construction, when you add the extra cost of the walls they may not be too far in front.

I would guess that most of the average houses in your area, apart from architect designed one offs, would use metal nail plate roof trusses, who do the design and the supply, so your builder really has no hand in the engineering of the roof design.

About engineering design, most builders looking at shots like this, of the hold down bolts required for modern construction in cyclonic areas, probably think it is a bit extreme. Well…. I believe that with global weather changes etc. this type of construction may be “coming to your area soon”.

What is happening up here is that the developers are using a variety of roof design elements in any one single house. They have hips, dutch gables and gables. They use awnings over windows and doors. They make feature gables over entrances etc. They change the mix in various forms so that the outside appearance of very similar house plans is very different.

A lot of it is more about looks and marketing, than strength and weatherproofing. Any design feature you want can be engineered and built. It really depends on how much you must spend. If I were still building, I would have to do the same, because that is what is selling now. A plain box with gable ends is a thing of the past.

Check things out in your own area as different regions have preferences but remember (in Australia) we are all governed by the requirements of the BCA, so styles are starting to change in response to this.