Life’s a Pitch
Some readers may think this is just common sense but I’m never surprised by how often I’m asked, “What kind of roofing can I use on my roof?”
The answer to me is pretty clear cut – but there are also some simple ideas that might get you to reconsider using different profiles on lower pitches, and some other little tricks which builders and contractors can use to save a lot of money by simply raising the pitch slightly.
When sizing up any standard home, you’re usually looking at a roof pitch that ranges from 18 degrees to 35 degrees. As far as I’m concerned, the best of these are fitted with corrugated metal roofing – I just can’t bear the sight of those cheap-looking tiles, given that I specialise in metal.
Occasionally you may see these steeper pitched roofing installed with tray deck Trimdek style or even Klip-Lok profiles, but these are rare because it generally costs more to install these kinds of roofing profiles.
Our housing landscape is changing though. At present a significant portion of houses are being built with flatter pitched roofs and box gutters with parapets, to maximise the build size of the home on seemingly ever-decreasing house block sizes.
If you stick to the normal profile specification, this style of roofing is relatively expensive to install. With a building that has a roof that only has a pitch of 1 degree, you only have one option for the roof, and that’s a clip fix roof profile. Every major roll-former has one – some of the better known profile names include Klip-Lok, Speed Deck, Apdeck, Metlok and so on.
This is an expensive option, as not only is the cost of the roofing material itself around 20% dearer per square metre than standard corrugated, but you also have the cost of the clips at around $2 per unit – and you need two clips per square metre to fix the roof.
You also have a more expensive installation cost, simply because it takes longer to install this style of roofing. You have the clips to install, as well as making sure that every sheet is running perfectly square with the guttering and the parapets, because clip fix roofing is not as easy to manipulate while installing as corrugated is. And if the building is out of square, it will be far more noticeable with this style of roofing.
Then you have the flashing of a clip fix or tray deck roof which takes longer than a corrugated too.
You also have to wait until the entire roof is installed before you can order the flashing for this kind of roofing because there are just too many variables that can affect the outcome. Ordering the flashing before the roof is laid – as you would do with corrugated – can become a costly exercise.
The big benefit of clip fix roofing is that it can hold much more surface water than corrugated roofing can. The higher ribs and wider trays allow for installation on lower roof pitches, and with seemingly more and more one-in-a-hundred-year weather events happening, it’s certainly a worthwhile consideration.
If you add all of these different factors together and design an adequate gutter system, a clip fix roof on a typical domestic house can work out to be around 60% more expensive to install than a standard corrugated roof. This 60% can easily amount to thousands of dollars.
For example: a clip fix roof of approximately 250 square metres will cost around $13,500 to $15,500, depending on the flashing configuration and local market factors.
A corrugated roof of the same size would cost around $7,500 to $9,500, and if the roof was 400 square metres, you’d be looking at $21,000 to $25,000, as compared to $12,000 to $15,000. That $10,000 difference could be better used elsewhere by your client – or simply saved from the total build cost.
So how do you fix such a basic but costly issue?
Simple: by raising the roof pitch from, say, 2 degrees (1 in 30) up to 5 degrees (1 in 12), you’ll likely save around $6,000.
If the roof sheet is 5 metres long, for example, the fall from top of sheet to the gutter line at 2 degrees is 167 mm, and at 5 degrees it’s 417 mm – so by raising the pitch of the roof by 250 mm you can save thousands of dollars. Most new flat roof installations are built with parapets around them, so in most cases you’ll be able to change the pitch without altering the aesthetic appearance of the house, and save money in the construction.
I’m sure there are plenty of architects and building designers out there who haven’t woken up to this alternative solution – just make sure you take a bit of the saving for your own pocket. Knowledge is everything.
Peter Coll knows his metal roofing with over 20 years of experience in design, manufacture and installation. He is the General Manager of Interline Roofing in Victoria and the Director of the Residential Metal Roofing Industry Association of Victoria.