Fail to accurately calculate roof pitch and you’ll end up with significant errors in your overall building calculations. Those mistakes will translate to financially devastating consequences for you if you’re a home owner working on your own roof, or for your reputation and your business if you’re the tradesperson working on someone else’s property. Here’s why failing to accurately calculate roof pitch is such a big deal…and how we can help you get it right every time!
Sometimes You Need to Calculate Roof Pitch
If you’re installing, repairing or replacing a roof, there’s a huge pitfall lying in wait for you: getting the maths wrong when you calculate roof pitch can have a huge impact on your home. If you’re having a sudden, traumatic flashback to high school maths class right now, you’re not the only one! The pressure’s on, but you’re not at school anymore and a fail mark isn’t the worst thing that could happen.
Roof pitch – why the big deal?
Roof pitch is the angle at which the roof on a building sits. Overseas, it’s often expressed as a ratio or as ‘rise over run’. ‘Rise’ refers to the vertical distance between the roof rafters and the roof’s highest point, under the ridge. ‘Run’ means the horizontal distance between the external wall of the property to the mid-point of the wall. In Australia, roof pitch is most accurately expressed in degrees as an angle.
Being able to quickly and accurately calculate roof pitch is important for a number of reasons:
Roof pitch places limitations on design and materials in a roof
Your roof pitch or slope is one of the factors that might limit your choice of roofing materials. Manufacturers’ specifications and Australian standards dictate what roofing materials and construction methods are suitable for roofs with a particular pitch.
Roof pitch can also affect the design and appearance of a property. For example, it dictates whether you can have eaves on a property. It also has a direct impact on street appeal, as properties with flatter roofs will be regarded as less attractive than their steeper-sloped counterparts by some potential buyers. A more sharply pitched roof also lends itself to greater potential to more effectively utilise the roof void for storage, extra accommodation or implement character features such as soaring ceilings.
Roof pitch is also a relevant consideration when it comes to building design at the very earliest of stages. Generally, if your building is a very large one, the roof pitch will be lower because the dimensions of the building would otherwise necessitate an impossibly tall and prohibitively expensive roof. Generally speaking, the bigger the roof, the flatter the pitch for that reason.
Also, the steeper the slope or pitch of a roof, the more materials required to construct it. In this way, the overall cost of a build or renovation is directly affected by roof pitch.
Roof pitch – safety and access considerations
Roof accessibility is a factor that is also determined by roof pitch. It has a direct bearing on a number of safety considerations that come into play when you’re considering carrying out work at height. Roofs that are steeply pitched call for more rigorous safety regulations, for starters.
If you’re getting a tradesperson to carry out the work, occupational health and safety regulations and Australian standards might mean they have to use specialised equipment such as harnesses and roof scaffolding to work on your roof. It may be more difficult and time consuming for them to carry out the work. That’ll blow out your budget and your timelines.
If you’re a home owner, your roof pitch also has a bearing on the ease with which you can access your own roof safely to check and maintain it. A steeper roof pitch means potential access difficulties and thereby increases the chances that you might not detect roofing and drainage problems before they become entrenched and expensive.
Roof pitch and its influence on the weight of the roof
Because roof pitch affects and limits the range of roofing materials open to you, it also has a flow-on effect when it comes to the projected weight of the roof. That translates to careful consideration as to the structure that needs to be in place to support the weight. Again, this can affect the overall design of your property, including room configuration, and can severely limit your ability to reconfigure the floorplan or remove walls if renovating.
Roof pitch and solar panels
Being able to accurately calculate roof pitch is also important when it comes to installing solar panelling. Your solar panelling is manufactured to perform optimally when installed at a particular angle.
Drainage problems arising from miscalculation of roof pitch
Roof pitch is also a vital consideration when it comes to choosing suitable guttering and roof plumbing for your property. Roof pitch is an issue that affects how susceptible your roof is to problems such as blocked gutters and downpipes, too.
You have to calculate roof pitch correctly in order to avoid these drainage problems. As a rule of thumb, the flatter your roof, the more susceptible it is to drainage problems. For that reason, you should only use certain materials on certain roofs. Use the wrong materials and you’ll get a build-up of debris and moisture which can backflow up the roofing material, causing water ponding, stagnation and eventually, ingress. Only then will you realise you’ve got a roof leak. Often, by then, the leak has done considerable damage. Left for long enough, your leaky roof can cause mould and mildew, timber rot and attract termites who love a warm, moist environment.
Roof pitch problems that leave you with a leaking roof call for leak repairs, even replacement of the entire roof, which is a costly exercise. That’s a bitter pill to swallow because you can avoid them if you calculate the roof pitch correctly in the first place and a select suitable roofing materials accordingly.
Other problems when you wrongly calculate roof pitch
If you make a mistake when you calculate roof pitch you’ll also set yourself up for some other significant problems:
- You’ll run the risk of voiding the warranty on any products you install as part of a repair or renovation.
- You might not be covered by your property insurance for any damage that occurs as a result of your poor choice of materials
So, given the risks of getting it wrong, how do you accurately calculate roof pitch?
Getting to the nitty gritty – the maths behind calculating roof pitch
You can most accurately calculate roof pitch from inside the roof space, with reference to the internal supporting structures of the roof comprised of the rafters and joists as well as an imaginary vertical line drawn up from a point directly under the roof ridge.
Imagine you’re looking at an internal cross section of the roof. To calculate the pitch of a particular section of the roof, you need to picture that section of roof as a right-angled triangle. A right-angled triangle is made up of three sides: the opposite side, the adjacent side and the hypotenuse. The slope of the roof (which is diagonally across from the 90° angle) is the hypotenuse of the triangle. The horizontal side of the triangle is the ‘run’, also known as the ‘adjacent’ side and the side of the triangle that rises up vertically is the ‘rise’, or ‘opposite’ side.
If you don’t know the length of the hypotenuse, you can find it out by using Pythagorean Theorum, an equation that uses the rise and the run.
You then need to plug these figures into the correct sine, cosine or tan mathematical equation to calculate roof pitch. And this is where the wheels come off for most of us!
How it can all go pear-shaped when you calculate roof pitch
One of the most common mistakes you can make when you calculate roof pitch is to choose the wrong equation. For that very reason, we’ve developed a roof pitch calculator to take the pain out of trying to figure it out. You only need enter the measurements for the rise and run and we’ll take care of the rest, giving you the peace of mind of an accurate calculation every time.
That aside, if the person who built your property didn’t calculate properly and you’re seeing the tell-tale signs of roof pitch problems, you need to act quickly. Contact us at Action Property Inspections today on 1800 642 465. We’ll send a friendly, experienced and professional building inspector your way to compile a comprehensive building inspection report and give you advice as to your options.