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How to Calculate Roofing Materials and Supplies

Any problems with your roof are typically a bit of a nightmare. It’s a major structural component in your property, and it’s arguably the most crucial part of your property for keeping the weather out! Oh, and it’s really high up.

Repairing roofs—or entirely re-roofing—is a big, expensive job, so being smart with your money is all the more important.

The larger the job, the more it will cost in materials and tools. You don’t need to be a veteran roofing contractor to know that. Unfortunately, profit margins rarely scale as readily as the cost of materials do, meaning a little sloppiness with your calculations can almost entirely erase your profit as a contractor. And, for those of you out there with a knack for DIY who decide to tackle your own roofs, not being smart with your spending can erase all the financial benefits of tackling the job yourself.

So, being smart when purchasing your roofing materials is important, but what does being smart in this context entail? In this post we are going to look at how to figure out how much roofing material is needed. Let’s dive in.

Don’t Neglect Time

Any sufficiently experienced contractor will no doubt have learned this lesson already, but it is crucial to place realistic value on your time, whether you are a contractor quoting for a roofing job, or a DIY handyman working out if it makes financial sense to do it yourself.

Adequately valuing your time does not just mean putting a reasonable price on it, but also not underestimating how much time you will need to carry out any given task. If you are experienced at roofing, you will probably have a good idea of how long it takes to do something, but if you aren’t, you should do a little research and find out the average times for a job like the one you are considering. Also, if you are relatively inexperienced, be sure to factor in that it will probably take you a little longer than your average roofing contractor.

Future Maintenance

This one applies more to homeowners than to roofing contractors—though it will still apply to roofing contractors who give lengthy guarantees with their work. Calculating the cost of a roof is not just a single snapshot in time if you are living with that roof for the foreseeable future or responsible for its condition under the terms of a warranty.

This is relevant when pricing materials, because a cheaper material that could reasonably need replacing in five years time should be factored in if you are going to be the one paying for its replacement. It’s important not to be too short-sighted, especially if you are running a business. It may look good on the books when you do the work using cheaper materials, but it will look a lot worse if you then have to do the job again for free in a few years.

Roofing Supplies and Tools

You will of course need supplies for any roofing job, whether it is a relatively minor repair or a completely new roof. We’ve already talked about the need to factor in material quality for a job like this—cheaper isn’t always better—but there is also the matter of the tools you will use.

For a contractor who repairs many roofs, it can often be worth buying any tools you need (assuming they are within your price range) because you are more likely to need them in the future. We are, of course, talking about big ticket items, like scaffolding and cherry pickers. For DIY roofers, however, it is much harder to justify the cost of buying any tools much more expensive than a cordless drill, especially if the tools will not see use for anything else.

Fortunately, there are plenty of companies out there who will lease you the gear you need, so don’t jump into buying something expensive when you don’t need to.

Shop Around

This is less advice about buying roofing supplies and tools, and more of a good rule for life in general. Always do a bit of price comparison before buying anything. If you are experienced and buy roofing materials regularly, you will already have a firm idea of what things should cost, but if not, you should shop around a bit and see what the prices are elsewhere.

Be sure to factor in logistics when deciding where to buy your materials. For example, finding your supplies for $250 less out of town is less appealing if they don’t deliver, and you have to go on an eighteen-hour round trip to pick them up! By the same token, it can sometimes work out better to pay a little extra for supplies because they come with delivery, or because they have a generous returns policy, and you are a little uncertain about quantities.

How Much are Roofing Supplies

When buying roofing materials, the most daunting part is often deciding how much to buy. Knowing how to calculate how much roofing material is needed can not only save you time in taking unused materials back, it can also save you money. For example, if you purchase an enormous roll of membrane and only end up needing half of it, you can’t take the unused half back, but you might have been able to buy a smaller roll.

Obviously this will require you to have rough idea of how much you need (we’ll get into some maths in a moment), but also be as accurate as you can when doing the job. It may seem tempting to speed things along to get the job finished more quickly, but if you make mistakes and have to spend money on more materials, that time saving can quickly start to look less worth it.

How to Calculate Roofing Materials Needed

Different roof types will require different methods of calculating roughly how much you will need in terms of materials, but there are certain things you can carry across most roof types, such as surface area.

Roofing mediums—such as felt, shingles, and tiles—will typically tell you on the packaging how much of an area they will cover in square feet/metres. Working out surface areas is simple enough; just multiply the length of each flat surface by its width, then add all the surfaces together. If you are dealing with something like a curved roof, things will get extremely complicated, but if you are doing that, hopefully you have enough experience that you don’t need this article.

Roofing is typically measured in “squares”, which are 100 square foot sections of roof. So once you have the total area, you can simply divide it by 100 and use that amount to determine how many shingles or tiles you need in “squares”. The same applies for any underlayment you might need.

Trim Allowance

The chances of even a very experienced contractor managing to complete a roofing job with zero waste is practically non-existent, so don’t feel like it’s a slight against your roofing skills when we tell you to add a little trim allowance.

As a rough guide, you should add around 10% to the materials you need to account for things like awkward edges, mistakes, and other wastage.

Of course, if you are relatively inexperienced, you might want to increase that a little, but there is a fine line to walk between accounting for potential mistakes and wasting money. It may be worth buying less and factoring in multiple trips to get more supplies, since you can always buy additional supplies, but you can’t always return unused supplies.

Consider Using a Contractor

This post is partially aimed at contractors, so if that’s you, you can skip this section. For the rest of you intrepid handymen and women who like to get your hands dirty, we would just say to at least consider getting an experienced contractor on the case.

You may still decide you’d like to do it yourself, but at least weigh up the pros and cons before you do. Remember, you are not just factoring in the cost of materials, but your own time, time spent driving back and forth. And, frankly your own safety. Roofing is not the safest profession, and it gets more dangerous the less experienced you are. Using a contractor may cost a little more on paper, but it can certainly work out better value for money when you take everything into account.

Frequently Asked Questions

We’ve done our best to cover the key points in this post, but we know your time is precious, and you might not want to read through all that text just to find a relatively simple answer to a straightforward question. With that in mind, we’ve pulled together some of the more commonly asked questions regarding roof materials and the calculating of how much you need.

How much roofing material do I need?

The amount of materials will differ from roof to roof, on both size and style of roof. As a practice, roofing materials is measured in “squares”, which are 100 square foot section of roof. Start by measuring the surface area of every plane (single flat area) on the roof, totalling up the planes, and dividing the total amount a hundred. This will give you the number of “squares” you need. Be sure to add a little extra to account for wastage and mistakes. This is called “trim allowance”, and is typically around 10% on top of whatever you need.

How much for roofing materials?

As with any job, the cost of re-roofing a house, building a new roof, or repairing a roof will be entirely dependent on the size and scope of the job. As a rough guide, you can expect to pay around $5,000 at least for the materials needed to re-roof an average-sized Australian home with low-cost options, but that cost can easily get as high $25,000 if you opt for more expensive materials. Of course, if you are not doing the work yourself, you will need to the factor in the cost of labour for your contractor. Another way to get a rough idea is to assume a cost of between $60 and $150 per square metre of roof.

Can I do roofing myself?

There is no law saying you cannot perform roof repairs on your own property, however you should be realistic with yourself regarding your ability to carry out the work. If you are not experienced in roofing, or you are not comfortable with heights, it may be best to hire a contractor to take on the work for you. It’s always nice to save money, but your safety and wellbeing is more important.

How long does a new roof last?

Different materials have different levels of resistance to the wear and tear of mother nature, but on average, a new roof should last between twenty and twenty-five years. This can be significantly reduced if cheaper materials are used and the roof is not properly looked after, but will rarely go longer than that without needing some attention.

Can a roof be repaired?

Roofs can certainly be repaired when the problem is relatively minor damage or wear and tear. If there is major structural damage—such as would be the case if a tree had fallen through the roof—an entirely new roof may be necessary. There will also be times when a repair is less practical; if it is going to cost $18,000 to repair a roof when a complete re-roof is $20,000, it may make financial sense to get the whole thing done.

Final Thoughts

Whether you are a contractor with many happy clients under your belt, or a homeowner looking to flex your DIY muscles and save a little money in the process, it always pays to be prepared and plan ahead. A little extra time spent working out what your expected materials and labour will be could save you quite substantial costs by the end of the work.

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about us

We have been in business for over 30 years as a commercial & residential roofing company. RVA is the sister company of Sydneyroof.  At RVA we are focused on Industrial & Domestic roof ventilation, fibreglass skylight panels, and roofing utilities. We believe these areas of the roofing industry have been largely marginalised.  We however, are focused on taking this part of the industry and creating a service-oriented response to our customer's needs.

Why Us?

Competitive Prices

Our pricing is transparent and highly competitive. We do our best to take the guesswork out of the final cost at the beginning.


We take pride in our workmanship and are proud to warranty our workmanship for 5 years, in addition to the manufacturer's warranty.

Over 30 Years Experience

Nothing says commitment like longevity! We are proud of our commitment to our craft and our customers.