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How to Calculate Roof Size for Slates

Jan 25, 2024

Slate roofs are hugely popular for various reasons – durability, longevity, eco-friendliness, and an attractive, timeless appearance. If you’re working on a construction project for a client wanting a roof with a long lifespan, point them in the direction of natural slate.

The price tag tends to be higher than other roofing materials, but the return on investment is unparalleled. If your customer decides to go ahead with the installation of a slate roof, you’ll need to be able to work out how much slate you need by calculating the roof size.

In most cases, they’ll expect you to be the person sourcing materials, so getting the right amount is paramount.

New to this type of calculation? Don’t worry, we’ve got you covered with our guide to calculating roof size for slate tiles. Let’s get into it.

How Can I Calculate How Many Roof Slates I Need?

To know how many slate tiles you’ll need, first establish how big the roof is in square metres. Luckily, it’s not too difficult to do.

Start by measuring the length of the rafter. This typically runs from the ridge line of the roof to the gutter. If we imagine the length of the rafter is 5 metres long and the ridge line length is 10 metres long, the face of the roof is simply the two numbers multiplied – in this case, 50 metres squared.

A standard roof has two sides, so you can multiply the number by two, which, in this case, becomes 100m2. Don’t forget to reduce the number to account for chimneys and skylights.

If you’re working with a flat roof rather than a standard up-and-over roof, the calculation will be slightly different, given that you can measure from the ground to get the length and width of the structure. With a flat roof, you don’t even need to go up onto the roof to get an accurate measurement – you can do so by measuring the external building.

Once you’ve got those measurements, multiply them to work out the square meterage of the flat roof. Bear in mind, though, that felt tends to be the better material for flat roofs, rather than slate.

If the shape of the roof is more complex than that of a traditional Gable-shaped roof or flat roof and has multiple sections or ‘valleys, you’ll need to calculate the size of each section and then add them up.

How many slates per m2 calculator?

The following table shows the required number of slates per square metre for effective coverage:

How can I fix natural slates on a roof?

The installation of a natural slate roofing depends on the slate type, the style and the design. There are two methods of fixing natural roofing slates: nailing and hook fixing. You can watch a video on how to fix roof slates here:

For over 30 years, SIG Roofing has been the ‘go-to’ distributor of natural slate from a range, largely sourced directly from the quarries. Quality is at the forefront of everything we do, so we work closely with our producers to ensure that we supply slate that not only meets your performance criteria but also meets your aesthetic requirements within budget.

We know from our extensive experience that no two projects are alike, so we ensure that every slate is carefully selected to match your roofing requirements and geographical area.

What Natural Slate should I use for my roofing project?

The natural slate you choose should align with your project’s requirements and budget. Regardless of the slate type you opt for, you’ll not only secure your home but also enhance its enduring beauty and overall value. For personalized advice on selecting the ideal slate for your roofing needs, consult with experienced roofing professionals or reach out to our Technical Solutions Team for guidance on roofing take-offs and estimations. Or have a look at our roofing brochure to view our range of natural slate available or read our article on natural slate comparison to learn more.

SIG operates fully stocked branches across the country, including Belfast, Omagh, Dublin, Limerick, and Cork, offering next-day delivery of CUPA Pizarres Spanish Slate in 600 x 300 and 500 x 250 sizes nationwide. Contact us today!

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