Roof Tiles: How to Calculate the Required Quantity
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Why you should calculate the roof tiles you need for a job accurately
It is important that you take the time to work out just how many tiles you need to complete a roofing job for the following two reasons:
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Buy too many and you will be spending money needlessly and see the unused tiles going to waste.
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Fail to order enough and you will need to extend the time to finish the project, as well as leaving parts of a roof open to the elements while you wait for the remaining tiles to arrive.
How to work out the size of a roof area
The first step to understanding the number of roof tiles you need to order is by working out the size of the roof that is being created or replaced.
You will find it very simple to calculate the square meterage of a classic rectangular gable roof design. All that is required is to multiply the slope height of a roof with its length, before doubling this number for a final answer that is based on the area of both sides of the roof.
Putting this calculation into a working example is to imagine you have a job to tile a roof that is ten metres long and with a slope height of seven metres. The roof area will be:
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(10m x 7m) x 2 = 140m2
About to start a project on a roof with an unconventional shape? You should divide the shape into individual rectangles and squares, so that the square meterage of each section can be calculated using the method explained above. These then just need added together for the total roof area.
What to consider with the roof tile’s design
Now that you know how large the roof is that you are working on, you will next be looking to order the correct number of tiles for the job you are carrying out.
Depending on the preferred roof design selected by the property owner, you can be working with different sizes of tiles.
A Redland Rosemary clay roof tile measures 265mm x 165mm, for instance, while an Eternit Thrutone artificial slate tile is 600mm x 300mm. Therefore, you will need more of these Redland Rosemary tiles than the Eternit Thrutone alternative to complete the same roofing project.
The headlap of a tile must also be factored into your calculations. This is the specification of how much overlap is required from one tile being placed next to another one, with more tiles being needed as the required headlap gets larger.
Many tiling manufacturers assist you a little bit here by informing you about the tile coverage per square metre for their products.
How to work out how many roof tiles you need
At this point, you will have all the details necessary to calculate exactly how many roof tiles you need for the job you are tasked with completing.
The equation to remember is to multiply a manufacturer’s tile coverage per square metre by the roof area you are working on.
Let’s use the earlier example where we calculated that a fictional project involved a roof area of 140m2. If the manufacturer of the roof tiles selected specified 20 tiles being needed per m2, this is how you complete the sum:
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140m2 x 20 = 2,800 tiles needed
We hope these calculations will help you with your next roofing project. For more helpful advice in this area of the trade, have you checked out our very useful guide on how to work on a roof safely?