Crunching the Numbers: Calculating Roofing Material

Whether you are renovating, re-roofing, or DIY-ing a new shed in the backyard, choosing the right cladding is always an exciting part of the process. It’s all about matching your imagination with the roof sheeting profile that is going to bring it to life. LYSAGHT® roofing manufactured from COLORBOND® steel is available in a range of popular styles and offers the perfect options to help transform your DIY-dream into reality.

Once you know what you want, your next step is to work out just how much of it you need. This might be a tall order if you have limited experience in construction or roofing, but don’t worry, you can follow these steps to efficiently and accurately calculate what you need for your next project. 

 

Critical considerations

 

When you are calculating how much roof sheeting (AKA cladding) you will need, there are three key dimensions to consider:

1. Sheet Width:

This is the total width of the roofing sheet as it is manufactured, including any edges that might overlap with adjacent sheets. It is the actual physical width of the sheet.

2. Maximum Cover:

 Width This is the effective width of the roofing sheet when installed, accounting for the recommended overlap between one sheet and the next. This is the measurement that gives us the coverage area of each individual sheet on the roof.

The maximum cover width is less than the sheet width due to the overlapping sections needed for proper installation and weatherproofing.

3. Sheet Length:

 This is the actual length of the roofing sheet as produced by the manufacturer. It's the physical measurement from one end of the sheet to the other. The length of the sheet is usually determined by the specific requirements of the roof to be covered. Sheets can be cut to custom lengths to fit the dimensions of the roof and thereby minimise the number of seams or joints, helping to enhance the waterproofing and aesthetic appeal of the roof.

 

Calculating material usage

 

LYSAGHT® roofing offers options for practically any roof design but, no matter which roof profile you select, the process for calculating materials will always remain the same.

As we take you through the calculation process, we will use LYSAGHT CUSTOM ORB® corrugated cladding as an example.

Always remember 

Sheet dimensions will differ per profile. Make sure you refer to your product’s installation manual for specific data and specifications.

Find my installation manual 

 

Step 1: Measuring roof width

 

The first piece of information you need is the width of your roof section. An accurate measurement here is crucial to avoid any sheet wastage or shortage. 

To illustrate these next steps, let’s use an example roof section that measures 7000mm across. 

 

Step 2: Establishing maximum effective cover width

 

Roof sheets overlap at the joints to create a watertight seal that protects your structure. The size of this overlap varies per profile and needs to be taken into consideration when calculating the number of sheets you require.

To manage potential wastage and avoid any shortage issues, it’s important to identify the maximum effective cover width that your selected LYSAGHT® roofing profile offers per sheet. This is achieved by measuring the overlap and subtracting it from the total sheet width.

For example, CUSTOM ORB® has a sheet width of 838mm, but during installation, adjacent sheets will overlap at the sides by no less than 1.5 corrugations. This means we can determine that each CUSTOM ORB® sheet has a maximum effective cover width of 762mm.

 

Step 3: Calculating sheet requirements

 

Now that you’ve established your roof width and the maximum effective cover width of your chosen roofing sheet, you can calculate the number of sheets that your project needs in one simple equation.

Simply divide the total width of the roof by the max cover width of a single sheet. 

In our example, the total roof width is 7000mm and the max cover width of our CUSTOM ORB® roofing sheet is 762mm. That means our calculation should look like this:

7000mm ÷ 762mm ≈ 9.18 sheets 

There you have it; our example project will require 10 sheets. Make sure to round up your total if it doesn’t result in a whole number to avoid shortage. 

You may want to add a few extra sheets to your total to accommodate for cut outs and overlap that may result from roofing features like vents and skylights.

 

Final calculation considerations

 

This simple calculation can be used with any roof and profile cover width and will ensure that you’re able to accurately resource what you need. Follow these steps each time and you’ll stay on top of your project’s budget and avoid any unnecessary delays.

LYSAGHT® roofing styles, including corrugated, rib & pan, standing seam and flat underside, can all be custom cut in bespoke lengths to bring your vision to life. From DIY pet-projects to major commercial undertakings, you can rely on LYSAGHT® roofing to give form to your imagination and your accurate calculations to effectively make them a reality.

Need some ideas? Find the perfect profile for your project.

Or explore our Residential Roofing Brochure for more inspiration from the full range. 

 

 

Last updated 7 February 2025

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