Photo from Unsplash

Originally Posted On: https://www.rpsmetalroofing.com/what-is-a-linear-foot-in-roofing-and-how-to-calculate/

What is a Linear Foot in Roofing and How to Calculate

There are many different building industries and tech industries where the linear foot remains a fundamental way to measure. It’s no different for roofers. It’s primarily a measure of length, but because of its versatility, it can be used to measure area or volume, too. In the roofing industry, the linear foot is a significant measurement and it’s used today to determine the quantity of materials needed to cover a particular surface area. In roofing, this can mean the calculation of shingle needed or the sheet sizes necessary for roofing projects. 

How to Calculate Linear Feet for Roofing Materials:

There is a specific way to calculate linear feet in roofing, and we’ve condensed the ‘how’ into a list for you below:

• Start by measuring both the width and length of the roof. This will give you the total square footage of the roof. (Length x Width = Square Feet). So a roof measuring 20 feet in length but 10 feet in width equals 200 square feet. 
• From here, you can determine the width of the roofing material being used. You can divide the total square footage by the width of the material to get the linear feet required. If we take the earlier result of 200 square feet, and then divide that by a material width of 3 feet, then we need 66.7 linear feet of material. You can round that up to 67 linear feet. Linear foot measures length while square foot measures area so linear feet should always be used for accuracy’s sake.
• Always make a note of any possible waste. There is waste generated during an installation and that includes trimming, cutting and any additional materials for vents or flashing. Waste should always be factored into the linear footage required.

Why Roofers Calculate in Linear Feet

Did you know that linear feet provide an accurate representation of the length of the roofing material needed? It does more than square feet can do, because square footage measures area and not just length. The materials used in roofing are usually sold and installed in lengths.

When roofers use linear feet to measure, they can account for the actual size of the materials needed. Not only that, but the measurements are far more precise this way. This avoids too much wastage, allows for better and easier calculating and reduces costs. Measuring in linear feet also helps to simplify the entire process, so any roofing project can be easily set up and accurately calculated.

Benefits of Calculating in Linear Feet

There are plenty of benefits in using linear feet for roofing and those benefits are exactly why people in roofing still use it. Some of the benefits are listed for you below:

• Material calculation precision. Roofers find materials easier to calculate when they do it in linear feet. This is precision that allows them to calculate the material for a full roofing project to minimize waste and ensure that the right money is spent on the right amount of material. Roofing materials are often sold in sheets or long rolls. These can be hard to cut to the right square footage so when it’s sold by the linear foot, it’s much easier to buy.
• Complexities in roofing. Roofs are made in all different shapes and sizes, so it stands to reason that it can become pretty complex to organize the materials fitting the right roof size. When roofers use linear feet over square footage, it’s so much easier to install those roofing materials and that’s because the measurements are already taken into account. There are slopes, ridges and valleys to take into account in roofing materials and linear feet can do that.
• Ease of installation. When you use linear feet in roofing, you can easily install roofing materials. Measurements are taken into account early in the process and this can significantly reduce installation time. This makes the job much easier for contractors who are trying to simplify the planning and execution of the installation itself.
• Materials can be used with more accuracy and efficiency. When you measure in linear feet and not square feet, roofers have the opportunity to optimize the materials used. This ensures that every piece of the materials in the roof can be used with efficiency and not wasted. Excess waste is a big problem in roofing but it doesn’t have to be, and it makes it much easier to avoid it when measuring with linear feet. With more efficiency, both costs and environmental sustainability are elevated. 
• The measurements are standard. It’s important that roofers have a standardized measurement across the industry. With it being consistent, it’s easier for roofers and experts in the field to communicate and collaborate the right way. Suppliers, contractors and manufacturers are all able to be better involved in the roofing process and with standardized practices, it’s easy across the board.
• Materials are easy to order. When you order materials for the roof based on linear feet, it’s so much easier to choose the materials to order and communicate with suppliers. That way, you get accurate quantities of materials and you avoid overspending and over ordering. 
• Cost estimation is easier. If you want to ensure that you are able to manage your budgets more easily, then linear feet measurements allow for that. You can gain precision in your cost estimates, which can really help roofing contractors and homeowners alike to budget with accuracy. Their projects can then be planned better financially and costs controlled more easily.
• Warranties are easy to comply with. Almost all roofing material manufacturers talk about their warranties when they are based on the correct use and installation of materials. When you use linear feet, you can ensure that the right amount of material is used which can be crucial for complying with warranties.
• Roofs will be building code compliant. Often, building codes will specify the minimum requirements for roofing materials based on their linear measurements. When you adhere to these requirements, the structural integrity of the roof remains intact and they will stay compliant with building codes. This will save on costs in the long run when there are no fines for not being compliant!
• Bidding can be more accurate. When you bid on roofing projects, you’ll find that contractors are easily able to provide more accurate and competitive quotes at the same time. Linear measurements can lead to a more successful project outcome with contractor help and the bid can be won.

Common Mistakes Made When Calculating Linear Feet.

Despite linear feet being the right measurement to use in roofing, it’s not without its flaws. There are several mistakes that can occur and they’re pretty common across the sector. With too many mistakes, a roofing job can be a total disaster and so it’s vital to ignore some of the key mistakes below:

• Some people ignore the complexities of the roof. We talked about the roof being difficult to measure, but linear foot measurements can oversimplify it all. In the case of roof designs like dormers and irregular valleys, it can be a mistake to miss these out and not account for them at all.
• You didn’t account for the overhang. Another thing that people often forget is the overhang of the roof. This can lead to a bigger shortage of materials and as overhangs can contribute to the total roofing area, forgetting these could be a costly mistake that you can’t just take back.
• Mis-measuring. If you’ve had linear feet in mind but you’ve calculated everything in square footage, you may find that there are significant errors made in the completion of the measurements. Using the wrong type of measurement can result in materials being incorrectly estimated. This can be completely avoided from the beginning!
• You forgot about wastage. If you don’t consider waste such as cutting off the scraps or using damaged materials, you’re going to underestimate the calculated linear feet measurement. Getting this wrong can lead to project delays and issues that can always be avoided from the beginning of the project.
• You made mistakes in your measurements. Errors in the measurements of the length or width of the roof can lead to your linear feet calculations being wrong. You have to double and even triple check the measurements to ensure accuracy. This will ensure that you are making a share that you order the materials you need from the beginning.
• You assumed a uniform width. If you choose to assume the width rather than measuring it first, you won’t have the right size of materials for your roof. Some materials have a variety of widths and these should all be accounted for so that you don’t end up with the wrong size of everything. 
• The manufacturer guidelines have been ignored. With different roofing materials come different installation guidelines. If those guidelines are ignored in any way, you end up with an improper installation and a voided warranty. If you don’t ensure that the measurements and guidelines have been adhered to, it’s the house that suffers and you end up out of pocket.
• You didn’t think about the slope. The slope of the roof can affect the actual surface area that needs to be covered. When you don’t account for it in your linear feet measurements, you will end up underestimating how much material you need. 
• Underestimating materials. That leads us onto the next mistake! If you don’t calculate the flashing and accessories needed properly, you will end up with a misaligned amount of materials.