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How Much Does A Flat Roof Cost Per Square Foot

How Much Does A Flat Roof Cost Per Square Foot

2021 Cost Of A TPO Roof | Single Ply Membrane

6th of February 2019 by Costi Serban

There are a number of factors to consider when replacing a flat roof. These would include the size of your roof, what materials you are using, the type of weather that the roof may encounter, as well as the overall cost per square foot. While all these factors are important, most of our clients consider the cost first.

Generally speaking, the cost of flat roofs are provided in a measurement unit called a square. Each square is equal to one hundred square feet. In most cases, the general cost per square of flat top roof is somewhere between $350 and $1200, which means that a square foot of a new flat top roof, fully installed, including labor can cost between $3.50 and $12.00. It should be noted that these prices are only estimates based on industry standards, and a true estimate given by a qualified professional roofer is a more accurate method of determining costs. At Mass-Tech Roofing and Building Co., we believe in honesty and being a trustworthy contractor to every homeowner who reaches out to us.

Like everything else, the quality of the material used, as well as the kind of material used will adjust the cost. And this is one area that you dont want to mess around. The brutal winters and storms that can frequent the Boston area can wreak havoc on a buildings roof, so choosing the right roofing material can mean the difference between having long lasting protection and replacing the roof in a very short time indeed.

Factors That Impact The Price Of Flat Roof

  • Height of the Roof:

    Tall flat-roofed properties tend to be more expensive that shorter houses, because a flat roofer will need to add a chute to bring the old roofing material down to the bottom.

  • Accessibility:

    Generally, houses in Toronto are closer together than houses in Mississauga, so properties that are not as easily accessible for a dump truck to enter may require the need to remove old flat roofing material using wheelbarrows. This will tend to increase the price of your flat roofing quote. In some cases, the roofer may need to consider going from one roof to another to access the flat roof as well.

  • Existing Flat Roof Layers:

    The number of layers on the flat roof has a big impact on the cost of replacing your flat roof. A flat roof with nothing on it will be much cheaper to install new flat roof material vs a flat roof with 8 inches of the old roofing material. And the cost is ever higher in older from the 1920s -1940s where fibrous material were used on flat roofs.

  • Obstacles:

    The numbers of obstacles on the roof has an impact on the cost for replacing your flat roofs. Obstacles can include siding, vents, AC units and posts on decks. For example, if you have a house with a siding and posts all the way around, then before new flat roofing material can be installed, a roof contractor will need to take the siding off, cut the posts out or flash each posts.

What Are The Supply Costs Of A Flat Roof Replacement

Because labour accounts for a large portion of any flat roof budget, it’s also a good idea to obtain a feel of how much the project will cost without additional labour fees. When the labourers offer a quote, this gives you an indication of how much they charge.

So, how much does a flat roof in the UK cost per square metre? This, in most cases, is dependent on the substance.

If you want to do it yourself, all you must do is figure out how much the supplies will cost. Doing it yourself can save you a lot of money, especially if you’re planning to replace the roof on a two-story expansion, where you’ll save roughly £300.

Flat roof replacement cost per square metre are as follows:

Felt usually costs £2 – £10 per m2, rubber costs £9 – £12 per m2 and fibreglass costs £2 – £3 per m2.

The lead will cost you £2 – £4 per kg and fibreglass insulation costs £6 – £10 per m2, PIR insulation boards cost £5 – £15 per m2 and spray foam insulation costs £5 – £12 per spray can.

Therefore, the size of your flat roof will have a significant effect on your overall costs, as the larger the roof, the more materials will be needed. The table below will breakdown the supply costs of a replacement flat roof:

£5 – £13 per spray can

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Bur Tar & Gravel Or Other Asphalt Roofs Perform Poorly With Insulation

Most contractors will not recommend a BUR roof is installed with underlying insulation, since the roof membrane is usually stretched towards the edges of the roof where there is no insulation. This causes stretching of the membrane since the roof tends to heat or cool faster in these areas, causing both excessive contraction and expansion of the roof membrane. This is in sharp contrast to the rest of the roof membrane, which will not shrink or stretch as much, due to underlying insulation. This tug of war causes wear and tear on the roof membrane, especially near the edge of a roof. In the case of a BUR roof, without reflective coatings, the surface temperature can exceed 150 degrees Fahrenheit on a summer day. Cooking a roof membrane like this can cause it to tear and crack prematurely. And once a roof membrane is compromised, water can seep in and quickly cause large areas of a roof to deteriorate. Just a few months of water penetration can cause major deterioration of a roof membrane.

Image: A three dimensional cut-away of a BUR roof .

Green Roof Vs Cool Roof Cost

Average Roof Replacement Cost Per Square

The cost difference between a green or cool roof depends on where you live. While installation costs may not be all that different, homeowners in warmer climates might see greater energy savings with a cool roof. However, it might cost more to turn an existing roof into a cool roof. Find a roofing contractor who can offer the best eco-friendly roof solution for your home.

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Planning Your Metal Roofing Project

As you begin planning your roofing project, consider the following three tips to help make it a successful project:

  • Determine what is going to be done with your old roofin some cases, you will not have to pay for the removal of the old roof, since it may be possible to install the metal roof on top of what is there.
  • Check with your municipality/HOA before you buyas with any modification to the exterior of your home, you might violate local HOA statutes by installing a metal roof.
  • Ask the roofing companies you have requested bids from how long their proposal is good for. Any number of factors in the metals market could cause the price to go up if you sit on the bid too long before giving the go-ahead.

How To Use The Calculator

1) Measure your house/building from corner to corner.

If there are overhangs, be sure to include these into the Dimensions field. 12 overhang over 100 foot eave span adds 100 sq. ft. to the total roof area, which can cost as much as $1,000 or more.

2) Enter the exact number of large penetrations / curbs .

Penetrations require special flashing work and will add significant cost for each unit. If you do not include them, you will see a huge discrepancy between this estimate and one from a contractor, because he WILL include these.

3) Enter the length of parapet walls .

The parapets can add significant roof surface and extra work, so do not discount them. Your roofer WILL charge you for these.

4-6) Select insulation thickness, roof pitch, tear-off layers. Use our easy Roof Pitch Calculator to estimate the pitch on your roof.

7) Select job complexity.

This can be vague, but if you have multiple penetrations, curbs, roof-to-wall flashing, difficult drainage, choose the Medium or even Complex setting. Also, be aware of ease of access to the roof. If your contractor needs to hire police detail, or if your roof is 7 stories off the ground, the cost WILL go up.

8) Select the material you want.

You can get a price for the chosen material, and then re-calculate again for a different one, to compare. EPDM rubber roofing is the most popular choice, because its the most budget-friendly option. TPO is the second most frequently installed flat roof on residential properties.

20-40 years

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Roofing Square Feet Vs Squares

Installation prices arent expressed in square feet, but rather in squares 100 square feet.

Asphalt and composite roofing shingles may cost as low as $12.20 per square to install. On the higher end, asphalt can reach $20.10, while composite shingles may be even pricier depending on the particular material.

Wood and fiberglass shingles usually cost around $15.20 per square. However, high-quality wood shingles can reach a price of $25.30 or more.

Metal tiles and concrete roofing costs from about $20.10 per square. In contrast, the installation of high-end metal roofing will have a minimal price of around $45.50 and may go over $61.

Clay tile roofing installs on average for $30.15 per square foot, similar to PVC roofing.

Interestingly, solar shingles are in the medium price range when installation is considered. This type of roofing may cost somewhere in the neighborhood of $22 per square.


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Calculating asphalt cost is relatively simple. When we come to metal roofing, matters get a bit more complicated due to the greater choice of specific materials.

Metal roofing can be done in several different types, most prevalent of which are tin, steel, and copper.

Tin is undoubtedly the least expensive metal roofing option. However, with an average price of $880 per square, it costs more than double the price of asphalt. Steel is even pricier, reaching around $1,550 per square, and copper roofing can cost about $1,950.

Galvanized Steel Shingles Roof Cost

How Much Does A New Roof Cost?

Galvanized Steel Shingles cost $3 to $3.50 per square foot and start at $7.50 per square foot installed for interlocking steel shingles. The two common types of galvanized steel used in roofing are G-60, which is a low-end product used for roofing on garden sheds or workshops, and G-90, which is used for residential roofing applications. During the manufacturing stage, the metal is treated with a thin coat of zinc oxide and painted with a resin-based architectural coating called Kynar 500 to preserve the finish.

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How Much Does A Membrane Flat Roof Replacement Cost

You should budget between around $14.00-$17.00 per square foot for a smaller membrane flat roof replacement and around $12.00 per square foot on slightly larger projects. When you get into larger commercial projects, the cost per square foot drastically decreases.

If youre using insulation thats thick enough to insulate the entire structure, it will cost more than if you’re just using fabric insulation and gluing the membrane to it.

Diy Roof Replacement Vs Hiring A Roofer

For homeowners looking at replacing their roof instead of hiring a professional, an asphalt roof will cost $3,000 less to $6,000 less . However, while small roof repairs are cheap and relatively easy to carry out by the homeowner, as long as safety precautions are taken, roofing a home is better done by professional roofers. The downsides of completing the work as a DIY project are:

  • In removing the original roof, you may cause issues that will lead to leaks.
  • Once the old roof is off, you could miss structural issues or things that will contribute to more leaks.
  • You might not create a perfect weather seal to protect your home from the rain when installing the new roof.
  • You could introduce issues that translate to increased utility costs from heating or cooling.
  • You could fall from your roof.
  • You could negatively impact the resale value of your home.

Your roof is the single biggest surface barrier between you and the elements. Given the importance of the roof, and the potential for significant problems, we suggest looking for bids from the roofing professionals we have on HomeGuide before making a final decision to do the work yourself.

Get free estimates on HomeGuide from trusted roofing companies:

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Difficult To Perform Maintenance

Gravel Removal

When you are on a gravel-covered roof, you cant see the underlying tar layer. You may be able to tell your contractor where a leak is coming from, but your contractor will need to remove the entire areas gravel to find the leak, this means extra time and cost compared to a membrane or polyurethane foam roof where you can spot examine the roof quickly.

A contractor can move or remove the gravel from a roof with a vacuum or the old-fashioned way by shoveling.

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Problems With Tar And Gravel Commercial Roofs

Roofing Shingles Calculator

When you think of a commercial roof, you may think of black tar being mopped on a flat roof. Thats because tar and gravel roofs are one of the oldest commercial roof types in the US. But does one of the oldest types of commercial roofs have problems you should know about? Of course!

At West Roofing Systems, we want to make sure that our future clients have the best information available. For this reason, we created an article that explores the potential problems you can have with a tar and gravel roofing system to give you all the information you need in choosing which roof is the best fit for your facility.

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How Much Does A Flat Roof Replacement Cost

If its time to replace your flat roof, your biggest concern is probably how much it will cost you. Unfortunately, its hard to find anything cost-related because the roofing industry doesnt like to talk about it.

We understand how frustrating that is to homeowners like you. After all, how can you be comfortable spending your hard-earned money on a flat roof replacement without an idea of the price?

Here at Bill Ragan Roofing, we want to take those frustrations off your shoulders. Thats why well be giving you an idea of the budget youll need for a flat roof replacement.

But before we get to the cost, you need to know which type of material is right for your flat roof replacement.

Factors That Influence The Price


If you are looking for a way to save money on your next project, consider buying trusses in bulk. For example, it will cost less per 10 trusses than how much you would pay for only one.

Design Loads

The truss has the capacity to hold considerable weight, but there are cases when it needs to hold more than average. In this situation, the design has to be different. For instance, you may have to change the standard gable end truss to the scissor type. This would increase the costs by up to 25%.


As mentioned above, you can choose from two types of materials: steel or timber. The cheapest option will always be wood.

Roof pitch

The costs will increase if the roof is steeper as there would be more boards necessary.


The standard spacing for a roof is two feet, but in some situations, customers may ask for trusses every 16 inches in order to create their own more robust structure.

The span

The length at the bottom is known as the span, and the trusses are not all the same size. For example, if the span is 26 feet long, you would need 16-foot and 10-foot pieces of lumber to create the bottom cord, leaving no scrap behind. The price would get higher if the truss has to be customized and the scrap is left over.

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Commercial Flat Roof Replacement Cost Per Square Foot

Depending on the material, commercial flat roofs typically cost between $4 and $9 per square foot to install. Most of them are much bigger than residential roofs, with 10,000 square feet being the average. Owners of commercial buildings can expect to pay between $40,000 and $90,000 for their flat roof depending on the material type as well as the need for drains, vents, and extra underlayment.

Is There Any Reason My Roof Cant Be Restored

Flat Roof estimate and how we price a new flat roof.

Saving 50% on a massive capital expense is a huge factor for almost all business owners and facility managers. The vast majority of roofs we inspect are absolutely a candidate for our signature restoration solutions.

The only reason that a roof cant be restored is if the roof leaks have become extensive and have gone on for a long period of time. In these cases, the roof insulation is likely also destroyed and possibly full of mold. This means total replacement is the only way to fix the roof system permanently. This is just another reason to not let roof leaks go for too long. After all, the most favorable commercial roofing cost per square foot comes from restoration.

We always tell potential customers, if you have questions about your roof, ask us for a free roof inspection.

Lock in Your Commercial Roofing Cost Per Square Foot

So, now you have a ballpark idea of what the commercial roofing cost per square foot is for restoration and replacement. If youre ready to take the next step, our team is here to help. The first step is to find out if your roof is in shape for restoration with a free inspection. After that, well provide you with the full quote to restore or rebuild your roof.

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