A Roofers Guide to Low Slope Roofing Materials, Installation, and Maintenance

Share This Post

Share on facebook

You want a roof that’s unique and contemporary, one that stands out from the neighbors in the best possible way.

To that end, you’re considering an upgrade to low slope roofing.

Low slope roofing can make a big statement, but it comes with its own unique needs as well. Here’s everything you need to know before you take the plunge and start your remodeling project.

What is Low Slope Roofing?

Low slope roofing refers to roofing that is nearly flat or slightly pitched. It is NOT a flat roof because no roof should be flat–otherwise, water won’t run off the roof and will instead gather to create rot in your building structure.

Most low-slope roofs have three components:

  1. Weatherproofing layers
  2. Reinforcement
  3. Surfacing

The weatherproofing layers are one of the most important components of the whole roof. As the name implies, this layer is what keeps nature out of your house.

The reinforcement layer adds strength and structure to the roof, helping it hold its shape against the effects of time, weather, and other conditions.

The surfacing is what protects the weatherproofing and reinforcement from sunlight and weather. Some surfacing materials have additional benefits, like fire resistance or increased solar reflectivity.

Know Your Pitch

Do you have a low pitch roof?

You see, your roofing materials are determined by a number of factors–and the slope of your roof is a make-or-break variable. If you want to install a certain kind of shingles, for example, that may not be possible if your roof pitch is below a certain ratio.

So, in order to know your roof slope, you need to understand what pitch is.

A roof’s pitch describes the angle, slant, or slope of the roof. It’s designated using a ratio, which is made up of two parts:

  1. Numerator (the vertical height of the roof)
  2. Denominator (the horizontal length of the roof)

Fortunately, to make your life easier, the pitch denominator is always shown as 12. So, the roof pitch ratio tells you how much rise there is in 12 units of horizontal distance.

Before we go any further–while basic mathematics tells us that 12/12 can be reduced to 1/1, this is not done when calculating the roof pitch. Don’t simplify the pitch down to the lowest denominator. Leave it at 12. Otherwise, your contractor will have no idea what you’re talking about.

Let’s say your roof has a pitch ratio of 5/12. In plain English, that means that for every 12 feet of horizontal length, the roof changes 5 feet in vertical height (a fairly moderate slope).

Low slope roofs can have ratios as low as 1/12 but are generally between 2/12 and 4/12. For context, a high slope roof can get as high as 18/12. Picture classic Victorian houses and you can imagine a high slope roof–think the soaring, almost vertical peaks of the haunted Addams Family house.

Visualizing Pitch

If you’re confused by ratios and everything we just mentioned, don’t worry. It’s a lot simpler than it sounds.

Picture a right triangle. When we talk about the pitch ratio, all we’re talking about is the rise of the roof over the run of the roof.

So, to come back to our triangle, the bottom of the right triangle is the horizontal length of the triangle (or, the horizontal length/denominator of your roof). The vertical side of the triangle is the height of the triangle (or, the vertical height/numerator of your roof).

The angled line connecting the two is the slope of the roof. That’s all that the roof pitch ratio expresses.

Calculating Your Roof Pitch

With that in mind, let’s take a closer look at how to calculate your roof pitch.

In order to figure out the pitch of your roof, you’ll need an 18 to 24-inch level, a tape measure, and a pencil.

You can measure on the roof itself, but this method works just as well inside your attic (plus, you don’t have to worry about falling off the side of your house from inside the attic).

First, measure 12 inches from the end of the level and make a mark with your pencil.

Next, place the end of the level against a roof rafter. Make sure it’s perfectly flat. Then, use your tape measure to measure vertically, straight up from the 12-inch mark on your level. That number is the number of inches that the roof rises in 12 inches.

So, if you had six inches, your ratio would read 6/12. If you had eight inches, your ratio would read 8/12.

Why Flat and Low Slope Roofs Exist

Flat roofs are extremely rare in residential homes–in fact, they’re more commonly seen in commercial buildings than anything else.

But there are rare exceptions to the rule. There are two main reasons for choosing a flat or low slope roof over a higher pitch:

  1. Aesthetics
  2. Convenience

In commercial buildings, flat roofs have the key advantage of providing an easy place to install outdoor HVAC units (so that they don’t have to go in high-traffic areas).

Residential homes don’t have this problem, but if you’re building an add-on to your house, low-sloped roofs are often more aesthetically pleasing. They also avoid the biggest problem associated with flat roofs, which is a lack of drainage and subsequent buildup of snow and water.

How Roof Pitch Affects Your Choice of Materials

Now you know what your roof pitch is and how to calculate it.

With that in mind, let’s take a closer look at your roofing materials.

The roof pitch changes the materials that can be used on the roof because it affects how your roof handles weather and wind pressure. Certain materials are better suited to the conditions created by low slope roofing than others. Even a small change in your slope ratio can change the best choice of materials for the job.

The Best Materials for Low Slope Roofs

The best materials for low slope roofs should account for the unique needs of your roof.

Because low slope roofs don’t drain as readily as roofs with a higher pitch, the material used to build them should be especially resistant to wind and water damage. You don’t want any potential leaks because it’s much easier for water to pool on your roof.

And if you’re like most homeowners, you’re not regularly inspecting your roof for signs of wear and tear. So you should probably look for a roof that can hold up well no matter what your climate might throw at it.

With that in mind, here are some of the most popular types of roofing materials for low slope roofs.

Metal

Metal roofs can be quite attractive as low slope roofs, but in order for it to work, there must be careful planning involved.

Common metals used in these roofs include:

  • Steel
  • Aluminum
  • Copper
  • Stainless steel

First, you have to account for thermal expansion and contraction. In general, you’ll need pans between 18 and 24 inches. Anything larger or smaller will overstress the solder joints.

Second, you have to be thorough in soldering a metal roof. It should be fully soldered anywhere that snow or water might gather. This can get quite expensive and fiddly depending on the slope of your roof and the type of metal you use.

The solder joints require expert care and should be done by roofers with experience installing metal low slope roofs. They also require routine maintenance to ensure that everything is up to snuff, which can be an issue in residential homes.

You should also make sure to account for a movement joint partway across the roof. If you’re replacing your current low slope roof with a metal one, this can make your life more complicated, as preexisting conditions in the roof structure itself often dictate where you can put movement joints and solder joints.

Built-Up Roof

A built-up roof is a style of roof with a long history of performance. That’s probably why it’s one of the most common materials used in low slope roofs.

Built-up roofs consist of multiple layers of roofing felt, or tar paper, are mopped into place using coal-tar pitch, or bitumen. This creates a watertight membrane to protect your roof against creeping moisture.

Generally, built-up roofs consist of three parts:

  1. Bitumen material
  2. Ply sheets
  3. Surfacing sheets

Depending on the construction quality and the climate the roof is exposed to, built-up roofs typically have a lifespan between 15 and 30 years, though some can last as much as 40 years. It provides excellent water protection, ultraviolet protection, and a degree of fire protection thanks to the aggregate top layer.

Single-Ply Membranes

Single-ply membranes are factory-manufactured sheet membranes which fall into one of two categories:

  1. Thermoplastic
  2. Thermoset

Thermoplastic materials can be repeatedly softened or hardened when heated or cooled, while thermoset materials solidify permanently after heating.

Common thermoplastic membranes include PVC and TPO, while thermoset membranes include EPDM.

Single-ply roofs can be installed in a number of ways–it depends largely on the type of single-ply membrane. Generally, these kinds of roofs are well-suited to a low slope, as they create a single bonded layer across your entire roof that keeps water at bay.

PVC Membrane

PVC roofing membranes are made from two layers of PVC roofing material with a layer of polyester in between them for reinforcement. This type of roofing also requires an insulation board. Additives in the roofing layers make them UV stable and flexible even as they keep water and grime at bay.

PVC is a popular and versatile roofing material, especially when it comes to low slope roofs. That’s because it’s generally quite budget-friendly and durable.

PVC is installed using heat-welding, which helps to ensure that the roofing material lasts a long time. This process creates a bond between each individual roofing sheet, forming one solid layer that spans your entire roof.

EPDM

Another type of single-ply membrane is EPDM, or ethylene propylene diene terpolymer, which is a remarkably durable rubber roofing membrane.

EPDM comes in two thicknesses: 45 or 60 mils. The sheets are strong and remarkably durable, especially if you use 60 mil sheets.

As a material, EPDM lends itself nicely to low slope roofs, as it’s cost-effective and highly wind resistant. Like PVC roofing, it’s installed as a single, bonded sheet, which makes it quite effective at keeping water and moisture out of your house.

EPDM is also quite difficult to ignite–so much so that it can actually inhibit the growth of a fire.

And, of course, there’s the lifespan. Even without much maintenance, EPDM roofs can last up to 50 years. They’re hardy, low maintenance roofs that perform quite well in extreme heat and extreme cold alike.

Modified Bitumen

Finally, there’s modified bitumen.

Modified bitumen is created by chemically modifying asphalt for greater strength and flexibility. This modified asphalt is then constructed over a heavy layer of fiberglass or polyester.

As you might imagine, this type of roof is remarkably durable. They don’t tend to last as long as some other types of roofing (up to about 20 years at least) but for the lifespan they have, they have a high tensile strength that makes them difficult to crack.

They’re also highly resistant to wind, water, and fire damage and are unlikely to sustain damage even in a severe storm.

This type of roof is usually installed by melting the seams together, which helps keep leaks out.

Advantages

You know about what a low pitch roof is, how it works, and how to find the right material for your roof.

But one thing we haven’t touched on yet is why you should get a low pitch roof.

The truth is, there are several advantages to choosing a low slope roof over all the other kinds of roofs–if your home is designed to work with this type of roof.

Low-pitch roofs were quite popular in modern-style homes built in the 1960s, which looked flat with a minor slope to help with drainage. That doesn’t mean your home won’t work with a low slope roof, but it does mean you should talk to your roofing contractor about the best roof slope for your house.

Installation

One big advantage of low slope roofs is the installation costs.

To put it simply, a larger roof with a steep slope requires more material and effort to build. The more time and effort it takes to build the roof, the more expensive it will be to construct said roof.

Low slope roofs are far easier for builders to work with than other types of roofs because it’s easier for them to move around during the installation process. In addition, the supports are installed from the side of the building, which means that workers don’t have to lift up large trusses.

Low slope roofs also tend to require less material, so even if you go for a pricier roofing material, your cost will still be lower because you’ll need less material for the job. But most low slope roofs use a material that can be rolled and sealed, which is infinitely easier to do on a flatter roof.

Heating and Cooling

But the benefits of low slope roofs extend well beyond installation. In fact, they have a key advantage that homeowners will appreciate: they tend to have lower heating and cooling costs than steep roofs.

This is for one simple reason.

When a roof has a steep slope, it creates more space in the house overall. The roof and attic are also the biggest energy drains on your whole house, since hot air rises into the attic. This creates a greater strain on your heating and cooling system, especially if your roofing and insulation are old.

A low slope roof limits the amount of air in the top of your home and makes the whole house much easier to heat and cool. That doesn’t mean you should eliminate your attic altogether–a small slope is recommended for drainage and a small attic is a good idea for ductwork and storage.

Disadvantages

With all of that in mind, we would be remiss if we didn’t tell you a few key disadvantages that come with low slope roofs.

The good news is that they’re fairly obvious–and fairly easy to counteract if you know what you’re dealing with.

Limited Material Options

One of the big drawbacks with low slope roofs is the limited options available to you.

This is because low slope roofs, by design, have to account for different factors than a regular roof. The materials that might work on a steeper slope may not work that well on your roof.

This is because your roof’s slope changes how water is distributed across the whole roof. High pitched roofs don’t let water sit because, well, simple physics. But on a lower sloped roof, it’s a lot easier for water to pool.

Knowing this, you have to select materials that are especially water resistant. Otherwise, you’ll spend all of your time fighting rampant mold problems and water damage.

If you’re particularly attached to a roofing material, this could be a serious downside for you.

Drainage

A related downside of low sloped roofs is the drainage problem.

Once water enters your home, it’s an insidious problem. It can take a while to notice the water damage, and by the time you do, you could be facing serious repair costs. Leaks can result from anything from incorrect flashing to poor adhesion at the seams to plain old bad workmanship.

Either way, when you build a low slope roof, you have to go the extra mile to account for the drainage problem, and you have to be extra careful about checking your roof to ensure that you don’t have any standing water accumulating there.

Maintenance

Because low slope roofs are more susceptible than others to water buildup, you’re going to face higher maintenance costs as a homeowner.

It’s simple when you think about it.

Because water and ice tend to build up on low slope roofs, the roofs receive more wear and tear than they would if the slope were steeper. This will increase your maintenance costs over the overall lifespan of your home.

That said, maintenance is easier to do because low slope roofs are easier to work with. They’re easy to walk around on, which makes them much easier to repair. So your labor costs will be lower than they would if your roof had a high pitch.

Thinking of Installing Low Slope Roofing?

Knowing what you know, are you thinking of installing low slope roofing?

It’s a unique style of roofing that makes you stand out, and if you’re willing to put in the work to maintain it, it can actually be quite rewarding. The key is knowing yourself as a homeowner.

If a low slope roof sounds like the right fit for your home, we’re here to help you get the roof of your dreams.

Whether you need a brand new roof for a brand new house, you need to restore your roof and you want to upgrade, or you just want to get your roof redone, we can help.

Point Roofing has a long-standing reputation for excellence in customer service and experience. We’re proud to bring over a decade of experience to our Boise clients, and we’d love to speak with you about your roofing project.

If you’re ready to start the conversation, use our contact page to get in touch.