Materials, Installation, and Maintenance (Guide)

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

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

  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

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

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

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 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.


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

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.


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.


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

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


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.


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

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.


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

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

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.

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