BUSI 441 Project 1: Reserve Fund Study
Estimating Roofing Replacement Cost
In Project 1, Part One, section (b) you are instructed to identify the roofing type and area for your subject
building. The section specifies the following:
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Roof:
y
y
y
y
type: built-up, torch-on, IRMA, etc.
total square footage of the roof areas, number of roof drains and vent stacks
don't forget to measure the roof area above the elevator shaft is there is one
physical age, condition, repair history
This document outlines guidelines and suggestions for completing this section of Project 1, as well as Part
Two, sections (a) and (c), where you are required to estimate the replacement costs and the life cycle.
MEASURING ROOF AREA
First and foremost, you will need to measure the surface area of your subject building's roof, to determine the
number of roofing squares that require replacement.
How to take roof measurements at ground level:
The first task in determining roof replacement costs is to measure the roof area. Due to safety restrictions we
do not recommend that you measure the roof of your subject property at the roof level. It would be best to
measure at the ground level. The first thing you need to obtain will be the exterior dimensions of the building,
in other words the buildings perimeter. Use a measuring tape to calculate the length and width of the outside
building walls. To determine the roof area multiply the building dimensions of width times the length. This
will give you the area of the main roof surface.
If your roof has an overhang you will have to estimate its width and length as this area is usually also covered
by the roof membrane. Most flat or low pitch roofs do not have overhangs, but an overhang is typical for
pitched roofs. Most overhangs range in width from 12 inches to 36 inches -- estimate what you think the width
is, again, from the ground.
Example: if your subject building has a pitched roof and is 200 feet long and 50 feet wide, after multiplying
both sides your would find the main roof area of the building is 10,000 square feet. If there is an overhang that
is approximately 2 feet wide, you would multiply the 2 foot width of the overhang by 400 feet (200 feet on
each side) to cover the area of the overhang. You add the result 800 square feet to 10,000 for a total 10,800
square feet as the basic roof area of your building (before adjusting to the multiplier, discussed below).
Keep in mind that some buildings do not come in perfect rectangular forms, and often will have funky
architectural twists. So, if your building resembles a complex geometrical figure, such as several pieces of
domino pieces next to each other on the table, then you can estimate the areas of each respective piece first,
and then add together for a grand total.
If your subject building has small gable roofs or dormers, you can ignore them as they will make minimal
difference in the total area. If there is a mansard roof (barn style), then estimate the height of the close to
vertical sections (again from the ground), and add the area of these to the calculation.
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
Converting covered roof area to roofing squares
The roofing industry likes to keep things simple and work with small numbers, so you need to convert the
larger numbers expressed in square feet of roofing surface to a simple number of roofing squares. One roofing
square has 100 square feet, or a 10' by 10' foot area.
Converting the area in square feet to roofing squares is accomplished by dividing the total area by 100. For
example, a 10,800 square foot roofing area would be described as 108 roofing squares.
Measuring the pitch of a roof
An accurate measurement of roofing area requires calculating the pitch or steepness of the roof. Calculating
the roof's pitch is actually quite simple and can be useful information. However, for the purpose of this
exercise you do not need to undertake this process -- these details are provided only for your information.
Defining Roof Pitch: The pitch of a roof is a ratio that measures the steepness of the roof. The base number
used in the measurement is 12, and the pitch is the number of units that the roof rises over the base number.
Because the base is 12, you can think of the pitch as the number of inches the roof rises for every foot or
twelve inches the roof extends horizontally. This change in roof height is also called the "rise" and the change
in the horizontal plane is also called the "run".
With this in mind, a perfectly flat roof would have a "pitch" of 0 in 12; for every 12 inches the roof extends in
the horizontal plane the roof rises zero inches. A roof with zero pitch is completely level and, of course, would
not shed water! Completely flat roofs are uncommon, although "ponding" roofs are used in some hot areas to
collect and store water to cool the house. They are very effective, but need to be able to withstand the
considerable weight of the water.
As the pitch rises, the roof becomes better at shedding water. What is referred to as a "flat" roof, actually has a
pitch of 1 to 3 in 12; it rises a couple of inches for every 12 inches horizontal. This is common on multi-unit
residential and commercial buildings. This roof pitch requires "hot" tar or rubber roofs to seal out the water
that can pool during heavy rains or snow.
A common roof pitch for what is referred to as a “peaked” or “sloped” roof is usually in the range of 5:12 to
8:12 pitch. This is a good pitch for shedding water but not prohibitively steep for access and work, although it
takes some experience to feel comfortable on any roof! This is probably what the average person perceives as
the "normal" roof, one that is neither too flat nor too steep,
A roof that has a 12 in 12 pitch has a rise equal to its horizontal projection. If the roof is pictured as a triangle,
then a roof with a 12 in 12 pitch has the roof-top makes a 90 degree angle. Roofs with this pitch and steeper
are used on traditional architecture such as English or Tudor as well as with mansard roofs.
Measuring Roof Pitch: To measure roof pitch, you need a framing square and a level. You need to safely
access the downward sloping underside of the roof. Hold the long end of the square against the roof, with the
point of the square extending toward the centre of the house, and the short end extending upward to the roof
edge (making a right-angle triangle, where the roof edge is the hypotenuse). The long end of the square should
meet the roof edge at 12 inches. Use your level to ensure it is horizontal. The inches on the vertical part of the
square will indicate the pitch. For example, if it measures 5 inches, then the roof is 5:12 pitch.
There are more detailed methods for measuring pitch, but this is sufficient for a rough calculation. Above all,
in making any roofing measurements, please keep in mind that safety is the paramount concern!
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
Calculating the roof area by applying a roofing pitch multiplier
Once you have derived the two-dimensional ground measurements, you need to convert them to a threedimensional roof measurement. Mistakes are often made in this step, especially when dealing with a complex
roof.
The diagram below illustrates three categories of roofing slopes:
Low Slope / Pitch
At least a 4:12 pitch, meaning that roof rises 4 feet for every 12
feet of its base horizontal length. This roof slope is considered
walkable and is easy-to- install. A low pitch roof will not be
greater than 5:12 slope of roofing steepness. Multiplier: 1.15 to
1.25 times the number of ground squares.
Medium pitch / slope
Ranges from 6:12-9:12 pitch. Not considered walkable and
installation requires special equipment such as roofing jacks and
planks. The higher degree of complexity of installation makes
them more expensive. Multiplier: 1.25 to 1.4 depending on the
steepness and complexity (dormers, valleys, endwalls, referred
to as how “cut up” the roof is.
High pitch / slope
A pitch 9:12 or greater. High slope is the most difficult and
dangerous to install, requiring special safety protection and fall
arrest equipment. As a result, it has the highest price.
Multiplier: can range from 1.41 for a simple gable roof up to 1.7
for a high sloped and cut up roof, or greater. A 1.5 multiplier
might be a reasonable average for high slope roof with and
slight to moderate cut up.
For your subject, make a reasonable assumption as to what you think the pitch of your subject property's roof
is, low, medium, or high pitched slope. Then, based on the parameters above, determine a reasonable
multiplier. For example, if you determine the roof is medium-pitched, around 7:12, then the multiplier will be
in the range of 1.25-1.4. The total roofing area is the roofing squares times the multiplier.
For example, assume that your roof has a medium pitch of 6:12, and is moderately cut up with an end wall and
two valleys. You may decide to use a middle of the road multiplier factor of 1.35, while keeping in mind that
average values could range from 1.25 to 1.4 as per the table above for medium-pitched roofs.
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
Let's return to our earlier example where we have a simple rectangular-shaped building with a medium-pitched
roof that measures 200 by 50 feet and has a 2 foot overhang. We calculated the roofing surface as 108 roofing
squares. Applying a roofing multiplier of 1.35 equals 145.8 squares of actual roofing surface, rounded up to
150 squares.
Now that you know your roof size in squares and have an understanding of the level of difficulty to install a
new roof, we can estimate the cost to install a new roof on your subject building.
ROOFING COSTS
Replacement roof prices will depend on the type of roofing material and installation costs. For the purposes of
this exercise we have limited the pitched roofs to using 30 and 40 year asphalt shingles for replacement. If you
wish to use another type of roofing material such as metal, cedar shakes, tile, or slate roofs you will have to
obtain pricing on your own. Keep in mind there are a number of factors to consider with the various types of
roofing material. For example, if you were to upgrade an asphalt roof to a tile roof you would have to upgrade
the roof trusses to hold the extra weight, and add strapping for attaching the roofing materials. Removal and
disposal costs will vary, as will life cycles.
The prices you may expect to pay will be somewhat different depending on the roofing company you are
working with and how busy the roofing industry is at the time the replacement is required.
As a general guideline, you may use the following price estimates when calculating the replacement cost of
your subject building's roof.
0:12-2:12 Low Pitch or Flat Roofs:
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EPDM (ethylene propylene diene terpolymer) single-ply rubber is the most popular and cost effective
low pitch membrane. Material and labour to remove and dispose of existing roofing, and then supply
and install an EPDM cover is $650- $750 per roofing square.
TPO (Thermoplastic Polyolefin) is a PVC single-ply material. Heat welded with a mechanical welder
(no torch), it is a recycled product and can count towards LEEDs points. Material and labour to
remove and dispose of existing roofing, and then supply and install a 1 ply TPO cover is $1,000$1,050 per roofing square.
SBS (Styrene Butadiene Styrene).is another two-ply type of roofing material that can be applied in 1,
2, or 3 layer systems. For the purpose of this exercise we will assume if SBS is used it will be the
more common 2-ply system. Material and labour to install a 2 ply SBS system would be $1,000
$1,050 per roofing square.
IRMA (Inverted Roof Membrane Assembly) roofing systems are used more in commercial
applications, but basically refer to a process of insulation known as inverted roof membrane
assemblies. The simplest explanation of this process is that the insulation is placed on top of the main
roofing material rather than under it. Hence, the idea of “inverted”. The flat roof system is expected
to do all that any roof is expected to do, and in the case of many buildings, even more is expected in
the way of energy conservation and protection. Yet, the very nature of flat roofs creates additional
problems over traditional sloping roofs. Material and labour to remove and dispose of existing
roofing, and then supply and install an EPDM cover is $1,250 -$1,300 per roofing square.
Usually when a low pitch or flat roof is replaced, the drains and the lead stacks are also replaced at the same
time. For the purposes of this exercise assume the above replacement costs allow for roof drain and lead stack
replacement. For your information, the cost to replace a drain is around $400 each and the cost to replace the
lead on a plumbing stack is around $40 per stack.
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
Most low pitch or flat roofs have a parapet wall around the circumference of the roof. These walls are
generally 3-5 feet high and are generally clad in metal or stucco. In many situations the cladding on the roof
side of this wall will require replacement when the roof is replaced. For the purposes of this exercise, to
determine the cost to re-clad a parapet wall assume the wall is 4 feet high, determine the circumference from
prior measurements and add a cost of $10 per square foot to apply new wall cladding on the parapet wall, with
capping.
In some situations, when replacing a low pitch or flat roof, the insulation values may also be added or tapered
insulation may be installed to improve drainage. For the purposes of this exercise, you may assume no
upgrades in insulation will be added
4:12-5:12 Pitch roofs
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30 year shingle with tear off and disposal of old: $350-$375 per roofing SQ
40 year shingle with tear off and disposal of old: $400-$425 per roofing SQ
6:12-9:12 Pitch roofs:
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30 year shingle with tear off and disposal of old: $550-$600 per roofing SQ
40 year shingle with tear off and disposal of old: $600-$650 per roofing SQ
10:12-12:12 Pitch roofs:
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30 year shingle with tear off and disposal of old: $650-$700 per roofing SQ
40 year shingle with tear off and disposal of old: $700-$750 per roofing SQ
These costs do not include any decking replacement, if required. The amount of decking that needs to be
replaced can only be determined during the tear off and will depend on the condition of the membrane being
replaced. The more leaks experienced prior to replacement, the more rotten decking or plywood that will need
to be replaced.
If you feel the gutters (eaves troughs) will require replacement at the same time as the roof, then calculate a
cost of $8.50 per lineal foot and add $15 for each corner. For new downpipes, calculate $6 per lineal foot of
downpipe. This assumes access is reasonable and can be achieved with a cherry picker or raised bucket. If
scaffolding is required, add $1,500.
DETERMINING THE LIFE CYCLE OF THE EXISTING ROOF
Flat to Low pitch roofs
Determine the installation date of the existing roof, as a starting point to determining its remaining life cycle.
If the current roof is a BUR (built-up roof of tar and gravel), then the life cycle varies from 15 to 18 years and
will depend on how well the roof has been maintained. BURs are not used much anymore as their life span is
too short and the labour involved in their replacement is not that much different than the materials cost for
more advanced products available today.
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
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Life cycle for an EPDM (Ethylene Propylene Diene Terpolymer) roof is around 20 years assuming
proper installation and maintenance.
Life cycle for a TPO (Thermoplastic Polyolefin) roofing system is 20 years.
Life cycle for an SBS (Styrene Butadiene Styrene) roofing system is 25 to 30 years.
Life cycle for an IRMA (Inverted Roof Membrane Assembly) roof is 25 to 30 years.
Low, Medium and High Pitched Roofs
Although asphalt shingles are rated by their life cycle, such as a 30 or 40 year shingle, they usually do not last
for 30 or 40 years. A 30 year shingle is usually replaced after 25 years and a 40 year after 35 years. Although
a shingle may last a bit longer, they are typically replaced in advance before leaking begins.
If you do not know the life of the shingle on your subject property, then estimate the life cycle remaining with
an educated estimate and the level of deterioration. Consider the following when making your determination.
Over time, shingles begin to curl, cup, and twist along the edges. As the old shingles continue to wither under
weather conditions, the tabs begin to shrink and cause a wider space between them. Rain water and moisture
tend build up behind the shingles and eventually cause decay to the roof plywood.
The need to replace an asphalt shingle roof depends on how much they are curling up and at what stage
deterioration starts. Sooner or later, every roof needs to be replaced, usually due to the long-term effects of
weathering. If a residential roof is more than 20 years old, it is a prime candidate for re-roofing. To determine
if you need a new roof from the ground, walk around your subject building with binoculars and inspect the
roof for cracked, curled, or missing shingles, as well as any excessive loss of the protective mineral granules.
DO NOT CLIMB ON THE ROOF; walking on the roof is dangerous and can damage the roof.
Look at the shingles and check for wave-like and ripple formations along the rows. Inspect the tabs for
adhesive failure or lifting and dull spots on the surfaces, as well as broken tabs or loose shingles. Loose grit on
the surface, around roof jacks, chimneys, and step flashing is an indication of shingle decay. On an
intersecting roof, check along the valleys for gaps, cracked tar joints, rusted out metal valleys, and granule
formation in the eaves trough. Inspect along the ridge for loose roofing nails and ridge caps. With all these
indicators, one can determine the severity of the problem and when to replace the shingles.
Asphalt roof shingles don't last forever, as demonstrated by their 10-40 year warranties. Shingles under
constant exposure to the sun will fade in colour and deteriorate at a faster rate than if they receive less sunlight.
In colder climates, moisture buildup under a leaky asphalt shingle roof (underlayment) speeds up the rotting
process of roof membrane. Therefore it is essential to change the shingles before it becomes very costly to fix.
Consider these factors when determining remaining life cycle
Roof experts say to replace asphalt shingles at the first sign of wear, but others suggest waiting until the
shingles are lifting up, shrinking, and breaking apart before any major work is done to the roof. Make a
reasonable assessment as to when you think the shingles need to be replaced.
©2009 UBC Real Estate Division
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Estimating Roof Replacement Cost
CALCULATING THE OVERALL ROOF REPLACEMENT COST
Based on the above pricing let's assume that your subject building has a medium-pitched roof with asphalt
shingles, with a total of 150 squares of roof area to be replaced. For a 30-year shingle, the cost for replacement
is $550 per square, for material, labour, and warranty, including the cost of tearing off and disposing of the
existing roofing.
Thus, we have:
Roofing: 150 squares H $550
$82,500
Gutters: 400 lineal feet
Downpipes: 4 H 40 foot runs
$3,500
$1,000
Total Roof Replacement Cost
$87,000 (plus applicable taxes)
Note that roof installation costs will vary depending on access to the work area (e.g., from alleyway, crane
required, man lifts, chutes required), disposal requirements, dumping fees, etc. For your estimate for your
subject property, you must factor in any irregular or extraordinary factors that will affect the cost of replacing
its roof and explain your methodology in calculating these costs.
©2009 UBC Real Estate Division
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