Roofing Costs

Learn How to Estimate Roofing Costs on Your Rehab Projects

How to Estimate Roofing Costs

Estimating Rehab Costs
How to Estimate Roofing Costs


As a house flipper, you will need to be able inspect a property's roof condition and determine whether it needs to be repaired or completely replaced. You will also need to be able to accurately quantify the # of squares of roofing and estimate an approximate budget. Roofing work is an expensive rehab item, so being able to inspect and diagnose the roof condition and estimate the replacement costs is critical in creating accurate budgets for your rehab projects.

Basics of Estimating

Roofing Costs

Roofing contractors measure and estimate the size of roofs in a unit of measure called a square.  A square is equal to 100 square feet or a 10ft x 10ft area.  

So for example, if your home was perfect square of 50 feet wide and 50 feet long,  that would equal a surface area of 2,500 square feet or 25 squares.

50ft x 50ft = 2,500 sf
2,500 sf / 100 sf per square = 25 squares

Roofing Square Calculation
Roofing Square Calculation 2

Unfortunately, most homes are not a perfect square and have pitched roofs with complex shapes, valleys & dormers, which makes the exact measurement of roofs more difficult.

Calculating the Size of Your Roof

There are two different ways that you can calculate the size of your roof:

  1. Measuring on the Roof
  2. Estimating the Roof Size from the Ground

Measuring on the Roof

For the most accurate calculation you will need to get on the roof and draw a diagram of the roof shapes and measurements.  Once you have the roof shapes measured, calculate the area of each shape and add up all the areas to calculate your total roof area.

Estimating the Roof Size from the Ground

While measuring from the ground isn’t as accurate as getting on the roof, it is faster, safer and gives you a rough calculation of the property roof area.

Assuming you have a rectangular shaped house, you can simply multiply the length by the width of the house.

Unfortunately, houses are not typically a perfect square or rectangle.  If you have a house that is a complex shape, you will have to breakdown the floor plan into segments to calculate the building footprint area.

Building Footprint Calculation

In the example on the right the floor, plan has been broken down into 4 different segments.  The area of each segment is calculated by multiplying the length by the width.

The 4 segments areas are then added together to calculate the building footprint.

Next, you need to convert the property square footage to squares by dividing by 100.

Building Footprint Calculation

Area 1 = 25 FT x 40 FT = 1,000 SQFT
Area 2 = 15 FT x 15 FT = 225 SQFT
Area 3 = 10 FT x 20 FT = 200 SQFT
Area 4 = 10 FT x 20 FT = 200 SQFT

Total Area = 1,625 SQFT

Roofing Footprint Calculation

Roof Pitch

Once your calculate the roof footprint, you will need to factor in your roof pitch or roof slope.  Roof pitch or roof slope is the number of inches the roof rises vertically for every 12 inches it extends horizontally.

The slope of a roof is split up into three categories.

  1. Flat Roof: (Anything under a 2:12 pitch)
  2. Low Slope: (A 4:12 pitch to a 2:12 pitch)
  3. Steep Slope: (A 4:12 pitch to a 21:12 pitch)

To factor in your roof pitch, you can use the roof pitch multiplication table on the right:

Most roofs are 4/12 up to 7/12, so when in doubt a safe multiplier would be 1.15 (7/12).

​In our previous example, we measured the property's footprint to be 1,625 square feet.  If we assume that our roof's slope is 6/12, then we need to use the 1.118 multiplier.

1,625 sf * 1.118 = 1,625 / 100 square feet per square = 16.25 squares

16.25 * 1.118 = 18.1675 squares

Material Waste

When your roofing contractor purchases & installs your roofing materials, the roofer will buy an extra 10% of material to cover waste of scrap materials.

So in the above example, the roofer needs to purchase 16.25 squares of roofing, with an additional 10% of material that will be scrapped/wasted.

18.1675 x .10 = 1.81675 extra squares in waste
18.1675 + 1.81675 = 19.98425 squares or 20 squares


A final factor that you may want to consider is an allowance for contingency which will cover any uncalculated square footages such as roofing overhangs, valleys, gables, etc.

Generally, if you have a complicated roof structure with may overhangs, valleys, gables & elements, a 10% contingency would be recommended.

19.98425 x (1+ .10) = 21.982675 squares of roofing or 22 squares

Quick Rule of Thumb

So maybe all of this math is a bit overwhelming, but now you know how professional roofing contractors estimate the size of your roof.

With that said, since we now know how professional roofers estimate costs, we can now simplify this down to a quick rule of thumb.  

We know that we first need to calculate the square footage of the roof footprint.  Once we find the footprint of the roof, we need to factor in the roof pitch, waste factor & contingency.

Earlier, we discussed the average roof is 4/12, which added about 5% (1.05 multiplier) to the square footage. With the added in amount for waste at 10% & contingency at 10%, we’ve roughly added about 25% to the calculation.

For this reason, as a quick rule of thumb, you reasonably can take the building footprint square footage & multiply it by 1.25 to get the roughly calculated roof area.​

Roof Size = Building Footprint x 1.25
Roof Size = 1,625sf x 1.25
Roof Size = 21 Squares

FlipperForce House Flipping Software Founder Head Shot
Quick Rule of Thumb
Multiply the Property's Footprint x 1.25 to calculate the rough square footage of the property's roof. The extra 25% will cover the slope, material waste & 10% for contingency.

Material Costs

Installation Costs

There are several different types of roofing materials that are currently used on residential properties. Below we discuss the different roofing options and their pros, cons, life spans and costs of each:

3-Tab Asphalt Shingle Roofing

3-Tab Asphalt Shingle Roofing

$225 to $450 / sq (lab & Mat'l)

'Three tab' shingles are the most economical and popular type of asphalt shingle.

Architectural Asphalt Shingle Roofing

Architectural Asphalt Shingle Roofing

$250 to $500 / sq (lab & Mat'l)

Architectural shingles provide more architectural dimension, more durability & provide a longer warranty, but are generally 20 to 40% more expensive than 3-tab shingles.

Wood Shingle Roofing

Wood shingles

$500 to $800 / sq (lab & Mat'l)

Metal Roofing

Metal Shingles

$500 to $800 / sq (lab & Mat'l)

Clay Shingle Roofing

Clay Shingle Roofing

$1,000 to $2,000 / Square

Slate Tile Roofing

Slate Tile Roofing

$1,000 to $2,000 / Square

Asphalt Shingles

Asphalt Shingles are the most common residential roofing material in the United States and will likely be your material-of-choice for your flip projects.  Asphalt shingles are manufactured in two styles, three-tab or architectural shingles.

3-Tab Asphalt Shingles - Three tab shingles are the most economical and popular type of asphalt shingle

Architectural Shingles - Architectural shingles provide more architectural dimension, more durability & provide a longer warranty, but are generally 20 to 40% more expensive than 3-tab shingles.

3-Tab Asphalt Shingles
3-Tab Asphalt Shingles
Architectural Asphalt Singles
Architectural Asphalt Shingles


  • Least expensive roofing option
  • Easy to install
  • Widely available at home improvement stores
  • Comes in a variety of styles/colors


  • Shorter life span

Life Span:  20 to 25 years
3-Tab Asphalt Cost Range: $225 to $450 / SQ
Architectural Asphalt Cost Range: $250 to $500 / SQ

Wood Shingle Roofing

​Wood shingles were the go-to roofing choice for hundreds of years, but due to their cost & flammability, wood shingles have lost popularity.
​Generally, wood shingle roofs on a flip project would only be selected if you were seeking a specific architectural look.  Be sure to check with the local HOA & your local building/fire codes to determine if wood roofs are allowed in your neighborhood.

Wood Shingles
Wood Shingles


  • Rustic natural look
  • Natural product made from cedar, redwood or southern pine


  • Flammable, fire codes may prohibit use
  • Can mold, split or rot in wet climates
  • Short life span of 15 to 25 years

Life Span: 15 to 25 years
Cost Range:  $500 to $800 / Square

Metal Roofing

Metal roofs are gaining popularity, but would likely only be used on a flip project if you were seeking a certain architectural-look.  Again, check with your local HOA covenants to see if metal roofs are allowed in your neighborhood.

Metal Roofing


  • Resistant to extreme weather conditions
  • Durable, lasts longer than asphalt or wood
  • Lightweight & easy to install


  • Relatively expensive, some options are affordable at $300 to $500/SQ, but most are $600 up to $800/SQ
  • Lower grade aluminum roofs can be dented
  • Can be noisy in rain storms

Life Span: 40 to 50 years
Cost Range:  $500 to $800 / SQ

Clay, Concrete or Tile Shingles

Clay Tile Roofing
Clay Tile Roofing
Slate Tile Roofing
Slate Tile Roofing

Clay, Concrete or Slate Tile Roofing are some of the most expensive materials used for roofs.  These types of roofs are typical on certain home styles such as Mediterranean, Mission, Southwestern or Spanish style.  You would likely only install these types of roofs on a property to match the property architectural design, and meet neighborhood HOA requirements.  


  • Resistant to extreme weather conditions
  • Durable, lasts longer than asphalt or wood​


  • The most expensive roofing option available, so should only be considered for architectural purposes to meet HOA requirements.

Life Span: 40 to 50 years
Cost Range:  $1,000 to $2,000 / Square

Note: If you are changing from a lightweight roof system (asphalt or wood) to a tile roof, there will likely be additional expenses for structurally reinforcing the roof framing.

Installation Timeline

A roofing crew can typically re-roof an asphalt shingle roof on smaller to average size properties (1,000 to 2,000 sf) in 1 to 3 days.

On small properties an efficient roofing crew can completely tear-off and re-roof a property in a single working day.

On a typical 1,500 sf property that needs 16 to 20 squares of roofing you should expect the project to take 2 days at most.

Note: More labor-intensive wood or tile shingles installations will likely add several days to the duration.

Cost Summary

Other costs

The installation costs mentioned above are for a complete re-roof with new roofing shingles, however those costs may not includes these other costs listed below:

  1. Roofing maintenance and repairs ($200 - $500 total) - Miscellaneous roofing maintenance in repair work would include fixing/replacing missing roof shingles, sealing around the chimney's/roof penetrations.
  2. Roofing, patch section (varies by size) - Patching and replacement of the existing roof will vary by size, but it will typically be at the higher $ per Square range.  
  3. Plywood roof sheathing ($35 - $50 per 4' x 8' Sheet) - Over time the sheathing on a roof can become damaged from water and will need to be replaced.  Roofing contractors will generally charge a price per 4'x8' sheet of plywood sheathing.  E
  4. Gutter replacement ($6 - $10 per Lineal Foot) -
  5. Premium for 2 layer tear off ($150 - $250 per Square) - If your roof has more than one layer of roofing currently installed,
  6. Premium for steep pitched roof ($150 - $300 per Square) - Work performed on steep roofs (7/12 or greater) is much slower than work performed on flatter roofs.  For that reason, your roofing contractor will generally charge a premium for steeper roofs.
  7. Fascia board ($3 - $8 per Lineal Foot) -
  8. 12" Soffit board ($3 - $8 per Lineal Foot) -

Price Considerations

#1 Type of Roof (asphalt shingle vs expensive tile)

The most obvious factor that influences roof pricing is the type of roofing material being installed.  Asphalt shingles are the cheapest and easiest to install roofing material available, with tile roofing being the most expensive and labor intensive.

#2 Roof Size (small patch vs large re-roof)

In construction, there is a term called economies-of-scale.  The larger the project, the more efficient the contractor can be installing the roofing.  So in other words, on smaller projects you should expect to pay more per square of roofing. If your project only requires a small roof patch, the price per square will be significantly more expensive. As the size of the roofing project increases the price per square should decrease due to efficiencies and economies of scale.

#3 Number of Layers

Previous homeowners (or even house flippers)may have tried to cut costs on re-roofs by installing a new layer of roofing over the old layer of roofing.  Some insurance companies won't insure homes with multiple layers of roofing and in many cases multiple layers can invalidate the roof warranty. If your house has multiple layers of roofing your roofing contractor will likely charge a premium for the additional labor required to tear off extra layers of roofing.

Multiple Layers of Roofing

#4 Roof Sheathing Replacement

Roof decking on homes built before the 1960s were often built with 1x8 wood shiplap because exterior grade grade plywood was not available. Shiplap boards are also commonly used under wood shingle roofs. The problem with shiplap boards is that they shrink over time leaving large gaps between the boards which leaves more opportunities for new nails to miss the wood completely which causes eventual leaks. If you have an older home that used 1x8 wood shiplap or a home with wood shingles you may have to install new plywood sheathing over the existing shiplap decking in order to provide a solid substrate for your new roof.

roof decking

#5 Pitch of the Roof

On most moderately pitched roofs the roofing crew can easily install the roofing materials directly on the roof. As your roof gets steeper the roofing crew may be required to work from ladders or install scaffolding which can be significantly less productive than direct installation. If you have a steep roof pitch on your house you should expect your roofing contractor to charge a premium to account for this lost productivity.

#6 Roof shape (hips, gables & features)

If your roof has odd shapes, roof elevation changes, & features it will take more time for the roofing crew to measure, cut and to install the roofing materials. Each of thease shapese and transitions will also require roof flashing materials.

#7 Location & Project Access

The location of your home and project will have a significant impact on the cost as well.  If you are installing the roof in downtown San Francisco the roof will obviously cost much more than the same roof being installed in Suburbia.

#8 Seasonality

Spring and Summer is peak roofing season and roofing contractors are generally swamped with work, so if you are getting a roof installed during this time you will likely pay a premium.

Writing a Scope of Work & Getting Bids

Roofing contractors will generally provide an all inclusive bid to 'furnish and install' all labor and materials on the project.

Here is an example of how to write a Scope of Work that insures your Roofing Contractor provides an all-inclusive bid.

Example Scope of Work

All Roofing work is to be Contractor Purchased, Contractor Installed.

  1. Furnish and install new architectural roof shingles, roof vents, flashings & components as required by local building codes.
  2. Architectural Shingle Specification: Input Roofing Product Information.Alternate materials and manufacturers that provide savings will be considered, but must be approved.
  3. Remove existing asphalt shingles as necessary to install new roof shingles.
  4. Replace damaged or rotted plywood sheathing as necessary. Plywood replacement will be priced by each sheet required to be replaced. Price per sheet: $_______________
  5. Repair any loose or damaged gutters or downspouts.
  6. Hauloff demolished roofing materials and debris.
  7. Final Cleaning: Clean up all scrap roofing debris, screws and anchors from project site.

Example Scope of Work Document

Download our Scope of Work Document template, compatible w/ Google Docs & Microsoft Word
Scope of Work Document Template Example

Scope of Work Document Download

Download the Editable Scope of Work Document available in MS Word or Google Docs
Microsoft WordGoogle Docs

Other Resources

Rehab Repair Estimator Software
HomeAdvisor Cost Guide
Fixr Cost Guide
Homewyse Costs Guide

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