How to Build a Canopy or Porch Roof

Updated on April 8, 2019
ITS4YOU LM profile image

With over 30 years of experience as a carpenter, I'm an expert at building roofs and housing fixtures.

In this article, we are going to explore how to build a porch roof the easy way. Undertaking this task on your own will save you hundreds of dollars and will be a great learning experience.

What You Need to Know to Build Your Own Porch Roof

  1. Know the pieces of a porch and gable roof.
  2. How we use run and rise to find the angle of a potential roof.
  3. How to make a simple, but effective, roofing square.
  4. How to work out the lengths of rafters.

Gable Roof
Gable Roof

1. What Is a Gable and Porch Roof?

Gable roof: The most common porch roof is a gable roof. The gable roof is a triangle-shaped roof that projects along a ridge down the center of the enclosure. The sides are sloped at a particular pitch rise over run in order to shed snow and water. This type of roof consists of two roof sections sloping in opposite directions, placed such that the highest, horizontal edges meet to form the roof ridge. This is the classic, most common roof shape in parts of the world with cold or temperate climates.

Parts of a Gable and Porch Roof

  • Ridge
  • Rafter
  • Purlin
  • Ceiling joint
  • Wall plate

Before we can start to build any kind of roof, it helps to know a few basics. Below are illustrations showing the main components of a gable roof followed by a porch roof (as mentioned above).

Porch Roof
Porch Roof

2. How to Use Run and Rise

The next thing we need to know is how to work out the angles. Now, before you say, "I hate trigonometry! I couldn't do that in school!" you may be pleased to know that most of the best traditional roofers couldn't do complex math either, so they devised this method. A roof was worked out by run and rise. To work out the angle of our roof, we need to find the distance it travels (run) and the height (rise).

Run and Rise
Run and Rise

Calculating Run and Rise

A roof is calculated by foot per run. For those who are not familiar with imperial measurements, there are 12 inches in a foot (1 foot) so calculations are worked out by how much the roof rises per foot/every 12 inches.

In the next picture, you will see that for every inch a roof rises there is an equivalent angle. For example, if a roof rises 10 inches after travelling 12 inches (1 foot), the angle of the roof would be 40 degrees. If it rises 12 inches after travelling 12 inches, it would be a 45 degree pitch roof.

Run and Rise
Run and Rise

How Do These Measurements Correlate to My Roof?

The run:

  • When talking about the basic construction of a porch roof, the run would be the distance out from the wall along the ceiling joist.
  • This is less then the thickness of the ridge.

The rise:

  • The rise would be the height from the top of the ceiling joist to the top of the ridge.
  • The formula to work out the angle is the rise (in inches) divided by the run (in feet).
  • So, if the run was 26 inches (distance out from the wall) minus a 2 inch thick ridge board that would give us 24 inches, or 2 feet.
  • If we had a rise of 20 inches (height from top of ceiling joist to top of ridge) we would divide 20 by 2, giving us 10. This would be equal to a 40 degree pitch roof.

3. How to Make a Roofing Square

The next thing we need to do is make a roofing square (unless we have one) and the easiest way to do this is to cut the corner off a sheet of ply board, making it roughly 24 inches on one side and 16 inches on the other side. Then, starting from the corner, in both directions, mark it out at 1 inch intervals.

Roofing Square
Roofing Square

4. How to Work Out the Lengths of Rafters

Pythagorean theorem: We can use Pythagorean theorem (run2 + rise2=c2), then find the square root. In our example, our porch roof would be 24 squared (576) plus 20 squared (400), which added together equals 976. Then, taking the square root of 976, we get 31.24. So, your rafter length would be 311/4 inches

Example: 242 + 202 = 976

√976 = 31.24

Using a roofing square:

Let's say our roof is a 10 in 12

  • 10 x 10 = 100, then 12 x 12 = 144 add them together = 244
  • Find square root, which is 15.62
  • This means that for every 12 inches our roof travels, the rafter will be 15.62 inches longer.

But, as not all roof runs work in to exact multiples of 12, we need to take it a step further to make it easier.

  • once we have our square root of 15.62, we need to divide it by 12 = 1.30.
  • This means that for every inch our roof travels, our rafter will extend by 1.30 inches.
  • So, if our roof run is 24 inches, then we would multiply 24 by 1.30 = 31.2 inches or 311/4 inches.
  • If we were doing a big gable roof with a span of say 20 feet that would be 240 inches minus a 2 inch ridge board = 238 inches.
  • divided by 2 = 119 inches.
  • Multiply by our 1.30, making our rafter 154 3/4 long.
  • If you drop a tape measure across our square, between the number 12 and number 10, you will see that it measures exactly 15.62.
  • Multiply this by 10 feet and minus the 2 inch ridge. This would get you 154.75.
  • You could also divide 15.62 by 12 and get 1.30.
  • Change our 10 feet into inches = 120 x 1.30 - 2 inch ridge = 154.75
  • In our porch example, we would multiply our 24 inches by 1.30, giving us a rafter length of 31.2 or 311/4.

(See image below) To cut our rafter, we place our square on to our timber. Lining up the marks 10 and 12. We draw a line down the top cut side (no 10 side) we then measure down the timber 31.2 inches, put our square back on, lining up the 12 and 10 again, but making sure this time that the no 12 is on our bottom mark, then draw a line for our bottom or seat cut.

Rafter lengths
Rafter lengths

Recommended Reading

If you want to learn more about roof framing, or simply want to improve the skills you have, then I recommend these books from firsthand experience:

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

    New Guestbook Comments

      0 of 8192 characters used
      Post Comment
      • profile image

        Timothy Macg 

        3 years ago

        it is a great article i enjoyed it,my porch is going to build by my self and a help i find on http://iwilldo.co keep up good work

      • roofingvancouve1 profile image

        roofingvancouve1 

        6 years ago

        I like the way you have laid it out in sequence. Nice job

      • profile image

        jp_smith86 

        6 years ago

        Thanks for sharing. High performance reinforced EPDM flat roofing systems from AR Systems. We supply Duoply, new reinforced EPDM flat roofing systems to roofing contractors for residential, commercial and industrial projects.

      • profile image

        sandra65 

        6 years ago

        easy and simple guide lines

      working

      This website uses cookies

      As a user in the EEA, your approval is needed on a few things. To provide a better website experience, dengarden.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

      For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://dengarden.com/privacy-policy#gdpr

      Show Details
      Necessary
      HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
      LoginThis is necessary to sign in to the HubPages Service.
      Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
      AkismetThis is used to detect comment spam. (Privacy Policy)
      HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
      HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
      Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
      CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
      Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
      Features
      Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
      Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
      Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
      Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
      Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
      VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
      PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
      Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
      MavenThis supports the Maven widget and search functionality. (Privacy Policy)
      Marketing
      Google AdSenseThis is an ad network. (Privacy Policy)
      Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
      Index ExchangeThis is an ad network. (Privacy Policy)
      SovrnThis is an ad network. (Privacy Policy)
      Facebook AdsThis is an ad network. (Privacy Policy)
      Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
      AppNexusThis is an ad network. (Privacy Policy)
      OpenxThis is an ad network. (Privacy Policy)
      Rubicon ProjectThis is an ad network. (Privacy Policy)
      TripleLiftThis is an ad network. (Privacy Policy)
      Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
      Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
      Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
      Statistics
      Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
      ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
      Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)