Roofing Reality Check: Top 3 Considerations for Solar Roof Panels

Written by Laurel Hamilton of Run on Sun
Updated November 11, 2016
Solar panels on the shingled roof of a home in Southern California.
Per fire code, solar roof panels must sit at least 3 feet from all ridges. (Photo courtesy of Angi member Kathleen R. of Banning, California )

Considering solar roof panels? You'll need to assess your roof's size and layout, how much shade it gets and what condition its in.

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So, you are considering a solar roof panels for your home or business. And why not, given the myriad of social, environmental and economic benefits! But how do you know if your roof is a good candidate?

This is one of the top questions to consider carefully before investing in a solar power system. Find the answer by focusing on three things: space, shade and roof condition.

1. Do I have enough space for solar roof panels?

The size of your solar system is dependent on your usage needs and the amount of energy you want to offset. However, it is not uncommon to find homes and businesses that are “footprint-constrained,” which means their system size is limited by the space available.Keep two things in mind as you look at your roof and ponder how big is big enough: solar panel size and fire code constraints.

Solar panel size

Though there are many different solar roof panels, they are typically the same size. At Run on Sun, we use LG panels that measure about 65 inches by 40 inches and can be placed in either a portrait or landscape layout.

Solar panels on the roof of a home near Boston, Massachusetts
Carefully consider the size of solar panels and the surface area of your roof. An average home needs 15–18 panels to offset the bulk of electricity. (Photo courtesy of Angie's List member Mark G. of Taunton, Massachusetts)

Panel energy ratings vary; 285- to 320-watt panels are currently available from LG. For an average home (5 kilowatts), that means you would need around 15–18 panels to offset the bulk of your electricity.

Fire code

Another limitation is that fire code requires three feet of clear space from all ridges. If you have an irregular shaped roof with many valleys and peaks, it may make the layout very challenging. Given that the panels are rectangular and racking is mounted parallel to the roof, rectangular spaces are ideal.

However, the 3-foot rule does not apply to uninhabited spaces such as garages and carports, making them good options if your home lacks the perfect solar roof.

2. What if my roof is shaded?

Shading from trees, tall buildings, chimneys or even parapets on flat roofs can significantly degrade the energy output from solar panels. Sometimes all that’s needed is a generous trimming of any trees that have gotten a little out of control over the years.

Other times, it may mean you really won’t get your money’s worth out of a solar panel roof. However, if the shade elements are few and only during a short time each day, your roof may still be a viable candidate.If this is the case, talk to your solar contractor about inverters. One of the main benefits of micro inverters is their ability to handle shaded roofs. String inverters, on the other hand, would be a bad choice as the entire system would degrade when any single roof solar panel is shaded.

Solar roof panels positioned in partial shade.
Some shade can be managed with the right methods, such as keeping trees trimmed and installing micro inverters. (Photo courtesy of Laurel Hamilton of Run on Sun)

3. Should I re-roof my house before adding a solar system?

This may be the most important and frequently overlooked question to consider when researching if solar is right for you. Part of what makes solar a great investment is the lifetime of the system, rated at 25 years or longer.

But if you have to re-roof during that time, there are added costs to remove and reinstall the system. If you plan to re-roof during the lifetime of your solar array, be sure you select components, such as the racking system, from companies that will:

  • A. Still be around in 15­ to 25 years

  • B. Be able to provide compatible replacement parts for pieces lost during removal and reinstallation

Avoid newer companies testing out “state-of-the-art” racking systems, and cheap companies banking on the solar boom alone.

Row of solar panels on the roof of a San Diego-area home
Solar panels may help your roof last longer by protecting it from the elements. (Photo courtesy of Angie's List member Alan R. of Lemon Grove, California)

For this reason, we always ask owners the age of their roof. In Southern California, a roof more than 10 years old should get a makeover before installing solar. If you are unsure of the condition, it is a good idea to have a professional roofer take a look and give you an expert opinion.

Sometimes solar contractors can offer this as part of their free assessment. Run on Sun, for example, works with a very reliable roofer who is happy to take a look at any roof in question!

If your roof still has some life left in it but not enough to outlast the solar system, you could re-roof only the area where the solar array will cover and plan to do the rest later. An added benefit is that the solar panels will actually protect your roof from the elements, helping it last longer.

Unfortunately, you will likely find someone willing to put solar panels on your roof even if it isn’t a good candidate. If they aren’t discussing the above issues with you, then red flags should be flying!

To ensure you get the best investment possible, do your research, take a good long look at your roof and discuss all of your concerns with your solar contractor.  

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About this Experts Contributor: As the projects coordinator of Run on Sun in Pasadena, California, Laurel Hamilton has been installing solar systems for 2 years. She loves helping people make informed decisions about investing in their own solar systems. Follow this contributor on Twitter @RunOnSun or on Facebook.

As of November 11, 2016, this service provider was highly rated on Angi. Ratings are subject to change based on consumer feedback, so check Angi for the most up-to-date reviews. The views expressed by this author do not necessarily reflect those of Angi.

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