When is a roof too steep for solar panels?

If your house has a steep roof, solar installation crews might have difficulty or not be able to work on your roof at all. This article explains why.

Photo of houses with steep roofs in San Francisco.
Credit: Joseph Sintum (Unsplash)

With most home solar installations, the solar panels get installed on the roof. This means that crews need to be able to walk around on the roof, move equipment, and work safely.

While flat roofs are easy to work on, roofs with steeper pitches can pose challenges. With very steep pitches, the logistics of the installation become too difficult for some solar installers, and they’ll turn down the job.

Companies that are more experienced can work with steeper roofs, but they may add a surcharge to the project price.

Do you have a house with a steep pitch? This article will try to provide some useful tips to help you figure out if solar can work for you.

Roof pitch explained

The pitch of a roof is its slope or steepness. A low pitch means that the roof is relatively flat, while a high or steep pitch means that the roof is steeply angled.

In the United States, roof pitch is expressed as a fraction, with the bottom number (denominator) always being 12 and the top number (numerator) referring to the rise per 12 inches.

For example, a 4/12 pitch refers to a roof that rises 4 inches for every 12 inches (1 foot) in horizontal distance. This translates to about an 18° angle.

Here’s a table of roof pitches and the corresponding angle in degrees.

Roof PitchAngle (in degrees)
1/124.76°
2/129.46°
3/1214.04°
4/1218.43°
5/1222.62°
6/1226.57°
7/1230.26°
8/1233.69°
9/1236.87°
10/1239.81°
11/1242.51°
12/1245°
13/1247.29°
14/1249.40°
15/1251.34°
16/1253.13°
17/1254.78°
18/1256.31°

To do this conversion yourself, calculate the arc tangent of the pitch. For example:

arctan(3/12) = 14°

What is considered a steep roof?

Once a roof pitch is about 9/12 or higher, that’s steep enough that some solar installers may consider it to be a difficult roof to work with.

Working on any roof requires safety precautions, and steep roofs require additional equipment such as harnesses, scaffolding, guardrails, and even netting. It takes time to set this safety equipment up, and the steep pitch slows down the installation work: moving equipment around becomes harder, and crews have to move more carefully and slowly.

Most solar installers consider a 12/12 pitch (45°) to be steep. Very steep roofs that have a greater than 50° angle pose an extra challenge for even the most experienced crews.

Price adders for steep roofs

Solar installers may tack on extra costs for projects that involve a steep roof. Surcharges like this are known as “adders” in industry lingo.

The adder for a steep roof will vary substantially from one company to another, but as a rough guide you can expect something in the range of $0.15 to 0.25 per Watt. This means that if you’re having a 6 kilowatt system installed, the average steep roof adder would be somewhere between $900 and $1,500.

Some solar installers may simply say no

Because of the extra cost and complexity, many solar installers may decline to provide a quote on a project that involves a steep roof. Especially in cities where home solar is popular, good solar installers are often very busy and would often rather turn down a difficult project and keep their crews working on installations that take less time and have lower costs.

A steep pitch can increase the load on your roof

Another issue is that solar panel racking hardware and your roof will have maximum load limits, and a steeply pitched roof could cause the allowable limits to be exceeded.

When solar panels are installed on a steep pitch, there is a greater load placed on the supports that attach the racking system to the roof. It’s not just the weight of the system that must be considered, but also external loads such as heavy snow or high winds.

Because a steep pitch will increase the calculated load of the system, it’s possible that the limits will be exceeded once snow or wind loads are accounted for. These are limits are determined by your local building codes.

Does a steep roof impact your solar energy production?

In the continental United States, the ideal angle that will maximize your solar production will be somewhere between 25° and 35°, with higher angles being better in northern latitudes (like Seattle, WA).

If your roof is quite steep, your solar panels will be outside of the ideal angle for your solar panels.

This will reduce your solar production, but the impact will be quite small. This is because much of the light received by solar panels comes from atmospheric scattering: this means that the entire sky sends light to your solar panels. It’s not just light directly from the sun.

A deviation from the ideal angle might impact your solar production by only a few percent, which isn’t enough to worry too much about.

However, a steeply pitched roof might cause a different problem: shading from nearby buildings. If you’re in an urban setting and the houses are close together, a steep pitch makes it more likely that your neighbor’s house will shade your roof for part of the day.

Shading has a major impact on solar production. Unlike trees that can be removed, there’s nothing you can do if a neighboring building shades your house.

Local solar installers are more likely to be able to work with your roof

If you ask a solar installer for a quote for an installation on a steeply pitched roof, you may find that they’ll politely refuse.

The best thing you can do in that situation is to look up local solar installers. Unlike the big national brands that work in a wide geographic area and often rely on subcontractors that have varying degrees of skills and experience, local companies work within a limited area. They’ll be more likely to have experience with the idiosyncrasies of the local housing stock, including steep roofs.

For example, if you live in San Francisco where steep roofs (like the ones pictured at the top of this article) are common, a San Francisco-based company will likely be more able to successfully install solar on them.

TAGS:
#Roofing

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