How are solar panels installed on a roof?

Depending on the type of roof you have and aesthetic considerations, there are different ways to mount solar panels on your roof. Here's an overview of the choices.

An photo of a solar panel racking system.
Credit: Simmitri

The most visible part of a home solar system is the panels. Around 95% of homeowners choose a roof-mounted (rather than ground-mounted) system, so how the panels are attached to the roof is a key detail of the installation.

Solar panels are attached to a roof using a mounting system. The most common type is a rail-based system, which uses aluminum rails as the structure onto which the panels and other components, such as wiring and inverter components, are attached. These rails in turn are attached to mounting points called footings that are bolted into the structural beams of the roof.

Another type that is becoming more popular is a railless mounting system. As the name suggests, railless systems don’t have rails onto which the equipment is mounted. Instead, the solar panels are attached directly to footings that are fixed to your roof.

There are pros and cons to both types of mounting systems. While there are aesthetic considerations that might cause a homeowner to ask their installer to choose one type over another, technical demands will usually be the deciding factor. In addition, whether you have shingles, tiles, or metal on a flat or pitched roof will often dictate how your solar panels are mounted to your roof.

This is a pretty complicated topic, so I’ll link to other articles I’ve written that are specific to particular roof types. But first, let’s start with the basics of how solar mounting systems work.

What goes on your roof with a home solar system?

With a roof-mounted solar array, the equipment that goes onto your roof includes the solar panels, the wiring to connect them, and the mounting system. If you choose a microinverter or power optimizer-based inverter, there are also electronics mounted behind each panel.

Depending on the size of your system, you’ll probably have at least a dozen solar panels in your system, up to as many as 30 panels or more. (You can use our solar calculator to get a quick estimate.) This will cover a significant area on your roof.

In some cases, the installer will prefer to install the panels on sections of the roof that face south. This is because in the Northern hemisphere, the sun spends its time in the southern half of the sky. That might not always be possible: you might not have a south-facing roof segment, or have shading or structural issues that don’t make this possible.

If that’s the case, it’s often best to install on a west-facing roof. This is because many solar homeowners are required to have a time-of-use (TOU) plan that makes solar electricity in the evening more valuable. Since the Sun is in the western sky in the evening, having west-mounted solar panels means you’ll generate more electricity during the evening peak.

Not every homeowner has a TOU plan, in which case you can even install solar on an east-facing roof if that’s your best choice.

What is a rail-based solar mounting system?

This type of system is based on aluminum rails that are attached in rows to your roof. The rails are secured to the roof with footings (more about that later). You can see an example in the photo at the top of this article.

Rail-based solar mounting systems are strong and are the most common type in use. This popularity is advantageous because installation crews have a lot of experience with them.

Their strength can be an important factor in regions where a solar array can be subjected to strong forces, such as hurricanes. Because the rails provide rigidity, they are a good choice when high winds or heavy snow loads are a possibility.

Another benefit of rails is they provide a convenient mounting point for wiring and inverter components. Good wire management is a particularly underappreciated part of a solar installation. Poor wire management can be ugly, but can also lead to electrical problems down the road. Loose wires can flap around in the wind, eventually causing insulation to wear away, exposing the wire underneath.

On the other hand, rail-based systems may have higher costs and take longer to install than railless systems.

What is a railless solar mounting system?

As the name suggests, railless systems don’t use rails. Instead, the system is based on brackets and footings. The solar panels are attached to the footings with brackets, allowing the installer to lay out the grid of panels with a lot less equipment.

Solar panels have aluminum frames, which provide a lot of structural rigidity that allow them to withstand severe weather such as hurricanes and hail. Railless systems take advantage of this feature, relying on the stiffness of the solar panel frame to allow the array to remain secure for a couple decades or more.

One benefit of a railless installation system is that there’s a lot less equipment involved. This means less weight on your roof and less gear for the installer to haul around. Most solar installers try to get a home system installed in just one day to minimize driving time, so this can be a significant cost savings.

In addition, railless systems can also have an asthetic benefit because there’s less equipment visible. Some manufacturers, such as SnapNrack, offer the option of a skirt that attaches to the visible edge of the array, hiding the gap between the panels and roof and giving the system a smoother appearance. When combined with all-black solar panels, this can give a solar array a really smooth appearance.

Railless solar installation system by SnapNrack
SnapNrack railless mounting system

A disadvantage of railless systems is that they may not be approved in hurricane regions. While solar panel frames are strong, the stiffness of a rail-based system adds extra strength that allows them to be used in places like Florida where hurricanes are an annual occurrance.

However, some railless systems such as the SnapNrack pictured above have been approved by Miami-Dade County.

How are solar panels attached to your roof?

With both rail-based and railless solar mounting systems, footings are the components that attach the system to your roof. You can see them illustrated in the image above; there are several used in a system.

While the exact design varies depending on whether you have shingles, metal, or a tile roof, footings are generally made of strong and lightweight aluminum and are bolted through the surface of the roof into the structural rafters below.

Roof construction diagram

All good footings incorporate waterproofing in their design using features such as a large flat sheet called flashing, a rubber grommet, or a combination of methods. Manufacturers often also recommend that installers apply a sealant to each bolt hole, but because sealants can eventually dry out and become brittle, it’s the design of the footing that is the main barrier against water entry.

One of the primary concerns of a solar installation is ensuring that it’s done without damaging your roof, so I wrote an article about roof leaks that goes into a little more detail.

How solar installations are done with different roof types

While asphalt shingles are the most common roofing material in the country, many homes have other products such as tile and metal. These materials can make it relatively easy to install solar panels, or make it so difficult that some solar companies will decline working on a project.

For example, it’s possible to install solar panels on a standing seam metal roof without drilling any holes, making this one of the easiest materials for solar installers to work with.

In contrast, clay tile roofs are so brittle that simply walking on them can crack them. This aspect of clay tiles can increase the cost of installation so much that many solar companies will say that it’s not worth it for them to take the job. Other types of tile, such as composite and concrete, are more durable and easier to work with. However, they still require special techniques, so a solar installation on any type of tile roof is typically a little more expensive.

Flat roofs are another special case

Earlier I said that solar panel mounting systems are attached to a roof using footings that are bolted to the rafters. One special case where this isn’t always true is a flat roof.

With a flat roof, contractors can use the same mounting systems they would with a pitched roof, but they also have the option of a ballasted rack.

Ballast is simply a heavy weight - often concrete blocks - that is used to anchor a racking system in place. These weights keep the solar array in place without the need for bolts or any holes in your roof. This is an attractive option, but it does have the disadvantage of placing additional stress on your roof. Which of these options is best for your home is best determined by your contractor, often in consultation with a structural engineer.

Bottom line: work closely with your solar installer to understand what’s being installed on your roof

Your home is probably your most valuable asset, so if you’re going to get a thousand pounds of solar equipment mounted on its roof, it’s a good idea to ask a few questions about what you’re buying and how it all works.

However, while the choice of the solar mounting system is sometimes influenced by aesthetic considerations - such as the decision to choose between a railless or conventional rail-based mounting system - for the most part, the choice is often best decided by the solar installer. Engineering considerations and the familiarity of the installation crew with the product are among the reasons why the homeowner should usually leave the decision to the experts.

That said, there are situations where the installer may ask you to make a choice, such as choosing a betweeen a “comp-out” or a tile replacement mount for your tile roof, or between an attached or ballasted rack for your flat roof.

Whatever the case, make sure that you work with a high quality solar installer who will keep your best interests in mind.

TAGS:
#Roofing #Racking Systems

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