solar panel roof load calculator

It’s no secret that solar energy adoption is on the rise. While solar energy already powers 4% of America’s homes, even more homeowners are looking to adopt this renewable resource to save money and live more sustainably.

A Pew Research Center study found that 1 in 4 homeowners plan to install solar panels in the next five years. If you’re one of these prospective solar energy system owners, you may have considered your home’s roof, and whether it would be a good fit for solar energy.

A suitable roof for solar panels is crucial to the photovoltaic system installation process, whether your roof needs to be reinforced or not. A solar panel roof load calculator can help you determine the size and weight of solar panels your roof can accommodate.

This article explains some of the core factors determining whether a roof can support a solar system and provide a formula to determine your roof load. This solar panel roof load calculator helps to establish the size and weight of the solar panels that your roof can support.

Factors to consider when installing solar panels on your roof

When installing a solar panel system, you must understand certain features of your roof and the solar panels you’re installing.

Solar panels differ in weight and length depending on the manufacturer, brand, and amount of energy output your home requires. Determining whether your rooftop can support the solar panels is essential before you begin the photovoltaic installation process.

It’s also important to note that your roof’s structure, material, and age will all affect your solar setup. With this knowledge, you’ll need to consider the weight and length of the solar panels you want to install.

Considering these variables, a solar panel roof load calculator can help you determine how much weight your roof can support. Let’s dive into more specifics on these factors.

1. The roofing structure

Most importantly, your roof’s structure must be able to withstand the weight and the size of your solar panel system. A roof structural analysis is essential before the solar panel installation process commences.

house with a rooftop solar system
Most solar panels are designed to fit almost any roof, as long as it’s in a good shape

Solar panels and their required mounting equipment typically weigh around 3 to 4 pounds per square foot. This weight is usually acceptable for any roof type in good shape; however, solar panels using weighted ballasts on flat roofs typically weigh a bit more since concrete blocks hold the system in place.

Despite the kind of roofing you have, there are solutions for all types of roofs. These roof reinforcement methods can help ensure that your roof can withstand the weight of your solar panel system:

  • Wood blocking – installing wood planks between roof rafters.
  • Sistering – when matching wood planks are secured parallel to the original rafter.
  • Building a knee wall – a permanent support in the attic of a house that is somewhat perpendicular to the ceiling.

The slope of your roof can also impact your panel’s solar energy output: the ideal angle for solar power generation is generally about 30 to 40 degrees. Roofs that are too steep may pose problems for solar installers.

Because the ideal roof angle is around 30 degrees, flat roofs may require extra racking equipment to tilt solar panels to the optimal angle. If the roof is flat, you can even install the panels and the racks without mounting them directly to your roof, with heavy concrete blocks to keep the panels in place.

rooftop solar panels with extra racking equipments for a bigger tilt angle
Flat roofs require additional equipment to increase the angle of the solar panel

Ultimately, solar panel contractors may be unable to confirm whether your roof is sound structure-wise. But you can always consult a professional photovoltaic contractor or a structural engineer who will help you determine if your rooftop can support solar panels.

2. The age of the roof

The age of your roofing structure is also essential to consider before installing solar panels. If your roof is almost at the end of its life, you may first install roof reinforcement or replace it before installing your solar system.

Generally, if your roof will need to be replaced in the next ten years or so, it’s recommended that you consider replacing it before investing in solar panels. This is because you may end up spending more money altering your roof later than if changes are made before installation since you will need to remove the PV system first.

How do you know if your roof will need to be replaced soon? The material your roof is made of can give you some idea.

Roof materialLifespan
Wood shakes and shingles15 to 20 years
Asphalt shingles10 to 30 years
Metal/steel50+ years
Slate50+ years
Tile and concrete50+ years

In addition, most solar panels have a lifespan of around 25 years, and thus your roof must have the capacity to withstand that weight for those years.

3. The roofing material

The material of your roof also plays a role in how much weight it can hold. Different materials have different capacities for supporting solar panels. Let’s dive into the specifics of the best roof types for installing solar panels.


Asphalt shingles are used on many houses and are one of the best roofing materials for solar panel installation.

Why? Because they are made from fiberglass or cellulose that is flexible, making the installation process straightforward.

Solar installers typically drill studs into the roof and attach mounts to the studs. The space between the panel and the studs is then sealed to prevent water from entering the home.

a metal fixture holding a solar panel on the roof
Metal solar panel fixture installed on an asphalt roof


Whether you have a corrugated metal roof, a standing seam metal roof, or a roof with metal tiles, this material is suitable for installing solar panels. The long lifespan of metal roofs makes them a popular choice for homeowners – your solar panel system will likely not outlast your roof.

Metal roofs are also stronger than other materials and can support the weight of the solar array, panels, mounting racks, and other hardware associated with your solar panel system.

solar panel on a metal sheet roof
Metal roofs are often strong enough to hold solar panels, hardware, and mounting racks

Depending on the layout of your roof, the installation process on metal roofs sometimes requires drilling into the roof, but often panels can be mounted without drilling. The proper sealing technique with metal roofs will prevent water from entering your home as well.


Tile roofs are growing in popularity in regions where high temperatures are frequent because they can actually keep homes cooler compared to other roofing materials, reflecting heat rather than absorbing it into the home.

In fact, tile roofing decreases the flow of heat into an attic of a house by as much as 70% compared to asphalt shingle roof tiles. Tiling is considered one of the most energy-efficient materials, even without solar panels.

solar panels on a tile roof
Tile rooftops are the most complex when it comes to installing solar panels

If you want to install solar panels on your tiled roof, the process can be a bit more expensive. This is because installation usually requires removing the tiles, and the solar mounting equipment is installed directly onto your roof.

However, while the cost may be higher, these materials are ideal for solar installation because they last a long time, and are more durable than others. They are also more waterproof than other roofing materials because clay and concrete tile roofs lay on top of a waterproof membrane, or underlayment that keeps water out.

Will solar panels damage your roof?

If you’ve gone through the process of repairing or replacing your roof lately, you may be concerned about whether the solar panel installation process will damage your new roof in any way.

Luckily, if your installation is done correctly, solar panels won’t cause any damage to your roof! Though some installation methods require drilling holes directly into your roof, they are covered up by moisture-resistant sealant that prevents the structure of your roof and house from damage.

However, it’s important to note that solar panels can affect your roof’s warranty since most roofing companies don’t want anything installed on your roof because it can increase the risk of roof leaks. Finding the right solar installer to offer their warranty through a third-party roofing company is usually an excellent solution to this issue.

4. The weight of the solar panels

An important element of the solar panel roof load calculator is the weight of your solar panels. Their weight is a significant factor that can help determine whether a rooftop can handle a solar panel installation.

On average, according to solar experts, the mounting equipment and solar panels themselves weigh around 40 points for residential modules, ranging between 33-50 pounds depending on the manufacturer.

Here are some examples of residential solar panel weights from popular brands:

Solar panelWeight
SunPower E-Series41 lbs
Trina Solar PC-0541 lbs
LG NeON43 lbs

These weights are typically within the acceptable limits of any roof. The point loads are other considerations to take into account since installers often want to minimize the number of mounting locations for them to reduce the risk of leakages.

Most residential and commercial roofs are designed to handle at least 20 pounds per square foot of weight. Roofs with stronger materials can hold more: a clay tile or metal roof can hold a load of approximately 27 pounds per square foot.

In areas where snowfall is heavy, roofs are often built to withstand more weight per square foot. Of course, some older roofs or those that have sustained prior damage may not have the capacity or structural support for PV systems.

5. The length of the solar panels

You should generally opt for highly efficient, small solar panels to keep costs down while installing solar panels on your roof. The number of solar panels you require will depend on your roof size and energy demands and how much of that demand you want to be met by solar energy versus the public utility.

Usually, residential rooftop solar panels are approximately 65 inches tall, 40 inches wide, and 2 inches thick. In feet, that measures 5.4 ft. by 3.3 ft. Every solar panel consists of solar cells, which are typically 6 by 6 inches. Residential solar panels typically contain 60 cells, while commercial panels have 72 solar cells.

leasing vs buying solar panels
It’s better to opt for smaller sized solar panels

Whatever your home’s energy demand, the length of your solar panels plays a role in both your energy generation and the weight of the load placed on your roof. Knowing how much weight your roof can withstand is critical to know before the solar installation process.

Determining your solar panel roof load

Calculating your solar panel roof load, whether on your own or with the help of experts, is critical to ensure your solar system investment is successful and doesn’t damage your roof.

In addition, you want to ensure that you limit your costs on solar panels while also optimizing the energy output of your solar panels. Accurate solar panel roof load calculations can ensure that your investment will pay off. 

If you live in an area where winter weather is frequent, it’s important to account for the snow load when factoring in if solar will fall within the roof’s available capacity. The blueprints of your house will typically list your snow load capacity, but structural engineers can also assess your roof’s snow load as well.

How to calculate your solar panel roof load

Before diving into how to calculate your solar panel roof load, let’s first understand the two key calculations involved: point load and distributed load

  • A uniformly distributed load is when weight is evenly distributed over an entire surface.
  • A point load is when the weight of an item is significantly concentrated in one (or more) places.

These calculations are critical to understanding how much weight your roof can handle in any given specific spot, as well as spread over the entire surface.

If you know the number of panels and the weight of individual panels of the solar system you’re interested in installing, simply plug these numbers into the formula below to determine your point load. If you don’t know these numbers, you can substitute the average weights and lengths of solar panels listed above for a good estimate.

The formulas listed below (and in this worksheet) can help you determine the solar panel roof load for your home or business.

Point load calculation 
1. Number of panels in the array
2. Number of connections to roof
3. Weight of individual panel
4. Mounting system weight
5. Total weight of the array1. X 3. + 4. = 5. 
6. Weight at each connection 5. / 2. 
Distributed load calculation 
7. Solar panel area
8. Total array area 1. X 7. = 8.
9. Distributed load 5. / 8. = 9. 

Conclusion on solar panel roof load calculation

This solar panel roof load calculator will help you understand whether your roof can safely support solar panels. Based on your roof’s material as well as the orientation and age of your roof, your home should be a good fit for solar panels.

Some roofs don’t have sufficient space to place a PV system and for a PV array. For example, some have shading issues that can significantly reduce solar output.

If your roof doesn’t have sufficient space or is too old to support a solar system and array, there are other options – you can opt for other options like ground-mounted PV systems. You can also go completely off the grid if you opt for solar battery storage.

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