Snow Load And Roof Capacity Required For Solar


Roofs Are Rated for Weight Capacity

Adding solar to the roof of a property adds additional weight. Depending on the type of roof, a different amount of weight is added.

Roof solar installation types:

  1. Flush mounted: 2.5lb psf
  2. Ballasted (flat roofs): 4-10lb psf

Most roofs are rated for a specific snow load. The snow load for a roof can typically be found on the blueprints. Most roofs have a snow load that varies from 20-50lb psf.

In addition, it's important to account for the snow load in our region when factoring in if solar will fall within the roof's available capacity. City zoning designates what the snow load is for a given area. For example, in Southeast Iowa the snow-load is typically is 20lb psf.

Here's an example of how adding solar impacts the snow-load: 
The roof has a snow load capacity of 25lb psf. The snow load is 20lb psf. Thus, there are 5lb psf of capacity available for solar. If this is a flush mounted system, then this would be enough capacity since it requires 2.5lb psf.

How to find out what the snow-load capacity of your roof is:

  • Do you have blueprints available? The blueprints will typically have the snow load rating listed.
  • If not, we can provide a structural engineer to assess the roof and determine its snow load capacity.


What can be done if the current snow-load capacity is not sufficient to add solar?
This will require one of our structural engineers to review the roof and determine the upgrades necessary to make it sufficient. The engineering cost and upgrade costs can be included in the solar installation project.

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Tags: weather roof solar construction snow solar on roofs

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