© 2019 By Apollo Structural

A Structural Engineer's Perspective: Solar Roof Retrofitting

June 17, 2017



Solar panel retrofits on residential roofs are becoming a common sight and this article is a write up on what a structural engineer considers for a solar roof installation project.


1. Can the roof support solar panels?


The roof is a very important part of our structure and the last thing we want to see is a sagging roof as a result of overloading the roof.  We want to make sure that the existing roof has enough capacity to withstand the additional weight of the solar panels.  Wind and earthquake considerations are taken into account when the additional load from solar panels are added to the roof.


2. How are the solar panels secured to the roof?


A solar panel detaching from the roof during a high wind event or earthquake should not occur and can cause serious damage.  We need to check if the rack has enough strength to secure the solar panels and make sure the rack is safely secured to the roof members to resist worst case earthquake and wind scenarios.


3. How many solar panels are on the roof?


We need to check how many panels and how much weight is added onto the roof. In California, we need to check to see if the additional weight onto the roof over the affected roof area is less than a 5% increase in the gravity loads on the roof and less than 10% increase in gravity loads on the lateral resisting system of the structure.  If both criteria mentioned above are satisfied, the roof framing system generally would not need to be upgraded.




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