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Introducing Solar Letters: The Fastest, Most Affordable Way to Receive Accurate Letters & PE Stamps

Castillo Engineering is excited to announce the launch of, which now provides the quickest, most cost effective structural letters, PE stamps, and post-installation letters for residential solar installation companies and overseas design firms. Solar Letters is unique in that it is backed by over 25 years of structural design and engineering experience in residential solar and leverages advanced automation to guarantee the fastest, most accurate letters and PE stamps or your money back. The company has the capacity to create over 100,000 solar letters per month; provides a dedicated team per customer to improve turnaround time; and ensures ease of ordering through its online portal and seamless software integrations to save you time. You will never experience any hidden fees with Solar Letters and you will also be able to take advantage of savings through tiered pricing - the more you order, the more savings you receive.

What are the main benefits of selecting Solar Letters?

  1. Fastest Turnaround - Same or Next Day: Solar Letters prides itself on its speed, as its team knows how important it is to permit your project quickly. Whether you use the Solar Letters portal or CRM integration,and you do not receive your letter by the next business day or less, you will receive a full credit.

  2. Lowest Price: Solar Letters will match or beat any documented competitor price. The company also offers volume discounts through its Permit Partner Program.

  3. Consistently High Accuracy: Solar Letters has the advantage of being able to utilize Castillo Engineering’s experience dating back to 1998, which has an industry leading 99.9% average first time approval rating. If a letter receives an AHJ rejection, you will receive a full credit.

What services does Solar Letters provide?

1. Pre-installation (Structural Letters & Electrical Stamps):

  • Roof Letter & Pages Stamped: This cost effective fundamental letter is what the majority of AHJs require. It states that a roof can handle the additional loads of the solar system and includes design stamps.

  • Installation Letter & Pages Stamped: This letter includes the roof only letter, additional calculations to determine the attachment separation, as well as design stamps.

  • Installation Letter & Pages Stamped + Electrical Stamp: In addition to the full calcs letter, this service consists of a thorough review and stamp of the entire design, including electrical. The precise review and stamp of the electrical design is performed by an in-house licensed electrical engineer.

2. Post-installation:

  • Post-Installation Letter (PIL): After the installation is complete, this letter verifies that the site observations have been performed by an in-house engineer. It states that the system has been installed per the permitted plans.

  • CAD Design + Stamps: Through our proprietary CAD designs, we optimize installations while reducing cost. Our approach guarantees high accuracy and the lowest bill of materials. We also include PE stamping for free.


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