How to Size Rafter Snow Loads

Check your local building codes. Every area of the country is divided into zones. Your snow load requirements are in your locality's code book. The law requires following these codes, which are imperative for keeping your home safe.

Go to the online site for the American Wood Council. On the worksheet enter the type of wood, the deflection limit, the type of joist, the grade of wood, the size of construction wood, the proposed spacing, the exterior exposure, wet service conditions, incised lumber, the calculated live load and the calculated dead load. Click "Submit" and the worksheet will calculate it for you. It is recommended that you follow the code in your cities code book.

Consult a span table. Go to your local library or bookstore and look for a reference material such as "Span Tables for Joists and Rafters 2005," according to the American Wood Council.