Table R802.5.1(4) indicates the rafter spans for ground snow loads of 50 psf or less where
the ceiling is not attached to the rafters.
Table R802.5.1(6) indicates the rafter spans for ground snow loads of 50 psf or less where
the ceiling is attached to the rafters.
On both tables, footnote a. requires adjustment of the allowable spans if ceiling joists are
located at a point higher than the point where the rafters are supported on the wall.

Example 1
 Ceiling not attached to rafters, rafter spacing 16 inches, rafter span of 13 feet.
 Table R802.5.1(4) indicates a 2" x 8" Southern Pine # 2 rafter will work with a dead load of 10 psf
and a 2" x 10" Southern Pine # 2 rafter will work with a dead load of 20 psf.

Determining Snow Loads and Rafter Spans
 Using the Residential Code of New York State

Using Figure R301.2(5), find the ground snow load for your area.
Our examples will be based on a house in the suburban Syracuse area.
Using the figure below we see that the ground snow load is 50.

Section R301.6, Roof load, states: The roof shall be designed for the live load indicated
in Table R301.6 or the snow load indicated in Table R301.2(1), whichever is greater.

TABLE R301.6 MINIMUM ROOF LIVE LOADS IN POUNDS-FORCE PER SQUARE FOOT
OF HORIZONTAL PROJECTION

For SI: 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa,
1 inch per foot = 83.3 mm/m.

Table R301.6

Table R301.2(1)

i. The ground snow loads to be used in determining the design snow loads for roofs are given
in Figure R301.2(5) for sites at elevations up to 1000 feet. Sites at elevations above 1000 feet
shall have their ground snow load increased from the mapped value by 2 psf for every 100 feet
above 1000 feet

Based upon 301.6 and the tables above we will use a snow load of 50.

Section R301.2.3, Snow loads, states: Wood framed construction, cold- formed steel
framed construction and masonry and concrete construction in regions with ground snow
loads 70 pounds per square foot (3.35 kPa) or less, shall be in accordance with Chapters
5, 6 and 8. Buildings in regions with ground snow loads greater than 70 pounds per
square foot (3.35 kPa) shall be designed in accordance with accepted engineering practice.

R802.5 Allowable rafter spans. Spans for rafters shall be in accordance with
Tables R802.5.1(1) through R802.5.1(8). For other grades and species and for other loading
conditions, refer to the AF&PA Span Tables for Joists and Rafters and applicable provisions of
ASCE 7. The span of each rafter shall be measured along the horizontal projection of the rafter.

Below are two examples for determining proper snow load and rafter sizing.

TABLE R802.5.1(6) RAFTER SPANS FOR COMMON LUMBER SPECIES
(Ground snow load=50 psf or less, ceiling attached to rafters, L/Δ = 240)

Example 2
 Ceiling attached to rafters, rafter spacing 16 inches, rafter span of 14 feet.
 Table R802.5.1(6) indicates a 2" x 10" Douglas Fir # 2 rafter will work with a dead load of 10 psf
and a 2" x 12" Douglas Fir # 2 rafter will work with a dead load of 20 psf.

TABLE R802.5.1(4) RAFTER SPANS FOR COMMON LUMBER SPECIES
(Ground snow load=50 psf or less, ceiling not attached to rafters, L/Δ = 180)

Section R301.7 states that the allowable deflection of any structural member under live load
listed in sections R301.5 and R301.6 shall not exceed the values in Table R301.7.

Note: L = span length, H = span height.

a. The wind load shall be permitted to be taken as
0.7 times the Component and Cladding loads for the
purpose of determining the deflection limits herein.

b. For cantilever members, L shall be taken as twice
the length of the cantilever.

c. For aluminum structural members or panels used in
roofs or walls of sunroom additions or patio covers,
not supporting edge of glass or sandwich panels, the
total load deflection shall not exceed L/60.
For sandwich panels used in roofs or walls of
sunroom additions or patio covers, the total load
deflection shall not exceed L/120.

Promoting the advancement of public safety in the Central New York region.