Talkin’ winter weather as it relates to the building code

Happy New Year

What a great Christmas and New Year break! After what seemed to be a very long fall, the weather finally turned very much like winter.

Trees are covered and quite burdened with the weight of all the snow. It’s amazing that more trees haven’t come down.

It’s equally amazing that the power hasn’t been interrupted more than it has.

But it’s good to see the snow, kind-of forgotten what it liked like!

Since this article is about ‘talking codes’ and not about ‘talking weather’ let’s get back on track.

The obvious topic to mention with all the new snow on the ground, is all the snow on the roof.

Even though the building code requires anywhere from 94 pounds to 110 pounds per square foot design capability for roof systems, is that enough?

Based on the NYS Codes, here is Section 1608.2 Ground snow loads, straight from the code books:

The ground snow loads to be used in determining the design snow loads for roofs shall be determined in accordance with ASCE 7 or Figure 1608.2.

When using Figure 1608.2 for sites at elevations above 1,000 feet (304 m), the ground snow load shall be increased from the mapped value by 2 psf (0.095 kN/m2) for every 100 feet (30 480 mm) above 1,000 feet (304 m).

Site-specific case studies may be made in lieu of snow loads in Figure 1608.2 or ASCE 7.

Ground snow load determination for site-specific case studies shall be approved and shall be based on an extreme value statistical analysis of data available in the vicinity of the site using a value with a 2-percent annual probability of being exceeded (50-year mean recurrence interval. 

Please note the minimum for the Town of Webb [as taken off the snow zone map in the code] is 80 pounds per sq. ft.

However, the requirement to add two pounds per sq. ft. for each 100 feet in elevations above 1,000, which is all of the town of Webb, is all too often overlooked.

You will find this requirement in the Building Code, Section 1608.2 [as shown above] and in R301.2 Climatic and geographic design criteria for the NYS Residential Code.

This two separate, but very similar sections, also allow for additional design in areas that have proven to get more snow than 100–110 pounds per square foot load capabilities.

Often this is left up to the Code Enforcement Officer having the authority of jurisdiction.

If he or she is requiring more than the code requires, it should be based on historical records.

So when is 110 pound per sq. ft. roof load design enough?

How much does snow weigh?

Will two feet, three or four feet of snow on your roof equal 100 pounds every square foot?

Right now two or three feet of snow is probably less than 100 pounds.

Wait awhile, get a few warmer days, get some rain or heavy wet snow, two or three feet of snow can easily weight over 100 pounds per square feet.

Because of the potential of huge accumulations of roof snow, many builders have used steep pitches and metal roof systems to encourage snow slid.

Good idea in the right locations, potentially deadly in the wrong locations.

Even if someone used a very steep roof pitch and a metal roof so the possibility of any great amount of accumulation is minimal, the code does not offer an exception.

It still needs to be designed to the minimum requirement as shown in the codes.

Just because the last few winters have been rather mild, knowing that history has proven itself in this great part of the Adirondacks with potential snow fall, it’s still a good idea to have your roof shoveled off.

Remember the days of trying to find the front door of camp?

Police warnings of kids climbing the snow banks and being able to touch the wires?

Digging a tunnel so Dad could get his car in the driveway?

It could happen again…