February 16, 2021
With excessive snow accumulation and rain expected, buildings could have major roof load issues. The information was created for clients who have Butler buildings, but we feel it is a great reminder for everyone.
Ice and Snow Removal
Excessive Snow Accumulation
Heavy and/or repeated snowstorms can create packed snow and ice such that only a few feet of depth may weigh 50 psf or more, imposing unusual and excessive loads on any building structure. Blowing and drifting snow can easily double these loads and rain on snow can also significantly increase these loads. An excessive accumulation of snow can cause a building to be loaded beyond design capacity creating a risk of building damage or even collapse.
What to Look For
Most snow-related losses occur at stepped elevations where blowing snow is carried from the roof of a higher building to the roof of a lower building. Such drifting normally occurs where the buildings are attached. However, drift loads can also form on closely adjacent buildings, over ridges, at valley conditions, behind parapets, next to rooftop units, and on below eave canopies or overhangs. Post-construction changes to the building site, added higher buildings, or significant tree growth can also cause drifting where none was anticipated.
Modifications to the structure, loads added after the original design (such as piping, roof units, hanging heaters, etc.), and prior damage to the structure are other areas of particular concern because they may have significantly reduced the capacity of the building to withstand snow loads.
What to Do
We recommend that you make end customers aware of the damage which can occur when excessive snow accumulation is present. Much of the public is unaware of the consequences of allowing snow build-up on their roofs. However, many property insurers are beginning to provide their insureds with information on what to do in the event of a snow emergency, such as advising building owners to activate a snow watch and removal crew to monitor snow depths and to remove excessive accumulations of snow from the roofs. Additional warnings from you may help prevent significant damage from occurring.
Building owners should also be advised to keep drains and gutters clear of ice and snow to facilitate melting run-off. Ice and snow build-up can cause excessive loads even without drifts. Heat tapes in gutters and downspouts may assist in preventing ice build-up, except during extremely low temperatures.
Building owners should also be aware of warning signs inside the building that may indicate excessive snow accumulation, including the deflection of purlins, the popping of ceiling tiles in dropped ceilings, and unusual noises. If any of these situations occur, the building owner should be advised to contact you immediately for assistance.
As a preventative measure, you should survey your past projects and those projects currently under construction for stepped elevation conditions that were not previously considered. Buildings with a stepped condition designed prior to the publication of the drift criteria in the 1981 MBMA Design Practices Manual, should receive special attention. If you have any projects that are of concern, please review them with your Regional Engineer for possible corrective action. If you are aware of field modifications, site changes, added loads or damage to buildings, these should also be addressed with your Regional Engineer.
In the case of a collapse or threatened collapse, contact your Regional Engineering Manager or Natural Disaster Contact phones.
Suggestions on How to Deal with a Roof Near Collapsing
If a roof is in danger of collapsing, it should be immediately evacuated and the following emergency procedures* are recommended:
In many situations, the most effective solution is shoring of the purlins. In most large cities, commercial shoring service is available. If not, timbers may be used.
In some cases, removing snow build-up may be sufficient. See here (**) for detailed snow removal information.
Large industrial heaters inside the building may also assist in melting snow and ice from the roof.
Personnel safety is of utmost concern both during the shoring operation and during snow removal. Adequate precautions must be taken.
Always provide proper safety precautions when working on the roof, especially along the edge of the roof. Never send one person on a roof to remove snow alone. Place ladders at the end of the building so sliding snow will not dislodge them.
Remove drifted areas first, down to the level of the snow on the remaining roof. Next, remove the snow from the middle 1/3 of each bay (from eave to eave), beginning with the most snow packed bay. Complete snow removal on the remainder of the building. On gabled buildings, remove snow on both sides of the ridge at the same time.
Remove snow in a pattern that does not cause an unbalanced loading condition. Avoid large differences in the snow depth between adjacent areas of the roof. Remove snow gradually in layers from all over the roof.
Remove snow from eave toward ridge, but be cautious of snow or ice breaking away and sliding down the roof. Prior to removing snow from the roof, remove all hanging icicles from eaves and gutters. These can be quite heavy and cause snow/ice to hang up.
Do not pile shoveled snow on other areas of the roof or on other roofs. Keep dumping area clear of all persons and property.
Always use plastic shovels. Do not use picks, axes, or other sharp tools.
Do not attempt to remove snow by washing it off with a hose. Snow acts as a sponge and will rapidly absorb water, increasing the loads on the roof and potentially causing failure.
Be careful to avoid hitting panel straps, fasteners, snow guards, etc. Care must also be taken in removing snow and ice around ventilator bases, pipe flashing, rooftop unit supports, conduits, etc., since such items are easily damaged.
Be aware of Lite*Panl locations. These panels are not intended to support roof foot traffic loads.
In Case of Collapse
In case of a roof collapse, mitigation of loss should be the first priority. Damage to contents is a major item and prompt snow removal is imperative. Once the snow is removed, the next step is construction of temporary cover to keep the weather out and allow clean-up to begin.
Documenting the snow loads and resulting damage is also essential. For your reference, the back of this page contains a procedure Butler uses in these situations. Your assistance in gathering this information would be most helpful.
Fast response by you to these emergency situations can help your client get back into business quickly. Butler Manufacturing stands ready to work with you in these situations.
Documenting Snow Loads and Resulting Damage
Builders should notify Butler (Area Manager, Region or Kansas City) any time a building suffers any damage or collapse due to excessive snow.
The most important task is to get to the site as quickly as possible to perform a full investigation.
Assistance from the Builder is necessary to make arrangements with the customer and accompany the Butler representative to the site. One or two laborers from the Builder’s crew would be very helpful.
• A good camera (quality 35 mm, digital, or 2-1/4 x2-1/4, NOT a Polaroid)
• Color print film
• 50′ tape
• Yardstick (with legible numbers suitable for photographing)
• A scale and suitable container for weighing snow.
Obtain pictures of:
• Building overall views from as many sides as possible
• General interior views
• Detail pictures of individual members which might indicate nature of failure
• Damages to contents or lack of damage
• Multiple photographs of the snow both on the building and surrounding areas, any drifts and snow sampling procedure
Make notes keyed to the above pictures as to description and location of parts. Sketch building plan showing failure area, collapsed position of main members, etc.
Snow Sampling Procedures:
• Obtain representative samples of undisturbed snow on the roof. Take samples as close to the collapse areas as is safely possible. Samples from other areas of the roof should also be taken. If the roof is inaccessible, take samples on the ground reasonably close to the building. Use the yardstick and carefully measure a 1 ft. x. 1 ft. area and the snow depth. Weigh this block of snow by using the scale and container (do not forget to subtract the weight of the container). Photograph samples and weighing procedure. This procedure must be repeated at several locations on the roof, if possible.
If possible, have one or two witnesses observe this procedure and record their names and addresses.
• Make a building plan sketch showing the snow distribution and where the weight sample or samples were taken. Identify snow drift locations and indicate any adjacent roofs or walls that would or did cause dumping or drifting conditions.
• Note snow depth on roofs of buildings in the general area and on the ground in the area of the building.
Hance Construction, Inc.
2171 Route 57
Washington, NJ 07882
Phone: 908-835-3501 | Fax: 908-835-3502
©2021 Hance Construction, Inc. All rights reserved.
By Stacey Ruhle Kliesch, AIA, AIA NJ Advocacy Consultant | Posted in Disaster Response | Tagged: #HanceConstruction, #SnowandIce | Comments (0)
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