Helping Varco Pruden builders protect building investments against winter weather threats.


THE RISKS OF EXCESSIVE SNOW ACCUMULATION

Heavy and/or repeated snowstorms can create such a high amount of packed snow and ice that only a few feet of depth may weigh 50 lbs. per square foot or more—imposing excessive loads on any building structure. Blowing and drifting snow can easily double these loads, and rain on snow can also cause significant load increases. Extreme snow accumulation can cause a building to be loaded beyond design capacity, creating a risk of damage or even collapse.

Most snow-related losses occur at stepped elevations where blowing snow is carried from the roof of a higher building onto the roof of a lower building. Such drifting normally occurs where the buildings are attached. That said, drift loads can form in any of the following locations or conditions:

  • On closely adjacent buildings

  • On or over ridges

  • At valley conditions

  • Behind parapets

  • Next to rooftop units

  • On below-eave canopies or overhangs

  • Through post construction changes to the building site

  • Through the addition of higher buildings As a result of significant tree growth

  • After modifications have been made to the structure (such as post addition of snow-retention devices)

  • If loads are added after the original design (such as piping, roof units, hanging heaters, etc.)

  • If there has been prior structural damage

All of these instances can significantly reduce the capacity of a building to withstand snow load.

 

HOW TO PREVENT DAMAGE AND PREPARE CUSTOMERS

Much of the public is unaware of the consequences of snow build-up on roofs, so we recommend you advise your customers about how to avoid damage that can occur. While property insurers are beginning to provide more information on what to do in the event of a snow emergency, additional warnings to your customers can also prevent significant damage.

Advise building owners to keep drains and gutters clear of ice and snow to facilitate melting run-off. Ice and snow build-up can cause exorbitant loads, even without drifts. Heat tapes in gutters and downspouts may assist in preventing ice build-up, except in extremely low temperatures.

Building owners should also be aware of warning signs inside the building that 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 contact you immediately for assistance.

As a preventative measure, always be sure that Varco Pruden is fully advised of any conditions that could potentially cause an accumulation of snow when placing an order. Conditions may include:

  • Stepped elevations

  • Closely adjacent buildings

  • Ridges and valleys

  • Parapets

  • Roof top units

  • Below-eave canopies

 

HOW TO DEAL WITH AN OVERLOADED ROOF

Worker safety is of utmost concern both during shoring operation and during snow removal. If a roof is in danger of collapsing, the building should be evacuated immediately, 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 services are available. If not, timbers may be used.

  • In some cases, removing snow build-up may be sufficient. Read to the end of this post for detailed tips on snow removal.

  • Large industrial heaters inside the building may also assist in melting snow and ice from the roof.

 

IN CASE OF COLLAPSE

If a roof collapses, your first priorities are loss mitigation and prompt snow removal. Once the snow is removed, you must construct a temporary cover for weather protection and to begin cleanup. Don’t forget to document the snow loads and resulting damage.

VARCO PRUDEN IS HERE TO HELP Here are our tips for rapid response in a snow-related emergency.

REMOVING SNOW AND ICE

Every situation varies, so careful planning must be conducted before snow/ice removal begins. Here are our top ten tips for removing snow and ice efficiently and effectively:

  1. Always provide proper safety precautions when working on the roof, especially along the edge. 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 workers.

  2. 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.

  3. 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.

  4. Remove snow in a pattern that does not cause an unbalanced loading condition. Avoid the large differences in snow depth between adjacent areas of the roof. Remove snow gradually in layers from all over the roof.

  5. Remove snow from eave toward ridge, and be cautious of snow or ice breaking away and sliding down the roof.

  6. Do not pile shoveled snow on other areas of the roof or on other roofs. Keep dumping area clear of all persons and property.

  7. Always use plastic shovels. Do not use picks, axes or other sharp tools.

  8. 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. Also, do not attempt to use chemical salts to remove snow.

  9. Be careful to avoid hitting fasteners, snow guards or other roof attachments. And be careful removing snow and ice around ventilator bases, pipe flashing, rooftop unit supports, conduits, etc., since such items are easily damaged.

  10. Be aware of skylight system locations. These panels are not intended to support roof foot traffic loads.

 

DOCUMENTING SNOW LOADS AND DAMAGE

Builders should notify Varco Pruden (Project Manager or District Manager) any time a building suffers damage or collapse due to excessive snow. Here are our top eight tips for documenting damage:

  1. Most importantly, you must get to the site as quickly as possible to perform a full investigation. A Varco Pruden representative can accompany you.

  2. Help your customer make arrangements and accompany the Varco Pruden representative to the site. One or two laborers from the builder’s crew are very helpful.

  3. Items to bring: A good camera 50’ tape; shovels; a yardstick (with numbers legible enough to be photographed); a scale and container suitable for weighting snow.

  4. Get photos or video of: The building from as many sides as possible; General interior views; Detailed photos of individual members which might indicate the nature of failure; Damages to contents or lack of damages; Multiple photographs of the snow, both on the building and surrounding areas, including any drifts and snow sampling procedure.

  5. Include notes with photos to describe the parts and their location. Sketch a building plan showing failure area, collapsed position of main members, etc.

  6. Obtain representative samples of undisturbed snow on the roof. Take samples as close to the collapse area as 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 procedures. This procedure must be repeated at several locations on the roof, if possible.

  7. 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.

  8. Be sure to note snow depth on the roofs of buildings in both the general area and on the ground in the area of the building.

Do you have questions about an upcoming or current project? Contact us today!

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