Snow damage remediation

An NRCA contractor member learns some business lessons from Mother Nature


Author's disclaimer: This article is presented in an effort to help other professional roofing companies approach snowstorms with the benefit of one company's experiences. My employees and I are not registered engineers, and the references to specific values simply are cowboy engineering.

From March 18-19, the Denver metro area received a record heavy, wet snowfall. Depending on the location, snowfall depth reports from 32 inches to 46 inches (813 mm to 1168 mm) along Colorado's Front Range and 50 inches to 88 inches (1270 mm to 2235 mm) in the immediate foothills were sustained. The Denver metro area population of about 2.5 million people struggled to dig itself out following what was called the worst storm since 1913. The storm was so severe that highways could not be cleared and schools, government offices and most private enterprises were shut down for two days to three days as the snow put its grip on virtually everything. Damage estimates for this storm have exceeded $34 million.

Concerns about building collapse because of the overweight snow conditions causing severe roof deflections on low-slope roof structures required an immediate response. Following is an account of what my company, B & M Roofing of Colorado Inc., Boulder, experienced during the process. It is provided as a reference for roofing professionals and formatted to serve as a checklist outlining the protocol my firm developed. The information, observations and conclusions are based on our response to about 25 structures involving more than 2 million square feet (371600 m²) of roof surface area.

The morning after

Following the storm, two employees and myself made it into the office. The telephones started ringing almost immediately. Most of the early requests were for information concerning risks caused by the weight of the snow; there already was mention of roof collapses in the area by the local media. Several customers requested snow removal services. We devised a plan—one worker contacted all the project managers and superintendents. They, in turn, contacted foremen, who then touched base with each of their crew members. It worked like a "phone tree." Within two hours, we were able to contact about 50 employees and put them on notice. Our foremen began assembling the crew members, which meant helping each other get out of their driveways, neighborhoods and subdivisions. With the use of cell phones, we were able to keep our status updated at all times.

We prioritized our projects and commitments based on structures that presented the greatest potential for loss of property or life. We decided to approach each project with a team lead by a project manager who did the initial investigation and snow load evaluation and quantified the amount of weight on the roofs. Our project managers also developed a remediation plan and communicated it to our superintendents who organized our crews.

Within three hours, we were in the remediation business with people on-site moving and removing snow. We finished 25 projects during a four-day period. Following the storm, schedules for leak repairs and future preventative maintenance kept us busy for the next 30 days.

The roofing contractor

Typically, we focus on roof coverings. Most roofing firms, as in our case, do not employ structural engineers and have limited structural knowledge and assessment capabilities. However, building owners, facility managers, property managers and former customers often turn to roofing contractors during weather crises and seek advice concerning actual or potential structural damage to their roof assemblies. The storm in March was no exception.

As a contractor, I immediately was made aware of the need to respond to situations in which buildings were at risk to collapse—jeopardizing lives and properties. Initially, using our labor resources to shovel snow off roofs seemed to be the best way to assist our clients. Although that was true, it was other elements—such as structural assessment, information sharing, roof load evaluations and snow weight calculations—that provided ultimate value to our customers.

Assessment

The No. 1 need, first consideration and most critical element of snow remediation efforts is to assess the superimposed structural load following a significant snow event.

To do this, you have to determine how much the snow weighs. After consulting television media reports and government weather bureaus for weight determinations, we realized certain structures were in jeopardy. According to the media and National Weather Service reports, the water density of this storm equaled 1 inch (25 mm) of water per 6 inches (152 mm) of snow (5.2 pounds of water per square foot [25 kg/m²] per 6 inches [152 mm] of snow). The simple calculation was that 1 inch (25 mm) of water=5.2 pounds per square foot (25 kg/m²). Therefore, our customers' structures had 30 pounds per square foot to 40 pounds per square foot (146 kg/m² to 195 kg/m²) of additional weight. Local building codes require structures to be designed and constructed to withstand 30 pounds per square foot (146 kg/m²) of live loading. This storm clearly had the potential to load structures beyond design capabilities.

Snow weight is measurable and quantifiable with some relatively simple methods. But actual field measurement is the only reliable method. Based on what we first knew—1 inch (25 mm) water per 6 inches (152 mm) of snow—we developed the figures in the chart to approach the initial water density and weight quantification.

Assessment protocol

After determining the superimposed structural load through the following assessment techniques, our employees developed a remediation protocol. When in a similar situation, contractors should consider performing the assessment in the following fashion:

  1. Develop an accurate sketch of the roof being assessed.

  2. Measure and record snow depths across the roof, and be sure to measure drifted areas. Sketch in snowdrift sizes, and quantify the extent of snowdrifts.

  3. Measure and record the actual snow weight on the roof by shoveling or carving out a 1- by 1-foot (0.3- by 0.3-m) column of snow through the snow's full depth. Place the shoveled snow in a plastic trash bag; weigh the contents; and record the weight. If the snow on the roof has varying snow depths, weigh deep and shallow areas. Record all the readings on the roof sketch at the points of measurement. Note: We found the water density of snow initially following the snowstorm to be consistent. If 16 inches (406 mm) of snow weighed 20 pounds per square foot (98 kg/m²), areas with 24 inches (610 mm) of snow weighed 30 pounds per square foot (146 kg/m²) and areas of snow with 32 inches (813 mm) of snow weighed 40 pounds per square foot (195 kg/m²). If the moisture density is consistent, the measurements will verify conditions. It was our experience that during melting periods after the storm, water density within the snow varied greatly. Near drainage areas, snow and water density increased significantly (as much as two times). Snow density may vary, but water density (the weight of water) is consistent.

  4. Mark the locations, spacings and directions of the building's primary and secondary structural beams on a roof plan.

  5. Inspect, record and quantify deflection; this is useful information for structural engineers. Structural steel bar joists (spanning 40 feet to 45 feet [14 m to 12 m]) that typically are used in our region deflected as much as 3 inches (645 mm). These measurements caused alarm because a 2-inch (51-mm) deflection was our maximum comfort zone.

  6. Assume any roof areas where snow weight exceeds a building's design load requirement as an area for potential structural damage.

  7. Enlist a structural engineer. Inform the engineer of your data; formulate a snow remediation plan; and take action accordingly.

Remediation plan

A remediation plan should consist of the following:

On overloaded roof structures ...

  • Snow should be cleared from all roof drainage areas. We shoveled snow off buildings in overloaded areas or relocated it to roof areas that still had capacity. There were buildings that had high parapet walls, and snow had to be boomed off those structures.

  • You should clear 10- by 10-foot (3- by 3-m) or larger snow areas at internal roof drains/scuppers. This point is important. As the snow began to melt, we were able to document the amount of weight and time in which the weight of water evacuated the roof surface. Sections of the roofs that had cleared waterways and drainage areas evacuated water weight four times as rapidly as areas that did not receive attention. This allowed owners to reoccupy their buildings 24 hours to 72 hours sooner.

  • Clear 6- to 8-feet- (2.1- to 2.4-m-) wide areas adjacent to gutters and roof edges so water can drain off roof systems. The snow should be cleared down to the roof-covering surface on these areas. These efforts dramatically will enhance water (weight) evaluation of a structure when melting occurs. Following our visual inspections, we determined three measurements per roof area were adequate for roof systems that had consistent snow covering. Individual areas that had snow drifts were measured separately to quantify the amount of weight on those areas. Roof leaks were secondary, and other than noting them on our roof plans, we did not address them during our remediation efforts.

On overweight areas at structural midspans ...

  • Reduce weight to design limits by shifting snow to other parts of the roof that can accommodate additional weight or removing the weight amount necessary to protect the roof structure. For many of our projects, we shoveled snow in some roof areas and transferred it to other areas of the structure that could accommodate additional weight.

It is not necessary or feasible to totally shovel off snow from large roof areas with high parapet walls. The assessment will quantify how much snow must be removed.

A snow remediation plan should begin early after a snowstorm. Keep in mind, your crews also are snowbound, and they have to dig out of the snow at their own homes. Once we had two or three employees mobile by 9 a.m., they had to assist other crew members simply to exit neighborhoods.

Once your employees are mobile, immediately get the equipment they will need, especially heavy plastic scoop shovels, to remove snow. We bought out the only open hardware store's scoop snow shovel supply. Based on our experience, I suggest your crews be given the following: plastic trash bags, measuring tapes, bathroom weight scales, flashlights (power will be off in some locations), cameras (thank God for digital technology), etc. You also may need ladders because roof hatches may not be functional; we couldn't physically open them because the snow weight made that impossible. We had to access some roofs with ladders from the outside of the buildings.

Although you may be rushing to help your customers, don't forget safety. Employees need to bring proper clothing with them, and because surfaces are slippery and icy, roof edge protection and fall protection take on a new dimension. Snow-covered roofs also present huge tripping hazards. Each project was assessed for safety needs by our foremen who held separate safety meetings and project planning meetings before anyone accessed roof areas. Throughout the day, our teams kept in contact and shared what they were learning with each other.

Have field technical groups and project managers immediately do the assessment work. Once the remediation plan is in place, have superintendents or foremen execute the work. Communicate the plan to the entire crew, and assign specific tasks for each crew member. Two distinct teams working in sequence and centrally dispatched can accomplish a significant amount of snow remediation.

Other experiences

While assembling our crews and assessing roof systems, we learned a few other tips. For example, your remediation work includes working with more than a building owner and your workers. Building code officials, police departments and fire departments shut down businesses until they can demonstrate buildings are safe to occupy. Our efforts and work, including documentation, helped many retailers open their stores—with confidence that the buildings were stable—earlier than their competitors. Retail and grocery operations can have profitable selling days following storms as cabin fever sets in and people off from work are ready to get out of their houses. Every hour counts in protecting a structure from collapse and getting a business back on track.

Remember, a snow remediation plan cannot address everything. Unforeseen hazards we encountered and worked to overcome included the following:

  • Broken gas lines. We had to coordinate with the gas provider and mechanical contractors. In some cases, our craftsmen were able to locate and operate shut-off valves on the roofs.

  • Snow-clogged unit-heater exhaust flues that created asphyxiation conditions within building interiors. We shut off gas and pilot lights and removed snow to allow the mechanical equipment to function properly once it was restarted.

  • Travel obstacles and unsafe roads while traveling to job sites. Many of our service crew members and foremen used four-wheel drive vehicles during this time period.

From our experience, big box-style structure merchandisers; building additions; manufacturing facilities with large numbers of rooftop mechanical units and process piping above, below or suspended from the roof deck; and canopies were the most prone to collapse or have structural failure.

Interior building indicators of overloaded snow we observed included sagging ceiling grids or a loss of ceiling tile (dislodged), display-case damage where electrical conduit chases attached between a floor slab and the underside of a roof structure, fractured dry wall, and deck deflection and deck movement at screened-in mezzanine areas.

Closing comments

During snow remediation processes, thoroughly discuss with your customers billing rates and your workers' capabilities and response times to which your firm can commit. Get these details figured out quickly because there will be many more challenges ahead and you will want to work and coordinate with local authorities, engineers and building managers.

As building owners and building department officials hear about total roof collapses, the anxiety about loss of property and life escalates enormously. It is important for you to stick to your established communication outline and process; worry usually is a result of a lack of information, updates and data.

And prepare for an after-storm service barrage. Prioritize your firm's response by previous customers, regular accounts and new opportunities. Most of our customers were understanding though concerned about building stability and safety.

After three years of drought conditions in our area, this storm tested our ability to respond, which our team did well. A crisis always will bring people together.

I am proud of our teams' ultimate response to the March snowstorm. We developed some new customers and provided an invaluable service for many of our existing customers.

Conrad A. Kawulok is president of B & M Roofing of Colorado Inc., Boulder.



For the Denver snowstorm from March 18-19 ...

If
6 inches of snow=1 inch of water

And
1 gallon of water=8.3 pounds
7.5 gallons=1 cubic foot

Then
7.5 gallons/ft³ X 8.3 pounds/gallon=62.3 pounds per cubic foot of water and 62.3 pounds/ft³ per 12 inches depth of water=5.2 pounds of water per 1 inch depth per square foot

Therefore
6 inches of snow created at least 30 pounds per square foot of additional weight.

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