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The AIA Corporate Architects and Facility Management (CAFM) Knowledge Community consist of architects working within and for businesses and corporations. Our mission is to share expertise in the strategic, tactical, and operational activities of real property and facilities management in order to deliver value to the owners we represent. 

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  • 1.  Snow Loading

    Posted 02-12-2015 08:49 PM

    When to shovel snow off of roofs and when to evacuate buildings.

    You may think the answer to both is, shortly before the roof caves in. I tend to have roofs shoveled when we are near the design load limit and monitor deflection. Deflection in main members can cause problems with supported fixtures. I have cleared personnel only once due to covers on the lighting fixtures swinging open and a storm just starting. It was the effect of reasonable L/360 deflection of the long roof members distorting the ceiling grid. I also tend to be conservative when considering that the Utility and HVAC Engineers may not be on the same page as the Structural Engineer especially if infrastructure is likely to have been added over time.  Contrarily I wouldn't want to evacuate or shovel too early and put a team at risk on a snowy roof, waist time and money doing so, and put my credibility on the line under questionable circumstances by shutting down the business for snow that would otherwise just melt off with no problems. Such is life as a Corporate Architect Facility Manger in a Biotech Plant in Andover, Massachusetts responsible for Civil Structural and Architectural Assets (CSA). I promise I won't throw a lot of corporate acrimonious acronyms at you in this article but I call this exercise CSA-CSI.  This is a field probably best known as Forensic Architecture but I don't get corporate acronym credits with that.  FYI this may not be PC but CYA on EH&S. I QC CD's prior to IFC not just for R&D but for all FTE's at PFE in AND.

    My CSA-CSI starts by understanding the load, I like to boil the variables down to facts literally by melting snow. The volumetric weight of snow can vary greatly. . The weight of snow is based on the overall water content of the mass. Determining water content removes the variable of different types of snow.  I take snow from the roof in a boiling beaker and melt it in a microwave to liquid form.  In a recent check, 2200ml of snow reduced to 450ml of water equals 20% water content. A uniform coating of 36" of this snow would equal 7.2" of standing water. A cubic foot of water weighs 62.4lbs so the weight is approx. 37.4lbs per square foot.  Be mindful of stratification of different layers but overall a good method to estimate weight.
     

    Regarding the structural capabilities in a campus setting of various buildings, I focus on the weakest roofs first and determine the design load.  Find the weakest link.  If over the years, original contract documents have been properly archived, you can determine the actual design load for each structure or you could otherwise validate through code requirements at the time of construction assuming controlled construction.  I am fortunate that most of the buildings that I manage have concrete roof decks and unoccupied mechanical penthouses but in terms of the weakest link, older buildings constructed under the 5th Edition Mass Building Code and a couple of acquired spec built warehouse buildings occupy my mind when the snow gets deep. Thankfully our building standards did not allow HVAC units on sleepers, we have dunnage racks which aid in dispersing snow loads and snow drifts. Expanding the concept of weakest link, news reports of actual building collapses in the region can also serve as an early warning system however you have to be able to discern the information.  The media can sensationalize these failures along with storm severity. It can create a jittery site population looking for assurances and you can become known as the "Roof Guy" pretty quickly.  Fortunately the broadcast and printed media also usually displays images of the collapsed structures which amount to prime examples of inexpensive enclosures and a barn or two build in the 1800s. Here are a few examples in New England in recent days.

    Not sure this one is an actual building.



    What's that, a splice in the top cord mid span?



    Hundreds of dollars worth of damage!

    A more reliable method I have discovered is to observe ceiling grids on upper floors.  The tracks nearest and perpendicular to the wall tell the tale of deflection.  The track attached to the wall is essentially supported by the floor structure below, and the parallel grids are most often supported from the roof structure above. The perpendicular track will tilt at an angle as seen in the photo below. The severity of the angle is directly related to the roof load. It beats climbing on a snowy roof anyway.  If the structure is visible and accessible from underneath, hanging a plumb bob can track deflection. Remember even though deflection can be visible, shear stress is also present and very hard to detect other than by calculation.

    I received an email from an EH&S colleague at another Biotech company who had recently closed a facility nearby with some photos. It was deflection causing damage to an overhead soffit detail (below)

       

    So keep em safe and do your CSA-CSI.



    -------------------------------------------
    Gary Ciccone AIA
    Corporate Architect Facility Manger
    Pfizer, Inc.
    Andover MA
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    AIA Conference on Architecture June 22-25 Chicago


  • 2.  RE: Snow Loading

    Posted 02-13-2015 06:37 PM
    Be aware that the moisture content of the snow can go up and down with outdoor relative humidity.  I'm not sure if they still do, but in the past in the Anchorage AK area the snow weight was part of the weather forecast.

    And, should it rain on your snow -- it gets really heavy really fast.  If you have low-slope roofs with interior drains, icing up of drains is a real problem.

    I do applaud your positive approach to dealing with the issue.

    -------------------------------------------
    Joel Niemi AIA
    Principal
    Snohomish WA
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    AIA Conference on Architecture June 22-25 Chicago


  • 3.  RE: Snow Loading

    Posted 02-16-2015 06:09 PM
    We have had clients that could not for some reason or another restructure the building to provide for additional snow load requirements and have specified to de-ice the roof and drain system to get the weight off, or provide serviceable paths. I thought this thread might find these projects interesting for this topic.


    Under a membrane around mechanical equipment - Rhode Island School



    Providing drainage and snow load protection - Bowling Green Ohio


    Snow Load Protection after roof collapse - Snoqualmie Pass Washington


    Before

    After

    This next one is a before, during installation and the performance after in Richmond UT at a food plant facility for Pep Farms



    Ice Problem



    Low voltage heating element under the membrane



    No more ice and a walkway is provided


    -------------------------------------------
    Ryan Bench
    Distribution & Marketing Manager
    Heatizon Systems
    Murray UT
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    AIA Conference on Architecture June 22-25 Chicago


  • 4.  RE:Snow Loading

    Posted 02-18-2015 06:40 PM
    Interesting topic. They just reported on the CBS Evening News that 74 roofs have collapsed in New England from this snow.

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    Ronda Bernstein
    Historical Consultant
    APT WASHINGTON CHAPTER INCORPORATED
    Washington DC
    -------------------------------------------



    AIA Conference on Architecture June 22-25 Chicago


  • 5.  RE: Snow Loading

    Posted 02-19-2015 10:45 AM
    An Update and Additional Information

    I probably should mention that we have a robust snow shoveling contract in place every season that includes roof shoveling in order to clear mechanical equipment and maintain access.  This contract ensures that we have the resources in place in the event that loading relief is required. I have added a few improvements this year to the roof shoveling program that included dedicated shovels made out of plastic  with a 2" radius on each edge and detailed plans of pathways, drains and equipment. The shoveling specs is for accumulation of 6" or more with a minimum 6" of snow to remain on the roof walkways, a shovel should never be within 6" of the membrane.

    We had another storm over the weekend that dumped an additional foot of light snow but with a lot of wind and drifting. The wind has cleared much of the accumulation and the snow is still very light and dry. I did a brief walking tour on the upper floor and noticed a light fixture opening. The occupant hadn't noticed if it was a recent defect or not so it has been repaired and will be monitored.

     


    A personal note, I strapped on snowshoes and checked on the summer cabin this weekend prior to the blizzard. I noticed one of my neighbors had at least a 6' drift which I removed with my roof rake. Here is what that looked like, it was more like chiseling limestone than snow. At first I thought about walking but my conscience did the math.  The wind has been  strong and it pushed all of the snow on this steeply pitched roof from the windward side to the leeward side. The prediction for this Sunday is wet stuff, now it gets interesting.

     


    -------------------------------------------
    Gary Ciccone AIA
    Corporate Architect Facility Manager
    Pfizer, Inc.
    Andover MA
    -------------------------------------------


    AIA Conference on Architecture June 22-25 Chicago


  • 6.  RE: Snow Loading

    Posted 02-19-2015 09:18 PM
    Roof snow loading has been a research area for Prof. Michael J. O'Rourke, RPI, for over 30 years.  He's developed codes and standards based on observations in the Adirondacks.  I expect he's making trips to Boston now to see what's happening.

    As was stated by another person, the building codes identify appropriate snow loads for the geographic area.  Of course, a 500-year event could exceed the code-specified required load.  It's an issue of risk versus the cost for the construction.  The bigger problem lies in drifting of snow due to roof configuration and adjacent structures.  Some of the images shown suggest problems with connections and not the main roof members.  We may have contributed to the roof problems as we increased the insulation on roofs, where most of the building heat loss occurs, allowing more snow to pile up.  I don't think more insulation is bad and I also don't think a melting system is necessarily a good idea; it's a big investment for an infrequent need.  Again, an issue of risk management.

    As corporate architects, it's important to identify and articulate the risks associated with facilities and to identify the cost of risk mitigation.  A critical facility with a flat roof would be well justified to have an ice/snow melt system as opposed to a retail facility.  Of course, the person who recommended, and installed, the ice/snow melt system last year is now a company hero when roofs are failing all around him/her.  

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    Theodore Weidner, Ph.D., PE, AIA
    Assoc. Professor
    Purdue University
    West Lafayette, IN
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    AIA Conference on Architecture June 22-25 Chicago


  • 7.  RE: Snow Loading

    Posted 07-31-2015 11:36 AM
    It looks like the snow mountains in the north parking lot have finally melted, Only trash piles left behind. 

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    Gary Ciccone AIA
    Corporate Architect Facility Manager
    Pfizer, Inc.
    Andover MA
    -------------------------------------------


    AIA Conference on Architecture June 22-25 Chicago