Façade Inspection Reports…….Changes

 Beginning February 14, 2011 there will be new and revised forms, filing fees and civil penalties for façade inspection reports:
New Forms
Façade Batch Intake Form (FBI1) 
Façade Cashier Civil Penalty Form (FCP) 
Façade Waiver of Penalty Form (FWP)

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The Unintended Consequences of White Roofs

The recent push in NYC and elsewhere to make roofing membranes white, must have been thought of during the summer.  Because in the winter, black is the way to go.
My recent investigations of roof deflections due to snow accumulation yielded an interesting observation….white roofs had more snow on them than black roofs.  Even in a literally ‘side by side’ situation of white versus black….the white roof had more snow.
We know that the color white reflects heat and the color black absorbs heat, so it stands to reason that in the winter, snow will accumulate faster on a white roof, since there is little or no latent heat.  A sunny day after the snow event would require the solar energy to penetrate more snow depth on a white roof than a black roof.  And, since most melting begins at the edges, this can’t happen on a white roof since the membrane is turned up the parapet.

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Snow Loads on Roofs

Here is a quick primer on snow loads for flat or low slope roofs, and whether or not you should be concerned:
  • Water weighs 5.2 lbs per inch of depth.
  • Fluffy snow, the type we get during very cold temperatures, is the lightest and is about 3% water.  12” of fluffy snow is equivalent to 0.36 inches of water or 1.9 pounds per square foot
  • Wet snow may contain 33% water.  Using the same math, wet snow 1 foot in depth may weigh 20.6 lbs.
Wet snow is common in our area and 12” of snow weighs 20.6 lbs per square foot.
Two feet of wet snow will weigh approximately 41.2 psf.
In NYC, your roof has a capacity of 40 psf for Live Load.   Large retail spaces are afforded a Live Load Reduction  which results in a capacity less than 40 psf….closer to 30 psf.   (For the purposes of this discussion, snow may be considered Live Load, because of its expected duration.)

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