15" of snow makes for a heavy load

[Amanda_931]

Posted by someone in New Mexico on another list.  Some of these are annoying but essentially trivial, some are going to be expensive to fix, one potentially terminal.  We'd get this kind of damage in southern Middle Tennessee as well with 15" of wet snow--about the only kind we ever get.  In fact we might bless the truly destructive ice storm of the late 90's for removing some of the breakables.

.................................

Since we are pretty much snowed in here in New Mexico due to the recent and
continuing snow storm, I took a 3 mile trip from my residence into Rio Rancho
along NM Hwy 528 and observed 5 building failures due to the 15" snow fall we
had.  I'm sure that in a city of 70,000 with 18,000 homes, there will be
numerous structural failures within the city and throughout the state,
especially in the rural areas.

Over and over we see posts on the list from people arguing that they have the
right to build what they want, where the want, and can ignore building codes
because the don't want to deal with the bureaucratic issues.  If we choose to
ignore the building codes, at least let's use some common sense and apply tried
and true structural and architectural principals.  Among these we should
include:

 1-Span tables with a safety load factor
 2-Footing/column attachment
 3-Joist/Rafter/column attachment
 4-Ledger sizing and attachment

As noted earlier, 5 building failures were observed.  The failures fall into the
following types

 1-Patio shed roof--undersized outer beam (span), broken in the center
 
 2-Stand alone detached car port-collapsed structure-added load from snow slide
from upper roof.  Failure    was due to insufficient lateral support (knee
bracing) between column and horizontal beams/rafters/joists (bridging)

 3- Attached add-on building-Failure in center of roof.  Failure caused by
undersized (span) rafters

 4-Patio shed roof add-on.  complete failure/collapse.  The rafters pulled away
from the wall ledger due to improper attachment to the ledger as a result of
added snow load from upper roof that broke loose and added an additional
horizontal load to the structure

 5- Stand alone structure-Failure in the center of the roof--cracked or broken
rafters/ceiling joists.  Failure due to undersized members (span) to support the
snow load

[Dimitri]

Amanda,

Thats why when you design anything you should always over design it above and beyond even building codes.

If a 2x2" peice of wood will do why not replace it with a 4x4" peice is my motto.  

Dimitri

[MountainDon]

Hey Amanda! This is right where I live! I measured 14 inches in my own yard. Proud to say that all the additions added to my home stood the test of the biggest single day snowfall ever recorded here! The snowfall itself was light and slow but relentless; never seemed to stop for over a whole day. There was virtually no wind, so the snow built up, flake by flake on everything, fences, branches, outdoor benches, roof tops, etc.

It was interesting to see the snow on my new metal roof slooooowly , almost imperceptibly, slide down the roof slope (only a 4:12) forming these beautiful "under" curls at the eves until their weight caused them to break of. An unexpected benefit of a metal roof! Benefit or curse... the snow slides off reducing roof load, but ending up piling upon the ground. Only a problem if there's a walkway situated there.

Also kinda funny watching the pups negotiating thru the depth of snow in their sideyard. They do seekm to be having fun although they come back in encrusted in snow!

This was a most unusual snowfall for this high desert locale. Played real havoc with interstate travel.

[desdawg]

Don, I can only say "Glad I am not there." I grew up in northern Montana where the cold winds blew in from Canada and the snow piled up deep. Many times Havre, MT, my home town had the dubious distinction of being the coldest spot in the nation. I just really don't miss that weather. I hope you are staying warm and able to get around.
Amanda & Dimitri, I agree about building stout. I think even when people look at the span tables they assume the lightest loading applies to them. Soaring lumber prices in the last couple of years haven't helped that situation either as this nation shipped it's forest products to another country to rebuild what we had destroyed.  :-/ That way we could pay more here for our own projects. Another fine example of your tax dollars at work.

[Amanda_931]

A few years ago my local lumberyard was getting 2x4's that came from Austria.  There was a mill capable of doing 2x4's from the area not 50 miles away.

I found that a particularly egregious use of shipping containers.

[desdawg]

Stuff like that has turned me into a pretty proficient scrounger. And I really enjoy working with new material.

[MountainDon]

Amanda & Dimitri, I agree about building stout. I think even when people look at the span tables they assume the lightest loading applies to them.

The snow load also killed at least a couple of commercially constructed steel parking carport roofs at apt complexes as well as one gas station gas pump cover roof (whatever those big flat roofs over the pumps are called.) Around here they're mainly sun roofs. But this snow amounted up to 26" in some places across the river in Albuquerque. Code design loads here call for 20 lbs per sq ft of snow if I recall correctly.

[Dimitri]

MountainDon,

Don't get me wrong, getting snow in New Mexico is a odd ball situation I'll admit. Still I like to double any safety factors when I make anything. "Just to be safe" you know.

Dimitri

[MountainDon]

Build it strong, build it once!

[Dimitri]

Build it strong, build it once!

Exactly.  

Dimitri