Re: Snow load evaluation

[Lewis Gardner <lgardner@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Dave Houston wrote:

> A concentrated load like an engine hanging from your chain hoist is quite
> different from the more evenly distributed snow load.

Very true.

As a practical matter deflection is a good indicator of the likelihood
of failure as in "when your doors begin to stick". Since calculating the
actual load and design factors in an existing house are beyond the scope
of anything short of inspection by a structural engineer I would tend to
stick to simple relative type observations.

If one were to attempt to design such a system, I think a measurement of
deflection of the most likely to deflect part of a roof structure
("midspan deflection of a rafter in the middle of the largest lowest
pitched section of the roof") would be a simple way to get the most
useful data. Over time this data would be helpful in sorting out
variables such as "wet" vs "dry" snow. It might be useful to someone.
That is the reason I posted.

As a practical matter, if you see a bunch of snow on your roof only an
idiot would not get out the snow removal tools! Especially if there have
been reports of other roof failures in your area. I would not wait to
see how far my roof would deflect before failure.