[Strawbale] Death in collapsing SB house

[Harry Kits]

Interesting discussion after the winter of snow we have had here in the
Ottawa area. Our first Ottawa winter after over 20 years of Toronto winters;
those being much milder snow wise [except of course the one that the mayor
called out the army to deal with ;-)  ].

We have a steel roof at a 4/12 slope with all hips.  Total of 4 valleys.
The slopes without valleys regularly had that swoosh sound of the snow
sliding.  The ones with valleys never let go and only in the last couple of
days has it all melted.

Everything was engineered of course so I wasn't too concerned this winter.

I was curious though about how we could know when the snow load might be too
much or too extreme despite the engineering.  Does the engineering cover all
worst case snow load scenarios?

Any thoughts out there?

Harry

On Fri, Apr 11, 2008 at 11:18 AM, Matt Chase <mattchase at canoemail.com>
wrote:

> Hi Sherwood
>
> Not sure where you're coming from, but here in Canada, the national
> building code has a feature for calculating snow loads that is as
> follows:
>
> There is a slope factor (given the symbol Cs) that is multiplied by
> the snow load to reduce it if one can count on sliding off of snow to
> occur.
>
> For "normal" roofs, it ranges between 1 (when the roof slope is less
> than 30 degrees, approximately a 7:12 slope) and 0 when the roof is
> steeper than 70 degrees (a very steep roof indeed!, a 33:12 slope).
> The factor Cs changes linearly with the angle, so right in the middle
> (i.e. 50 degrees) would give a Cs factor of 0.5, reducing the snow
> load by half.
>
> For unobstructed, slippery roofs (i.e. your steel roof), the range is
> between 15 and 60 degrees (3:12 to 21:12 slope).  For your 12:12
> slope (45 degrees) the factor Cs is equal to 0.33 which means that
> the snow load is reduced by 1/3 - a considerable reduction.
>
> Building codes where you are from probably have a similar means of
> treating the snow load.  So, you could probably build a lighter truss
> by making it steeper.  However, to make the roof steeper, you would
> also need some extra material simply to get up that high.
>
> There is a trade-off involved...
>
> Cheers,
>
>
>
> Matthew Chase
> MSc. Candidate
> Biosystems Engineering,
> University of Manitoba
> Winnipeg
> (204) 880-8403
> (204) 237-5315
> Sign up today for your Free E-mail at: http://www.canoe.ca/CanoeMail
>
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-- 
Harry Kits
6864 Gallagher Road
North Gower, ON K0A 2T0
cell - 613-806-1100

** Building near North Gower/Ottawa in 2007 **