[AT] Snow load

[robinson at svs.net]

On 7 Feb 2005 at 18:33, carl gogol wrote:

> Farmer-
> I'm just curious - can you tell how the trusses failed?  Did just a few of 
> them collapse in the middle or did whole roofs flop or buckle.  I have been 
> noodling around trying to understand the major ways that truss roofs fail 



	Hi Carl:

	I was not close enough to any of them to tell exactly what happened in each case but in 
general the tops of the walls were splayed out and the roof edges were still sitting on 
top of the walls (but not in the right place) and the center of the roof was much lower 
than the top of the walls. The fact that in several cases tool shed/pole barn roofs were 
not all the way down to floor level in the center led me to believe that there must have 
been stuff stored inside of the building that was still holding the roof up a little.
	Cross ties (equal to ceiling joist) are ultra important to bearing snow load and in far 
too many earlier (1950s to 1970s) tool sheds they were just fastened with a few nails at 
each end and were, as in my building, perhaps a bit too far apart. In my building which 
was built in the late 1950s they were not only just nailed but in a couple of cases it 
was deemed more important to place them an exact distance apart than to match them to the 
rafters so a couple are just toenailed to the upper plate. The nearest thing to trussing 
is a 2"x4" running from the center of the tie up to the ridge board at each tie. There is 
a 1"x4" "tacked" to the top center of the ties which runs from one end of the building to 
the other. There is no diagonal wind bracing in the roof at all. There is wind bracing in 
the 3 walls. It does have a small 18' x 18' garage building attached (added years later) 
to the long wall which I suspect has helped the building to stand by bracing it. It was 
attached very stupidly with a gable roof that runs parallel to the gable of the tool shed 
and they connect together at the eves. A truly stupid way to build it. Begging for leaks 
and it does not disappoint...   :-)   The tool shed was not a pole building but has a 
poured footer (on 3 sides) and 2 rows of 12" blocks and regular stud walls. Not 
especially a great building but it beats the hell out of outdoors.   :-)  
	I will be anchoring it down more. I expect to use some short 1"x4"s about 3' long that I 
will nail into the side of about every third rafter and run down at a slight angle and 
nail into a stud a couple of feet below the upper plate. The ties themselves will be 
bolted in place. In a couple of spots I will use homemade iron brackets to attach them 
solidly to the rafters and the upper plate.
	I have gone over much of the steel roof with neo-screws to tighten down any loose 
places. When I get a nice day I want to go over the whole roof with more of them.
	I have a shed roof above a couple of horse stalls on the barn next to it that I 
"cobbled" back together after one of the worst "professionally" done  repair jobs I have 
ever seen let go. It still looks awful but it keeps the rain out. I believe instead of 
stripping it off and replacing it I will screw 1"x6" strips across it and put a new roof 
on above the old one. The vented air space between the layers should make the horse 
stalls cooler when the sun shines on it. I see no problem with leaving the now sound but 
ugly old roof in place. It is a steep roof and fairly small with heavy rafters.


-- 
"farmer", Esquire
At Hewick Midwest
      Wealth beyond belief, just no money...

Paternal Robinson's here by way of Norway (Clan Gunn), Scottish Highlands,
Cleasby Yorkshire England, Virginia, Kentucky then Indiana.


Francis Robinson
Central Indiana USA
robinson at svs.net