[Greenbuilding] re glass panels as porch roof

[RT]

Reuben wrote:

> figured [double-walled polycarbonate] would lighter, easier to fasten,
> consistent across the full length (5 equal patio doors)

BC John wrote:

> I worry about non laminated glass as tempered can still cut

Clark wrote:
> the first one was torn-off by ice 10 years ago.battens holding the glass  
> down were cedar 5/4 x 3

> The main roof is 7.5/12 (aka 10/16, the golden mean) steel, allowing the  
> ice to slide,that time taking my panels with it.

Reuben mentioned initially that the porch roof would be 35 ft in length.

The IGUs from three, six-ft wide patio doors would yield 12 sheets of  
glass, nominal coverage 12 x 3' = 36 ft.
(The actual width of the glass would be ~ 34", spaced 1.5" between edges  
of the glass ( {[1/2" bearing + 1/4" expansion clearance for each sheet]  
x2} + 1" batten bearing surface = 2.5" batten

The above bearing/batten details  would be the same regardless of whether  
the panels were glass or plast-ecchhh!.

One of course can use the store-bought extruded aluminum glazing bars,  
clamping bars and batten caps but for residential apps, the cost can be  
prohibitive not to mentioned needlessly high in embodied-energy costs.

Wood is fine for all of the above components so long as it is detailed to  
anticipate and deal with water.

ie It used to be that the local building supply would carry metal studs  
and track made from galvalume stock.
The track for 2.5" studs could be modified slightly so that it would do  
nicely as snap-on weather-proof caps for 2.5" wide wooden clamping bars  
(aka battens) which could either be pre-painted if desired or left au  
naturel. The modification consists of bending a small lip onto the legs  
(at one of edge-stiffening creases already formed into the channel by the  
stud manufacturer) so that it would catch the edge of a rebate milled into  
the edge of the wooden batten, the rebate designed to function as a  
caulking allowance.

I prefer to custom-bend the batten covers from strips cut from sheet stock  
intended for exterior use and mill bevelled-edge wooden battens, slightly  
narrower than 2.5" at the top face).

No exposed fasteners and no rough surfaces to catch/hold snow or ice.


                              *

I think that the concerns about being cut by non-laminated tempered glass  
are unwarranted.

Plain tempered glass is virtually indestructable. Pretty much the only way  
that it can be broken is if the edge receives a sharp impact (which  
includes being pressed up against the shank of a metal fastener due to  
insufficient edge clearance (including expansion allowance) being provided.

I've had door panels that were temporarily leaned up against a porch,  
picked up by winds and thrown a few metres landing face-first on some  
large blast rock (ie sharp edges) without breaking more than a few times.  
It was easy to see where the rock impacted the face of the glass because  
the boulders left a streak of abraded stone dust across the face of the  
glass (which washed off).

I think that it was last year I mentioned on this list where I reported  
that ice & snow accumulations on a almost zero-slope sheet of 3 ft wide  
tempered glass on a walkway canopy, glass supported only along the  
longitudinal edges had deflected 1.5 inches at the midspan of the  
unsupported 3 ft width under the weight of the couple of feets-deep  
re-frozen snow/snow melt ... without breaking. I've had people tell me  
that cows have walked across their sheets of tempered patio door glass  
without breaking it.

In the unlikely event that tempered patio door glass does break, it will  
break by exploding into a gazillion little harmless ~ 1/4" chunks  ... not  
as large dangerous shards as would be the case with untempered glass.

Pretty much the only way to get cut is if one laid down nekkid in a pile  
of the chunks and purposely ground one's flesh into the glass chunks.

I'd venture that laminated glass would be more hazardous because it'd come  
down en masse, all of the broken mass being held together by the  
plast-ecchhh! sheet laminate so while one may not get cut by pieces of  
falling glass, one would get a pretty good bump on the head being hit by a  
60 pound mass o' glass.
                                                   *

And an off-topic "heads up" to listmembers who eat chicken nuggets and  
have small dogs:

http://www.youtube.com/watch?v=_ym0rxisOpw



-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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