[Greenbuilding] (Eyeballing) Circa 1766 (terra cotta) roof shingles

[RT]

On Wed, 13 Mar 2013 08:02:40 -0400, Alan Abrams  
<alan at abramsdesignbuild.com> wrote:

>  I'd eyeball the typical roof

Well, so much for AA-Man's eyeball.
[In the voice of the Soup Nazi] "NO MORE SINGLE-MALT FOR YOU !"

Even I could tell from a wee GoogleMaps partial-screen image on a little  
netbook that the clay tiles on those DC roofs were not of the flat variety  
like those on the Moravian bldgs in Winston-Salem NC, but rather, were the  
more common, rounded, half-cylinder variety.

Shoot, there are even some of the latter here in Ottawa, with a bunch of  
them clustered around the house at this spot  45.406045, -75.688962  (look  
for the herd of red roofs in the Google satellite image).

I suspect that they're able to survive because water likely doesn't have a  
chance to sit on the rounded profile for long enough to wet the clay  
sufficiently (in addition to being assisted by the roof slope) to pose a  
frost expansion risk.

I suspect that the story would be different for flat tiles. But then  
again, I could be full of hooey because I've never used either variety.

Actually, reflecting on the matter a little bit more, I remember a former  
colleague (who subsequently took a position at the Museum of Civilisation)  
telling me that at one of the first known European (ie Viking) settlements  
on this continent where the Museum had done extensive archeological  
research) they found clay roof tiles that apparently had been formed using  
their laps as moulds.

Rather ingenious I thought since not only does the thigh provide a rounded  
cylindrical shape with which to work, it also provides a natural taper  
which assists in locking the tile courses together. (ie wide end down on  
the lower course, narrow end down on the upper)

As for Vitruvius' recommendations, I think that the message might be  
simply:

     "Mortar ain't glue".

It should just be treated as gunk to fill in the irregularities between  
mating surfaces to better distribute loads over the bearing area and not  
as something attempting to make masonry units defy gravity (which they can  
do but it's because of geometry, not mortar-as-glue).


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

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