[Greenbuilding] Roof slopes (was Re: Glass roofing)

Michael O'Brien obrien at hevanet.com
Thu Aug 14 16:35:48 MDT 2014

Hi, Rob--

I'm puzzled, of course the golden mean can be generated by arithmetic, the formula is (1 + √5) ÷ 2.

Or did you mean you prefer the geometric option?



Mike O'Brien Photography

On Aug 14, 2014, at 3:08 PM, RT <ArchiLogic at yahoo.ca> wrote:

On Thu, 14 Aug 2014 16:49:07 -0400, Clarke Olsen <colsen at fairpoint.net> wrote:

> True, the temples are shallower, but the diagonal of a golden rectangle (10 to 16.14....) is an ancient proportion used for
> roofs in New England.
> On Aug 14, 2014, at 3:28 PM, candtcampbell at juno.com wrote:
>> I could have sworn that the pitch of a Greek pediment was something like 5.2 in 12.
>> My favorite pitch is 7.5/12, aka 10 in 16.

"7.5/12" and 10/16 are both Murrican (ie based on Imperial units) approximations of the diagonal of the Golden Rectangle -- close, but not perfect, Perfection being that which the Golden Mean is supposed to represent, derived by geometry rather than arithmetic.

Me ? I like 7/12 for roofs. 30 degrees. Easy to set up for cuts and joints. Not so steep that you slide off when walking around on it but steep enough that snow and rain don't accumulate on the outside and the inhabited roof volume is an interesting space  -- human scaled as opposed to slopes 12/12 or more which are better suited the Divine where much of the "soaring" space (or as one typo in a realtor's ad called it "sorrowing 20 foot ceilings") of the interior roof volume cannot be practically utilised.

Enginoids also like 30 degrees for roof slopes. Steeper than 30 degrees and live loading due to wind becomes a governing factor in the structural design --shallower than 30 degrees, gravity loads govern -- 30 degrees is the sweet spot between the two and is structurally very efficient.

=== * ===
Rob Tom  .  .  . T60BOM
Kanata, Ontario, Canada

A r c h i L o g i c  at  Y a h o o  dot C A
(manually winnow the chaff from my edress if you hit "reply")

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