[Greenbuilding] [BULK] Re: vented roofs

[Chris Green]

George J. Nesbitt wrote:
>    Too little attic venting is a problem, I have that problem at my 
> house. I would not recommend powered attic vents, there is little/no 
> evidence that they work, although people that have them swear by them. 
The ones here work quite fine (except when one of the grandsons threw 
mud up on the roof and some destroyed the fan motor...) The ones I'm 
referring to are basically the roof top version of bathroom fans, and 
the controls are set to turn the fans on when the attic temperature 
reaches a certain point, either 80 or 90F.
They are noisy, and there's three of these.


> Ridge and soffit vents is the best attic venting strategy, eyebrow 
> vents work too, but stick out more, although it is possible to do 
> venting that blends into shingle roofs.
We don't use ridge vents here because, I presume, they might allow the 
snow to be blown or drawn into the attic.

For a totally radical approach to passive roof cooling, Architect Dr. 
Eugene Tsui has embedded black flex tubing into one of the roofs he 
designed, shown on this page:
http://www.tdrinc.com/tsuihs.html
In the body of the text on this page, we are told:
> A series of black flex tubing is placed on the roof to act as passive 
> solar warm air vents. The house has proven itself to be cool in the 
> hot summer months and warm in the cold winter months, all without 
> mechanical air conditioning and heating machinery.
The pipes which stuck up above the roof, and when the sun heats them 
during the day,  the air inside the tubing is heated: the heated air 
rises, pulling cooler air from lower in the house. A solar assisted 
up-draft is set up through the tubing, and in the case of the  house 
shown on this page (his parents' place )  This cools the roofing 
material. Any heat absorbed by the ferrocement roof is drawn away and 
doesn't radiate into the interior of the building.
Unfortunately, I don't recall there being an illustration of this on his 
web site, but  I suspect the system would work better if the tubing had 
exposed ends which, being black, would absorb more heat than the lighter 
coloured cement roof.

The right hand side photo about 1/3d the way down the page, just under 
"Square Footage: 2000 square feet" shows a structure reminiscent of a 
rooster's or dinosaur's comb. A comb like this containing the tubing 
described above could be designed to work as a passive cooling/ venting 
system.
The challenge would be to come up with a way to incorporate this type of 
design into a more traditional styled building, and to prevent rain from 
running down the pipes into the attic. The benefit would be a system 
which uses only solar energy.

The Tsui house is in Berkeley, CA.

Cheers,

Chris Green.