Newsgroups: misc.consumers.house
Subject: Re: ridge vents help?
From: michael@sunbeam.ksc.nasa.gov (Michael D. Myjak x7-3286)
Date: 10 Nov 92 17:37:54
Followup-To: misc.consumers.house
Organization: NASA, Kennedy Space Center, FL.
In-reply-to: sands@apple.com's message of Tue, 10 Nov 1992 19:24:45 GMTLines: 66


   I am remodeling my house and have a clerestory roof.  It consists of 2x10
   rafters and a open ceiling inside with R-30 batting in the gaps.  There
   are big screened blocks at the bottom ends and no (!?) openings at the 
   top.  The roofing material will be composition, 25 year stuff, of lighter
   color.

   The clerestory roof, for those not familar, is a roof that does not meet
   at the ridge.  Rather one side goes much higher than the other and overlaps
   sufficiently so that a low row of windows can close the gap.

   I live in California and my main consideration is reflecting or resisting
   the heat in the summer.  I was amazed that the roofing material
   manufactures
   do not rate or talk about how reflective their compostion shakes are.  

   I hear that it is possible for the roof to get so hot that it will pull 
   moist air into the roof, which condenses in the evenings and water drips
   the next day.  It seems like a roof ridge vent will allow most of the
   trapped
   heat to exit but it is not clear how to do this with a clerestory
   construction.

   Comments would be appreciated...

   Michael

Well, I'll take a crack at it. 

Whether or not you can add a ridge vent (or ridge vent like) -system-
at this time depends on whether or not styrofoam bridging was added
between the insulation and the roof sheathing. This provides a gap or
air channel for the air to circulate from the soffit to ridge. Without
it, a ridge vent will provide no benefit. Of course, you could always
remove the ceiling and insulation and add the stuff... but its not
usually cost effective.  Same thing goes for radiant barrier as well.
Besides, A ridge vent is designed for houses with ridges... yours is
(probably) a peak with a facia and thats a slightly different animal.
If there truely is a ridge over and above the window area, then indeed
you can install a ridge vent on that half of the roof.

At any rate, assuming that the insulation was installed properly, then
you would simply treat either side of your clerestory roof separately.
For example, the side that comes up and over your windows should be
vented as one side while the side leading up to the windows will be
vented as the other side.  

What you need to do is mount vents (1 for every 150sq.ft of attic
space) in a line near the top edge of each roof.  They should be
placed along the edge, just below (~ 1 to 2 feet or a high as
possible) the windows and peak, depending on which side your working
on.  These are not "ridge vents" but they perform the same function by
allowing the air to vent from the soffit.

If you desire further information, checkout the November issue of The
Family Handyman. There in you will find an informative article of what
your up against.

--
- Michael D. Myjak			
  Senior Technical Specialist, Systems Analyst
  McDonnell Douglas Space Systems Company
  Kennedy Space Center, Fl., 32815
  MYJAK@TITAN.KSC.NASA.GOV

Gravity. It's not just a good idea. Its the LAW!