RE: [GBlist] vented rain screen

["Ralph Bicknese" <ralph.bicknese@christnerinc.com>]

The added gain in R-value in a rainscreen situation would be in the order of
magnitude of about R 0.4 to 0.9 depending on the ventilation rate, etc.  As
John suggested this is minimal and not a significant benefit of rainscreen
systems.

Improvements in R-value might be gained by adding various combinations of
radiant barriers (one or more) and perhaps that could push the r-value up to
R-3 to 4 or so.  But the radiant barrier could introduce other complications
to be dealt with.  For example, most radiant barriers are also very good
vapor barriers.  In most cases the vapor barrier should not be at the
outside of the insulation but on the inside surface.  There could be other
technical issues as well.

Cheers,
Ralph Bicknese

-----Original Message-----
From: John Salmen [mailto:terrain@shaw.ca]
Sent: Tuesday, November 21, 2000 5:21 PM
To: Brenda Bradford; greenbuilding@crest.org
Subject: Re: [GBlist] vented rain screen

this is not the answer you want - it depends.

Mostly it would depend on air flow which depends a lot on the type of rain
screen - if its pressure equalized or simply a cavity. In a pressure
equalized assembly the rain screen is divided into small compartments to
allow as minimal exterior air flow as possible or as needed to equalize air
pressure. In this scenario there would be a  small rise in the insulative
value of the assembly. The bigger gains is that the pressure equalized
assembly demands a very complete air barrier.

Another consideration is the width of the cavity - min. is an inch but
masonry cavities are typically required to be 2" which requires more
venting.

Interesting question and though the increased value would be very minimal
the design of a rainscreen can provide other benefits. For example if a
insulative foam layer is used as the air barrier the elimination of thermal
bridging can substantially increase the whole wall insulative value.

John Salmen
TERRAN E.D.S.


----- Original Message -----
From: "Brenda Bradford" <brendab@vandervort.com>
To: <greenbuilding@crest.org>
Sent: Wednesday, November 21, 2001 2:48 PM
Subject: [GBlist] vented rain screen


> Hello,
>
> Does anyone know whether the air space in a vented rain screen provides
> extra insulation value to the whole wall?  If so, is there a way to
quantify
> it?
>
> Thanks,
> Brenda
>
> "Leap - and the net will appear"
>
> Brenda Bradford
> David Vandervort Architects
> ph. 206-784-1614  ex.13
> fax 206-781-1911
>
>
> ______________________________________________________________________
> This greenbuilding dialogue is sponsored by REPP/CREST, creator of
> Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
> Environmental Building News and GreenSpec http://www.BuildingGreen.com
> ______________________________________________________________________
>


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________