Wall insulation/ventilation region 6 A

I am wondering if anyone has come up with a formual that calculates the minimum stand off for a canadian rain curtain that take into account the exterior wall insualating materials, r value, max. wall ht and building location/elevation?

I am also trying to locate some information relating to any benifits to reduced energy consuption a raincurtain might add. Feedback from my clients has been all over the place on the retoros we have completed and they most likely also include upgrades to the roof & attic insulation at the same time

Thanks

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Mathew E. Blanc
Blanc & Bailey Construction, Inc.
P.O. Box 383
18 Depot Street
Charlestown, NH 03603
Phone: 603-826-4626
Cell: 603-494-0517
Fax: 603-826-4114
E-Mail matt@blancbailey.com
www.blancbailey.com
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Asked by Matt BLANC
Posted Sat, 02/02/2013 - 15:18

Tags: GBA Pro help

1.

Matt,
A rainscreen gap installed between the siding and the sheathing adds only a very small R-value to your wall assembly. I wouldn't try to promote this method of siding installation for its R-value benefits. That would be an exaggeration.

The main value of a rainscreen gap is water management. It helps damp siding and damp sheathing to dry quickly. It also reduces inward solar vapor drive. These are real benefits, but they aren't R-value benefits.

When it comes to determining the minimum depth of a rainscreen gap, you'll hear different people mention different numbers. My own preferred number is 1/4 inch. That gives you almost all the benefits of a rainscreen gap, and is deep enough to avoid job-site problems due to irregularities in the sheathing or WRB.

If you are building in an area with very high rainfall, than a deeper gap (up to 3/4 inch), with ventilation openings at the top as well as the bottom of the wall, will increase the wall's drying rate.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 02/04/2013 - 08:39