20) Mooney walls/thermal bridging, breaking

by Gail on December 7, 2009

Today's "look"

Today's "look"

The following link demonstrates a very interesting construction technique that our architect Jonathan Ehling passed on to us. We would like to use it, if it is not too late!

Mooney Wall (this site link is filled with great advice, mostly about the use of solar energy) – retrofitable wall with high R value and low thermal bridging
This description of the Mooney wall appeared in the Breaktime discussion group of the Taunton Publishing discussion forums (Taunton publishes Fine Homebuilding magazine) — a good place to get all sorts of construction advice.

The Mooney wall provides high R value, low thermal bridging, and good resistance to infiltration.   All this at a low cost (especially if you are providing the labor).  Thermal bridging refers to the transfer of heat directly through the relatively low R value studs — this can reduce the R value of the wall substantially from the R value of the insulation placed between the studs.  For example a 2X6 stud wall with “R19″ insulation only has an R value of 13.5 when the thermal bridging of the wall structure is taken into account (see http://www.ornl.gov whole wall calculator).

The Mooney wall can be used for either new construction or as a retrofit to increase the R value of an existing wall.

Another example of using the Mooney wall here …

From the BreakTime Post:
The “Mooney wall” is the The brainchild of Mike Smith and Tim Mooney.  The primary purpose of the MW is to upgrade the insulation of a standard 2×4 (on 16″ centers) wall.   The MW is well suited to renovation work with superior insulating characteristics to standard 2×4, 2×6, and many variations.  In one thread I see Mike estimating the wall at a true R-18  (unlike the artificial R-19 of a 2×6 fiberglass wall, which doesn’t take into account the thermal bridging of the wood).

The Mooney Wall’s thermal bridge is restricted to the points where the 2×2’s (really 1.5″x1.5″) contact the 2×4 wall studs.  This is a vast improvement over the nearly 30% thermal bridge of a typical 2×4/2×6 wall.

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