Replies

1. 
   Riversong | May 05, 2010 05:02pm | #1

   This isn't Mooney's wall, but simply a variation on the decades-old cross-hatch wall system. His variety uses insulweb and dense-pack, but this wall can be insulated with any thermal barrier. I used this approach in the early 80's on an inner city renovation project to increase the R-value and decrease the thermal bridging of the wall framing. But I used a closed-wall dense-pack cellulose fill, which is easier and less expensive.

2. 
   JR | May 05, 2010 09:09pm | #2

   Based on your experience with this system, does it reduce thermal bridging,air infiltration & increase r value...while offering a less expensive alternative to other methods?

   Is there any drawbacks to implimenting this method?

   thanks,
   JR

3. GBA Editor
   Martin Holladay | May 06, 2010 05:10am | #3

   JR,
   The main drawback (compared to exterior foam sheathing) is that the method doesn't address thermal bridging at the rim joists — and may not even address thermal bridging at partition intersections, unless you've thought through your details carefully.

4. Expert Member
   Michael Maines | May 06, 2010 06:04pm | #4

   Every good idea needs a catchy name, and "cross-hatched wall" just isn't as memorable as "Mooney Wall." Do you really think Larson was the first guy to make "Larsen trusses" or Trombe was the first guy to use "Trombe walls?"

   The advantages to the Mooney Wall are that it's easy to visually verify the quality of your installation, it's faster and easier than stitching the side of each stud with insulweb, and it drastically reduces the amount of thermal bridging while keeping construction methods fairly close to standard practice.

   Are there better ways to insulate? Absolutely. But better insulation may or may not represent a good value to the customer. I haven't installed cellulose myself but I've torn apart enough walls to know that blowing blind is risky; it's too easy to miss a spot, particularly around tricky framing or in remodels. Foam in all its forms solves many problems but brings up other questions.

   Double wall dense-pack is probably the closest comparison to the Mooney Wall, but there are diminishing returns. I would estimate that the Mooney Wall represents the biggest jump up from conventional dense pack with the least amount of effort, the lowest degree of risk, and the least change in cost and construction techniques from standard construction.

   Partition intersections are easy to deal with using blocking between studs in the receiving wall and running poly or mesh behind the intersection. Foam is the only insulation that doubles as an air barrier, so you do have to caulk or use other air-sealing techniques.

   Drawbacks include trying to train your installer to glue the insulweb to the studs, or having to acquire your own densepack system. Rim joist thermal bridging is an issue, but setting your rim joist in 2" to receive rigid foam is a simple way to reduce that problem. Horizontal nailing confuses sheetrockers, carpenters and picture-hanging homeowners. Wall thickness is 5" and not 5 1/2", so standard extension jambs don't work (not that they ever do).

5. 
   Riversong | May 06, 2010 07:34pm | #5

   Every good idea needs a catchy name, and "cross-hatched wall" just isn't as memorable as "Mooney Wall." Do you really think Larson was the first guy to make "Larsen trusses" or Trombe was the first guy to use "Trombe walls?"

   "Catchy" is hardly as important as descriptive, and "cross-hatched" has been used in superinsulation publications since the 80's and is easily understood. The "Mooney wall" is merely one of many variations on this theme.

   And, yes, I am nearly certain that John Larsen was the first to design an exterior parallel-chord wall truss system for retrofitting existing buildings (and he has the patent to prove it). And I am nearly as certain that I and architect Bruce Coldham were the first to use a similar system to create an exoskeleton for new construction in 1993, and that I am the only builder using it consistently for the past 17 years, and certainly the only one doing so with rough-sawn lumber.

   But while engineer Felix Trombe and architect Jacques Michel popularized the idea of a wall as solar collector in 1964, it was invented and patented by Edward Morse in 1881.

6. 
   Riversong | May 06, 2010 07:40pm | #6

   JR,

   Yes, the cross-hatched wall is the simplest and least expensive method for improving the R-value of exterior walls and ceilings while reducing thermal bridging. It does nothing for air tightness - that requires a completely different set of practices.

   I would not use the cross-hatched system for anything but renovation, since it's a modest but simple way to improve an existing building's thermal performance during a major gut overhaul. For new construction, a double-wall or modified Larsen Truss (the Riversong Truss wall) is the most cost-effective and green system for superinsulating the thermal envelope, and with dense-pack cellulose it's the system with the best hygrothermal and healthy home effects.

7. 
   Riversong | May 06, 2010 07:42pm | #7

   JR,

   The Riversong Truss is also described in detail on the BuildItSolar website:
   http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm