Has anyone seen or done cross-strapping on the interior of a normal stud wall? I am thinking of standard 2x4 walls with 2x2 horizontal cross-strapping on the interior, then stabilized/wet binder blown cellulose insulation. Not trying for super insulated wall as I am in Vancouver (5700 HDD) but am looking for an insulation system that is simple (ie inexpensive) for the insulation contractor (I'll do the cross strapping etc.). I need to avoid exterior XPS or other exterior "vapor barrier" forming foam boards. Our climate doesn't agree with them. I am looking for R values, photos, personal experiences and details. Thanks John

The cross stapping will make it difficult to install the wet spray. You could have the cellulose or fiberglass blown behind a fabric stappled to the studs.

I have no experience with wet cellulose installation. Would horizontal 2x2 on 24" centers cause problems? I am assuming you mean voids behind each piece or other difficulties in building up the fill. (Not interested in regular dry cellulose because settlement would likely negate any increase R value in cross strapping/thermal bridging). Alternatively could I have it sprayed at the standard 2x4 stage, then cross-strap and have them come back? I realize there would be extra costs but is it possible to build a second layer of wet cellulose without blowing out the first one? Thanks John

A friend of our likes to build this way, has done a series of houses with 2x6 ballon framing, cross strapped 2x to the interior. Like smartwall said, dry, netted dense-pack cellulose works well for this method.

Here's a link to one of Chris' projects built in this fashion: Harmony House

Oh, and settlement isn't an issue with dense-packed cellulose (3.5 lb / cu ft+). At that density the fibers interlock and it can't settle any more, it really is drum tight against the netting.

AKA "Mooney Wall", cross-strapped can be easily done blown-in-bag using mesh (wet or dry, dense-packed or not. Wet-sprayed & dense-packed is usually well worth it for the long term perferformance though.)

http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm





http://www.builditsolar.com/Projects/Conservation/MooneyWall/MoreMooney.htm

Mooney Wall - love it!

Awesome to have such detailed information too.

Is there some special sealing around the electrical boxes? I am wondering if the mesh bulges or blows out around them.

John

We use rubber bands

The Mooney Wall looks like a neat idea. I wonder if it could be improved on just a bit by adding 1/2" XPS or Polyiso on the interior side. This would bring the wall thickness out to a standard 2x6 framed wall thickness of 5.5" (3.5" stud + 1.5" 2x strapping + 0.5" foam = 5.5"). This would make installation of standard exterior door casings for 2x6 walls fit better, plus it adds another thermal break and 2.5 to 3.0 of R value to the wall insulation. This could be done on the outside as well if using fiber faced Polyiso.

Great minds think alike!

All thermal breaks are good. The Mooney Wall approach reduces the unbroken thermal bridging to the intersections where they overlap.  But just 1/2" strips between the 2x4 and the cross-members would be as effective as full sheets on the interior (!). 

I'd think this is an application where double-layered pads/short-strips of 1/4" Thermablok aerogel may be be more cost-effective than full sheets of XPS or similar:



http://www.thermablok.com/

http://www.thermablok.com/pdf/Thermablok_Product_Information_20090601.pdf

But full stud-length strips of 1/2" XPS would have reasonable compression characteristics to handle the lateral members, would easy to field-fabricate, and wouldn't interfere with blowing insulation.  Low density iso would be too squishy to use between the framing in the same way- you'd need to find a source for 2lb density iso sheets in 1/2" thickness (and I'm not sure it exists.)  1/2" of aerogel would have an R value of ~4+, compared to R2.5 for XPS.  The thermal break on the rest of the stud with  2" (of framing + XPS/aerogel framing spacers) of cellulose offered is about R6-R7, so aerogel spacers would even that out considerably.