Newframeworks has been working on developing a new way to install strawbales for a couple of years and is now using this blog to document a build that incorporates its current design. This string of blogs will be posted here and numbered in sequence
The design has lots of history and collaboration from others. Ace, Ben and Jacob have been discussing alternative strawbale wall systems for years with other strawbale builders from NaturalBuilders Northeast, Mark Hoberecht of Harvestbuild, and others within the strawbale network around the world.
The standard strawbale wall system in the Northeast was a timberframe structure with a strawbale wrap for enclosure and insulation. We have built many of these and finally began to analyze results of economy and performance. Some of those performance metrics are summed up in a study NFW published in 2010. (clink here) This happened at the same time that the PassivHaus movement was coming on strong and encouraging us to think about how to both increase the insulation level of our walls and lower the air leakage rate.
The above report made it clear that we were both doing a good job with the standard timberframe wrap system, but that we were going to have a lot of trouble notching up the performance level to PH levels. We were also interested to make strawbale house more affordable and accessible and began realizing that the standard system was a lot of work and finicky. Enter Mark Hobertech who jumped on the PH wagon early and began developing his “Edge Plus” system of combining strawbale with stud frame. The basic idea of combining stud frame with strawbales was well documented in strawbale books Serious Strawbale and others, but Mark really started tuning the system for PH standards. Chris Magwood and Brian Fuentes have also developed systems that are aiming for PH as well but are following different paths using premanufactured SB panels.
NFW built a full scale model of its own Strawcell wall that it showed off at the 2012 Nesea conference in Boston in anticipation of building out the system the following year. NFW first tried out the system on a project that NFW design for a couple in CT. NFW traveled down to do the install and found that the new system probably cut the construction cost in half compared to the standard timberframe bale wrap wall system.
Everything about the new design seemed good and we are now on the verge of installing it in Marshfield, VT. This first blog is meant to give history and context to the new wall system as well and the basics of the design which follows below. The next post will begin to show the installation.
Overview of NFW Strawcell wall system:
Exterior siding (wood) over rain screen.
1/2″ insulated sheathing or 1″ rough sawn boards with weather resistant barrier.
2x exterior load bearing wall blown with dense packed cellulose.
Strawbale on edge or flat with strings cut and 1/2″ lath secured to 2×6 frame. Interior plaster directly on strawbale.
-No exterior plaster on bales. Cellulose insulation is blown against exterior of bales. Attention is given to permeance ratio between interior finish and exterior.
-Bale strings are cut and bales are feathered together, making initial squaring of bales as well as stuffing cracks for plaster prep not necessary. This creates better strawbale consistency throughout wall.
– 1/2″ vertical wood lath is used to fasten bales to frame for a consistent fastening system.
-Removing structural elements in plane of the interior plaster air barrier to create more continuous air barrier.
-Incorporates additional cellulose insulation between studs for additional overall performance of the wall system.
-Incorporates exterior weather resistant barrier and rainscreen siding that allows the installation of the bales down to the slab.