[GSBN] Straw on edge with stick (stud) frame

Jim Carfrae jim.carfrae at plymouth.ac.uk
Thu Jul 7 04:47:32 CDT 2016


Thank you to everyone for their input!

Martin, we use wool in the form of manufactured batts from ‘Thermafleece’ cut to match the stud spacing, so fit is usually pretty good. I’m aware of the potential for ‘chimney effects’ and try to design them out.

Jacob: The main difference between what I’ve been building and your StrawCell is that I use horizontal ladders made from small section baton in the straw part of the wall. The ladders are fixed to the studs, and are the width of the straw with ‘rungs’ that coincide with bale lengths, so they sit in the wall without modifying the bales. We put them in every second course, and they provide useful fixing points and help form the sills and lintels for openings.

Jim

From: Gsbn <gsbn-bounces at sustainablesources.com> on behalf of martin hammer <mfhammer at pacbell.net>
Reply-To: Global Straw Building Network <GSBN at SustainableSources.com>
Date: Tuesday, 5 July 2016 at 23:27
To: GSBN <GSBN at SustainableSources.com>
Subject: Re: [GSBN] Straw on edge with stick (stud) frame

Hi Jim,

The system Jacob mentions (invented?) uses “dense-packed” cellulose insulation between framing, and tight against the already stacked bales. I included this in a recent code change proposal for Appendix S – Strawbale Construction in the International Residential Code (IRC). You can see the added language underlined in the section below. It was approved in April and will be in the 2018 IRC. (The IRC is the model residential code in the U.S.)

Jacob, and others who practice this method in the northeast U.S. wanted this explicitly allowed in the U.S. SB code because it was being or they feared it being questioned or disallowed by building officials.


AS104.2 Purpose, and where required. Strawbale walls shall be finished so as to provide mechanical protection, fire resistance and protection from weather and to restrict the passage of air through the bales, in accordance with this appendix and this code. Vertical strawbale wall surfaces shall receive a coat of plaster not less than 3/8 inch (10 mm) thick, or greater where required elsewhere in this appendix, or shall fit tightly against a solid wall panel or dense-packed cellulose insulation with a density of not less than 3.5 pounds per cubic foot (56 kg/cubic meter) blown into an adjacent framed wall. The tops of strawbale walls shall receive a coat of plaster not less than 3/8 inch (10 mm) thick where straw would otherwise be exposed.


Related to this I’ve used 2x4 studs at 46” (117 cm) with stacked 3-string bales on edge in between. The studs nestle into the curved-corner joint between stacks of bales and stacks fit tight at bale ends.  A minimal roof bearing assembly the width of the bales bears on the studs (which are on the outside wall face only). I call it a “light post and beam” system.

David Arkin (on this list) and others have used a similar system, but with TJIs (‘truss joists’) installed vertically like studs, with bales stacked between them. Unlike the system I’ve used, it has a vertical framing member both inside and outside (the ‘flanges’ of each truss joist) and with great out-of-plane strength, allowing for tall walls or other high out-of-plane demand designs. It has minimal thermal bridging through the OSB web of each truss joist.

These systems don’t do one thing I think you’re trying to achieve. That is, adding a layer of insulation to the stacked straw bales. I like that you use wool between the studs in your system, as long as it’s packed tightly against the bales and framing. Trying to avoid uninterrupted vertical spaces that could be a “chimney” for fire.

Best.

Martin

Martin Hammer, Architect
1348 Hopkins St.
Berkeley, CA  94702
510-525-0525 (office)
510-684-4488 (cell)



On 7/5/16, 8:45 AM, "Jim Carfrae" <jim.carfrae at plymouth.ac.uk> wrote:
Thanks Bruce

I’m adding an extra layer of insulation to keep up with current standards like PassivHaus (I don’t build PassivHaus, but clients like to hear that you’re using similar levels of insulation….)

Unless anyone else wants to chip in, I’ll reference Jacob as the originator.

Jacob, If I continue using a version of this method would you like to be credited in the documentation for planning approval etc?

Jim


From: Gsbn <gsbn-bounces at sustainablesources.com> on behalf of Bruce EBNet <bruce at ecobuildnetwork.org>
Date: Tuesday, 5 July 2016 at 16:10
To: Global Straw GSBN <gsbn at sustainablesources.com>
Subject: Re: [GSBN] Straw on edge with stick (stud) frame


Jim —

I’ll chime in here just to say that I first heard of the system from Jacob, so as far as I know he deserves credit.  (Thanks, Jacob!).  You can add other insulation fairly easily, but generally don’t need to, other than to plug the thermal bridges created by the wood studs where there is no straw.

Bruce


On Jul 5, 2016, at 7:11 AM, Jim Carfrae <jim.carfrae at plymouth.ac.uk> wrote:


Hi Dan


My interest was mainly to do with combining the structural simplicity of a stick frame with the potential for significant extra insulation, as in the StrawCell example.

Does your system involve much additional insulation?

In the UK I have been using a 4 by 2 frame with wool as the insulation between the studs. This combines with the straw to reduce the U value from a nominal 0.16 W/m2K for a rendered straw wall down to 0.11 W/m2K for the hybrid wall.

Jim



From: Gsbn <gsbn-bounces at sustainablesources.com <mailto:gsbn-bounces at sustainablesources.com> > on behalf of Dan Smith <dan at dsaarch.com <mailto:dan at dsaarch.com> >
Date: Tuesday, 5 July 2016 at 14:48
To: Global Straw Building Network <gsbn at sustainablesources.com <mailto:gsbn at sustainablesources.com> >
Subject: Re: [GSBN] Straw on edge with stick (stud) frame

Hi Jim,

We’ve been working with a similar system of bales "on end" between 2x studs at 2’ o.c., with ply/fiber board on the exterior, and have a large addition to an adobe house planned to use it soon, working with Bruce King as engineer.  I’d be happy to chat as well and send details.

Dan Smith

d s a architects
1107 Virginia Street | Berkeley | CA 94702
ph. 510.526.1935 | www.dsaarch.com <http://www.dsaarch.com/>


On Jul 5, 2016, at 6:35 AM, Jim Carfrae <jim.carfrae at plymouth.ac.uk <mailto:jim.carfrae at plymouth.ac.uk> > wrote:

Hi Jacob

Thanks for the response.

I have been experimenting with a version of this technique myself, and I principally wanted to find out if:

1)    I was using someone else’s ‘protected’ design.

2)    It might feature in an upcoming academic paper, and I wanted to know who to reference as the originator.


The post that I saw had a photo of a demonstration wall section and a couple of SketchUp drawings – Was that you?

Cheers,

Jim



From: Gsbn <gsbn-bounces at sustainablesources.com <mailto:gsbn-bounces at sustainablesources.com> > on behalf of Jacob Racusin <buildnatural at googlemail.com <mailto:buildnatural at googlemail.com> >
Date: Tuesday, 5 July 2016 at 13:39
To: Global Straw Building Network <gsbn at sustainablesources.com <mailto:gsbn at sustainablesources.com> >
Subject: Re: [GSBN] Straw on edge with stick (stud) frame

Hi Jim,

We've been doing this technique for a few years now, in a few different ways. We coined a term "StrawCell" to describe the hybrid system, a web search for that term should turn up a few blog posts and videos. I'm not sure if I was the originator of the post, as others have been using this technique as well, but I'd be happy to chat further.

Cheers,

Jacob



On Mon, Jul 4, 2016 at 4:58 AM, Jim Carfrae <jim.carfrae at plymouth.ac.uk <mailto:jim.carfrae at plymouth.ac.uk> > wrote:

Hello

A couple of years ago details of a bale wall system using bales on edge against a stick frame were posted here.

I can’t find the original post, and would like to contact the originators of the idea.

Can anyone out there help?

Jim


Dr Jim Carfrae

Environmental Building Group
Room 302 Roland Levinsky Building
School of Architecture, Design and Environment
Plymouth University
Drake Circus
Plymouth PL4 8AA

07880 551922

jim.carfrae at plymouth.ac.uk <mailto:jim.carfrae at plymouth.ac.uk>




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