[GSBN] using loose straw insulation in roof

Bohdan Dorniak bohdan at bdcoarchitects.com.au
Wed Nov 1 17:22:18 CDT 2017

This has been an interesting discussion. 


Here in Australia during a bushfire test the AUSBALE representatives , Lance
Kairl, Frank Thomas and I witnessed what happened when a unrendered bale was
set alight – the strings burnt – the bale under pressure “exploded” and
burnt well. Rikki – wouldn’t that happen with the bales in the roof space.


I’m wondering what insurance companies feel about this?



From: Gsbn [mailto:gsbn-bounces at sustainablesources.com] On Behalf Of Rikki
Sent: Thursday, 2 November 2017 12:31 AM
To: Global Straw Building Network
Subject: Re: [GSBN] using loose straw insulation in roof


HI all, 


How interesting this debate!


One side note. I sent that last email on Oct 27, but GSBN didn’t receive it
until Oct 31. Anyone else ever experience a multi-day delay?


I got it today.


The biggest consideration about the insulation value came with the numerous
large gaps between bales and trusses that needed to be filled. 


If I were to use entire bales for insulation in the roof (forced into the
space between trusses or beams really tight!), I would then cut the strings
so that the straw expands a bit and fills in the gaps itself; this way
little or no stuffing is necessary. This technique is used in the CUT system
and works quite well. If the bales are in really tight they wouldn’t loose
much compression ( I understand that dense bales mean less oxygen and more
fire resistance, even if the density doesn’t affect the insulation value


 In northern Europe it is quiete common to use entire bales in the roof.
It’s curious how cultural differences are important in these decisions.
Several people mentioned the extra weight of the bales being  a problem.
Here in Spain, this is not true. Trusses are almost never used. Most roofs
have a huge “main” beam and then smaller beams resting on the wall on one
end and the mother beam on the other (placed at 50-60cm between each
secondary beam), and almost all people use tile or green roofs. When trusses
are used, they are BIG trusses at large distances, and the secondary beams
are placed horizontally. Both systems are “heavy. ” The beams which are
dimensioned for these kind of roofs can hold the weight of entire bales with
no problem. They are over-dimensioned anyway, so as to be more fire
resistant. Here the beams are calculated considering distance, weight and
type of wood. Then the size is multiplied by a “safety factor”, depending on
the use and type of wood.  From what you all say, I suppose this is not so
in the US.


I don’t like the idea of loose straw in the roof, but the only other cheap
(non-flamable) possibility I know of is natural sheep’s wool- which has it’s
own difficulties in processing. I would never use loose straw in a
contracted building, but I think we all know and understand that the needs
of low-income self-builders are a bit different. From what everyone has
said, I understand that the major problem with the loose straw is not
insulation value, but flammability
 so I guess each builder has to evaluate
if fire is a high risk or not-  especially depending on how the chimney and
electrics are installed.



p.s. I will be visiting friends and family in Santa Cruz (CA) and New
Orleans next month. Anyone know of any projects worth checking  out in these
areas? Answers off-list please!


El 1/11/2017, a las 13:58, Martin Hammer <mfhammer at pacbell.net> escribió:


Thanks for the info John. I was grasping at the straws of my memory for the
story on the “China” fire event (and almost said “or Mongolia”). Not sure if
we’re thinking of the same event. Either way the point is the same. In
addition to: Don’t install a chimney against insulation (straw or any
other). Thus "Section AS107.3 Clearance to fireplaces and chimneys” in the
IRC strawbale appendix.


One side note. I sent that last email on Oct 27, but GSBN didn’t receive it
until Oct 31. Anyone else ever experience a multi-day delay?


Martin (traveling at the speed of straw) Hammer



From: Gsbn <gsbn-bounces at sustainablesources.com> on behalf of John
Swearingen <jswearingen at skillful-means.com>
Reply-To: GSBN <GSBN at SustainableSources.com>
Date: Tuesday, October 31, 2017 at 7:04 PM
To: GSBN <GSBN at SustainableSources.com>
Subject: Re: [GSBN] using loose straw insulation in roof


Thanks for all that, Martin.  One note, if we're talking about the same
incident with Kelly, it was a clinic in Mongolia that caught fire shortly
after it was built, because the had installed the fire chimney after the
attic and insulation, and right against it.  The fire brigade was quite a
distance away, many hours, and because the straw was just smoldering, they
had time to move all the equipment and furniture out from the building,
without damage, and then the fire in the attic was extinguished.


John "Insolent Insulator" Swearingen


On Tue, Oct 31, 2017 at 6:52 PM Martin Hammer <mfhammer at pacbell.net> wrote:

Hi all,


Good discussion and advice on this.


The PAKSBAB (Pakistan) SB buildings use 12” (30 cm) of clay-coated straw for
insulation above the ceiling (photos and drawing attached) (second photo and
drawing courtesy of Darcey Donovan Messner). Andy Mueller and I used a
lesser depth of the same “loose straw-clay” for our SB building in Haiti
(photos attached).


Both make a noticeable difference in the building's thermal performance in
their respective climates. In both cultures thermal insulation of any kind
is rarely used. But as happy as I am to use this inexpensive natural
insulation in these and similar contexts, I worry about the flammability of
the “loose straw clay”. Even if the material resists ignition in the first
months or year after installation, I’ve seen evidence over time of clay
“dusting”, thus diminishing whatever protection it offered the straw


I remember reading (in a TLS article?) Kelly Lerner describe a straw
insulation fire that started (electrical source, as I remember) in the attic
of a SB house in China. It was not part of the prescribed design, but I
think it was reasoned that if it’s good in the walls, why not the attic? I
don’t remember if it was loose or baled straw, but either way it is an
indicator of the fire risk of straw as ceiling, attic or roof insulation.
This event gave SB a bad name in the region that took time to overcome..


That said, there are many factors at play. I can imagine reasonably
fire-safe ways to use straw (with or without clay) as ceiling, attic or roof
insulation. (Leaving the structural issues out of it.)


I found the following statement in TLS17 (1997):  "Robert Laporte, timber
framer and straw-clay builder, commonly uses straw-clay stuffed loose
between rafters as insulation, with the clay discouraging pests."  I don’t
know if Robert still practices this 20 years later. His partner Paula
Baker-Laporte who is on this list, might be able to say more.


Also, I’ve attached an article from TLS38 (2002) “Bales in My Roof . . . A
Costly Decision?” that speaks to some of the identified issues.


Lastly, to the extent that it's relevant, and as far as I know, Rikki is
still working is Spain (and maybe neighboring countries).


Martin Hammer



From: Gsbn <gsbn-bounces at sustainablesources.com> on behalf of John
Swearingen <jswearingen at skillful-means.com>
Reply-To: GSBN <GSBN at SustainableSources.com>
Date: Friday, October 27, 2017 at 6:57 AM
To: GSBN <GSBN at SustainableSources.com>

Subject: Re: [GSBN] using loose straw insulation in roof


Quite a long time ago we built a house using bales for roof insulation, with
site built trusses.The biggest consideration about the insulation value came
with the numerous large gaps between bales and trusses that needed to be
filled. The building was near a major farmland highway with large trucks
passing a few yards away, and the bales did an excellent job of dampening
the low frequency noise of the trucks. I would consider them again is a
similar situation, but not for insulation; the cost and difficulty of doing
a good job is too great, and other good alternatives are available.


This year we have again been up close and personal with fire, this time
dealing with melting levels of heat, generating tornado winds in
concentrations of timber buildings feeding off of each other. We have four
projects that came within yards of the worst fires, but none of them were
touched by flames, so we don't have any forensic information to offer.  The
closest endorsement we've had came from firefighters who came to defend our
house and we showed them our strawbale cabin with a grassy green roof.  They
immediately freaked, then looked, pondered, said "no problem" and moved on
to check out the wood structures.  Nothing like thick plaster and few inches
of wet dirt to slow down a hot fire..


Since we're designing a home in the same fire-prone region of Napa, we've
been looking at the weak links that would make a good plastered house
vulnerable. In an intense fire, assuming the plaster and roof are good, the
weak link is heat transfer (and breakage) through windows igniting the
interior, and we're thinking of mounding sprinklers on the exterior within
the window cavity, primarily for cooling. We've done this in urban
situations when a building has been inside the required setback in lieu of a
one-hour fire wall This would be a slightly different use from preventing
the spread of fire--primarily to cool the glazing area long enough for a hot
wildfire to pass. When firemen show up before and advancing fire, they do a
lot of wetting. We've installed large garden sprinklers on our roofs in the
forest, and the firemen are big fans of those. Water is their only friend. 


Any thoughts on this? 


John "I'm All Wet" Swearingen


On Thu, Oct 26, 2017 at 7:13 PM David Arkin, AIA <david at arkintilt.com>

Hi World:


Having just taught a few workshops where we measured the density of bales
and discussed the possible reasons for a minimum density, this is a timely
question.  We actually had some bales that didn’t pass the minimum 6.5
lbs./cu. ft. specified in the International Residential Code (IRC).  Reasons
for a minimum density include structural integrity, insulation properties,
and fire safety.  The use of loose fill that doesn’t achieve a minimum
density is not supported in this code, but that doesn’t rule out the
possibility that some version might be developed that could achieve similar
properties to loose fill cellulose and other materials.  


For insulation, the IRC and also the IBC specify a maximum flame spread
index of 25 and a maximum smoke developed index of 450.  An ASTM E84-98
Standard Test Method for Surface Burning Characteristics test of a Straw
Bale in May of 2000 yielded a flame spread index of 10 and a smoke developed
index of 350, thus verifying straw bale as a viable insulation material.
Note that this was a test of surface burning of a bale, not loose straw. 


Curiously, the IBC notes that Cellulose loose-fill insulation only needs to
meet the smoke developed index not exceeding 450 criteria, provided it
complies with CPSC 16 CFR Part 1200 and CPSC 16 CFR Part 1404, and further
stating that ‘each package of such insulation material shall be clearly
labeled in compliance with' [these].  


I’ve heard some folks in the UK have been experimenting with a chopped straw
insulation infill, but the exact parameters of the processing and the
resulting fire resistance I don’t have information on.  


That all said, I’ve never done it (put straw in a roof / ceiling), nor do I
recommend it, but neither can I say with certainty that it shouldn’t be


David A.

On Oct 26, 2017, at 4:57 PM, Bill Christensen <lists at sustainablesources..com
<mailto:lists at sustainablesources.com> > wrote:


In the ASTM tests that Bruce King coordinated back in 2007, one of the walls
was clay plastered. 

Yes, the clay cracked and the straw eventually burned (though the clay
plastered wall did better than cement, we believe because it spent the first
20 min or so "firing" as in a kiln, and the chemical changes from that
absorbed a lot of the heat).  

Loosely packed straw might not fare so well once oxygen can get to it.  

We had a problem because the clay plastered wall had a crack on the
exterior, which allowed more oxygen in between a couple bales.  Though we
had stuffed and cobbed those spaces maniacally, the fire followed the path
back through the wall.  We had to cut the test off at 1 hour because of this
- otherwise the clay plastered wall probably would have out-performed the
cement plastered one. 

The guys at the testing facility told us that "Everything burns...
eventually.   Everything". 

I have to agree with the earlier comments in this thread - loose straw as
ceiling insulation is just asking for problems, whether hit with clay slip
or not.  

On 10/25/17 4:56 PM, Bohdan Dorniak wrote:

Hi All

Graeme – I’d be worried about your statement about a “coating of clay” – in
our fire test of rendered strawbales by CSIRO - done in 2002 – the earth
rendered bale (render about 50mm thick – Frank Thomas did the rendering)
started to show cracking in the render.

Wondering whether eventually they would burn? 

Other considerations is the weight factor and stronger ceiling structures
(if using thicker coats of render).

That’s my 2 bob’s worth.



From: Gsbn [ <mailto:gsbn-bounces at sustainablesources.com>
mailto:gsbn-bounces at sustainablesources.com] On Behalf Of Misha Rauchwerger
Sent: Thursday, 26 October 2017 8:04 AM
To: Global Straw Building Network
Subject: Re: [GSBN] using loose straw insulation in roof


I believe another issue is whether the attic space is vented or not, as well
as the kind of roofing.  After the Oakland fires, I remember this being
debated furiously, because the codes require attic venting, and going with
something like polyisocyanurate rigid insulation without vents was
controversial.  Obviously the fire danger will increase if air can mix with
flammable insulation fuel (frieze block vents and ridge vents create a
perfect means for fully combusting the attic materials) . If it is encased
and covered with earth on the outside and inside (plaster on the ceiling),
as in a living roof, we can decrease the flammability factor.


The Lobo fire that swept through our neighborhood recently came right to our
friend's straw bale house with only superficial plaster damage on one
corner.  Of course there are far too many factors to say it was saved
because of being straw bale or not..


Then again, if you get a fire like just swept through Napa and Sonoma
Counties, all bets are off...



On Wed, Oct 25, 2017 at 1:38 PM, Graeme North <
<mailto:graeme at ecodesign.co.nz> graeme at ecodesign.co.nz> wrote:

This list is a fantastic resource for learned info and is greatly
appreciated I can tell you.


The fire thing is scary - there is no requirement in NZ for single dwellings
to have fire resistant ceiling materials, but we do need to have smoke
alarms near bedrooms and escape routes.

The really scary thing is that the fire people here advise that a dry house
with an open attic with light timber rafters or trusses for roof framing
will burn from end to end in 60 secs.

Goodness knows what adding an accelerant like straw (without a good clay
coating) might do. I would advise against it.


I would use straw coated with clay  - pretty much a LEM mix - if my
structure allowed it to happen easily and I was considering it for my own
house but the work required and extra weight decided against it 

and again recently I considered it on another design but the considerably
increased extra depth of the roof structure to accommodate it, along with
the extra cost, work, and weight, decided against it again so I went with
wool insulation in both cases.


I am also not convinced that cellulose/paper insulation with borax retains
it fire rating over time - I have seen examples of old (only a few years)
cellulose insulation that would not ignite when new,  ignite readily with a
match and it seems to keep burning quite happily.






On 26/10/2017, at 5:36 AM, Bruce EBNet < <mailto:bruce at ecobuildnetwork.org>
bruce at ecobuildnetwork.org> wrote:



Don’t you love it when someone else chimes into these discussions ahead of
you, and says everything you wanted to say?  


I sure do.  Thank you Derek and John;  what they said.


Bruce King

 <tel:%28415%29%20987-7271> (415) 987-7271

 <mailto:bruce at ecobuildnetwork.org> bruce at ecobuildnetwork.org





On Oct 25, 2017, at 7:56 AM, John Straube < <mailto:jfstraube at uwaterloo..ca>
jfstraube at uwaterloo.ca> wrote:


I would echo Derek’s concerns exactly. Loose fluffy straw burns very quickly
and you may as well say you lost the house.
Adding clay slips will increase the fire resistance to the point is
acceptable, as will dense bales with some sort of clay slip top, but once
you do that, you have a heavy and labor intensive roof insulation.
Cellulose with 20%+ borate treatment is inexpensive, gives good R-value, is
widely available, and is very good at fire resistance.

On Oct 25, 2017, at 10:00 AM, Derek Roff < <mailto:derek at unm.edu>
derek at unm.edu> wrote:

I have a different concern about using straw packed at low-densities in the
roof.  I think that the fire risk increase is much more of a problem than
the decrease in insulation value.  If you have seen flakes of straw or loose
straw burn, you will be aware that they are much more flammable than
standard bales.  Straw flakes are probably about half the density of a
building bale, and loose straw might cut the density in half again.  

Losing the roof in a fire usually means losing the whole house’s integrity
and value.  While enclosing the flakes or loose straw for the roof in
plywood, for example, would help somewhat with fire resistance, I recommend
against design choices that depend on a few things going right to avoid a
catastrophic failure in a fire.  

An additional consideration that has been mentioned here before, is that
while bales may be relatively inexpensive, placing them in the roof requires
increasing the size and number of the roof’s structural elements, which will
likely raise costs more than the amount saved by using bales instead of
other insulation materials in the roof.  Using lower density straw
diminishes that problem to some extent, but straw is still likely to be
significantly heavier than other kinds of roof insulation, for an equivalent
insulation value.  


Derek Roff
 <mailto:derek at unm.edu> derek at unm.edu

On Oct 25, 2017, at 4:34 AM, Rikki Nitzkin < <mailto:rikkinitzkin at gmail.com>
rikkinitzkin at gmail.com> wrote:


I don’t know if you all remember, but not long ago I asked about the MAXIMUM
density of a SB before it begins loosing thermal properties
 most people
agreed that we should not worry about a bale being too dense..

Now I ask about the opposite question: is there a minimum density?

The other day we were talking about using flakes of straw to insulate a
roof. One of the builders insisted that is was important that the insulation
cavity was filled with highly compressed straw, and another said that as
long as the cavity was properly filled (leaving no big holes for air to
circulate) that the density of the infill is not important, as the straw
(loose or dense, but enclosed in the insulation cavity) impedes the
circulation of air, and that is what insulates.

Can any of you technicians refer me to studies about insulation properties
and how they relate to density? or at least clarify my doubt: Is it
important to highly compact the insulation in the roof? and why
 so I can
explain it better.




Bill Christensen
 <http://sustainablesources.com/> http://SustainableSources.com
<http://linkedin.com/in/billc108> http://LinkedIn.com/in/billc108

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