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Re: GSBN:fire test -- your opinions?

Hello everyone - I am in support of Lorenzo's suggestion here (included below) about the need for fire separation at the roof/wall interface... The U.S. codes require a "nominal 2 inches" of wood at the boundary of the wall and roof cavities... Typically in conventional wood stick framing, this a U.S. 2 x 4 wood top-plate on the stud wall frame, which provides a nominal "one-hour" fire resistance at that point.

In our non-load-bearing straw-bale designs, we detail one layer of 5/8" (1.5 cm?) thick "Type-X" fire-resistive gypsum wall-board attached to the underside of the roof structure, prior to installing the bales/flakes up to the underside of the roof. In our load-bearing designs, we build the box-beam roof-bearing assembly up out of wood I-joists and OSB (oriented strand board) and put one layer of Type-X gypsum wall-board on the underside of the box-beam prior to putting it in place on top of the wall.

Each of these approaches also gives a nominal "one-hour" fire rating between roof and wall cavities. To increase this value, additional layers of Type-X can be added, gaining another "hour" of resistance per layer.

Using the gypsum wall-board in a non-load-bearing wall/roof system saves us the complexity (and potential for gaps) of putting stucco or plaster on top of the walls, and also protects the bottom edges of the framing, continuously. In a load-bearing wall, using the gypsum wall-board avoids the challenge of putting a viable layer of plaster on top of the wall prior to putting the roof-bearing assembly on. My concern here would be that the plaster/stucco coating cracks from the loading of the roof, leaving gaps for the fire to work its way through.

Tom Hahn
Principal Architect, Sol Source Architecture & Building Research
Licensed Builder, GreenMeans Ecological Construction Consultants
Scottsdale/Phoenix, Arizona, USA
<<a  target="_blank" href="mailto://THahn@ssiarch.com";>mailto://THahn@...>
<<a  target="_blank" href="http://www.ssiarch.com";>http://www.ssiarch.com</a>>

hello you all,

Thats  a very reallistic approach of factual situations.
In a house fire , even when flames start at a low positition (kitchen for
ex.) heat reaches always the upper surfaces, ceiling or roof. And
accumulates there, where a lot of wood in variable thickness is available.
This is how the whole roof begins to burn. In a strawbale wall, the weak
point would then be beam/roof plate as you sayed.
To make a good testing , leading to improve resistence to fire, I suggest
that top bales would be carefully covered with a good layer of earth,
possibly mixed with enough sand and chopped straw, in order to get a reall
"shield" under the beam/roof plate. The earth coat should ideally be 2 or 3
inches thick.
Tests coul d be done on a specially built "portion" of wall with its
connection to a piece of roofing structure. And this is good against water
too: when firemen will turn out the fire, water wont be running straight
into the walls.

Lorenzo Robl?s
Mazeuil, France  lorobles55@...

----- Original Message -----
From: "Rikki Nitzkin" rikkinitzkin@...
To: "'GSBN'" GSBN@...
Sent: Tuesday, May 02, 2006 10:35 AM
Subject: RE: GSBN:fire test -- your opinions?

HI all,

Has anyone thought about testing Clay-lime Plaster?  I have found that
adding a small amount of lime into a clay plaster makes it much more
resistant to water, and fire as well I imagine.

If I were to test lime I would do it without cement, supposing that if
anything the cement would make it more fire-proof and lime (and clay) is
plenty good enough with no cement.  Why is it that Americans are so in love
with cement (being an expat myself and Polish I feel free to make jokes
about both!)?

As for sticking to the walls, I should think that spraying limewash onto the
bales with pressure (so it penetrates) before plastering should allow the
plaster to stick just fine.  As for fire resistance, there is a Spanish
engineer who actually dips the bales in recently slaked lime before
building, and he has taken a blow torch to the bales and says they refuse to
burn...What would dipping just the inside/outside faces of the bales in a
lime-wash do?  Would that make the plaster stick more? Be more resistant to
fire?  Sort of like Tom Rijven&#xAB;s "French dip" but with lime instead of clay.

And sorry to drone on, but another builder I know mentioned that the fires
tend to start in the roof and work their way into the bales through the roof
beams/roof plate...so shouldn&#xAB;t we test how long it takes the fire to work
into the bales from above, not the sides?  I don&#xAB;t know how this could be
tested as I am no engineer.  Just thoughts...

Rikki Nitzkin
Aul?s, Lleida, Espa?a
(0034)657 33 51 62
www.casasdepaja.com (Red de Construcci?n con Balas de Paja)

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