Do rainscreen details make the home less fire resistant?

Eric, Here is a link to an earlier discussion on the subject:
http://www.greenbuildingadvisor.com/community/forum/general-questions/19...

wow, at first i wanted to say thanks, but after seeing what that link turned into, i'm not sure!

here is a different idea/question: What are other's thoughts on using a bit of fiberglass insulation along the bottom and top of the rain screen? my thinking is thus: fiberglass is not combustible yet it allows air-flow. will it stop flames and embers? if so then it seams like it might be a better product then using a "bug screen" at top and bottom of the rain screen. thoughts? how much would it take to stop a flame?

I don't think fiberglass would be a good choice. It doesn't do well when it gets wet, as it may well at the bottom the cavity. My first though would be Cor-A-Vent but I don't know how fire resistant it is. What about something along the lines of stainless steel wool?

would fiberglass dry slow? good questions...this is what I was hoping to find...solutions to an interesting problem...unlike the other discussion which focused more on what a rain screen is and whether or not it is needed. i'll look into how fire resistant Cor-A-Vent is.

Cor-A-Vent is only "heat resistant" which i think means it won't melt in the sun.

Rock wool has a much higher melting point than fiberglass, and wicks less moisture. Using rigid rock wool panels with a minimal rainscreen gap (2-3mm) as a capillary break would be fairly moisture-purging and fire-resistant. (It would be nice to see test data on that sort of assembly first though.) Using strips of lower-density rock wool in place of Cor-a-Vent would prevent the ember penetration issue, though it will slow the drying convection currents.

That idea sounds promising...seems like there would be more testing with these ideas already out there. How do rigid rock wool panels compare structurally to plywood?

Mineral fibres can act as a wick, as a catalyst. Turning a small thermal load into an intensive heat. Similar to a gas lamp/light.

Contact a civil engineer about chimney effects, about fire safety.

Here a European experience:

http://www.aftonbladet.se/webbtv/nyheter/inrikes/article14468019.ab

http://www.dn.se/nyheter/sverige/kraftig-brand-i-mjolby

good input, thank you. so is there truly no safe rain screen developed yet?

Well, there is.

But not for the design you have in mind:

"While the home may be sided with non-flammable siding, there is a nice air gap and plenty of oxygen flow behind this siding with the flammable plywood behind it. "

The problem with rain screens is the gap, the 'chimney' and the effect it has during a fire.
No one would build a chimney from non-fire proof materials.

The plywood in your design would feed the fire. No matter how safe the actual screening is, such a wall is a fire risk. Timber burns.
The big disadvantage during a fire (behind a screen) is that it is difficult to tackle, the exact point of combustion hard to determine and the rain screen doing what it is designed for: keeping water away.

I would think that a good compromise would be, as Dana suggests, a minimal rainscreen gap, enough for venting/drying purposes, but not enough to encourage rapid inflow of hot combustion products. Metal mesh covering for the openings, perhaps wrapped around something like Coravent, would act as a flame arrestor. Protection against combustion due to a multitude of small glowing embers blown up against the house is one thing. Protection against envelopment of the house by severe high temperature forest fire like conditions is another.

Hein, what rain screen design do you prefer?

" Hein, what rain screen design do you prefer? "

One which fullfills it's purpose.

...and does not increase fire hazard risk? do you have solutions? anyone else?