fire retardant wood trusses

[shepherd]

I am in the schematic design stage of a small commercial project, and I need a non-combustible roof framing system. I am looking at either fire retardant wood trusses or light gage metal trusses. Does anyone have any experience with relative cost differences between these two system? I've called a few local wood truss suppliers, but none provide the fire treatment. (Perhaps this tells me light gage is the way to go). I'm not too familiar with the wood truss industry, but could the manufacturer not purchase lumber already fire treated, and construct the trusses as usual? Is anyone aware of corrosion issues of plated wood trusses and the fire treatment? Any insight would be appreciated.

 

[planitarch]

I have not heard of a "non-combustible" wood product. There is fire treated plywood. Are you sure you need "non-combustible," and not just a minimum fire resistance rating?

 

[concretemasonry]

You may want to consider the insurance rates for the owner depending on the building contents.

Some insurance companies have lower contents rates for wood trusses than metal trusses because of the failure mode. As I understand it, a wood failure is more predictable (loss or crossection) than the sudden steel collapse due to temperature. - Allows more predictable fire fighting without danger and more could be saved.

I did not believe it at first, but I was shown insurance quotes by an owner (unsprinkled building).

Dick

 

[COEngineeer]

It sounds like your only option would be metal trusses.

 

[shepherd]

Thanks guys

Rated roof is not required in our case. IBC 03 Table 601 footnote c allows fire retardant wood roof trusses and girders in Type I and II (non-combustible), although maybe it is not correct terminology to say it is non-combustible. Just got the preliminary cost estimate, it appears the firetreatment added about $4/sq. ft.. I've got no frame of reference to know if that is reasonable. I can't imagine switching from wood to light gage would be anywhere near that. Good point about insurance rates, I'll bring that to the architects attention as well.

 

[DonPhillips]

Last year, I would saw the metal framing would be more competitive but right now, lumber prices continue to fall, per the lastest ENR. You may want to look at the costs a little closer since metal may not be cheaper at the moment.

Glad to see you saw that in the footnotes. If it is a small commercial building, I wonder why you would want to classify the building as I or II unless the architect has already made that decision, perhaps for insurance purposes.

Don Phillips

http://worthingtonengineering.com

 

[tdsull]

Check quickly with a few truss manufacturers. With fire treated wood trusses you need to use stainless steel connector plates and the money and aggravation goes way up trying to find a decent manufacturer. I have had excellent luck with a light gauge steel truss company out of Detroit, they ship anywhere.

 

[Loui1]

I've used fire retardant wood trusses before and they generate additional liability issues, and are not cost effective unless you need them for a small portion of a large roof. The wood becomes brittle from the fire treatment and is easily damaged during construction. Then you have the whole corrosion issue to contend with. All the connectors likely will need to be stainle$$.

If you're talking about an entire roof area, I'd go lightgage. I'd recommend asking the WTCA. Do a google search for them.. i think the website is something like

http://www.sbcindustry.com

 

[SperlingPE]

Comparing typical 4x2 bottom chord trusses @ 2'-0" o.c. with metal trusses at 2'-0" o.c. - WOOD is less expensive

Add to wood cost - fire treating, special connectors, extra shipping if fire treatment is not local.

With the added costs, consider using metal trusses at a greater spacing (4'-0" or 5'-0" o.c.) with a metal deck instead of plywood. Metal trusses might get more competitive.