ECN Forum Forums Photo Discussion Forums Photos for General Discussion I-Joist Drilling

Always use a sheet that comes from the manufacturer of your specific joist

I saw these joists being made on 'This Old House' via satellite, when Norm (or Steve?) visited a manufacturer. The glue used was 'Recorcinol', which is a catalyst wood glue, ( ie sets by a chemical reaction ) so it won't melt in a fire, just chars.
Rest easy,
Alan

The glue might not melt in a fire, but the web of the joist sure does...rather quickly at that. The only drawback to these is just how quickly they fail in a fire.

Ryan, I will have to beg to differ as to the performance of these joists, and other wood products, in fires.

People see wood, and they think of a blazing campfire. The fats is, as demonstrated daily in ASTM fire tests of various assemblies, wood generally chars, slowly burning through and gradually losing strength. Wood also is a poor heat conductor, so the heat of the fire is not transferred nearly as quickly through the material as it would be with metal.
The bigest surprise is that, where the strengths of the materials are comparable, and especially in a "load bearing" application, wood constructions have a performance in these fire tests virtually identical to steel.
(Not to write steel off....steel can be much, much stronger, allowing for grearer spans, etc.)

I have seen this with all forms of wood products, be they timber, plywood, or engineered.

Interesting...the fire jobs that I have had to inspect the joists failed much quicker than the other wood elements.

Structural steel beams, columns etc. have to be protected by a fire retarding casing, or by 'intumescent' paint, which foams into a carbon-rich protective shell on burning.
This is because at around 660F the iron molecules re-arrange into a "different metal", similar to the structure of aluminium or copper. (BCC molecular lattice changes to an FCC lattice). At around this temperature, though steel actually increases in strength, it becomes very brittle and shock sensitive- known as 'blue-brittleness' due to that being the color of the metal (often seen in tempered tools). Higher than 660F, the strength falls away fast, and by 1550F will rupture at less than 2 tons/sq in. Being a good heat conductor, it will rapidly attain the above temperatures in a fire if not sheathed. If you look at photos of burned buildings, you often see the steelwork has sagged or collapsed. The point of sheathing is to retain some structural integrity long enough to give the occupants of a burning building time to get out. Eventually, practically all common building materials fail in a fire, but wood in thick sections chars slowly, even if directly exposed. I'm not quite so sure about those thin webs, they sure won't give 30 minutes grace once alight, and are a critical structural element of the beams. But, they are usually sheathed themselves by the flooring and ceiling plaster-board (sheet-rock?)- which by the way is a good fire protecting material.
Alan

Guys from my experience as a Fire Officer,
I'd say that given a high enough temperature, anything will burn.
Concrete will burn and that is one of the first things that we look for in an Arson investigation, where an accelerant has been used.
Every material known to Man has an Ignition temperature.

quote
"Every material known to man has an Inition temperature."

Except French barbeque charcoal.

Alan.

I would sooner have a lam beam or tue wood then a prefab truss!!! the nail plates pop off under heat and the truss literally falls apart!!!! Kills alot of Firefighters......