[SIZE="1"] associated with several importers and manufacturers.[/SIZE]
Very interesting stuff. Now here is my dumb limey question.
What qualifies a roof structure as "stick built". Most all new construction over here is using the kind of prefab trusses shown failing rapidly failing but older "1930's and before) tend to be in-situ constrcted , using bigger timbers but less intermediate bracing - is that what "stick built" means?
I could be wrong Ian, but I would think that "Stick Build" would be closer to "Timber Framed"
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
William Arthur Ward
Thanks Tod. Great information and timely.
I guess that part of the reason as well is that where land makes up a very large part of the cost of housing (comparatively) then the added cost of a more labour intensive building method becomes proportionally less of the total cost. I guess that in Tokyo you have a whole different set of pressures again!
In my line (architecture), stick built means framed in place with dimensional lumber - usually 2 by's. Trusses are often made with the same types of materials, but are pre-engineered for efficiency (strength vs. amount of material used), factory built, shipped to the site, and lifted into place. Engineered trusses consume less material and make sure you have members where you really need them. Also, the connections are engineered as well. They also install much faster than stick building a roof. My guess is they've found that in the case of a fire, the gusset plate connections fail quickly because they only bite into the first 1/2 inch of material (which burns off quite quickly). Nailed lap joints, on the other hand, use a heavier gage of metal (more fire resistant) than the gusset plates and penetrate much deeper into the material.
Typically, trusses are a better product. My neighborhood is about 100 years old - predominantly brick bearing wall homes with stick built floor plates and roofs. It predates engineered wood framing - a lot of guess work went into it - a lot of bad guess work. I have worked on many homes in my neighborhood and others of similar vintage and have yet to come across one that didn't have significant problems with the stick framing - generally at the stair openings and the roof framing. Renovation typically includes structural modification to address failure.
Timber framing is another animal altogether. This involves large solid wood members. Timber structure performs quite well in a fire if the connections are done right. What happens is the fire chars the outer inch or so of the members, which then insulate the core of the timber from the fire. It will still fail, but lasts much longer than other wood construction and even steel.
Thanks Paul - that's kinda what I guessed. I was interested to see in the video that the pint of inital failure appeared to be exactly where your explanation would predict. The diagonal bracing between the horizontal bearer and the angled bearer can be seen making a clean seperation rather than any of the timbers burning through.
We had a fire at home a couple of years ago and the forensics guy from the insurance company timed the fire by how much of the adjacent skirting board was charred. I seem to recall he worked on 1mm of char per minute of burn and his timing and the other known facts about the fire agreed. Interesting stuff this!
Neat video - does make sense that the smaller framing pieces using light gauge metal fastening would go first in a fire. I noticed the same failure point that Paul did. I wish they had a shot of the plates afterwards to see if the cleats or the wood failed.
Back in the late '90's I was at Batamat in Paris (really big building/construction trade show) and trusses were making a big splash. Not to say they hadn't been used previously, but for some reason there were a number of companies featuring them and their benefits. Batamat was a really cool experience - got to go twice. They've got everything related to building construction there - usually in full scale!
Good information, Paul. Do you know why they don't "nail" the gusset plates in more than 1/2"? I expect those are applied by machine. Seems the machine could drive the plates in with fingers longer than 1/2". It would just mean stamping the plates out with longer fingers.
Go into the world and do well. But more importantly, go into the world and do good.