2008 February Lumber Talk.com: Professional-Level information and how-to-build articles for wood, timber, and lumber professionals and users. 2008 February » Lumber Talk

In 50 Ways Firefighters Die Retired Deputy Chief FDNY Vincent Dunn lists timber trusses as a major cause of death among firefighters because of their weight and the fact that when they collapse, they often allow walls to fall as well.

Truss construction is a dangerous roof or floor design when exposed by fire. The large surface-to-mass
ratio of the truss and many small, interconnecting members makes it vulnerable to early collapse.
Wood truss roof collapses have killed 28 firefighters over the past three decades. Truss roofs kill
firefighters working below the truss, on top of the truss, and outside the truss roof building. When a
timber truss roof collapses, it can cause the collapse of an outside bearing wall.

28 firefighter deaths in the last 30 years are attributable to truss collapses. It seems to me this problem can be approached from at least two sides. First, designers might be able to consider fire retardant materials that will decrease the chances of truss failures due to fire. Second, if firefighters are somehow made aware that they will be working in or around a structure that has timber trusses, they may be able to avoid them in case they do fail. I have absolutely no idea how to deal with the the second approach. Posting signs with the design qualities of the burning building does not seem feasible and there is not time to look up the structural design elements of a building before running into it. Looks like this is might be a design issue.

By Chris | February 15, 2008 - 5:15 pm - Posted in Specs & Data, Treated Wood

Basic lumber dimensions are not as basic to many people as you might think they are. I get asked about actual lumber dimensions on a regular basis. Most people know that a 2×4 is actually 1.5″x3.5″ but the measurements get a little hazy with the large boards like 2×8’s and 2×12’s.

Lumber Dimensions

Here is a simple chart to clear up the confusion about 1x, 2x, and 4x nominal lumber dimensions versus actual lumber dimensions. The chart also includes the equivalent metric lumber dimensions. This chart applies to treated and untreated pine construction grade lumber.

lumber dimensions chart

This chart applies to the lumber dimensions of “quarter” measurements. The nominal dimensions are said as “five-quarter by four” or “six-quarter by six” etc. These are not all that common but you can usually find “five-quarter” decking whose actual dimension is 1″x5.5″.

five quarter lumber dimensions

Timber Dimensions

Lumber cut 5 inches or thicker is generally classified as timbers. Timbers are usually cut “rough” to actual dimensions. In other words, what you see is what you get. A 6×6 is 6″x6″, a 10×10 is 10″x10″ and so forth.

Post Dimensions

Round stock dimensions can get a little complicated but we will keep it simple here. A thorough discussion including large poles requires getting into the differences between poles and pilings and classes of utility poles and what you are using them for and it goes on and on so…so for the purpose of this article, I will stick to small posts.

Small posts are usually measured by the top size (the little end). So, if you want a 4″ top x 8′ long fence post, you would ask for a “four inch – eight” post. The line between posts and poles is a fuzzy one but after about ten or twelve feet long, whatever it is that you want usually become a pole. If you are using it in water to support a structure it is probably a piling, which is used upside down and measured by the butt (the big end)… and see how it easy it is to get complicated when discussing poles?

If you want square posts make sure you are clear about that when you ask for “posts”.

Lumber Dimensions Questions?

If you have any questions about lumber dimensions, let me know with a comment. I am always happy to help.