Anatomy Of A Roof Beam:
The Need for a Common Language
"You keep using that word. I do not think it means what you think it means.” -- The Princess Bride
If you are reading this, chances are you already have a pretty good idea of what a roof beam is. The term roof beam is often used informally to identify a variety of roof frame parts: ridge boards, rafters, headers, joists and so on. In some houses, these same parts are actually cut from lengths of beam stock—muddying the issue even further. But, if you were to sift through all of the usual definitions for “roof beam” in a wood-framed structure, the description would probably shake out to be something like this: a typically squared length of timber that spans an area of a building—horizontally or at a slope—and is usually intended to be a primary load-bearing part of the roof framing. And, as it turns out, this pretty much describes the roof beams discussed throughout this article. I will be focusing on the "roof beam."
Roof beam: a typically squared length of timber that spans an area of building usually intended to be a primary load-bearing part of the roof framing.
Roof beam is often used colloquially to refer to any beam associated with a roof:
Joists or rafters
ROOF BEAM ANATOMY
The parts of a roof beam (starting from the outermost end) are
Overhang - the portion that "overhangs" beyond the exterior wall
Projection - a sub-portion of the overhang, the length that "projects" beyond the roof edge
Span - the portion that "spans" between walls (or posts) within interior spaces (these are often exposed in post and beam construction, such as mid-century modern homes)
We can further break down the roof beam into two categories:
Through Beam - a single length of beam that goes "through" the entire space
Spliced Beam - a beam with the illusion of being a single length but is "spliced" in the interior of a wall (or above a post)
A Closer Look
The outward ends of roof beams can often be seen jutting past a supporting exterior wall or post, then over to (and often beyond) the roof-edge framing that they carry. This is referred to as an overhanging roof beam configuration, and the portion of the beam extending beyond its support is called a roof beam overhang or a roof beam tail. Incidentally, the overhanging roof-assembly itself is apparently so lofty that it’s been bestowed with two names: the one comprising the (usually) lower horizontal part of a roof is called an eave, and the one along the gable end of a roof is called the verge.
The part of a roof beam that extends out past the roof-edge framing is referred to as its projection. Roof beam projections are usually (and conspicuously) the only part of a structure not protected by the roof covering. This exposure leaves them highly vulnerable to opportunistic wood-decay fungi, i.e., those that exploit weather-related dampness to get a foothold. Without intervention, the resulting wood rot can spread well back into roof-protected spaces—and even into the home’s interior. To avoid these worst-case scenarios, rot-damaged roof beams must be repaired.
The definition of anatomy - a separating or dividing into parts for detailed examination (Webster's) fits here well. When talking with a contractor about your roof beams, especially about dry rot, you'll want to be able to use the names for the parts of a roof beam. Moreover, it's important for any homeowner to have a basic understanding of a roof beam to be able to assess any repair or restoration being offered. Not all roof beams are created the same, even though they might appear to be so.
The Roof Beam Overhang, A Closeup
If we were to isolate just the overhang portion of a roof beam, we can further breakdown the nomenclature.
Like many terms in the building trades, these terms and definitions tend to be applied differently by different trades in different circumstances. Here's how I, a roof beam specialist, define them:
Edge - the narrow surfaces found at the top and bottom of the roof beam.
Face - the portion that has the greatest surface area found on the left and right "side."
End - the surface sporting the tree rings and end grain found at either "end" of a beam. On the overhang, only the exterior end is exposed and is particularly vulnerable to moisture damage and dry rot.
Point - where three surfaces (planes) come together on the ends.
Corner - where two surfaces (planes) come together.
The majority of visible aging and/or decay begins in the overhang. Therefore this is the area where a homeowner will begin to notice issues arising. Having ready access to definitions and nomenclature will hopefully help you navigate working with anyone in the building trades to maintain, repair or restore your roof beams.
The wood in the above photo is what the typical roof beam in a Mid-century Modern home, like what Carter Sparks designed for The Streng brothers, would look like when the home was being built. This sample was cut from slow-grown, old-growth lumber. You can see this by the compact growth rings and its beautiful appearance. Old-growth lumber’s superior strength, stability and decay resistance are also widely attributed to such tight ring patterns. If your roof beams no longer resemble this original appearance, look for signs of dry rot.
Why The Anatomy and Names Matter
If you are in need of maintenance, repair or full restoration of your roof beams, a licensed contractor will give you a bid for the work to be performed. The bid should be in writing and clearly define what work will be performed. If it doesn't, you are in peril of not getting what you think you are paying for. Any contract you sign should either have exacting language or include a bid that does. If you don't have a clear understanding of the language being used, it's easy to end up without what you need, including your hard-earned cash.
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* parts of the above are excerpted from a roof beam dry rot repair book I'm currently writing