Valley Framing: Exterior vs. Interior
As component design professionals, we are all familiar with the concept of valley trusses, right? Or are we…
We are used to seeing valley trusses form some type of framing above the top chord of common trusses. But what about the valley that is below the bottom chord of trusses? In this article, we will explore a bit of a different mindset regarding the “valley” application.
Many truss designers would ask themselves: “Why or how would I use trusses to build in a valley on the inside of a building?”
As we can see here, there are multiple parallel chord conditions all terminating at the same point. This creates an interior valley condition.
As we can see below, when all is said and done, this makes a very nice ceiling condition from the interior. Very appealing from the inside of the structure.
Let’s take a look at some of the more common areas of concern regarding valley trusses:
Conventional Framing Cons
- Often times, live valleys are framed with structural ridge beams that can be very large, expensive, and difficult to set.
- Finding ample quantities of lengthy, wide lumber that is true can be problematic, costly, and detrimental to forests.
- Span charts are more conservative than they have been in the past due to lumber value changes, so “wider” lumber is required to span the same distance.
- Connecting valley rafters and perpendicular ridge beams all at the same location often times requires special engineering and connector fabrication.
- Using trusses over several common connections can be done easily with connectors that are stocked at most truss plants.
- When engineers look at in an uplift situation in a hand framed system that was framed “in compression” it has sort of a “starburst point” that can be the catalyst to catastrophic failure in a large wind event.
Carpenter Cop outs
- Use girders with layouts marked on the bottom chord to show where the trusses should be set. (This is critical to reducing call backs and crane time). Drop the top chords and raise the bottom chords so the blocking can be done with purlins.
- Framing crews that lack the skill set necessary to frame a live valley can set trusses quickly and easily.
- In most cases when a walk through valley is framed with trusses all load bearing points can be on the exterior walls
Cost Cash In
- Material costs are lower and less labor time is required when interior valleys are framed with trusses.
- Interior valleys framed with trusses can be done with smaller connectors and no special engineering.
- Obviously, when you use trusses rather than a large portion of the building being framed on site you sell more trusses.
- Some companies will even include purlin frame “overlay” gables on a bottom chord valley condition like they would on a top chord condition than has been dropped for purlins.
Please use the comments section below to let us know why or how you use trusses to frame a valley on the inside of the building.
Rick Walker – Project Manager
Gould Design, Inc.