10 Critical Details Often Missing From Building Plans

What happens if the roof pitch is missing or inconsistent?

One of the first details that can go missing on building plans is the roof pitch. This might be missing altogether, or it might appear differently depending on the view. A proper set of plans should include a plan view or overhead view that displays the pitch for each section of the roof. There should also be a cross-section that shows the same pitch. The problem we run into is when the plan view says 6/12 and the cross section says 4/12. This usually happens when boilerplate details are used by a designer or architect without checking for consistency. If the pitch is missing or contradictory, the truss designer has to make a call or an assumption, which slows the project down.

Why is heel height important on truss plans?

Another common missing detail is the height at the heel. Heel height determines how much space is available for insulation, where the gutter line will sit, and what type of fabrication is required at the truss end. A raised heel requires specific information about how high that heel will be. A standard heel requires clarification on the chord size, whether that will be a two-by-four or a two-by-six. Without that information, a truss designer is forced to assume or delay for confirmation.

How does soffit type affect truss design?

Plans often leave out or contradict the type of eave or overhang. An open soffit typically shows a bare rafter resting on the bottom chord of a standard heel. An enclosed soffit usually has a cantilever overhang, which extends the bottom chord outward to provide a place to attach soffit material. If one part of the plan shows an open soffit and another part shows an enclosed soffit, the truss designer has no way of knowing which one is correct without clarification.

Why does overhang length matter?

Overhang length tells the truss designer how far to extend the truss beyond the outside wall. Gutters sit at the end of that overhang, so this detail is critical. Saying “typical overhang” is not enough. Twelve to twenty-four inches is common, but shorter or longer lengths are also used. This length should be specified in both the cross-section and plan view. Overhang length also affects how different roof pitches meet. For example, if a 6/12 pitch meets an 8/12 pitch, they may need adjustments to align at the same eave line. This can be handled by shortening the overhang on the steeper pitch, raising the heel on the steeper pitch, or using a cantilever overhang.

What should be detailed at the blocking line?

Another frequently missing item is the blocking detail at the bearing line or eave of the truss. There are multiple options. A block might match the depth of the top chord and be tipped out perpendicular to the roof pitch, often with vent holes. Another option is a vertical block at the outside of the bearing, which transfers shear down into the wall with clips and nails. With a raised heel, sometimes a full-depth block is required to provide room for insulation. The important part is that this detail is specified so the project can be estimated and designed correctly.

Why do beam dimensions need to be clear?

Beams are another area where information is often missing. Plans may show the location of a column base but not the size or exact placement of the beam that sits on it. Sometimes dimensions are shown to the centerline of the beam, but the actual out-to-out or face-to-face dimensions are missing. Without this, truss designers cannot determine how trusses will bear on or interact with that beam. It is also important to note whether a beam sits above the bearing plate, which makes it a beam, or below the trusses, which makes it a header. The distinction changes how trusses connect and whether they need to be designed around interference.

How do point loads impact truss design?

Point loads from beams onto trusses are another missing detail we see. A roof or floor truss often carries a load from another part of the structure. For example, a girder truss might carry a second or third floor above it. The beam sitting on that girder imposes a concentrated load. That load must be calculated and provided by the engineer of record. Without it, the truss designer cannot properly account for the additional stress.

Why does truss to wall connection matter?

Trusses often tie into walls of different levels. For example, a lower roof truss might bear into the wall of an upper story. The plans should indicate whether the truss ties into a ledger, a hanger, or another connection method. This information is also provided by the engineer of record. Without it, the truss designer has no way to finalize the design.

How do parapet heights affect commercial buildings?

Parapet heights are often overlooked in commercial designs. Parapets act as screens that provide space for signage and hide rooftop mechanical equipment. To design trusses correctly, we need to know how high the parapet will extend from the bearing wall or from the bottom of the truss. Missing this detail can cause redesigns and project delays.

What happens when these details are missing?

When details like roof pitch, heel height, soffit type, overhang length, blocking, beam dimensions, point loads, truss to wall connections, and parapet heights are missing, it slows down the design process and often causes costly delays. A truss designer either has to make assumptions or stop and request clarification, both of which impact timing. Including these ten details in your building plans ensures smoother truss design, more accurate estimation, and on-time delivery of trusses to your job site.