Raising Flat Ceiling to New Heights

In home renovations, few projects can change the feel of a space like vaulting a ceiling. I have worked on dozens of homes throughout the U.S. involving flat bottom trusses, and many times these homes, such as the home I recently inspected in Golden, CO, were built in the 1970s. My goal was to determine if we could vault the existing trusses throughout the entire second floor of the home, and if so, what ceiling pitch was going to be practical. This change could dramatically open up the space and enhance its visual appeal.

In this post, I will share insights into evaluating the trusses, making modifications, and addressing the engineering challenges that come with such a significant alteration.

Inspecting the Trusses

The first step was to inspect the attic and gather crucial data about the existing roof trusses. After a quick mental note of the exterior roofing material (this had an asphalt shingle roof), I crawled into the confined attic space to measure the geometry of the trusses, including roof pitch, metal connector plate sizes and locations, span between supports, panel point locations, splice locations, spacing betweeen trusses, lumber size/species/grade, and any lateral bracing attached to the trusses.

As I make my way through the attic, I take a plenty of photos and visually assess the condition of the trusses. I want to document any lumber or plate damages or previous modifications, such as an attic fan install or previous truss repairs. In this case, there were no previous modifications or damages visible.

Modeling New Truss Configurations

After collecting and organizing my field data, I collaborate with a truss manufacturer who uses truss design software to recreate the truss using the information I provide, then models the vaulted truss configuration. Using various design iterations for modifying the vault pitch for this truss, I work with the truss designer to determine how to make the new proposed truss configuration structurally feasible.

Generally, the pitch of a ceiling vault can be changed to approximately half that of the roof pitch. For instance, if the roof pitch is 6/12, a ceiling vault pitch of 3/12 is likely achievable. However, this is merely a guideline. When the roof pitch is shallower, such as 4/12, the design forces in the truss are greater from the start, making it more challenging to create a ceiling vault.  This challenge is further complicated by heavier roof loads such as high design snow load or roof tiles. The location of the vault may also affect the new design because the vault peak does not have to coincide with the roof peak.

It's also important to take into account the current design standards for a particular home. When this home was originally built, the building code was significantly different. Over the years, codes have changed and new code requirements haveemerged, requiring design updates that must be considered with this truss modification. For example, snow and wind loads were different when the home was first built, lumber and connector plate values have changed, and even the structural methods used to calculate the truss designs have been updated over the years.

Creating a Repair Plan

With the new truss configuration modeled successfully, I draft a recreation of the original truss using CAD and show the new members added to create the desired vault configuration. I typically plan on using 3/4" thick oriented strand board (OSB) sheathing to create gusset plates on each side of the truss, at the intersections of the original truss and the newly added members, and connect them with specific nails or screws. I apply engineering mechanics and my experience to establish the necessary geometry for the gussets and determine the best type, quantity, and arrangement of fasteners, whether they are nails, screws, or bolts.

Once I have detailed the graphical depiction of the new truss profile with gussets appropriately designed, I provide clear, step-by-step instructions for constructing the depicted modifications.

The Importance of Gable End Wall Assessment

An important yet frequently neglected aspect of vaulting ceilings is ensuring the structural integrity of the gable end wall. Elevating the ceiling throughout the home removes the original flat ceiling diaphragm, which formerly restrained the gable end truss (horizontally) at the wall top plate. This may result in a hinge point that could cause cracks under wind loading.

To maintain lateral stability, I considered one or more of the following elements:

• Provide additional mechanical connections between the end wall and gable truss interface.

• Add studs in the wall to create a "balloon-framed" end wall.

• Integrate some type of lateral bracing into the end wall.

  
  

These elements need to be evaluated on a case-by-case basis. For this particular case, I met with the building contractor, and we decided that the best course of action was to add balloon-framed studs to the wall (cutting through the original top plate) and attach the studs to each gable end stud in the truss, which were typically spaced at 24 inches on center. I detailed this connection and wrote a step-by-step procedure so it was clear how the wall modification was going to be constructed. This eliminated the potential hinge point, making the exterior wall better suited to withstand perpendicular wind loads.

Final Thoughts

Raising a flat ceiling to new heights offers not only a visual upgrade but will likely also increase the home's value. If you’re dreaming of more headroom and openness, but your home has flat-bottomed trusses, don’t risk guesswork.

Structural modifications to trusses require professional analysis and a plan that’s field-ready and safe. Contact CENSPACE for expert help with truss modifications, vaulted ceilings, and structural design.