Before a roofing contractor ever pulls a single asphalt shingle off your house, the framing underneath determines what is actually possible during your roof…
Before a roofing contractor ever pulls a single asphalt shingle off your house, the framing underneath determines what is actually possible during your roof replacement. Calgary has two very different roof structure types sitting under its housing stock, and homeowners rarely think about which one they have until a roof inspection brings it up. That gap in knowledge causes confusion at quoting time, especially when a homeowner has seen a neighbor add skylights or convert a roofline and assumes the same work applies to their own home.
The framing type - rafters or trusses - affects pricing, timelines, what modifications a roofing contractor can safely make, and how the structure handles Calgary's snow loads and wind events. This matters more with every passing decade as older homes reach the point where a second or third roof replacement is due, and homeowners start asking for upgrades like metal roofing or added roof pitch that their original structure was never built to handle.
This article walks through the practical differences between rafter framing and pre-fabricated trusses, what each one allows or restricts during a roof replacement, and when a small structural fix during reroofing is normal versus when it signals a bigger problem.
Most Calgary bungalows and character homes built from the 1960s through the early 1980s were framed on site, rafter by rafter. A carpenter cut each board to length and nailed it in place at the ridge and the wall plate, one at a time. This method produced a solid, if labor-intensive, structure with an open attic space, since there is no webbing of interior support members running through the middle of the roof cavity.
Homes built from the 1980s onward almost universally use pre-fabricated roof trusses instead. These are engineered at a factory, built from smaller dimension lumber connected with metal plates, and delivered to the job site ready to lift into place. Trusses use a triangulated web design that distributes load efficiently across less material, which is part of why truss construction became the industry standard - it is faster to install and more predictable from an engineering standpoint.
The practical difference a homeowner notices:
Neither system is inherently better for a roof replacement. What matters is that a roofing contractor identify which one is under your shingles before quoting any structural changes, because the two respond very differently to modification.
Homeowners often request upgrades during a roof replacement that go beyond a straightforward tear-off and reinstall: steeper roof pitch, a different roofline profile, skylights, or mounts for solar panels. Whether any of that is possible depends heavily on the framing underneath.
Rafter-framed roofs offer more flexibility here because each rafter can, in some cases, be modified or sistered with additional framing to change the slope or add a dormer. It is still structural work that requires proper engineering, but the on-site, piece-by-piece nature of rafter construction makes localized changes more feasible.
Truss roofs are a different story. A roof truss is engineered as a complete unit - cutting, notching, or altering one truss member can compromise the whole assembly, since load paths are calculated for the truss as designed. Changing roof pitch on a truss home during a roof replacement usually means replacing entire truss sets, not modifying existing ones, which changes the project scope and budget substantially.
Both systems can typically accommodate skylights and solar panel mounts, but the approach differs:
This is one of the most common surprises homeowners run into: a skylight placement that looked simple on paper gets shifted a foot or two once the roofing contractor opens up the roof and sees where the trusses actually land.
A roof replacement quote assumes the structure underneath is sound. When it is not, the project changes from a straightforward reroofing job into something requiring structural assessment first. Homeowners should watch for a specific set of warning signs, particularly in older Calgary homes that have been through several decades of freeze-thaw cycles and snow load.
None of these signs should be addressed by simply installing new asphalt shingles over the existing structure. A roofing contractor who notices sagging or dips during a roof inspection needs to stop and evaluate the framing before quoting anything, because shingles - regardless of quality - cannot correct a structural problem. In cases involving noticeable sag or repeated drywall cracking, an engineer's assessment should happen before any reroofing work is scheduled, not as an afterthought once the tear-off has started.
Alberta climate conditions mean roof structures have to handle substantial and sometimes rapid snow accumulation, along with the weight of ice buildup during freeze-thaw cycles. Building codes account for this with specific snow load requirements based on location, and Calgary's requirements have been revised upward over the decades as engineering standards improved.
This creates a real consideration for older, rafter-framed homes being considered for upgraded roofing materials. A homeowner who wants to move from asphalt shingles to metal roofing, or to a heavier product like slate and tile, needs to know that these materials carry meaningfully more dead weight than standard shingles. A rafter system built in 1968 to the snow load standards of that era was not necessarily engineered with the assumption that it would one day carry metal roofing panels plus the accumulated snow load Calgary can produce in a heavy winter.
Before quoting a roof replacement involving a material upgrade on an older home, a roofing contractor should:
This is not a step that should be skipped to save time on a quote. A roof replacement is a long-term investment, and installing a heavier material on a structure that cannot support it creates a problem that will surface eventually, often after a heavy snowfall makes the decision for you.
The roof decking - the plywood or OSB sheathing fastened directly to the trusses or rafters - is what asphalt shingles, metal roofing, or any other material is actually attached to. It is also the layer most homeowners never think about until a roofing contractor points out a problem during tear-off.
A proper roof inspection before a roof replacement includes checking:
Skip sheathing is a common finding in older rafter-built Calgary homes, particularly those that originally had wood shake roofing. Asphalt shingles and modern underlayment generally require solid decking, so a roofing contractor working on one of these homes will often need to add plywood over the existing boards before installation can proceed. This adds cost and time to the project, but skipping it compromises the warranty and performance of the finished roof installation.
Decking condition is directly tied to storm damage history as well. A home that has experienced repeated ice damming or a roof leak that went unaddressed for a season is more likely to need decking replacement, not just new shingles, during its next roof replacement.
Some degree of structural attention during a roof replacement is routine and should not alarm homeowners. Other findings mean the project needs to pause for a proper engineering review.
Generally normal and affordable to address during reroofing:
Signals that call for an engineer before proceeding:
A roofing contractor with proper workmanship standards will tell a homeowner directly when a finding falls into the second category, rather than proceeding with a standard roof replacement and hoping the issue does not matter. This kind of honest assessment costs a homeowner more upfront - an engineer's report is an added expense - but it prevents a much larger problem down the line, particularly with Calgary weather putting recurring stress on the structure every winter.
Knowing whether your home is rafter-built or truss-built, and understanding what condition that structure is in, changes how a roof replacement should be planned and priced. Homeowners considering material upgrades, added skylights, or roofline changes should ask their roofing contractor directly which framing type their home has and what that means for the specific work requested - before finalizing a scope of work, not after the tear-off begins.
Contact Raico Roofing for a free quote.