Roof Truss

Where a rafter roof is built stick by stick on top of the house, a truss roof arrives largely finished. Each truss is a pre-engineered, triangulated assembly of smaller lumber pieces, connected with metal connector plates, built in a factory to an exact structural specification and delivered to the site ready to be lifted into place.

That internal web of diagonal and vertical members is what lets a truss span a wide distance without needing a load-bearing wall in the middle of the house to hold it up. The tradeoff is that the web fills much of the attic space, which is why truss-framed homes typically have a choppier, less usable attic than a rafter-framed one.

Because each truss is engineered and manufactured to a specific design, on-site changes are far more limited than with rafters. Cutting, notching, or removing a structural member of a truss without an engineer's sign-off can compromise the whole assembly, since the design depends on every member carrying its calculated share of the load.

Speed is the other side of that tradeoff. A crew can set a whole roof's worth of trusses in a day or two once they arrive on site, compared with the slower process of cutting and fitting rafters piece by piece, which is a large part of why trusses became the standard framing method on most new residential construction.

Knowing whether a roof is truss-framed or rafter-framed matters most before any attic conversion, skylight, or renovation that touches the framing. A truss roof's internal webbing is not something to modify casually; any change belongs in the hands of someone who understands what that specific truss design is carrying.