Why Roof Trusses Are More Popular Than Rafters
Roof framing has undergone a quiet revolution over the past half century. Trusses are gradually replacing the conventional rafters, to the point that nowadays more than 80 percent of new residential construction makes use of trusses to support the roof. Why has this change occurred and what are the
Posted — UpdatedAlthough the actual installation process is slower than for trusses, rafters require a shorter lead time to prepare, so if you are in a hurry, rafters will be the quicker way to go overall. They are also more suitable for remote locations, where transporting a pre-assembled truss system to the site would be overly complicated, or for small roofs, when going through the process of site-specific truss design would not be cost-effective.
Trusses are lightweight engineered units consisting of top and bottom chords supported by a webbing of lumber in a triangle shape. Because they are pre-assembled to your building specs offsite, often using automation such as computer-driven saws, they are much faster and more economical to install than rafters. Although they make use of smaller (and therefore cheaper) pieces of lumber linked with tooth plate connectors, trusses are very strong and stable, capable of spanning great distances of as much as 60 feet. This reduces the need for interior load-bearing walls and allows for a more open floor plan, in tune with today's trends, on the stories below.
However, truss systems do come with some distinct disadvantages. The pre-built truss system is heavy to transport and lift into place. You are likely to need an 18-wheeler and a crane -- together with adequate road access -- for the job.
The webbing which supports the chords tends to impinge on the space directly underneath, a pronounced disadvantage if you would like to convert your attic or the area above the garage into usable living space. Scissor trusses allow for somewhat of a cathedral ceiling, unlike other styles, for example, cambered trusses.
Once a truss system has been installed, it will be difficult and even dangerous to try to modify it. Cutting any part of the webbing or even drilling a hole to accommodate electric wiring can undermine your truss roof's integrity. You'll need to consult a professional building engineer if you must make alterations.