Roof Vent Retrofit from the Outside In
Reroofing is the perfect time to lift the hood and make short work of an otherwise awkward venting job.
Synopsis: This article details the process of venting, air-sealing, and insulating the area along exterior walls where the rafters meet the top plate. By combining the work with roofing replacement, most of the job can be done from outside. A series of step-by-step photographs shows the process of removing the sheathing and propping up the roof; building, adding, and fastening baffles; and reinstalling the sheathing.
The roofs in a lot of older houses with unconditioned attics aren’t properly vented, and that can be a problem in many climates. Ventilation helps keep the roof deck dry, and, combined with air-sealing and insulation, helps prevent ice dams when it’s cold.
The most challenging part of venting, air-sealing, and insulating an attic in an old house is dealing with the area along the exterior walls where the rafters meet the top plate. The space between the rafters and ceiling joists is cramped, making it a difficult spot in which to maneuver and work. This is especially the case on lower-slope roofs (less than 6-pitch), where all of the action takes place in a tight spot just out of reach.
One solution is to combine the attic insulation and ventilation upgrade work with roofing replacement. This way, instead of working inside the attic, most of the work can be done from outside.
Pop the hood
After stripping off the old roofing, we use a modified framing nailer to free up the bottom course of roof sheathing and expose the top plate, rafters, ceiling joists, and existing insulation.
The conventional way to remove roof sheathing is to yank the nails using a cat’s-paw-style puller, but I find it faster and less damaging to just punch the nails through the sheathing. There are tools made specifically to remove nails or drive them through lumber, but we just use an old framing nailer that I modified by grinding 3⁄8 in. from the end of the driver nose (the business end of the nailer). With the nose ground down, the nail driver projects about 5⁄8 in. from the nose when you pull the trigger, which is more than enough to punch nails through the 1⁄2- in. roof sheathing.
After driving the nails through the sheathing, we lift the panels and either slide the loose sheets up the roof or tilt them up like the hood of a car, bracing them with scrap wood in order to provide some shade to work under.
It’s up to you whether it makes sense to work in smaller or larger sections. For efficiency on this project, we kept an eye on the weather and opened long sections of roof at a time so we could production-build the vent baffles.
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