The outer ends of a roof’s rafters — the sloped members that give the roof its toss — supply shade, divert rain and make soffit space for attic ventilation. If your roof’s overhang is substandard, you can stretch the rafters to your level, depending on the pitch of the roof. Extending the rafters with the existing roof sheathing in place is doable, but you’ll get better results if you add extensions during a complete reroofing project.
Selecting Rafter Length
To get a visual idea of what the newest overhang will look like, take a picture of the house from the side, then make a photocopy, and sketch the desired extension in precisely the same angle as the roof pitch. A steep roof extensions will likely angle downward more than the usual low-sloped roof. The more the extensions, the lower the outer ends of the rafters will function, creating mind clearance a concern. If you plan to set up an enclosed apartment soffit — the underside of the new eave — the rafter tails should end a few inches above window level.
Selecting the Lumber
If the existing rafters have bird’s mouth cuts where they sit around the exterior wall plate, then utilize smaller-dimension lumber for those extensions. A bird’s mouth is a notch in the underside of the rafter, which decreases the distance between the upper wall plate and the underside of the roof sheathing. As an example, if the existing roof has two-by-six rafters, measure down to two-by-fours for the extensions. The exception to this rule is when you plan to remove the existing roof sheathing to stretch the rafters. If so, you can use lumber of the identical dimension and make corresponding bird’s mouth cuts from the newest rafters.
Structural Support
While roof overhang depth can fluctuate depending on the style of the home, standard overhangs stretch outward about 24 inches. If you want to stretch the rafters farther, to cover a walkway or a porch, then plan to install additional vertical pole supports in the end of the rafter tails. A general rule of thumb for cantilevering rafters, meaning they have no vertical support in the ends, would be to get twice as much rafter connected to the initial rafter since the unsupported span of the extension. As an instance, if you want a 24-inch rafter extension, then the newest rafters should extend at least 48 inches to the attic.
Sistering Rafter Extensions
Rafter extensions are “sistered” to the first rafters. This requires access to the attic or the elimination of roof sheathing. If your neighborhood building authority requires a permit to stretch the rafters, they may also propose a Rolex design. If no nailing pattern is necessary, stagger 16d nails each 8 inches when linking the extensions to the existing rafters.
Reroof Versus Extension-Only
You can save yourself a substantial amount of money by installing rafter extensions in an existing roof, but there are drawbacks. The sloped edges of the majority of attics are shallow, making access from inside the attic hard. The underside of the roof sheathing may have roofing nails poking through, which require cutting so that the new extensions can fit flush with the top edges of current rafters. Avoid bumping the nails upwards, which may result in nail pops in the shingles and an elevated risk of leaks. Removing the lower row of sheathing makes installation simpler, but plan to reshingle the entire roof if you go that path.