Drilling Holes In Rafters

Magnettica

How big a deal is it to drill a few holes in the rafters? I've unfortuneatly done this more than a few times over the years to pull electrical wires. Usually on attic remodels or if they're getting finished. Now I read in this book on blueprint reading that drilling holes in rafters is a big no-no. So how big a deal is this?

mdshunk

If they're trusses, you MUST NOT drill holes in any part of the truss assembly without a sealed engineer's document stating the placement and the size of the hole you're permitted to drill.

The notching and boring rules for rafters are much different than the rules we've learned for joists and studs. Here's your code on rafters and trusses:


R802.7 Cutting and notching. Structural roof members shall
not be cut, bored or notched in excess of the limitations speci-
fied in this section.
R802.7.1 Sawn lumber. Notches in solid lumber joists, raf-
ters and beams shall not exceed one-sixth of the depth of the
member, shall not be longer than one-third of the depth of the
member and shall not be located in the middle one-third of
the span. Notches at the ends of the member shall not exceed
one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness
shall not be notched except at the ends of the members. The
diameter of the holes bored or cut into members shall not ex-
ceed one-third the depth of the member. Holes shall not be
closer than 2 inches (51mm)to the top or bottom of the member-
, or to any other hole located in the member. Where the
member is also notched, the hole shall not be closer than 2
inches (51 mm) to the notch.
Exception: Notches on cantilevered portions of rafters
are permitted provided the dimension of the remaining
portion of the rafter is not less than 4-inch nominal (102
mm) and the length of the cantilever does not exceed 24
inches (610 mm).
R802.7.2 Engineered wood products. Cuts, notches and
holes bored in laminated veneer lumber, glue-laminated
members or I-joists are not permitted unless the effect of
such penetrations are specifically considered in the design of
the member.
R802.10.4 Alterations to trusses. Truss members shall not
be cut, notched, drilled, spliced or otherwise altered in any
way without the approval of a registered design professional.
Alterations resulting in the addition of load (e.g., HVAC
equipment, water heater) that exceeds the design load for the
truss shall not be permitted without verification that the truss
is capable of supporting such additional loading.

mdshunk

For completeness sake, here's the rules on joists and studs:

R502.8Drilling and notching. Structural floor members shall
not be cut, bored or notched in excess of the limitations speci-
fied in this section. See Figure R502.8.
R502.8.1 Sawn lumber. Notches in solid lumber joists, raf-
ters and beams shall not exceed one-sixth of the depth of the
member, shall not be longer than one-third of the depth of the
member and shall not be located in the middle one-third of
the span. Notches at the ends of teres shall not exceed
one-fourth the depth of the member. The tension side of
members 4 inches (102 mm) or greater in nominal thickness
shall not be notched except at the ends of the members. The
diameter of holes bored or cut into member shall not exceed
one-third the depth of the member. Holes shall not be closer
than 2 inches (51 mm) to the top or into member the member, or
to any other hole located in the member.Where the member
is also notched, the hole shall not be closer than 2 inches (51
mm) to the notch.
R502.8.2 Engineered wood products. Cuts, notches and
holes bored in trusses, laminated veneer lumber, glue-laminated-
members or I-joists are not permitted unless the effects
of such penetrations are specifically considered in the design
of the member.
R602.6Drilling and notching—studs.Any stud in laminated members
wall or bearing partition may be cut or notched to a depth not
exceeding 25 percent of its width. Studs in non bearing parti-
tions may be notched to a depth not to exceed 40 percent of a
single stud width. Any stud may be bored or drilled, provided
that the diameter of the resulting hole is no greater than 40 per-
cent of the stud width, the edge of the hole is no closer than 5/8
inch (15.9 mm) to the edge of the stud, and the hole is not lo-
cated in the same section as a cut or notch. See Figures
R602.6(1) and R602.6(2).
Exceptions:
1. A stud may be bored to a diameter not exceeding 60
percent of its width, provided that such studs located
in exterior walls or bearing partitions are doubled and
that not more than two successive studs are bored.
2. Approved stud shoes may be used when installed in
accordance with the manufacturer’s recommenda-
tion.
R602.6.1 Drilling and notching of top plate.When piping
or ductwork is placed in or partly in an exterior wall or interior-
or load-bearing wall, necessitating cutting, drilling or notch-
ing of the top plate by more than 50 percent of its width, a
galvanized metal tie of not less than 0.054 inches thick
(1.37mm) (16ga) and 11/2 inches (38mm) wide shall be fas-
tened to each plate across and to each side of the opening
with not less than eight 16d nails at each side or equivalent.
See Figure R602.6.1.
Exception:When the entire side of the wall with the notch
or cut is covered by wood structural panel sheathing.

Magnettica

Thanks MD.

By the way, what Code is that from?

Looks like I'm ok considering I never drill a hole bigger than 3/4" in a 2x6 rafter.

Thanks for all the info.

mdshunk

The IRC. It's pretty much the standard resi code, with some modifications, all over the US now.

beaglejazz

I also need to drill some holes to pull wire and install sprinkler pipes in rafters that are supporting a cathedral ceiling. The rafters are 4 x 8, so does this mean that my holes can be 2.67" in diameter (1/3 of the 8" member depth)? Or, is 4" considered the member depth and my holes can therefore only be 1.33" in diameter?

HallisseyDesign

Lets do this the logical way. Don't be stupid you have worked in this business long enough to know when you are going to big with a notch or hole. It is not rock science but don't cut 3/4's of the rafter out and then hang a shelf from it too. You can run your sprinkler lines and electrical lines with no problems. Have fun in the attic were it is 140 degrees!