What to check before cutting service holes in framing
Before cutting a service hole through cabin framing, mark the proposed route on the structural set, identify the exact member and product, and check the rule that applies to that member. For solid-sawn joists, rafters and studs, consult the building code adopted for the project. Engineered products have product-specific rules. If the drawings, adopted code and applicable product instructions do not clearly cover the proposed opening, pause and ask the designer or manufacturer for a decision before drilling.
- APA says field holes and notches reduce engineered wood members’ published design values. Holes outside published tables may be acceptable after analysis of hole size, span, spacing and loading. [3]
- APA lists separate technical guidance for glulam, laminated veneer lumber and I-joists; use guidance for the identified product rather than transferring a rule between products. [3]
- The 2021 Wood Handbook provides technical background on wood properties and points readers to manufacturer and trade association information for current product design details. [2]
- A 2003 study tested holes drilled at midspan in nominal 4-by-8-inch Douglas-fir lumber and reported that hole location may be as important as hole size. [4]
Start with the structural set
Trace the route on the current structural drawings before laying it out on the framing. Identify which joists, studs, beams or other members it crosses, and compare the route with the floor, wall and roof framing plans and details. The Canada Mortgage and Housing Corporation’s Canadian wood-frame construction manual includes framing details for plumbing, heating and wiring. Its catalogue record dates the publication to 1997, so use it as historical background, not as current approval for a cabin in another jurisdiction. [1]
Identify the member and its rule
Record the member’s type and identifying information from the drawings and, where applicable, its product marking. For solid-sawn framing, check the cutting, drilling and notching provisions in the building code adopted by the jurisdiction. Confirm the applicable local code and edition before relying on its provisions. APA’s guidance lists separate technical notes for glulam, laminated veneer lumber and I-joists. The U.S. Forest Products Laboratory’s 2021 Wood Handbook provides general background on wood properties and points readers toward product-specific design information. Neither the handbook nor a rule for one product approves a cut in another. [2] [3]
Check the opening against that rule
Confirm that the proposed opening’s size, shape, position and spacing from other openings meet the applicable code or product instructions. APA states that field holes and notches reduce the published design value of engineered wood members. Holes outside published tables may require analysis that considers hole size, span, spacing and loading. Edge notches in beams and I-joists need manufacturer verification or a designer’s check. Do not apply these engineered-wood instructions as a universal rule for cabin framing. [3]
Mark, inspect and record the route
Once the route is approved, mark it on the framing and compare the mark with the drawing before drilling. Check both sides of the member where accessible, and confirm the route will not cross a connection, reinforcement, bearing area or another marked restriction. These are practical inspection steps, not a substitute for the applicable code, product instructions or design decision. If the framing differs from the drawing or the member’s identity cannot be confirmed, stop and get clarification rather than moving the hole by eye. Record the approved route and the source of the decision before insulation or lining conceals it.
When the rule does not fit
Do not borrow a limit from a similar-looking member. A 2003 study published in Forest Products Journal reports bending tests on nominal 4-by-8-inch Douglas-fir lumber, with holes drilled at midspan in three locations relative to the edge. The authors report that hole location may be as important as hole size. The study concerns those tested members and does not approve a proposed cut in another product or configuration. Give the designer or manufacturer the member identification, span, loading information, hole dimensions and location, then wait for written direction before proceeding. [4] [3]