How to Drill a Top Plate and Restore It

Why this matters

The double top plate is the one piece of a wall that ties every stud together and carries whatever sits on top: joists, rafters, trusses, the ceiling. A vent, a duct or a cable going up into the attic has to pass through it, and the hole changes two things the tech did not build. It cuts the plate's width, which past a point the code says must be bridged with a steel strap, and it opens the fireblock that plate was serving as. A plate bored at 60 percent and left unstrapped fails the rough inspection, and an open hole around the pipe is a chimney from the wall cavity into the attic. This card owns the procedure; the framing limits live in Notching and Boring Limits in Wood Framing.

The steps

1. Identify the wall and what it carries. Before laying out a hole, decide whether the wall is an exterior wall, an interior bearing wall, or a non-bearing partition. Look in the attic: joists or truss bottom chords that land on and end over this wall, or rafters bearing on it, mean bearing; ceiling joists that run past it continuous, or trusses that clear-span over it, usually mean a partition, though a truss can still be designed to bear on an interior wall. This comes first because the strap rule in the IRC (R602.6.1 in the 2021 edition, as adopted by your jurisdiction) applies to exterior and interior load-bearing walls, so the wall type decides whether step 5 is required. Skip it and a bearing wall goes unstrapped because it looked like a closet wall. If you cannot tell, treat it as bearing.

2. Locate the hole within the plate. Three places on a plate are wrong for a hole, and each one costs something different:

• Directly under a bearing point. Where a joist, rafter or truss bears on the plate, the load comes down through the wood right there. Move the hole into the bay between bearing points.
• At or near a plate splice. In a double top plate, the joints in the upper and lower plates are offset from each other (at least 24 in under R602.3.2 in the 2021 edition, as adopted), so that the plate stays continuous across every joint. A hole beside a joint in one plate leaves the other plate carrying the wall alone at that spot. Look for the butt joint in the attic and stay clear of it.
• Where something already runs. Cables often cross the top of the plate in the attic or run up the same stud bay. Scan the bay, and look in the attic before you drill. See related: How to Scan a Wall Before You Cut or Drill.

Confirm the location from both sides: a small pilot drilled up at the bay's centerline should appear on top of the plate where you expect it, which keeps the full-size hole out of the wrong bay. Hazard: drilling overhead throws chips into the eyes, so wear safety glasses, and in an attic, step only on framing members, never on the ceiling between them. See related: How to Move Through an Attic Without Stepping Through a Ceiling. Loose-fill that looks like vermiculite (gray-brown, glittery, pebble-like) may contain asbestos: stop and do not disturb it.

3. Size the hole and compute its share of the plate. The hole is the pipe's outside diameter plus enough room to get it through and to seal around it. Then divide the hole diameter by the plate width, in the same unit, and compare to 50 percent. A nominal 2x4 plate is 3-1/2 in wide; a 2x6 plate is 5-1/2 in. Compute it rather than eyeball it, because modest-looking holes cross the line easily in a 2x4 wall. A 3/4 in hole for a cable is about 21 percent of a 2x4 plate and needs no strap. A 2-1/8 in hole for a 1-1/2 in plastic vent, whose outside diameter is 1.900 in, is about 61 percent and does. Do not shrink the hole to dodge the ratio: a hole too tight to seal around fails step 6 instead.

A notch, where the plate is cut in from its face rather than bored, counts the same way: measure what is removed against the width.

4. Bore it. Use a bit long enough to pass through both plates, which together are 3 in tall, in one pass from one side. A self-feed bit in a right-angle drill grabs hard at a nail or at breakthrough and can spin the drill into a wrist or face: use the side handle, set the clutch if there is one, brace so a bind pushes the drill away from you, and wear eye protection. Insulation fiber and old plaster dust come down with the chips; work in a respirator under your shop's written program per 29 CFR 1910.134, and in a house built before 1978, treat painted plaster or drywall you disturb at the top of the wall as possible lead paint and follow the lead-safe rules for the work. If the bit hits metal, stop and find out what it is before you go on.

5. Strap the plate, where the cut is over half its width. R602.6.1 in the 2021 edition requires, for an exterior or interior bearing wall where the cut, bore or notch exceeds 50 percent of the plate width:

• a galvanized metal tie at least 0.054 in thick (16 gauge) and 1-1/2 in wide,
• fastened across and to the plate at each side of the opening with at least eight 10d nails (0.148 in diameter, at least 1-1/2 in long) at each side, or equivalent,
• extending at least 6 in past the opening on each side.

The exception, stated whole: no tie is required where the entire side of the wall with the notch or cut is covered by wood structural panel sheathing. Sheathing on the far face of an exterior wall does not obviously satisfy that for a hole bored through the plate's middle; ask your inspector before relying on it rather than assuming.

The tie has to lie flat and take all its nails, which decides where it goes. On top of the plate beside the pipe it usually will not fit: a 2-1/8 in hole centered in a 3-1/2 in plate leaves 11/16 in of wood on each side, too narrow for a 1-1/2 in strap. So most straps go on the face of the plate, inside the wall cavity, which means reaching the top of the wall from the room. Plan that access cut along with the hole, and put it where the patch will be least visible. See related: How to Cut an Access Opening You Can Patch Cleanly.

 Face of a double top plate, seen from the room

 |<- 6 in min ->|<- opening ->|<- 6 in min ->|
 +-------------------------------------------+
 | upper top plate     (   )                 |
 |=====o==o==o==o======(   )=====o==o==o==o==| <- strap
 | lower top plate     ( H )                 |
 +-------------------------------------------+
   8 x 10d nails       hole      8 x 10d nails
   this side           bored     this side
                       through
                       both plates

The drawing shows four nail heads each side for clarity; the strap takes eight each side, staggered through its punched holes. Hazard: hand-nailing overhead at the top of a wall puts your face under the hammer and the nail; wear eye protection, and if a nail bends, pull it and drive a new one in a fresh hole rather than flattening it, since a flattened nail is not one of the eight.

6. Fireblock the hole around the pipe. The top plate of a stud wall is the fireblock between the wall cavity and the attic, and R302.11, as adopted, requires the openings around vents, pipes, ducts, cables and wires at ceiling and floor level to be filled with an approved material that resists the free passage of flame and products of combustion. Fill the annular gap, the ring between the pipe and the wood, with a sealant or foam marketed and approved as a fireblock, or mineral wool packed tight, as your building official accepts. Ordinary gap-filling foam is not a fireblock because it fills the hole. Work from the attic side, where the whole gap is visible. See related: Fireblocking and Draftstopping.

The same bead usually does the air-sealing job the energy code wants at an attic penetration; see How to Air-Seal Penetrations Into the Attic. Then put the attic insulation back over the plate to its original depth. See related: How to Restore Attic Insulation After You Work in It.

7. Record it before anything covers it. Photograph the strap with its nails, a tape across the opening showing the hole size, and the fireblock from above, before the access cut is closed and the insulation goes back. On a permitted job, leave the access open until the rough inspection is signed. Note the wall, hole size, plate width and percentage. Skip this and the only evidence of the strap is behind drywall. See related: The Penetration Record SOP.

Worked example: a new vanity vent in a hall wall

A plumber is adding a second lavatory in a bathroom of a single-story house. The new 1-1/2 in vent rises in the interior wall between the bathroom and the hall, a 2x4 wall, and has to pass through the top plate into the attic.

Step 1. In the attic, the ceiling joists from both sides land on this wall and end there, lapped and nailed over it. The wall is an interior bearing wall. The strap rule applies.

Step 2. The joists sit at 16 in on center and the hole falls between two of them. A butt joint in the upper plate shows 30 in to the north; the hole is well clear of it. A cable crosses the plate top 5 in south of the bay's centerline. The pilot comes up at the centerline, 5 in from the cable. Nothing in the attic resembles vermiculite; the insulation is blown fiberglass.

Step 3. Outside diameter 1.900 in; the plumber picks a 2-1/8 in bit. 2.125 divided by 3.5 is 0.607, about 61 percent. Over 50: strap required.

Step 4. Bored from the attic down through both plates, 3 in of wood, with the right-angle drill's side handle braced. No nails hit.

Step 5. The strap goes on the hall face of the plate. The plumber cuts an access opening at the top of the hall wall, 20 in wide by 5 in tall, centered on the bay. Strap length: the opening is 2-1/8 in, plus at least 6 in each side, so at least 2-1/8 plus 12, or 14-1/8 in. The plumber cuts an 18 in length from a roll of 16 gauge, 1-1/2 in galvanized strap: 18 minus 2-1/8 leaves 15-7/8 in, or 7-15/16 in on each side, which is past the 6 in minimum and long enough for eight nail holes clear of the opening on each side. Eight 10d nails go in on each side, sixteen in all.

Step 6. From the attic, the gap around the vent, about 1/8 in all round, is filled with a fireblocking sealant the local building department accepts. The fiberglass is raked back over the plate.

Step 7. Photos: strap and sixteen nails through the access cut, a tape across the hole reading 2-1/8 in, the sealed collar from above. The notes read "hall/bath bearing wall, 2x4 plate 3-1/2 in, hole 2-1/8 in, 61 percent, strapped per R602.6.1, fireblocked". The access cut stays open for the rough inspection, then is patched.

What changes the answer

A 2x6 wall. The same 2-1/8 in hole in a 5-1/2 in plate is 2.125 divided by 5.5, about 39 percent, under 50, and needs no strap. It still needs step 6: the fireblock does not depend on the percentage.

A partition. The strap rule names exterior and bearing walls only, though some inspectors want a strap anyway. The fireblock is required either way.

A hole that takes the whole plate. A 3 in drain, at a 3-1/2 in outside diameter, does not fit through a 2x4 plate at all. That is a framing change, the wall reframed in 2x6 or a furred chase, not a strap, and it goes through Notching and Boring Limits in Wood Framing and possibly The Structural Cut Approval SOP.

An engineered top plate or a steel-framed wall. An LVL or other engineered plate follows its maker's rules, and a steel top track follows its own; neither is covered by R602.6.1.

How to verify you got it right

Put the step 3 number next to the photos. Every hole over 50 percent in a bearing or exterior wall shows a strap with eight nails each side and at least 6 in past each edge of the opening; every hole of any size shows a continuous fireblock collar with no daylight around the pipe; and the notes carry the hole size the photo's tape shows.

References

• International Residential Code, 2021 edition, R602.6.1 (drilling and notching of top plates), R602.3.2 (top plate joint offsets) and R302.11 (fireblocking), as adopted by your jurisdiction
• 29 CFR 1910.134, respiratory protection program
• See related: Notching and Boring Limits in Wood Framing
• See related: Fireblocking and Draftstopping
• See related: The Penetration Record SOP