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Sill Plates

Written for Canada. Plans are metric, but many crews and suppliers work in feet and inches, so this site gives both: millimetres and metres, with feet and inches beside them. Codes are the National Building Code of Canada 2020 (NBC 2020) Part 9 as your province adopts it. A number marked Confirm has not been checked against every province, so check it with your own authority before you act on it.

Reviewed by a working tradesman with 17+ years in the field.

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The sill plate is the first wood on the foundation. Keep it treated, sealed, bolted and level.

I am a:

Tap your level and the boxes below open to the advice for you. Remembered on this device.

What it isThe first piece of wood on the foundation: a treated plate on a gasket, bolted down, that everything above is built on.
Your jobClean the wall top, lay the gasket, drill snug holes, set the plate level and tighten it down.
The hard ruleTreated wood (or a separator) on concrete, a continuous gasket, and a level plate before you frame.
The checkTreated wood, gasket, anchors, washers, nuts and level.

By the end you can

  • Say what a sill plate does and what size the code names.
  • Explain why the plate is treated and sealed.
  • Install the gasket, plate, washers and nuts in order.
  • Check level and moisture protection before framing.
Stop and read

Treated lumber: wear gloves and a dust mask or respirator when cutting or drilling, and do not burn offcuts. Exposed bolt threads can cause impalement and trips, so cap them until the plate goes on.

Do not change anchors. If a bolt is missing, bent or out of place, tell the lead or engineer. Do not enlarge a hole far past the bolt to make it fit.

The big idea

The sill plate is the first piece of wood on the foundation. It gives you a level base to build on, spreads the load into the concrete, holds the anchor bolts, and keeps the framing from soaking up moisture from the concrete. Getting it level, sealed and dry makes every later step easier.

A cross-section of the top of a foundation wall. A foam sill gasket sits between the concrete and a pressure-treated sill plate. An anchor bolt cast in the wall passes through the plate with a washer and nut. A rim joist, floor joists and subfloor sit on the plate and wall framing stands above.
Sill plate on a foundation wall. A treated plate on a foam gasket, held down by an anchor bolt, washer and nut, with the floor framing and wall above. Not to scale. Size, spacing and embedment: confirm in the code or drawings.

What the code says

From Part 9, Section 9.23, as printed in the Vancouver Building Bylaw 2014 (a municipal reprint, possibly older than your province's edition; I read it through a summarising tool, so check the exact wording):

  • Size: sill plates that provide bearing for the floor system are not less than 38 mm × 89 mm (1 1/2 in × 3 1/2 in) (Article 9.23.7.1).
  • Level: set them on a full bed of mortar, or directly on a foundation whose top is already level (Sentence 9.23.7.2.(1)).
  • Seal: the joint between an exterior sill plate and the foundation is sealed in accordance with Subsection 9.25.3 (Sentence 9.23.7.2.(2)). A foam gasket is the usual way, but the text I read does not mention gaskets.
  • Decay and moisture: wood framing that is not pressure-treated and sits on concrete in contact with ground or fill is separated from it by not less than 0.05 mm polyethylene film or Type S roll roofing (Sentence 9.23.2.3.(1)). That separation is not needed where the wood member is at least 150 mm (6 in) above the ground (Sentence 9.23.2.3.(2)).
  • Anchors: see Anchor Bolts. Washers and nuts, 100 mm (4 in) embedment, bolts spaced not more than 2.4 m (7 ft 10 1/2 in) in the standard case (Article 9.23.6.1).

The text I read does not give a bolt hole size. Keep the hole just big enough, and follow the drawings.

Materials and gasket

  • Pressure-treated lumber marked to the standard your building department accepts is the usual choice. Use the grade and size the drawings call for.
  • Field preservative on cut ends and drilled holes, as the treated-lumber maker allows.
  • Fasteners and washers made for treated lumber.
  • Sill gasket (sill seal): a continuous foam strip under the plate that seals the air gap, stops moisture wicking up, and fills small low spots. Check that the concrete is flat first and fix high spots. Do not use gasket to make up a large gap: use non-shrink grout.

Installation

  1. Clean. Clear debris, water and ice from the top of the foundation.
  2. Check. Check the top of the concrete with a laser or level so you know what you are building on.
  3. Gasket. Lay it the full length with no breaks at the joints.
  4. Drill. Mark and drill the bolt holes just big enough for the bolt.
  5. Set. Set the plate over the bolts and tap it into position.
  6. Fasten. Add washers and nuts and tighten as the code or drawings require.
  7. Check. Check level and straightness before framing.

Example (numbers made up). A foundation 36 m (118 ft 1 in) around needs 36 m of gasket (plus a little for waste) and, at 2.4 m o.c., about 36 ÷ 2.4 = 15 bolts if the spacing were exactly even. The drawings decide the real count and end distances. The plate is 38 × 89 mm (1 1/2 × 3 1/2 in).

Moisture protection

  • Use treated wood and keep the gasket continuous.
  • Keep the plate above finished grade. The 150 mm (6 in) figure in the text above is the point where separation is not needed; confirm the clearance for your project.
  • Keep soil, mulch and stucco from touching the plate.
  • Make sure water drains away from the foundation (see Grading, Downspouts and Window Wells).

Common mistakes

  • Untreated lumber directly on concrete
  • Bolt holes drilled too large
  • No gasket, or gaps in it
  • Plates on a wet or dirty top
  • Under- or over-tightened nuts
  • Plate not level
Pro note

A level sill makes every floor, wall and roof line after it easier. Take the time to get it right.

Weather note

Rain soaks the concrete and spoils gasket adhesion. Cold stiffens the gasket. Clear frost from the wall top before you place the plate.

What the inspector looks at

Treated wood, gasket, anchors, washers and nuts, and the sill's level, before framing begins. Confirm what your building department checks.

✅ Check yourselfTap a question
In the Part 9 text I read, what is the smallest sill plate that provides bearing for the floor?
38 mm × 89 mm (1 1/2 in × 3 1/2 in), Article 9.23.7.1, as printed in a BC municipal reprint. Check your edition and your drawings.
How must a sill plate be levelled?
By setting it on a full bed of mortar, or directly on a foundation whose top is already level (Sentence 9.23.7.2.(1)).
An untreated wood member sits on concrete that is in contact with the ground. What does that text require?
It must be separated from the concrete by not less than 0.05 mm polyethylene film or Type S roll roofing. Pressure-treated members are excluded (Sentence 9.23.2.3.(1)). Most builders use a treated plate.
How is the joint between an exterior sill plate and the foundation sealed?
In accordance with Subsection 9.25.3 (the air barrier rules, Sentence 9.23.7.2.(2)). A foam gasket is a common way to do it. Confirm what your building department accepts.
A wall 36 m (118 ft 1 in) around has bolts at 2.4 m (7 ft 10 1/2 in). How many bolts in a closed loop?
36 ÷ 2.4 = 15 bolts at most spacing. Lengths are made up. Also check end distances on each plate piece against the drawings.
A bolt hole is drilled much too big. Does it matter?
Yes. The hole should be just big enough, because an oversized hole lets the plate shift. Ask the engineer if it was drilled far oversize.
🧰 Gear for this stepMust-haveRent itNice to have
  • Must-haveLayout and measuring:
  • Must-haveCutting and drilling:
  • Must-haveMaterials: treated sill lumber marked to the treated-wood standard your building department accepts, continuous foam sill gasket, washers and nuts for treated lumber, field preservative for cut ends, non-shrink grout for larger gaps
  • Must-haveSetting and tightening:
  • Must-haveCleaning the wall top:
  • Must-havePPE: hard hat (CSA Z94.1), eye protection (Z94.3), green-triangle safety footwear (Z195), gloves, hearing protection; dust mask or respirator (Z94.4) when cutting treated lumber
👷 Who can do thisTap your level
Home DIY
A capable owner can clean the wall top, lay the gasket, drill the bolt holes and set the plate on a straight, level foundation. Do not change the anchor type, size or spacing on your own. If the concrete is badly out of level or an anchor is missing, ask the builder or engineer.
Laborer or helper
Sweep the wall top, carry gasket and plates, and hold materials while the crew sets them. Do not change an anchor or enlarge a hole. Tell the lead if a bolt is missing, out of place or the wall top looks uneven.
1st-year apprentice
Lay gasket, cut and drill plates and tighten nuts under supervision. Learn to read the top-of-concrete elevations and why a level sill matters for every line above it.
Apprentice, 2nd to 4th year
Roll out the gasket, mark and drill the plates and snug nuts as shown. Check the plate sits flat with a level. Ask before shimming a large gap, and report missing anchors before framing starts.
Journeyperson
You own the layout, the level, the treated material and the anchor positions and tightness. Decide when the wall top needs grout or a fix before the plate goes on. Stop and call the engineer for a missing or misplaced anchor.
Lead hand or foreman
Check the wall top, gasket, hole fit, washers and nuts, and level before anyone frames. Make sure the inspector sees the sill before it is covered.
Contractor or business owner
Price the gasket, treated lumber, grout and re-check time. Keep photos of the wall top, gasket and anchors before framing, and ask your insurer who carries the cost of rot or a failed anchorage.
Starting a new business
Know the sill plate and decay rules in your province's code and the treated-wood standard your building department accepts. Keep the inspection record and photos, and ask your lawyer or insurer about moisture and structural claims.
By Province:

Each province adopts its own edition of the National Building Code, and the treated-wood standard and sealing details can differ. I dropped the old per-province list because I could not verify it. Confirm with your building department.

See Canada by Province for the full comparison.

Sources:
  • Vancouver Building Bylaw 2014, Part 9, Section 9.23 (municipal reprint of NBC Part 9; read through a summary, so confirm the wording; Articles 9.23.2.3, 9.23.6.1, 9.23.7.1, 9.23.7.2)
  • Subsection 9.25.3 air barrier sealing, bolt hole tolerances and the accepted treated-wood standard were not verified.

Last reviewed October 2026. General information, not engineering or legal advice.

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