Hold-Downs

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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A hold-down keeps the end of a braced wall from lifting. The engineer picks it. You place it exactly.

The big idea

When wind or an earthquake pushes a wall sideways, its end tries to lift. A hold-down keeps it down so the wall can do its job. Whether a building needs them depends on its design and its seismic and wind loads. In engineered buildings and higher-load areas they are common and critical. If a hold-down fails, the wall fails, so give the connectors the same attention you give the rebar.

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). The text I read does not use the word "hold-down":

• Building frames shall be anchored to the foundation unless a structural analysis shows anchorage is not needed (Sentence 9.23.6.1.(1)).
• Where Sa(0.2) is above 1.2, or the 1-in-50 hourly wind pressure is 1.2 kPa or more, anchorage is designed under Part 4 (Sentence 9.23.6.1.(5)). That is where engineered hold-downs come in.
• Exterior columns and posts shall be anchored to resist uplift and lateral movement (Article 9.23.6.2).
• Where the wind pressure is 0.8 kPa or more, roof members are tied to the wall framing with connectors that resist a factored uplift load of 3 kN (Sentence 9.23.3.4.(3)).
• Walls with required braced wall panels shall be continuously supported by joists, blocking or rim joists so the required fastening can be installed (Sentence 9.23.9.8.(6)).

The bracing rules in Part 9 (Subsection 9.23.13) were not in the text I read. Product, rod size and embedment come from the engineer's drawings, and the maker's evaluation report sets the allowable load.

Types of hold-down

• Cast-in-place: rods or straps set in the concrete before the pour.
• Bolted hold-downs: a bracket fastened to the post and to the anchor rod.
• Epoxy-set rods: for retrofits or where the engineer allows (see Epoxy Anchors).
• High-capacity systems: designed for the project.

Parts of the system: the anchor rod in the concrete, the bracket, washer and nut, the structural screws or bolts into the post, and the post itself (double or triple studs as the drawings call for).

Placement and installation

1. Locate. Place at the locations on the drawings, not guessed. They are usually at the ends of braced or shear walls. Mark each on the formwork and check before the pour.
2. Set the rod. Place the rods as the drawings say, plumb, with enough thread for the nut and washer (the length comes from the maker).
3. Fit the bracket. Centre the rod in the bracket and keep it plumb and flat against the post.
4. Fasten. Use the screws or bolts the maker specifies and fill every hole it requires.
5. Tighten. Tighten the nut as the maker says, and check again after the framing shrinks if the maker or drawings call for it.
6. Inspect. Have the hold-downs inspected before the wall is covered.

Example (numbers made up). The drawings show 6 hold-downs, one at each end of 3 braced wall panels, and 12 screws per bracket. That is 6 × 12 = 72 screws to count and check. Count the real number from the maker's table.

Common mistakes

• Rod embedment too shallow
• Rod out of position, so the bracket will not fit
• Wrong or missing fasteners
• Bracket not flush with the post
• Nut not tightened
• Substituting a different product