Wood/Metal Framing Holdowns: Use and installation

ClarkDietrich CD8 HOLDOWN installed with anchor bolt and screws

Light gauge steel frame structures (SFS) have many benefits, they require less concrete foundation material, are almost 100% recyclable, and will not rot or fall prey to termites. However, in structural terms, they perform similarly to timber framed buildings, and so will require holdowns at shearwall locations.

In framing, holdowns are connectors used to anchor the bottom plate of a wall to the foundation or concrete slab. They are used in seismic or high-wind areas to resist lateral forces that can cause the wall to overturn or collapse.

Holdowns are made of galvanized steel and are installed at the end of a wall where it meets the foundation. They are designed to transfer the lateral forces from the wall to the foundation, helping to keep the structure stable during an earthquake or high winds.

Here’s our guide to holdowns, and when they are a necessary part of your build, including examples of real projects and engineering designs we’ve used on our own builds.

A light guage steel framed house build using holdowns in the corners
The wall frame above has holdowns fitted in each corner to prevent rotation of the shear wall.

Why Are Holdowns Necessary?

Holdowns are a framing accessory that secure your building against the powerful lateral and vertical forces that act on a shearwall in times of stress. Seismic events and winds create external forces. A shearwall takes these forces and creates a continuous load path which transfers them from the steel frame structure, into the concrete foundation.

The holdowns counter the uplift, and compression at either end of the shearwall, anchoring it in place and resisting the rotation of the wall. In short, the lateral forces of either an earthquake or storm-force wind will try to push over anything in its path. A properly secured shearwall should be able to resist events safely.

Common areas of concern we’ve helped clients with:

  • Seismic events/earth quakes in California
  • Snow loads in the US North
  • Hurricanes/High wind-loads in the Gulf Coast and Florida
Simpson Strong tie S/HDU4 Holdown used in steel framing to anchor the metal frame to the foundation
Simpson Strong tie S/HDU4 Holdown used in steel framing to anchor the metal frame to the foundation

What is a Shearwall?

A shear wall is a reinforced part of steel frame structure that acts as an anchor against parallel forces that act in opposing directions. Shear walls resist lateral forces that would overturn buildings not properly anchored or held down.

A shear force refers to the amount of pressure, or weight a beam, or other structural member can take before it fails. Not to be confused with ‘sheer force,’ which means ‘ultimate or absolute’ force.

Typical holdowns and anchor bolt spacing

The standard spacing for anchor bolts to the grade-level beam is one every six feet, embedded up to 12” in the concrete foundation. On a shear wall, this has to be increased to an anchor bolt every two feet.

Anchor bolts do exactly what they say they do, securely hold down the base track, but they don’t transfer loadings from studs into the foundation.This is the job of the holdown, which should also be secured deeper into the concrete footing, by 7” (minimum recommendation) to 16”. If a holdown position coincides with the spacing for an anchor bolt, then the holdown will take priority.

Clark Dietrich CD8 Holdown connection detail as described by a engineering detail
The architect or designer should recommend a minimum depth for the holdown that conforms to local codes, ground conditions, and structural calculations.
An engineering schedule for Holdowns used in a building the Miami-Dade area. Dictating concrete bolt depths and holdown sizing.

Here is a holdown bolting schedule for a high wind area (Sunrise, FL near Miami). Notice the minimum embedment lengths are either 9″ or 13″. They are using Simpson S/HDU4 and S/HDU9 holdowns with 5/8″ anchor bolts and 7/8″ anchor bolts.

Metal Framing Holdowns Installation:

To install holdowns you will need:

As with most construction activities, there is more than one acceptable method of installation:

Cast in Place: If you know exactly where your holdowns fall, the best way to install holdowns is for the framing contractor to set out and position the threaded rod used to secure them when, or just before the concrete foundation is poured. Before the concrete has had time to cure the contractor can easily make any final adjustments and clean off any excess cement.

If the framing contractor can have full control and access to the setting out at this point, then siting the track and studs later will be straightforward as everything should align. This will save time, and reduce the need for adjustments, or re-drilling.

Some contractors will leave it to the concrete team’s engineer to locate and coordinate their bolt positions, but this can sometimes lead to problems later when they don’t quite line up where they should.

Pro Trip: When the steel reinforcement cages are still visible before a concrete pour, it is sometimes possible to adjust the reinforcement to avoid clashes.

ClarkDietrich CD8 HOLDOWN installed with anchor bolt and screws
ClarkDietrich CD8 HOLDOWN installed with anchor bolt and screws

Drill and Set: It is possible to install holdown anchors after concrete has been poured. Once the concrete foundation has cured enough to take chalk and pencil marks, then threaded rods for holdowns and anchor bolts can be set out easily. The concrete should also still be reasonably soft, making it easy to drill.

The rods should be set securely with a proprietary two-part epoxy resin. In some regions, building inspectors may require pull-out resistance tests to be carried out to satisfy local building codes.

It should also be noted that a foundation that has been reinforced with rebar may be difficult to drill into should the reinforcement coincide with the anchor point.

Pro Tip: To prevent nut spin, use a thread adhesive or steel nylon locking nuts to secure the holdowns.

Pro Tip: Tighten holding down nuts by hand until they’re finger tight before finishing off with a hand wrench. Using an impact driver can overtighten nuts and could cause distortion.

Holdowns in Timber Construction

At US Frame Factory all of our holdown and clip products, and associated accessories are compatible with timber frame construction. Holdown installation is similar whether you are building in metal or timber.

When fixing a holdown to a timber frame shear wall there will be the choice of screws, nails, or bolt fixings dependent upon the type of holdown. In each scenario, the number and specification of the fixings are important and should be followed exactly to ensure the correct level of performance.

Notice in this detail holdowns are used every other stud, with different numbers of screws specified in each holdown. For example S/HDU9 has 18 #14 screws and a S/HDU6 has 6 #14 screws.

Which Holdowns Should be Used in What Scenarios?

The sizing of the holdown should be specified by the designer or engineer. If in doubt it does no harm to purchase the highest-grade holdowns, especially if you require a small number. A holdown is a key part of ensuring the safe transmission of force through a steel frame structure.

The point of holdowns is to establish a continuous load path taking the load from the wind on the roof and transferring it all the way down to the foundation. The elongation and deflection of the load path when under load, either from seismic activity or a wind strike, will determine the grade and arrangement of a holdown strategy for the shear walls.

We always recommend seeking professional advice.

Buildings With Multiple Floor Levels

Holdowns and anchor rods play an important part in transferring loads from the upper floors do the foundation. In the scenario below shear walls are the holdowns and concrete anchor bolts connect through the hollowcore slab floor system to allow load transfer between shear walls on different floors.

Holdown connection detail to connect shear walls to eachother through a floor.
Holdowns connecting shear walls on different floors.

Holdown brands and types.

There are several types of holdowns and brands. The three most common brands are Clark Dietrich, Simpson Strong-tie, and The Steel Network. We sell all three brands so you can get whichever one is specified in your drawing plans, or if you have some leeway we can get you the most cost effective one at the time. You can buy holdowns online at clips.usframefactory.com or by contacting sales.

Additional Resources

Metal Studs

Metal Trusses

Engineered Framing Details for Light-gauge Steel

Steel Framing: Shear Wall with X Bracing, engineering and building details

Leave a Reply

Your email address will not be published. Required fields are marked *