General Notes for Holdowns and Tension Ties
Code Reference Column in Load Tables
Product evaluation agencies play an important role in the building industry providing an independent third-party review of architectural and structural products. Evaluations use publicly developed criteria to determine if the product meets the intent of the building code. Building officials can use product evaluation reports, often referred to as “code reports,” to review and approve product use on a project.
The most prominent architectural and structural building product certification companies are ICC Evaluation Service (ICC-ES) and IAPMO Uniform Evaluation Service (IAPMO UES), which are both ANSI-accredited to ISO Guide 65 “General Requirements for Bodies Operating Product Certification Systems” as product certification entities. Simpson Strong-Tie currently maintains more than 60 ICC-ES ESR and IAPMO UES ER reports evaluated to the 2006, 2009, 2012, 2015, 2018 and 2021 International Building Code® (IBC) and International Residential Code® (IRC). We continue to submit product information to evaluation agencies in order to update reports or receive additional reports for products in compliance with the latest codes. Simpson Strong-Tie also has reports for the City of Los Angeles, California and the State of Florida.
We have simplified our code references to make this catalog easier to use. You can quickly determine whether a product has a code report by looking in the Code Reference column of the product load tables. A summary of the code references used is in the table below.
To determine which specific code report applies to a product and download a copy of the code report, you can use our Code Report Finder.
Holdowns and tension ties represent key components that comprise a continuous load path. In light-frame construction, holdowns are typically used to resist uplift due to shearwall overturning or wind uplift forces. In panelized roof construction, holdowns are used to anchor the concrete or masonry walls to the roof framing.
Holdowns can be separated into two categories — post-installed or cast-in-place. Cast-in-place holdowns, such as the STHD holdowns or the PA purlin anchors are installed at the time of concrete placement and attached to wood framing with nails. Cast-in-place holdowns are an economical anchorage solution with allowable loads up to 5,300 lb.
After the concrete has been placed, post-installed holdowns are attached to anchor bolts during wall framing. They are attached to the wood framing with nails, Strong-Drive® SD Connector screws and Strong-Drive SDS Heavy-Duty Connector screws or bolts. Post-installed holdowns have have allowable loads ranging from about 850 lb. up to nearly 20,000 lb.
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Holdown and Tension Tie General Notes:
- Allowable loads have been increased for earthquake or wind load durations with no further increase allowed. Reduce where other loads govern.
- To obtain LRF D values for cast-in-place holdowns (STHD and PA), multiply ASD seismic load values by 1.43 and wind load values by 1.67. For
post-installed holdowns, multiply allowable loads by 1.4. See evaluation reports for LRF D deflections. - Use all specified fasteners.
- The Designer must specify anchor bolt type, length and embedment. See SB and SSTB anchor bolts and PAB anchor bolts.
- Simpson Strong-Tie® Anchor Designer is available for quick and easy design of anchors for wind and seismic conditions as well as cracked and uncracked concrete.
- Anchor bolt nut should be finger tight plus 1⁄3 to 1⁄2 turn with a hand wrench, with consideration given to possible future wood shrinkage. Care should be taken not to over-tighten the nut. Impact wrenches should not be used.
- Post or beam by designer. Minimum no. 2 or better unless noted otherwise. Tabulated loads are based on installation into the wide face of a minimum
3 1/2" wide solid or built-up post or beam (in a3 1/2" wall), unless noted otherwise. Posts may consist of multiple members provided they are connected independently of the holdown fasteners. See common post allowable loads. - Holdowns are for use in vertical or horizontal applications.
- Tension values are valid for holdowns installed flush or raised off the sill plate.
- Defection at Allowable Tension Load is determined by testing on wood posts and includes fastener slip, holdown deformation and anchor rod elongation for holdowns installed 6" above top of concrete (4." for HTT). Holdowns may be installed any height above top of concrete without load reduction provided that additional elongation of the anchor rod is accounted for. Holdown deflections may be linearly reduced for design loads less than the allowable load.
- To accommodate a 1." max. offset anchor bolt, holdowns may be installed raised up to 18" above the top of concrete with no load reduction provided that additional elongation of the anchor rod is accounted for.
- Tabulated loads for bolted holdowns may be doubled when holdowns are installed on opposite sides of the wood member. Designer must evaluate the allowable load of the wood member and the anchorage.
- Tabulated loads for nailed or screwed holdowns may be doubled when holdowns are installed on opposite sides of the wood member. Member must be thick enough to prevent opposing holdown fastener interference or the holdowns are offset to eliminate fastener interference. Designer must evaluate the allowable load of the wood member and the anchorage. See common post allowable loads.
- Holdowns are for use in vertical or horizontal applications. Structural composite lumber columns have sides that show either the wide face or the edges of the lumber strands/veneers known as the narrow face. Values in the tables reflect installation into the wide face. See technical bulletin T-C-SCLCLM for load reductions due to narrow face installations
- Some holdown models are available in stainless steel. Refer to engineering letter L-C-SSHD for stainless-steel holdown allowable loads.
