Simpson Strong-Tie HDU and HDUE Holdowns: The Complete Guide for Framers and Contractors

If you've been framing residential or light commercial for any amount of time, you've seen holdowns on the plans. They show up on every shearwall detail, every braced wall panel, and increasingly on multi-story residential builds where wind and seismic loads demand solid connections from the post all the way down to the foundation. 

Simpson Strong-Tie has been the name behind most of those holdowns, and the HDU series has been their workhorse for years. But here's something worth knowing if you haven't already heard: the original HDU is being discontinued. Simpson replaced it with the HDUE series, and if you're ordering new holdowns right now, that's the one you want. This guide covers both, walks you through the full HDUE product line, explains the load tables in plain terms, and tells you exactly what you need to have on hand before you install one.

A holdown is a metal connector that ties a wood post or wall stud down to a concrete foundation anchor bolt. Its job is to resist uplift, which is the force that tries to pull the framing off the foundation when wind pushes against the side of a building or when seismic activity shakes the structure. Without a holdown, a shearwall panel can separate from the foundation at the bottom corner. That's a catastrophic failure mode, and it's exactly what these connectors are designed to prevent.

You'll typically see holdowns called out on a shearwall schedule in the engineered drawings. The schedule tells you the holdown model, the anchor bolt size and embedment, and sometimes the required post size. If you're working from an architect's plans or a full structural set, that information is already there for you. If you're doing a smaller job where you're doing your own sizing, Simpson offers a free Post-to-Foundation Designer tool on their website that walks you through the process.

Holdowns are code-required on shearwalls in most jurisdictions across the country. They're covered under ICC-ES evaluation reports that give building officials the documentation they need to approve the installation. Simpson's HDUE series is covered under ESR-2330, which lists compliance with the International Building Code, the International Residential Code, and the Florida Building Code.

Simpson announced the discontinuation of the original HDU bolted holdown series and introduced the HDUE as a direct, one-for-one replacement. If you've got plans calling for an HDU5, HDU8, or HDU11, the corresponding HDUE model replaces it with equal or better load capacity. Simpson published engineering letter L-C-HDUECONV25 that documents the full conversion table, so if your inspector wants documentation, that's the reference to pull up.

The original HDU series used bolts to attach to the wood post, which created two issues. Bolts require larger holes, which reduces the net section of the post, meaning less wood is left to carry the load. They also require pre-drilling, which adds a step to the install. The HDUE uses Strong-Drive SDS Heavy-Duty Connector screws. They go in faster, leave smaller holes in the wood, and come included in the box so you always have the right fastener.

The engineering also improved with the HDUE. The four larger models use angled screw patterns that engage the fasteners in both shear and tension, which raises load capacity while actually reducing the total number of screws needed. An overlapping back plate on the larger sizes distributes load more evenly across the wood section. Combined, these changes mean higher loads from the same basic footprint, and a simpler install than the bolt-based original.

The HDUE line runs from HDUE3 on the low end to HDUE17 at the top of the residential-grade lineup. Each model is sized for a different range of uplift demand. The number in the model name corresponds roughly to load capacity, so HDUE3 handles lighter residential applications and HDUE17 is built for high-demand shearwalls in narrow openings where there isn't space for a wider connector.

Gauge increases as you move up the series. HDUE3, HDUE5, and HDUE7 are 14 gauge. HDUE9 and HDUE13 step up to 12 gauge. HDUE17 is 10 gauge, the thickest and strongest in the lineup. All six models ship with the SDS screws and crescent washer included. The HDUE13 also includes a heavy-hex anchor nut because the standard nut isn't rated for the loads that model carries.

Note: HDG (hot-dip galvanized) variants are available for all models above and are required when the holdown will contact pressure-treated lumber or be installed in a corrosive environment.

The load table shows two sets of allowable tension loads: one for DF/SP (Douglas Fir-Larch and Southern Pine) and one for SPF/HF (Spruce-Pine-Fir and Hem-Fir). These are the two broad lumber species groups used in North American framing. DF and SP are the denser, stronger species, so they carry higher loads from the same connector. SPF and HF are softer, which means lower allowable loads.

The loads in the table have already been increased for wind or seismic loading, which means you don't apply a load duration factor on top. You take the number from the table and compare it directly to your design uplift demand. If the demand is 6,500 lbs and you're framing with Douglas Fir, you're looking at an HDUE7 at 7,015 lbs, which covers it.

For the HDUE9, HDUE13, and HDUE17, you'll see multiple rows per model. Each row reflects a different minimum post size. A wider post gives the screws more wood engagement and raises the allowable load. On the HDUE9, using a 3-1/2" x 3-1/2" post (a standard 4x4) gives you 8,425 lbs in DF/SP. Switching to a 4-1/2" x 3-1/2" post bumps that to 9,390 lbs. If the engineer has specified a post size, use the row that matches. If you're selecting your own, you can use the wider post to get more capacity without jumping to the next model.

If you need LRFD values instead of ASD, multiply the allowable loads by 1.4. And always check the anchor bolt note at the bottom of the table, because the higher-capacity models can exceed the tensile strength of a standard ASTM F1554 Grade 36 anchor rod, which means you may need a higher-grade bolt.

Source: Simpson Strong-Tie HDUE product page. Loads are allowable tension loads increased for wind or seismic. For LRFD, multiply by 1.4. Loads assume full screw penetration into supporting wood member. Verify anchor bolt grade against table footnotes for high-load models.

If the engineer has already specified the holdown model on the shearwall schedule, your job is straightforward: order what the plans say. If you're doing your own sizing, start with the design uplift demand from the lateral analysis and match it to a model with enough capacity for your lumber species and post size.

For practical guidance: the HDUE5 covers lighter loads like single-story walls and garage openings in low-wind regions. The HDUE7 at 7,015 lbs DF/SP handles a lot of two-story residential applications and is one of the most commonly specified models. The HDUE9 and HDUE13 are the right range for taller walls, closer stud spacing in shearwall panels, or higher seismic zones. The HDUE17 is for the heavy-duty end of residential construction.

When you're unsure, size up. A larger holdown doesn't weaken the structure and it costs a fraction of what it would take to fix a failed inspection or a callback. The price difference between an HDUE7 and an HDUE9 is small compared to the cost of a rejected field observation.

The holdown comes with its SDS screws and crescent washer. What doesn't come in the box is the anchor bolt. That's a separate item, and getting the size wrong is one of the most common mistakes on holdown installs. Here's what you need to know about each component.

Anchor bolt diameter is different for each group of models. HDUE3, HDUE5, and HDUE7 use a 5/8" diameter anchor bolt. HDUE9 steps up to 7/8". HDUE13 and HDUE17 require a 1" bolt. The bolt has to be cast in place. The embedment depth and steel grade need to match what the engineer specified or what the evaluation report requires. At the 1" diameter, some configurations exceed the tensile strength of ASTM F1554 Grade 36 rod, so confirm the grade before you order.

Simpson also makes the SABR cast-in-place anchor bolt, which is designed specifically for use with the HDUE series. It comes in five diameters to cover every model in the lineup and simplifies the anchor specification. If you want a single source for the bolt and holdown, the SABR pairs cleanly with the HDUE.

For the HDUE3 and HDUE5, all screws go in perpendicular to the wood face. Drive every screw in every hole. It's straightforward.

On the HDUE7, HDUE9, HDUE13, and HDUE17, you've got a combination of perpendicular and angled holes. Start by driving at least one perpendicular screw to set the holdown in position, then drive all remaining screws in order, including the angled ones through the tabbed holes. The tabs guide the fastener at 45 degrees, so you don't need to try to hold the drill at an angle by hand. The offset holes on the second back plate physically block a straight-in drive if you're trying to go perpendicular where it shouldn't go.

Don't overtighten the nut on the anchor bolt. Simpson specifies finger tight plus one-third to one-half turn with a hand wrench. Running it down with an impact driver will prestress the connection and cause premature deflection in service. This is probably the single most common installation error on holdowns and it's easy to avoid if you know about it going in.

Every HDUE model is available in G90 galvanized and hot-dip galvanized (HDG). G90 is the standard finish for dry interior locations where the holdown isn't touching treated lumber. It meets code for most residential applications in moderate climates. If the holdown is going inside a conditioned wall or a dry crawlspace with reasonable moisture control, G90 is your standard choice and the less expensive of the two.

HDG is required when the holdown is in contact with preservative-treated lumber. ACQ, CA, and similar lumber treatments contain copper-based preservatives that are corrosive to lighter galvanized coatings, and only the HDG coating is thick enough to resist that environment over time. If you're framing with treated lumber at the base of a shearwall, which is common in coastal construction or anywhere the bottom plate requires treatment, get the HDG version. It's also the right call for exposed crawlspaces with high moisture or coastal applications where salt air is a factor.

While the HDU series is being discontinued, both HDU and HDUE products are still available on totalfastening.com while supply lasts. If you're completing a job that was originally spec'd with HDU models and you need to match what's already installed, the table below shows what's available and the HDUE equivalent for each. For new work or new orders, go with the HDUE.

The HDUE series is listed under ICC-ES Evaluation Report ESR-2330, which covers the International Building Code and International Residential Code. It's also covered under the Florida Building Code under product approval FL10441. These reports are publicly available on Simpson's website and on the ICC-ES website.

For the transition from HDU to HDUE, Simpson published engineering letter L-C-HDUECONV25, which documents the one-for-one replacement table and load comparisons. If a building official or plan reviewer questions the substitution, that engineering letter is the reference to have on hand. It's downloadable from Simpson's website at no cost.

If you're buying holdowns for new work right now, order HDUE. The old HDU is still at distributors while supply lasts, but the HDUE is the current product and it performs better in most configurations. It's faster to install because you're not pre-drilling for a bolt, and the included SDS screws take one variable off the table every time.

Pick your model based on the design uplift from the plans or the shearwall schedule. Match the anchor bolt diameter to what the load table requires. Don't overtighten the nut. Use the HDG version whenever the holdown will contact treated lumber or be in a corrosive environment. That covers most of what you need to get this right on the job.