When you’re planning a pole barn, it’s tempting to think of post length as just wall height plus how deep you dig. But the reality is more nuanced—and getting it right saves you time, money, and frustration. Here’s what really goes into determining the proper post (or column) length for your build.
Why Post Length Is More Than Wall Height
You might start with a simple calculation: 12-foot wall, 4-foot hole, so you need a 16-foot post, right? Not so fast. In the real world, several factors can throw off your measurements:
- Digging isn’t always precise. Augers and excavators can dig deeper than planned—sometimes by several inches.
- Engineered laminated posts may be slightly shorter than their listed length due to the manufacturing process
- You need extra length above the truss carrier for a secure connection.
All these variables mean you can’t just add wall height to hole depth and call it a day.
Our Standard: 48 Inches in the Ground
At DIY Pole Barns, we set each post 48 inches deep. Big machines and auger bits don’t always stop exactly where you want them, especially if the soil’s uneven or the operator’s in a groove. This depth provides a solid foundation, resists wind uplift, and addresses frost line concerns. But since holes can end up deeper thanks to soft spots, rocks, or natural inconsistencies in the soil, your posts might end up further in the ground than expected. That extra depth reduces the amount of post left above grade, so you need to plan ahead.
Eave Side Posts: Go the Extra Inch
On the eave sides (the long walls), posts must extend above the truss carrier. Typically, you want 6–10 inches of post above the carrier for a secure truss attachment. Here’s how it adds up:
- Wall height: 12 feet
- Hole depth: 4 feet (48 inches)
- Extra above truss carrier: 6–10 inches
So, 12 feet + 4 feet + 8 inches (average) = about 17 feet. Round up to an 18-foot post to allow for trimming and margin.
Engineered laminated posts might run 1–3 inches short, so having extra length is a must. It’s always better to have more post than you need—you can always trim it later.
Gable Wall Posts: Follow the Roof Pitch
Gable wall posts (on the short ends) must match the slope of your roof. Each post’s height depends on its position along the wall.
Example Calculation:
- Wall height: 12 feet
- Roof pitch: 4/12 (4 inches rise per foot of run)
- Post location: 8 feet from the side wall
Step-by-step:
- Calculate rise: 8 feet × (4/12) = 2.67 feet (32 inches)
- Add to wall height: 12 + 2.67 = 14.67 feet above ground
- Add truss heel height (assume 8 inches): 14.67 + 0.67 = 15.34 feet above ground
- Add hole depth (4 feet): 15.34 + 4 = 19.34 feet total post length
- Round up: 20-foot post
Repeat this process for each gable post based on its location. Accurate measurements are critical—don’t rely on rough estimates.
A Handy Tip: Trim Posts After Trusses Are Set
Whether you’re working with eave or gable posts, it’s best to set them at full length. Once truss carriers and trusses are in place, you can trim the tops for a perfect fit. Use a chainsaw, Sawzall, or circular saw. Just make sure everything is set and secured before cutting.
“Let them run long, then trim them tight. Works every time.”
Build with a Margin, Not Regret
Planning ahead isn’t just smart, it’s essential. A post that’s too long? You can trim it. A post that’s too short? Well, they haven’t invented a board stretcher yet. Leave yourself some wiggle room, and you’ll thank yourself later.
At DIY Pole Barns, we engineer every kit with the proper post lengths already figured accounting for depth, pitch, heel height, and trimming room. No guesswork, just a better build. We factor in real-world variables so you can build with confidence.
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