Pole Barn — Planning Guide

A DIY planning document for building a 20×30’ storage pole barn in the field. Primary use: trailer storage and firewood. Neither of us has done this before, but we’re handy and willing to learn.

Table of Contents

1. Overview & Key Decisions
2. Permits & Zoning
3. Site Prep & Layout
4. Materials & Budget
5. Setting the Posts
6. Wall Framing (Girts & Headers)
7. Roof Framing (Rafters & Purlins)
8. Metal Roofing
9. Doors & Access
10. YouTube Channels & Search Terms

Overview & Key Decisions

Planned size: 20’ wide × 30’ long

Roof style: Mono-slope (shed roof) — one continuous slope, high side in front, low side in back. Simpler than a gable: no ridge beam, half the framing decisions, and water sheds naturally to the back/field.

Floor: None planned. Gravel or bare earth is fine. Firewood goes on pallets; trailer wheels getting wet is acceptable.

Ceiling Height

Recommendation: Go with 12’ front, ~8–9’ back. The extra 2’ costs maybe $100–200 more in lumber but makes the space dramatically more usable — you won’t regret it. Metal roofing manufacturers recommend a minimum 2:12 pitch (some say 3:12). Over 20’ of depth, a 2:12 pitch means a 3’4” drop (front 12’, back 8’8”).

Post Spacing

• Standard is 8’ on center along the 30’ length → 4 bays, 5 posts per row
• Front row posts: tall (12’)
• Back row posts: short (~8’8”)
• 2 rows of posts × 5 posts = 10 posts total

Permits & Zoning

Do this first — before buying anything.

Every county is different. A 20×30 (600 sq ft) barn almost certainly requires a permit in most jurisdictions.

Checklist

• Call your county building department — ask: “Do I need a permit for a 600 sq ft pole barn / post-frame storage building?”
• Ask about setback requirements — how far from property lines, road, and existing structures
• Ask about frost line depth in your area — this determines how deep your post holes need to be (typically 3–5’ in most of the US)
• Check for any HOA covenants or deed restrictions on your property
• Ask if the property is in a flood zone (relevant for floor decision)
• Ask what drawings/site plan they need for the permit application

What to Submit (typically)

• Site plan showing the barn location on your lot with dimensions and distances to property lines
• Basic structural drawing (a kit’s included plans often satisfy this)
• Your plot/survey if you have it

Costs

Permit fees for a residential storage building typically run $50–$500 depending on county. Agricultural exemptions sometimes apply on rural land — worth asking.

Reference: diypolebarns.com — Permit Requirements · themetalshopllc.com — Do You Need a Permit?

Site Prep & Layout

Site Selection

• Choose ground that drains away from where you’ll stand/work — you said you don’t care about water in, but you’ll still want it to not pool badly
• Avoid areas under large trees (roots, falling branches, shade on any future solar)
• Consider access: can the trailer get in and out easily?
• Orient the open side (front, tall side) toward where you want to drive in

Clearing & Leveling

1. Mark out a 22×32’ working zone (2’ overhang on each side)
2. Clear vegetation, roots, rocks
3. The ground does not need to be perfectly level — the posts can be cut to different heights to compensate — but close to level makes life easier

Layout

Use the batter board method to establish exact post locations:

1. Drive stakes 2–3’ outside each corner of the barn footprint
2. Run string lines between them at the correct height
3. Use the 3-4-5 rule (or measure diagonals) to confirm 90° corners — diagonals of a 20×30 rectangle should both be 36’1”
4. Mark each post hole center with spray paint or a stake

YouTube search: "batter boards layout pole barn foundation"

Materials & Budget

Rough Estimate (DIY, no kit)

A pole barn kit from a supplier (Hansen, Sutherlands, Menards) includes engineered plans and pre-cut materials, typically $8,000–$12,000 for a 20×30. Kits take a lot of guesswork out and the plans satisfy permit requirements — worth considering for a first build.

Lumber Notes

• Posts must be pressure-treated, ground-contact rated (UC4B or UC4C). UC4B minimum for direct burial; UC4C if soil is very wet or corrosive. Do not use standard UC3B deck lumber for in-ground posts.
• All fasteners in contact with treated lumber must be hot-dipped galvanized or stainless steel — the treatment chemicals corrode regular hardware quickly.
• Select lumber in person at the yard; reject warped, heavily knotted, or twisted boards.

Reference: 20×30 free DIY plans — myoutdoorplans.com · diypolebarns.com construction guide

Setting the Posts

This is the most critical step. Posts out of plumb or at the wrong spacing will create problems for every step that follows.

Post Hole Depth

• Minimum: Below your local frost line + 6” of gravel at the bottom
• Typical depths in the US: 3.5’–4.5’ in most regions; up to 5–6’ in northern climates
• Call your county building department — they’ll tell you the required depth
• For a 12’ post with 4’ burial, you’ll buy 16’ posts and cut them to final height after setting

Tools Needed

• Auger/post-hole digger: Rent a 2-person gas auger (8” or 10” diameter) — ~$80–120/day. This is the right tool; hand-digging 10 holes 4’ deep in any real soil will take forever and break you.
• Digging bar (for rocks)
• Level (4’ level minimum)
• String line and line level
• Concrete mixing tub or wheelbarrow (or order ready-mix)
• Temporary bracing lumber (2×4s)

Step-by-Step

1. Dig all holes to required depth. Add 4–6” of gravel to the bottom of each hole for drainage (slows rot at the post base).

2. Set one corner post first. Drop it in, check plumb on two adjacent faces with your level, and brace it temporarily with 2×4 stakes driven into the ground at 45°. Don’t pour concrete yet.

3. Set the opposite corner post on the same wall. Use string lines at a known height to get it at the right elevation relative to the first post. Check plumb and brace.

4. Fill in intermediate posts along that wall using string as a guide for alignment.

5. Repeat for the other wall — front row (tall posts) and back row (short posts).

6. Check everything before pouring:

   • All posts plumb (level on both axes)
   • Spacing consistent (measure between each adjacent post)
   • Diagonal measurements equal (confirms square)
   • String lines confirm tops will be at the right heights

7. Pour concrete. Two options:

   • Dry-pour Quikrete: Pour dry bag mix into hole around post, then add water. Quick and strong enough for posts. About 2–3 bags (60 lb) per hole.
   • Wet-mix: Mix in a wheelbarrow and pour in. Stronger but more work.
   • Fill to 2–4” below grade so the concrete doesn’t act as a water trap against the wood.

8. Let cure 24–48 hours before loading with any framing weight.

9. Cut posts to final height using a chalk line snapped across all posts at the correct height — front row at 12’, back row at ~8’8” (or whatever your slope calculation gives). Use a circular saw or reciprocating saw to trim.

Concrete Method Debate

Direct burial (post in ground with concrete collar) is the traditional method and perfectly fine for a storage barn. Some builders prefer post bases / standoffs anchored to a concrete footing — this keeps the wood above ground and extends life significantly, but costs more and is more complex. For a first build storing a trailer and firewood, direct burial with good UC4B posts is standard and fine.

Reference: Hansen Buildings — Pole Barn Construction · Sutherlands — Post Frame Basics

YouTube search: "pole barn post setting concrete step by step" · "how to set posts for pole barn auger" · "quikrete dry pour fence post"

Wall Framing (Girts & Headers)

Girts are the horizontal 2×4 or 2×6 boards that span between posts on the walls. They give you something to attach siding to and add rigidity.

Layout

• First girt: 6–8” above grade (acts as a splash/skirt board — keeps the bottom edge of siding off the ground)
• Remaining girts: every 24” up the wall
• Top girt: flush with post tops, acts as the top plate

Installation

1. Mark girt height on each post with a chalk line
2. Nail or lag-bolt girts to the outside face of posts (face-nailing) or use joist hangers for a stronger connection
3. A typical 10’ wall needs about 5 girts per bay

Door Opening(s)

Decide where the doors go before you frame girts. For the trailer, you’ll want a minimum 12’ wide × 10’ tall opening (wider is better — trailers are wider than you think once you account for fenders and ramps). A 14–16’ wide opening is more comfortable.

• Frame the door opening with a double header (two 2×10s or LVL beam) spanning between posts on either side
• The posts adjacent to the door opening carry extra load — they may need to be doubled up depending on span (check with your lumber yard or an engineer)

YouTube search: "pole barn wall girt framing tutorial" · "pole barn door header framing"

Roof Framing (Rafters & Purlins)

For a mono-slope (shed) roof, the framing is straightforward: rafters span from the tall front wall to the low back wall at a consistent slope.

Calculating Rafter Length

For a 20’ wide building with a 2:12 pitch:

• Rise over 20’ run: 2/12 × 20’ = 3’4”
• Rafter length (Pythagorean): √(20² + 3.33²) ≈ 20’3” (plus overhang)
• Add 12–18” overhang at each end for eave protection → buy 22’ or 24’ lumber, or splice

Rafter Sizing

For a 20’ span with standard snow loads: 2×10 or 2×12 at 24” on center is typical. Have a lumber yard or online span calculator verify this for your region’s snow load — don’t guess on roof framing.

Span calculator: search "rafter span calculator" or use the American Wood Council’s online tool

Purlins

Purlins are the horizontal boards that run perpendicular to the rafters (along the 30’ length) and give the metal roofing panels something to screw into.

• Size: 2×4 laid flat is standard; 2×4 on edge is stronger for longer spans or high snow areas
• Spacing: 24” on center is typical for most metal roofing panels
• Start at the eave (bottom) and work up — do not start from the peak
• Stagger joints so they don’t all fall on the same rafter
• Fasteners: use screws rather than nails for purlins — better pull-out resistance

Sequence

1. Cut all rafters to length (identical — it’s a mono slope)
2. Mark and notch the bird’s mouth cut where each rafter sits on the top plate (front and back)
3. Set rafters every 24” along the 30’ length (about 14–15 rafters)
4. Brace temporarily while you check alignment
5. Install purlins working from eave to ridge

Reference: FBI Buildings — Purlin Installation · Hansen Buildings — Purlin Guide · APB Buildings — Purlin Installation Guide

YouTube search: "mono slope shed roof framing tutorial" · "pole barn purlin installation" · "rafter bird's mouth cut how to"

Metal Roofing

Metal is the right choice here: durable, fast to install, and sheds water well.

Panel Types

For a first build, any of these works. AG panel or corrugated is what you’ll find at most farm supply and lumber stores.

Quantities

For a 20×30 building with 12” overhang on eaves and rakes:

• Roof area: (20’ + 1’ overhang) × (30’ + 2’ overhang) = ~21’ × 32’ = 672 sq ft
• Add 10–15% waste → ~750–775 sq ft of panels
• Each AG panel covers about 3’ of width → need about 11 panels per 30’ run length
• But you’re also spanning ~21’ with one sheet (or two overlapped sheets if panels don’t come long enough)

Most suppliers will cut panels to custom lengths — order them at the exact rafter length + overhang to avoid splicing.

Minimum Pitch

• Metal roofing manufacturers typically require 2:12 minimum for exposed fastener panels (AG, R-Panel, corrugated)
• Some require 3:12 — check the spec sheet for whatever brand you buy
• Your planned pitch should exceed this

Installation

1. Install closure strips (foam) along the eave and ridge — these fill the gap between the panel profile and the structural framing, keeping out birds and insects
2. Start on the side opposite the prevailing wind so wind can’t get under the panel overlaps
3. First panel: set flush at the eave, overhang 1–2” beyond the fascia board, square to the building
4. Fasten into the raised ribs (not the flat valleys) with self-drilling hex-head screws with rubber washers — typically 1.5” or 2” pancake-head roofing screws. Do not over-tighten (compresses the washer too much and creates a leak point)
5. Panel overlap: overlap each successive panel by 1 rib; apply butyl tape sealant at end laps
6. End laps (where two panels meet lengthwise): overlap at least 6 inches, use butyl tape between
7. Install ridge cap last, with foam closure strips underneath; overlap ridge cap sections by 6”
8. Install rake trim along the gable ends

Safety

• Metal gets extremely slippery when wet or dew-covered — only work in dry conditions
• Walk on the raised ribs, never the flat valleys
• Use rubber-soled boots
• Use a roof bracket or toe board for anything over a few feet of slope

Reference: CMT Components — How to Install Metal Roofing · diypolebarns.com — Metal Roofing Trims · roof-installation.com — Corrugated Panels

YouTube search: "metal roofing installation pole barn step by step" · "AG panel roof installation DIY" · "how to install corrugated metal roofing"

Doors & Access

Options

Sliding doors (barn-style):

• Classic look, no swing clearance needed inside or outside
• Roll on a top-mounted steel track; gravity hold at the bottom
• Good for very wide openings (12–16’)
• Hardware kits: $100–300 depending on door weight/size

Swing doors (hinged):

• Simpler to build, just large hinges
• Need clear swing space outside (a problem if snowy or if you’re backing the trailer in)

Roll-up doors:

• Most convenient for vehicle access
• 12’×10’ roll-up: ~$800–1,500 for a quality door
• Requires a header with enough clearance above for the drum

Recommendation

For a trailer and firewood barn, a pair of swing doors or sliding barn doors covering a 12–14’ opening is a good first build. A roll-up door is nicer long term but costs more and adds complexity.

Firewood Access

Consider a smaller separate door on the side wall (a standard 36” door) specifically for easy firewood access without opening the whole front. This is cheap to add during framing — just leave an opening and frame it out.

What Else to Think About

These didn’t make the original list but are worth a conversation:

Ventilation: Even without finishing the interior, some airflow helps keep firewood dry and prevents condensation on the trailer. A simple ridge vent or soffit vents are easy to add during construction.

Electrical: Running one circuit (20A) to the barn for lights and a plugin is very nice to have, especially for working in there on short winter days. Conduit run underground from the house is not a huge job. Permits required — worth doing while you have the trench open.

Gutters: With a mono-slope, all water comes off the back wall. If the back faces anything you care about (fence, garden), a simple gutter with a downspout keeps it tidy.

Gravel floor: You said you don’t care — but 4–6” of compacted gravel inside is a relatively cheap (~$200–400) upgrade that makes the space much more usable: no mud, better drainage, cleaner for the trailer.

Anchoring / Wind uplift: Check if your county requires the posts to be designed for wind uplift. Post depth + concrete collar usually satisfies this, but worth confirming.

YouTube Channels & Search Terms

Channels Worth Following

• Perkins Builder Brothers — professional builders who document real projects with commentary on technique; very clear explanations
• Fix This Build That — DIY outdoor structures including post-frame work
• 731 Woodworks — shop and outbuilding builds including post-frame
• Lumnah Acres — homestead building projects

Recommended Search Queries

Copy these into YouTube:

Open Questions to Decide Together

• Orientation: which direction does the front (open/tall) face? Want sun? Wind shelter?
• Door type: swing, slide, or roll-up?
• Electrical: yes now, or rough-in conduit only?
• Gravel floor: worth doing now vs. later?
• Permit required? — call county building dept
• Kit vs. lumber-only: do we want engineered plans included, or figure it out from scratch?
• Timeline: is there a season we want to target?