How To Make A Garden Bench From Decking | Weekend Build Guide

Want a sturdy outdoor seat that matches your deck boards and shrugs off weather? This guide walks you through a rock-solid build using standard framing timber and deck boards, plus smart sizing so the seat feels good for everyone. You’ll get a clean cut list, clear steps, and pro tips that keep the project tidy and safe.

Project Overview And Dimensions That Feel Right

Comfort lives in the details: seat height, seat depth, and back angle. A simple target that works for most folks is a seat height around 16–18 in and a seat depth near 15–18 in, with a back that leans a touch for support. These ranges come from practical seating guidance used by furniture makers and woodworkers (seat height 16–18 in; depth 15–18 in). For a deck-board top, aim for a finished seat height of ~17 in after slats and frame.

Materials, Tools, And Cut List

Below is a complete shopping and cutting plan for a 48 in-long, 17 in-tall, ~18 in-deep garden seat. Adjust lengths to suit your space; keep the joinery and spacing the same for strength.

Cut List And Hardware

Part / Item	Qty	Dimensions / Notes
Seat Slats (Deck Boards)	6–7	5/4×6 or 1×6 decking at 48 in; leave ~1/8 in gaps
Front/Back Rails (Frame)	2	2×4 at 48 in
Side Rails (Frame)	2	2×4 at ~15 in (sets inside depth)
Seat Supports (Joists)	3	2×4 at ~15 in; spaced ~16 in on center
Legs	4	4×4 at ~16 in (plus slats = ~17 in seat height)
Back Posts (If Adding Backrest)	2	4×4 at 30–32 in, bolted to rear legs
Back Rails	2	2×4 at 48 in; set for a slight lean (5–10°)
Back Slats (Deck Boards)	3–4	5/4×6 or 1×6 at 48 in; ~1/8 in gaps
Deck Screws	~150	#8–#10 exterior-coated, 2½–3 in for slats to 2x framing
Carriage/Lag Bolts + Washers	8–12	3/8 in x 4–5 in for legs/frame/back posts
Wood Preserver / Sealant	1	Exterior-grade; recoat per label
Tools	—	Drill/driver, circular saw or mitre saw, square, clamps, sander

Garden Bench Made With Decking Boards — Step-By-Step

This section lays out the build in clean, repeatable steps. Pre-drill near board ends to prevent splits, and keep your work on a flat surface so the frame stays square.

1) Mill And Pre-Finish The Parts

• Cut all framing pieces and slats to length. Label parts with pencil so assembly stays organized.
• Ease sharp edges with 120–150 grit. Rounded edges shed water better and feel nice on the legs.
• Brush end-grain with preserver. End-grain drinks moisture, so give it an extra coat.

2) Build A Square Seat Frame

• Lay the two long rails parallel. Fit the two side rails between them to form a rectangle ~48 x ~18–19 in overall.
• Glue isn’t required outdoors; rely on mechanical fasteners. Drive two 3 in exterior screws through each corner, or use pocket screws rated for exterior work.
• Check for square by measuring diagonals; nudge until both match.

3) Add Seat Supports

• Install three 2×4 supports inside the frame, spaced near 16 in on center. This keeps slats stiff and quiet.
• Toe-screw through the supports into the rails, or use exterior pocket screws.

4) Fit The Legs

• Stand the frame on edge. Clamp a 4×4 leg flush with each corner. The top of each leg should sit even with the top of the frame.
• Drill for 3/8 in carriage or lag bolts through the rails into the legs. Two bolts per leg, spaced vertically. Add washers and tighten snug.
• Re-check the frame for twist before locking everything down.

5) Lay The Seat Slats

• Start at the front: position the first deck board with a slight overhang (⅛–¼ in) for a soft edge against the legs.
• Set ~1/8 in gaps between boards for drainage and seasonal movement. Use spacers for consistency.
• Drive two screws into every support under each board. A good rule is to choose a screw long enough to penetrate at least 1 in into the framing below; #8–#10 exterior screws in the 2½–3 in range fit well for 5/4 or 1 in deck boards.

6) Add The Backrest (Optional But Worth It)

• Extend the rear legs up as back posts or through-bolt separate posts to the rear legs.
• Set the back rails between posts with a gentle lean (about 5–10°). This tiny recline turns a plain seat into a lounge-worthy spot.
• Fix back slats with the same gap and screw pattern as the seat.

7) Sand, Seal, And Finish

• Knock down any proud edges. Round outside corners your hips and hands touch.
• Brush or roll on an exterior sealer. Keep finish off hardware heads so a driver bit can bite later.

Sizing Notes You Can Trust

For comfort, keep the seat height near 17 in with a depth around 16–18 in; these figures come from proven furniture dimensions used by experienced builders. If you’ll add a 2 in cushion, trim the leg length to keep the finished seat near the same height once the cushion compresses.

Fasteners, Gaps, And Durability

Use corrosion-resistant screws designed for outdoor projects. Drive two fasteners per slat at every support and keep board gaps near 1/8 in for drainage. Where legs bolt to rails or where back posts meet the frame, through-bolts with washers beat long screws for clamping force and long-term stability.

Why Screw Length Matters

Pick a screw that clears the slat thickness and still bites at least 1 in into the support below. With common 5/4×6 decking, that puts you squarely in the 2½–3 in range for most builds. Stainless or polymer-coated screws resist staining and corrosion in wet seasons.

Safety And Setup

• Wear eye and hearing protection, and use a dust mask when sanding.
• Clamp parts before drilling; keep hands clear of the bit path.
• Pre-drill near board ends to avoid splits.
• Follow local code where relevant, and stick with exterior-rated timber and hardware.

Plan Variations And Upgrades

Hidden-Fix Slats

If you prefer a clean look, hidden-fastener clips designed for deck boards can work on a bench top too. They take more time and need compatible boards, but they leave no visible screw heads.

Armrests

Add short 2x blocks at the top of the back posts and run deck boards over them to form arms. Keep edges rounded and fix with two screws at every contact point.

Storage Shelf

A slatted shelf under the seat keeps shoes or plant trays off wet ground. Use the same 1/8 in gaps and two screws per support.

Time And Budget Planning

This project fits neatly into a single weekend for one person with basic tools. Costs vary with timber choice and hardware finish. Use the guide below to set a realistic plan.

Build Time And Cost Guide

Scope	Time	Typical Cost (USD)
Seat-Only (48 in, no back)	4–6 hours	$90–$160 (timber + screws + sealer)
Seat + Back	6–9 hours	$120–$220
Seat + Back + Armrests	8–10 hours	$150–$260

Finishes And Care

Oil-based exterior finishes warm the color and shed water well but need a light recoat every year or two. Clear sealers keep the natural look and are quick to refresh. Pigmented deck stains even out mixed timber tones and help with UV. Whatever you choose, hit end-grain and horizontal faces first and keep hardware heads free.

Seasonal Checks

• Re-tighten bolts and any screws that back off after the first week of sun and rain cycles.
• Clean with a soft brush and a mild deck wash. Skip pressure-washer blasts at close range; they can gouge timber and raise grain.
• Top up finish before long wet spells.

Responsible Timber Choices

Where legs touch paving or soil splash, pick pressure-treated stock or naturally durable species, and seal any fresh cuts. Posts that stand close to damp ground last longer with heavier treatment classes. If you’re in a region that follows Use Class ratings, material listed for ground-contact duty is the safer bet for legs and lower rails near splash zones.

Quality Checks Before You Sit Down

• Rock-solid feel: no racking when you push the ends.
• Even gaps: ~1/8 in between all slats for clean lines and drainage.
• No proud fasteners: every screw sits just below the surface.
• Soft edges: fingers, backs of knees, and forearms meet rounded wood, not sharp corners.

Quick Reference: Build Steps At A Glance

1. Cut and label parts; seal end-grain.
2. Assemble a square seat frame.
3. Add three seat supports at ~16 in on center.
4. Through-bolt four legs to the frame.
5. Lay and fasten seat slats with 1/8 in gaps.
6. (Optional) Add back posts, rails, and slats with a slight lean.
7. Sand touch points and apply exterior finish.

Helpful References

For fastening patterns, board gaps, and general deck-board practices, you can scan the AWC deck guide. For seating comfort ranges, see woodworking guidance that pegs seat height near 16–18 in and depth near 15–18 in, such as this seat dimension reference.

Wrap-Up: Why This Build Works

You’re matching materials to the outdoors, using screw lengths that bite deep, and locking legs with bolts instead of wishful thinking. The result is a bench that looks made-to-measure next to your deck boards, feels comfortable on day one, and stays tight through seasons of sun and rain.