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HDPE Liner Installation

Three views of the 30 mil HDPE liner: against the cedar, in build order, and captured under the cap strip
Footprint 14 ft x 10 ft U-shape
Wall Height 20 in (4x 2x6 cedar)
Liner 30 mil HDPE, walls only
Base 1/4 in galv. hardware cloth
Staples 1/2 in stainless, 6 in O.C.
Top Edge Cedar cap strip, screwed
1 Diagram 01 · Sliced Cutaway
Liner in Context with Cedar Walls

Front-left quadrant of the arm is removed so you can see the liner draped against the interior wall face, the hardware cloth at the base, and how the cap strip captures the top edge.

CEDAR 2x6 4 courses stacked to 20 in finished height
CAP STRIP 3/4 in x 1.5 in ripped cedar, screwed over the liner fold
30 MIL HDPE food-safe, walls only, stapled then capped
1/4 IN HARDWARE CLOTH vole barrier at base, drainage stays open
SOIL / HUGEL FILL logs then garden mix, installed after the liner
Diagram 01
Sliced Cutaway
Cedar 2×6 wall 4 courses · 20" tall Cedar cap strip 3/4" × 1.5" · screwed 12" O.C. 30 mil HDPE liner Interior wall face · full height Liner fold-over 1" lap captured by cap strip Stainless staples 1/2" · 6" O.C. under cap 1/4" hardware cloth Base only - NOT under HDPE Cut plane Wall removed for view Cedar end-grain (cut) Shows 5.5" actual 2×6 depth Soil column (fill) Goes in last · ~17" deep 20" 30° ISOMETRIC · Front-left quadrant sliced · 1 ft ≈ 44 px
Front-left quadrant removed to reveal the interior wall stack-up. Sliced cutaway shows a 6 ft segment of one arm for clarity; the full U is 14 ft x 10 ft.
2 Diagram 02 · Exploded Isometric
Wall Assembly, Install Order

Layers pulled apart in install sequence. The liner goes on after courses 1-2 are up and the hardware cloth is stapled, then you build courses 3-4 over it and cap the top edge.

KEY SEQUENCE INSIGHT The liner goes in between courses 2 and 3, not after the wall is fully built. This lets you trap the bottom edge under hardware cloth and the top fold under the cap strip without awkward overhead stapling. See Section 7 of the build guide.
Diagram 02
Exploded Isometric
Step 7 - Soil fill Hugel logs + garden mix · last Step 6 - Cedar cap strip 3/4"×1.5" · captures liner fold Step 5 - Courses 3 & 4 Stack over liner · screw 12" O.C. Step 4 - Staple 30 mil HDPE liner Interior faces only · fold at top ⚠ Do NOT cover the base Step 3 - Courses 1 & 2 Screw to 4×4 posts · 3-4-5 square Step 2 - 1/4" hardware cloth Overlap seams 6" · staple to course 1 Step 1 - Prepare ground Level site · remove sod · confirm square 7 6 5 4 3 2 1 THIS DIAGRAM SET · LINER INSTALL 30° ISOMETRIC EXPLODED · 1 ft ≈ 32 px · Shows a 6' arm segment
Layers pulled apart in install sequence.
3 Diagram 03 · Top-Edge Detail
Where the Liner Meets the Cap Easiest To Botch

Zoomed corner section, this is the part that is easiest to botch. Fold the liner 1 in over the top of course 4, staple at 6 in on center, then screw the cedar cap strip down to pin the fold permanently.

WHERE BUILDS GO WRONG Most DIY raised-bed liners fail at the top edge, they sag into the soil within one season because the fold was not captured. The cap strip is the non-negotiable detail. It is 15 minutes of ripping cedar scrap and costs nothing.
Diagram 03
Top-Edge Detail
3/4" tall 1.5" wide Fold ≈ 1" 6" O.C. 5.5" (2×6 actual) ① Cedar cap strip Ripped from scrap cedar · 3/4"×1.5"Screw down 12" O.C. · traps liner ② HDPE top fold Fold 1" over top of course 4Crease firmly before stapling ③ Top-edge staples 1/2" stainless · 6" O.C. along foldHidden under cap strip when done ④ Wall-face staples 1/2" stainless · 8-10" O.C. verticalOnly enough to hold liner flat ⑤ 30 mil HDPE Food-safe · not PVCCovers full 20" interior face ⑥ Cedar 2×6 Course 4 shown (top)Course 3 below split line ⑦ Course split Between courses 3 & 4Offset joints on long runs TOP-EDGE DETAIL · Iso-cross section · 1" ≈ 32 px · Looking at interior corner of course 4
Fold captured under the cedar cap strip.
4 Dimensions and Assumptions
Dimensions and Assumptions
  • Pulled from the U-Bed build guide: 14 ft x 10 ft U-shape footprint, 20 in wall height, 4 courses of cedar 2x6, 4x4 corner posts cut to 20 in.
  • Cap strip sizing (3/4 in x 1.5 in) is a recommendation, the build guide mentions a cedar cap strip along the top edge without specifying dimensions. Ripping from a 2x6 scrap on the table saw is the simplest source.
  • Staple spacing (6 in on center under the cap, 8-10 in on center on wall faces) is industry standard for 30 mil HDPE, the build guide does not specify on center spacing.
  • Liner fold (1 in) is the minimum needed for solid staple purchase and cap coverage. Go 1.5 in if the roll width allows.
  • The sliced cutaway shows a 6 ft segment of one arm for clarity, the full U is 14 ft x 10 ft overall.
The Manor · Back Yard · U-Bed Liner Diagrams Build reference · diagram set