36″ opening garden arbor plans

Parts

Cut list

Kerf 1/8″ included. Every cut runs edge to edge.

Steps

• Tape measure
• Speed square
• Pencil
• Drill/driver
• Clamps
• Safety glasses
• Hearing protection
• Dust mask
• Circular saw or miter saw
• Miter saw, or circular saw in two passes, for 4×4 posts
• Post-hole digger
• Wheelbarrow and hoe for mixing concrete
• 4′ level
• Line level and string
• Jigsaw
• 1/2″ drill bit, 8″ long
• Socket wrench
• Stepladder
• Sander, 120 and 180 grit

Underlined words have a short explanation: hover or tap them. All of them are on the glossary page.

1. 1Before you start

   Read every step once, start to finish, before you buy or cut anything. Each step names the parts it uses by letter; the parts list gives their sizes.

   Set up somewhere flat with good light. A pair of sawhorses with a sheet of plywood on top makes a fine work table.

   Wear safety glasses whenever a tool is running, hearing protection for saws, and a dust mask for sanding and for cutting treated wood or sheet goods. Tie back long hair and loose sleeves. Keep children and pets out of the work area.

   • Tip At the store, pick straight boards: hold each one up to your eye and look down its length. Skip boards that bow, twist or have big knots near the ends.
   • Tip Measure twice, cut once. Most mistakes are a misread tape, not a bad cut.

2. 2Cut and label the parts

   Cut every part on the cut list. Cut the longest parts first: if one goes wrong, it can still become a shorter part.

   To mark a cut, hook your tape on the end of the board, make a small V with its point exactly at the measurement, and draw a square line through the point with a speed square. Put an X on the waste side.

   Cut on the waste side of the line, so the blade's kerf (about 1/8″) comes out of the scrap, not your part.

   Write each part's letter in pencil on a face that won't show, and stack the parts by letter.

   Sand the faces before assembly while they're flat and easy to reach: 120 grit, then 180.

   ✓ Lay the parts out and count them against the parts list. Measure a few: if one is off by more than 1/16″, recut it now.

   STOP. Let the saw reach full speed before it touches the wood, keep both hands clear of the blade's path, and never reach under a board you're cutting. Support long boards on both sides of the cut so the blade doesn't pinch.

3. 3Pick the boards and the screws

   Cedar for the arbor: look for boards with mostly reddish-brown heartwood. Pale yellow-white streaks are sapwood, which rots years sooner; keep those streaks on the inside or skip the board.

   Pressure-treated pine: read the end tag. Parts that touch soil, sit in wet mulch or go in the ground must say "ground contact"; "above ground" lumber is fine for everything else. New treated boards are often wet and heavy: stack them flat with scrap sticks between them for a week or two in the shade so they dry and stop twisting.

   Sight down each board at the store like a rifle barrel. Skip boards that twist, bow more than about 1/4″ over 8′, or have big loose knots near where you will cut or screw.

   Use exterior screws only: coated deck screws (labelled for treated lumber, "ACQ compatible") or stainless steel. The copper in treated wood eats plain and zinc-plated steel within a few years. Indoor wood screws and drywall screws rust and snap outdoors.

   The four posts are always ground-contact pressure-treated, whatever you choose for the top: they sit in wet soil and concrete for decades.

   • Tip Buy one extra board of the most-used size. A split or a mis-cut then costs you nothing but a few dollars.
   • Tip Cedar splits easily: predrill every screw within 2″ of the end of a board with a bit about the size of the screw's inner shank.

   ✓ Every board is reasonably straight, and the screw box says exterior, coated for treated lumber, or stainless.

4. 4Call 811 and check the spot

   At least 3 working days before you dig, call 811 (or use call811.com). It's free. They send people to paint or flag buried gas, electric, water and cable lines near where the arbor will go.

   Check your property line on your survey or plot plan, and ask your town about setbacks, easements and whether this needs a permit.

   Pick ground that drains: not a low spot where puddles sit after rain, and not over a septic field.

   STOP. Don't dig until the marks are down. Hitting a gas or power line can kill you and is expensive to repair.

5. 5Mark out a square rectangle

   Hammer a stake at one corner of the arbor (outside faces of the posts). Measure 43″ along the long side and hammer a second stake. Tie mason's line tight between them, a few inches off the ground.

   For the first square corner, use the 3-4-5 rule: from the first stake, mark 3 ft along the string. Run a tape 4 ft out roughly at 90°. Swing it until the 3 ft mark and the 4 ft point are exactly 5 ft apart. That direction is square: set a stake 24″ out along it.

   Measure the last corner from the other two (43″ and 24″) and set the fourth stake. Run string around all four.

   Measure both diagonals, corner to corner. Nudge the stakes until the two numbers match.

   • Tip For bigger layouts use 6-8-10 instead of 3-4-5: the bigger the triangle, the more exact the corner.
   • Tip Batter boards (two stakes with a crosspiece set 2 ft outside each corner) let you take the strings down to dig and put them back in exactly the same place.

   ✓ Sides are 43″ and 24″ and the diagonals match within 1/2″. Spray marking paint along the strings, then pull the stakes you're about to dig around.

6. 6Mark the post centres

   The string rectangle is the outside of the posts. At each corner, measure 1 3/4″ in along both strings and mark the post centre on the ground with a dab of paint.

   Check: the centres are 39 1/2″ apart side to side and 20 1/2″ front to back.

   ✓ The two diagonals between post centres match within 1/4″ (each about 44 1/2″).

7. 7Dig the post holes

   Dig 4 holes 10″ wide and 36″ deep with a post-hole digger.

   That depth is 30″ for the post plus 6″ of gravel underneath so water drains away from the post end.

   Make the holes slightly wider at the bottom than the top, like a bell. Frost then can't grip the concrete and lift it.

   Pour 6″ of gravel in each hole and tamp it with the end of a 2×4 or the post itself.

   • Tip Your town knows the frost depth: it's how deep footings must go so winter frost can't push them up. Enter it in the options and the holes will be dug deep enough.

   ✓ Every hole is 36″ deep before the gravel and 30″ deep after it.

8. 8Set the posts plumb

   Stand a post in each hole. Run a string between the end posts at the height you want, to line up the ones in between.

   Hold a level against one face of a post until the bubble is centred: that face is plumb. Then check the face around the corner. Both faces must read plumb.

   Brace each post with two 1×4 or 2×4 boards: screw one end to the post and the other to a stake hammered into the ground, one brace on each of two sides at right angles.

   ✓ Every post is plumb on two faces, in line with the string, and the braces hold it there when you let go.

9. 9Mix the concrete

   You'll use 9 bags of 80 lb concrete mix for the 4 post holes. Mix one or two bags at a time in a wheelbarrow: concrete starts to stiffen in about 30–45 minutes (faster on a hot day), so only mix what you can place right away.

   Pour about 2 quarts of clean water into the wheelbarrow first, then empty one bag on top. (Each 80 lb bag needs about 3 quarts in total.)

   Mix with a hoe or square shovel: pull the dry powder from the corners and bottom into the wet middle and chop through it. Keep going until there are no dry pockets.

   Add the last of the water a cup at a time, mixing between each.

   Get the thickness right. It should look and feel like thick oatmeal or stiff peanut butter. A hoe dragged through leaves ridges that stand up, and a handful squeezed in a gloved hand holds its shape. Too dry: it crumbles and won't stick together, so add a little water. Too wet: it flows flat, water pools on top, and the concrete will be weak and crack. Then add some dry mix from a spare bag.

   • Tip More water makes concrete easier to push around and much weaker. Resist the urge.
   • Tip Rinse the wheelbarrow, hoe and shovel before the concrete sets on them. Don't wash concrete into drains or onto the lawn: let leftovers harden in a scrap box and throw them out.
   • Tip Buy one more bag than you need. Running out halfway through a pour is the most common mistake.

   ✓ Even grey colour throughout, no dry powder, no puddles of water on top; a ridge made with the hoe stands up.

   STOP. Wet concrete is caustic and burns skin. Wear waterproof gloves, safety glasses, long sleeves and long pants. Open bags slowly and wear a dust mask: the dust has silica. Rinse any concrete off your skin right away.

10. 10Fill the holes

    Shovel concrete into each hole around the post. Every 6″ or so, poke it hard with a stick or a piece of rebar to work out air pockets.

    Fill to about 1″ above the ground and shape the top into a little mound with a trowel, sloping away from the post so rain runs off.

    Check plumb again on both faces while it's still wet, and adjust the braces if needed.

    ✓ Posts are still plumb and in line after the concrete is in.

11. 11Let the concrete cure

    Concrete hardens by reacting with water, not by drying out, so keep the concrete around the arbor posts damp for the first 7 days: mist it with a hose morning and evening, or cover it with plastic sheeting held down at the edges.

    Keep it from freezing for the first week. Don't pour when it's below 40°F (5°C) or frost is forecast in the next two days. On hot days, pour in the early morning and shade it.

    You can walk on it or remove braces after 1–2 days. Wait 3 days before putting real weight on it. It reaches full strength in about 4 weeks.

    ✓ The surface is hard and grey-white when dry, with no powder when you rub it.

12. 12Trim the post tops level

    The posts were cut 2″ long on purpose, because holes are never dug to exactly the same depth. Now mark the real tops.

    On the post standing on the highest ground, measure 89 1/2″ up from the ground and make a mark. Carry that height to the other 3 posts with a long level on a straight board, or a string with a line level pulled tight.

    Wrap a speed square around each post at the mark and draw the line on all four faces.

    Cut on the line with a circular saw from two opposite sides (the blade won't reach through a 4×4 in one pass), or with a handsaw from a step on a sturdy stepladder.

    • Tip Brush a coat of end-grain preservative (copper naphthenate, sold as "end cut" treatment) on each fresh cut of treated wood: the treatment doesn't reach the middle of the post.

    ✓ A level laid across the tops (on a straight board for the far post) reads level, and every cut is square to the post.

    STOP. Never cut above shoulder height. Stand on a stable platform so the saw is in front of your chest, and wait for the blade to stop before lowering it.

13. 13Shape and bolt on the beams

    Cut the decorative tails on both beams (B). Lay a beam flat, mark 9″ in from each end (that's where the post will be), and mark 2″ up from the bottom edge at the very end. Join the two marks with a smooth curve: bend a thin strip of wood between two nails, trace it, and cut with a jigsaw.

    Use the first beam as the pattern for the second, so they match.

    Clamp one beam across the front faces of the front posts, tops flush with the post tops and 9″ past each post. Clamp the other across the back faces of the back posts.

    Drill two 1/2″ holes through beam and post at each post, one 1 1/2″ above the other, staggered slightly. Tap the carriage bolts through from the outside, add a washer and nut inside, and tighten until the head pulls snug into the wood.

    • Tip Drill with a long 1/2″ spade or auger bit, square to the face; have the helper sight from the side to keep the bit level.

    ✓ Both beams are level and 84″ above the ground at their bottom edge.

    STOP. Work from a stable stepladder with a helper holding the other end. A 2×6 that slips at head height comes down hard.

14. 14Set the rafters

    Cut the same style of curve on the bottom corners of each rafter end (C), starting 6″ from the end. Make one, then trace it on the rest.

    Stand 7 rafters on edge across the two beams, 9 1/4″ apart on centre, the end ones 2″ in from the beam tips. Each sticks out 6″ past the beams front and back.

    Fix each rafter to each beam with a hurricane tie (nails in every hole) or two 3″ screws toe-screwed through the rafter into the beam.

    • Tip Mark the rafter spacing on both beams first with a tape and pencil, then just line each rafter up with its marks.

    ✓ Sight along the rafter tails from the side: they form a straight line front and back.

15. 15Fit the side rails

    On each side, fit a bottom rail (D) between the front and back posts with its bottom 6″ above the ground, and a top rail right under the beams, its top 84″ up.

    Set them 3/4″ in from the outside faces of the posts (use a scrap of 1×2 as the gauge) so the lattice finishes flush. Toe-screw each end with two 3″ screws.

    ✓ Each rail is level and set back the same amount along its length.

16. 16Build the side lattice

    Screw 1 vertical strips (E) to the outside of each side's rails, 8 1/2″ apart on centre, plumb, one 1 5/8″ screw into each rail.

    Then screw 11 horizontal strips (F) across the outside of the posts and verticals on each side, 7 5/8″ apart on centre: 1 5/8″ screws into the posts and one 1 1/4″ screw at every crossing.

    • Tip Predrill every screw in the 1×2: it splits easily, especially near the ends.

    ✓ The openings are square and even; diagonals of a few openings match within 1/8″.

17. 17Protect it from the weather

    Decide how you want the arbor to look in five years. Bare cedar and bare pressure-treated wood both weather to silver-grey and still last many years; doing nothing is a real option.

    To keep the colour, use an exterior oil or semi-transparent stain: brush it on, let it soak in 15 minutes, then wipe off whatever is still shiny. Renew it every one or two years. Avoid clear varnish or polyurethane outdoors: sun cracks the film, water gets under it, and it peels.

    Pressure-treated wood must dry before any stain or paint. Sprinkle a few drops of water on it: if they bead up, wait; if they soak in within ten minutes, it is ready. This can take a few weeks to a few months.

    • Tip Finish on a dry day above 50°F with no rain forecast for 24 hours.
    • Tip Oil-soaked rags can catch fire on their own as they dry. Lay them flat outside to dry or keep them in a sealed metal can of water.

    ✓ The finish is dry to the touch everywhere, with no wet or shiny puddles in corners.

18. 18Plant the climbers

    Plant one climber at the outside base of each side, about 12″ out from the posts. Good choices: climbing roses, clematis, honeysuckle, or annual morning glory for quick cover the first year.

    Tie the shoots loosely to the lowest lattice strips. Train them up the sides and across the rafters over the next two or three seasons.

    Avoid wisteria unless you build with 6×6 posts: a mature vine weighs hundreds of pounds and can crush a light arbor.

    ✓ Ties are loose, and no shoot is wrapped tight around a strip.

19. 19Finish

    Ease every sharp edge and corner with 120-grit sandpaper so nobody gets a splinter.

    Sand all over with 180 grit, always along the grain (the direction the wood fibres run). Scratches across the grain show through stain.

    Wipe off the dust with a barely damp rag and let it dry.

    Outdoors, use an exterior finish: a penetrating deck oil or exterior stain, or primer and exterior paint. Leave cedar bare to weather silver if you like. If it holds soil for food plants, leave the inside unfinished.

    Let it dry for the time on the can before using it.

    • Tip Try your finish on a scrap of the same wood first: stain looks different on every board.