How to put up a trellis

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Whether it's freestanding, attached to a building or sitting atop a wall or fence, a trellis provides privacy, shade and general ambiance by supporting vines and other foliage.

Designs are legion, and Joseph Guido, a contractor who has erected many, recommends a simple procedure for choosing one: "Walk around the neighbourhood and find a trellis you like." he says, "you're bound to see twenty or thirty different styles." He offered a few tips for putting up your favourite one.

"Walk around the neighbourhood and find a trellis you like. In a few city blocks, you're bound to see twenty or thirty different styles."

Joseph Guido; Building Contractor

Erecting a freestanding structure

"Erecting a freestanding trellis is very much like putting up a fence," says Guido. "You need to set posts securely, and the way I like to do that is to mount them on metal brackets set in concrete. That improves drainage and extends the life of the posts by several years." Once the posts are up, the rest of the trellis may consist of nothing more than a few cross beams, or it may incorporate latticed panels. "Just remember to use exterior-grade screws to attach everything," he cautions.

• Draw a design of the structure you plan to build and use it to map out the locations of the posts, which should ideally be no more than 2.5 m (8 feet) apart.

• Dig a hole at least 50 cm (20 inches) deep for each post, using a post hole digger.

• Fill the hole with concrete mix. Build the top about 5 cm (2 inches) higher than ground level and set a galvanized metal post holder into the concrete. Let the concrete set overnight.

• Bolt a post to each holder, using two coach bolts per post.

• Connect the posts in pairs by screwing parallel beams on top of each pair, then set perpendicular cross-beams on top of those and screw them down.

• Stabilise the posts as needed by joining them with wooden braces. Pre-fabricated lattice panels installed between posts with screws can also stabilise the structure.

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Attaching a trellis to a building

You may want to attach a trellis to the side of your house to support climbing plants that otherwise wouldn't grow there. It's important to avoid screwing vertical supports or lattice directly to the house, because the trellis needs space on all sides for plants to wind around it. Guido's advice is to attach spacers to the house -- using pressure-treated lumber -- and to attach the trellis to the spacers.

• Cut spacers that are about 30 cm (1 foot) long and install one on the siding near the top, bottom and middle of every support post. Attach it to the siding with screws or -- if the siding is brick or masonry -- screws and screw anchors.

• Caulk around each spacer to prevent water from seeping behind it.

• Screw the upright posts to the spacers using coated screws. Use the longest screws you can that won't penetrate all the way through the spacer and into the wall.

• Set posts for the front of the trellis as you would those for a freestanding structure.

  • Screw cross bracing or latticed panels to the posts according to your design.

Mounting on a fence or wall

"Many people mount a trellis on the top of their new wooden fence, and because that raises the height, I always check with the local building department first," says Guido. Planning permission usually isn't needed in the UK unless the finished structure exceeds 2 m (6 and a half feet) in height. "When mounting a trellis on a wooden fence, there's little more to do than screw it down, but adding a trellis to a concrete wall is a little more complicated." Guido described a procedure for installing pre-fabricated lattice panels.

• Snap a chalk line down the centre of the wall on which you plan to install the trellis.

• Mark the positions of the studs needed to support the panels. Don't forget to take the width of the studs into account -- you want to leave enough room to fit the panels between them.

• Drill a hole on each mark to a depth of 10 to 15 cm (4 to 6 inches) with a 1-cm (half inch) masonry bit. Use a spirit level to keep the drill horizontal and the bit vertical. Drill a similar hole in the bottom of each stud.

• Tap a length of 1-cm (half inch) steel reinforcing bar -- Guido calls it "re-bar" -- into each hole. Cut all the studs to the same length with a circular saw and tap one onto each steel post.

• Screw the panels to the studs, then screw a rail to the tops of the studs to cap the trellis.

Building a garden arbour

Guido lives in California and uses redwood almost exclusively for trellis construction because of its rot resistance. He also recommends cedar. "The basic construction of a trellis is uncomplicated, but that doesn't mean the final result has to look simple. Once the structure is stable, it's fairly easy to add arches." Guido offers a simple way to construct an arch for a garden arbour.

• Set the posts for the arbour and measure the distance between them that the arch must span.

• Cut a series of six 2.5 by 15 cm (1 by 6 inch) boards of equal lengths with ends mitred to 22.5 degrees. Adjust the lengths of the boards to complete the span between the posts.

• Assemble boards on the flat surface, then cut a second series with ends slightly staggered from those of the first and assemble these on top of the first series of boards.

• Screw the two series of boards together, then cut off the corners and shape the underside of the arch with a jig saw.

• Construct another arch in the same way. Screw one to the posts in the front of the arbour and one to those in the back, then join the two arches with a series of slats to complete the top of the structure.

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Protecting your project

A trellis has to withstand even more punishing conditions than a fence or deck -- besides being exposed to sun and rain, it's in constant contact with vegetation. To prevent rot from drastically shortening its life, give the structure a coat of waterproofing sealer before it gets covered with foliage. Guido recommends semi-transparent stain for sunny locations because of the ability of the pigment to block ultraviolet sunlight. "If you want to keep the wood natural, even a transparent liquid waterproofing treatment can make a big difference," he adds.