Pergola Construction

Freestanding or attached to the house

A freestanding pergola stands on its own four or more posts. It can go anywhere in the yard, over a patio at the far end of the lawn or around an outdoor kitchen, and it never touches the house, so there is no wall to flash. It needs more posts and footings, and the bracing has to keep it stiff in wind without help from the house.

An attached pergola uses the house for support along one side. It needs fewer posts, it reads as part of the house and it can shade a door or the windows of a room that gets too much afternoon sun. The trade-off is the connection to the wall, which has to be done carefully so it does not let water into the house.

We look at where the sun hits, where you will sit and what the house wall is made of before suggesting one or the other, and we will tell you when an attached pergola would mean fastening into a wall that is not suited for it.

Size is part of the same decision. A pergola should cover the table or seating it is meant for with room to pull out chairs, and it should be scaled to the house and patio around it so it does not loom over a small yard or look lost on a large terrace.

Posts on footings that stay plumb

A pergola is tall and open, which makes it a sail in a nor'easter even without a roof. Posts on footings below frost depth, commonly about four feet in Massachusetts, keep the frame from heaving out of plumb over the winters. Posts sit on hardware above the concrete so the end grain stays dry, and the frame is braced at the top with knee braces, beam connections or both.

Setting a pergola on an existing deck is possible but depends on what is under the deck boards. A post fastened to decking alone will rack and loosen. We open up the deck if needed to tie the posts into framing that can resist uplift and twisting, and add blocking or a new footing beneath when the existing frame is not enough.

Post size matters for looks as much as strength. A thin post under a heavy beam looks wrong, and a pergola built from undersized stock tends to twist as the lumber dries. We size posts for both, and on cedar or painted work we often build up or wrap the posts so they stay straight and the hardware stays hidden.

At the end we walk the finished pergola with you and go over what the wood or finish needs over the years.

Beams, rafters and how much shade you actually get

How much shade a pergola gives depends on rafter depth, spacing and which way the rafters run relative to the sun. Rafters running east to west block more of the midday sun. Close spacing and a layer of purlins on top increase shade further. We work out the layout so the shade falls where you sit at the time of day you use the space.

The ends of the beams and rafters are where a pergola gets its character. A simple square cut suits a modern house, while a cut profile can pick up the trim details on a colonial or a Craftsman. Proportion matters here as much as on a porch: beams and posts sized to look right for the span, not undersized to save material.

Materials include pressure-treated pine, cedar and cellular PVC or composite wraps. Cedar weathers well and looks natural. Painted wood needs upkeep. Fasteners and connectors are rated for the lumber and for salt air on coastal properties so they do not stain or fail.

Attaching to the wall without letting water in

The most common mistake we see on attached pergolas is a ledger screwed through the siding into whatever is behind it, sometimes just the sheathing, with no flashing. Water runs behind the ledger, sits against the wall and rots the sheathing and rim of the house where nobody sees it.

When we attach to the house, siding comes off where the ledger lands, flashing goes behind and over it, and the ledger is bolted into the house framing. Another approach is to hold the ledger off the wall on spacers so water drains behind it, then flash the fasteners. Either way, the pergola is never hung from a gutter, a fascia board or brick veneer, none of which are built to carry it.

On houses where the wall cannot take the load, such as a cantilevered floor or a bay, we put a beam on posts close to the house instead and keep the pergola independent of the wall.

Planning it with you before the posts go in

We start by walking the space with you, staking out where the posts will land and looking at the view from inside the house, because posts end up framing the windows you look out of. You get a written scope that covers the size, footings, materials, end details and how it attaches, if it does.

Permits depend on the town, the size and if the pergola is attached, and we check with the building department rather than assume. During the build we keep you updated, changes are agreed before they are made, and the patio or deck below is protected and swept clean when we leave.

The posts are the decision that is hardest to change, so we confirm their locations with you on site before any holes are dug. If something turns up while digging, such as a buried line, ledge or an old footing, you hear about it right away along with the options, and nothing changes until you agree.

Lighting makes a pergola useful after dark. String lights and low-voltage fixtures can be planned into the beams, and any line-voltage wiring, outlets or a fan under a canopy is done by a licensed electrician, with conduit run inside the framing where possible. At the end we walk the finished pergola with you and go over what the wood or finish needs over the years.

See the rest of our exterior work, or browse the gallery for rooms we have finished.