Standing in a Cary lumber yard last spring, I watched a homeowner spend twenty minutes trying to decide between a pergola, an arbor, and a trellis. He kept picking up the same pre-assembled arbor kit, putting it back, and staring at the pergola display. The problem is that these three structures get thrown around like they are interchangeable, but they serve completely different purposes. A pergola is not a big arbor, and a trellis is not a small pergola. Choosing the wrong one means wasting money on a structure that doesn't actually solve your problem. Let's cut through the confusion so you can pick the right one for your Cary yard.
What Is a Pergola, an Arbor, and a Trellis?
If you ask five different contractors for definitions, you will get six different answers. But after building these structures for almost two decades across McHenry County, here is how I break them down.
Pergola. A pergola is a permanent, freestanding or attached structure with a flat or slightly pitched roof made of open beams or rafters. It creates a defined overhead space, usually large enough for a seating area, dining table, or outdoor kitchen. Pergolas are typically 8 to 12 feet tall and 10 to 20 feet wide. The open roof provides partial shade and a strong sense of enclosure without blocking all sunlight. In Cary, most pergolas are built with pressure-treated pine, cedar, or a vinyl wrap, and they can be customized with retractable canopies or climbing vines for more shade.
Arbor. An arbor is a smaller, often arched structure designed primarily as an entryway or a focal point. It has a curved or flat top and is usually 6 to 8 feet tall and 3 to 6 feet wide. Arbors are built to mark a transition, like a garden gate or the entrance to a path. They are almost always intended to support climbing plants, such as clematis, roses, or wisteria. An arbor is not meant to sit under for extended periods, it is meant to walk through or admire.
Trellis. A trellis is the simplest of the three. It is a flat, lattice-like panel or framework that attaches to a wall, fence, or post. Trellises are purely functional: they support climbing plants, provide privacy screening, or cover an ugly wall. They come in sections that are 2 to 8 feet wide and 4 to 8 feet tall. A trellis is not a standalone structure. It needs a support surface. If you want to grow morning glories up the side of your deck, you want a trellis. If you want to sit under something, you do not.
Key Differences in Size, Function, and Installation
The size difference is not just cosmetic. It determines how much work is involved, what permits you need, and what your yard can accommodate.
Size and footprint. A pergola requires a solid foundation, usually 4x4 or 6x6 posts sunk into concrete footings that go below the frost line, which in Cary is about 42 inches deep. That means digging holes, pouring concrete, and waiting for it to cure before you even start framing. An arbor uses smaller posts (4x4 typically) and can often be anchored with ground spikes or shallow concrete footings, though I recommend a proper footing for anything that will support heavy vines. A trellis can be attached directly to a house or fence with screws and anchors, no concrete needed.
Installation complexity. A pergola is a multi-day project for a skilled carpenter. The roof rafters need to be cut, notched, and fastened so they are level and square. The structure must be braced against wind loads, which in northern Illinois can be significant. An arbor can be built in an afternoon by a handy homeowner if the kit is pre-cut. A trellis is a two-hour job, screw it to the wall and you are done.
Function. Pergolas create an outdoor room. They extend your living space and add real estate value. Arbors create a destination, a visual anchor that draws the eye through the garden. Trellises solve a specific problem, like screening a view or supporting a plant. If your goal is to add shade and seating, you need a pergola. If your goal is to frame a garden path, you need an arbor. If your goal is to grow something up a wall, you need a trellis.
Which Structure Best Fits Your Cary Backyard Goals?
Let me give you three real Cary scenarios I have seen play out.
Scenario 1: The entertainer. You have a deck off the back of your house, and you want to extend the time you can use it. Direct sun from 2:00 to 6:00 PM makes it unbearable in July and August. A pergola over the deck provides filtered shade, lowers the surface temperature by 10 to 15 degrees, and creates a defined space for conversation. You can add a retractable shade canopy for full coverage on the hottest days. In Cary, where summer humidity can hit 80 percent, that shade makes the difference between using your deck and ignoring it. Burns Carpentry builds custom pergolas that integrate with existing decks, matching the post style and roofline so it looks like it was always there.
Scenario 2: The gardener. You have a side yard leading to a backyard vegetable garden. You want to create an inviting entry that signals "this way to the good stuff." A cedar arbor with an arched top, planted with climbing roses on both sides, gives you that entrance. It does not need to be huge. A 5-foot-wide arbor with 7 feet of clearance is plenty. The installation is straightforward, and the visual payoff is immediate. You can build this yourself if you are comfortable with a post hole digger and a level, but if you want it to last more than three years without sagging, hire a carpenter who sets posts properly.
Scenario 3: The privacy seeker. Your neighbor's two-story window looks directly into your patio. You want screening but you do not want a solid fence that feels like a prison wall. A series of trellises mounted to your existing fence, planted with fast-growing ivy or honeysuckle, creates a living screen that softens the view. It takes two seasons to fill in completely, but the cost is low, and the effect is beautiful. This is a project you can absolutely do yourself. Buy the trellis panels at a local Cary hardware store, attach them with exterior screws, and plant your vines.
The honest truth: if you just want to grow something up a wall, do not buy a pergola. And if you want to sit under a structure, do not buy an arbor. Match the tool to the job.
Cost and Material Considerations for Cary Homeowners
Prices have shifted since the supply chain disruptions of the early 2020s. Here is what you can expect in 2026 for a typical Cary project.
Pergola. A custom-built, pressure-treated pine pergola measuring 12x12 feet runs $3,500 to $6,500 installed, depending on the complexity of the roof design and whether it attaches to an existing deck. Cedar adds 30 to 40 percent to the material cost. Vinyl-wrapped posts and beams push it to $7,000 to $10,000. The biggest cost driver is the foundation. If your yard has clay soil, which much of Cary does, you need deeper footings and possibly a concrete pier. That is not negotiable. Skip the footing and your pergola will heave in the first freeze-thaw cycle.
Arbor. A pre-built cedar arbor kit from a big box store costs $200 to $600. Installation by a carpenter, including proper footings, adds $300 to $800. A custom-built arbor from a company like Burns Carpentry, using thicker posts and joinery that will not rack, runs $1,200 to $2,500. The difference is longevity. A kit arbor with 2x2 rafters will wobble in five years. A properly built arbor with 4x4 posts and mortise and tenon joints will outlast your roof.
Trellis. Trellis panels cost $30 to $150 each. Installation is $100 to $300 if you hire it out. This is the one project where I will tell you to save your money and do it yourself. The risk of doing it wrong is low, and the cost of hiring someone often exceeds the value of the structure itself. Spend the money on a good plant instead.
One local note: Cary requires permits for any structure over 200 square feet or attached to a house. Pergolas usually fall into this category. Arbors and trellises generally do not. But if you are attaching anything to your house, including a trellis, check with the village building department. The rules changed in 2024 regarding attachment to the primary structure. Burns Carpentry handles permit applications for every project we build in Cary, so you never have to worry about it.
How Burns Carpentry Can Help You Choose and Build
I have been building these structures in Cary and the surrounding communities for over 15 years. I have seen the pergola that was built too low and felt like a cage. I have seen the arbor that was set in a wet spot and rotted in three years. I have seen the trellis that was screwed into siding instead of studs and pulled away in the first windstorm. Those mistakes are expensive and frustrating.
When you call Burns Carpentry, we start with a site visit. We look at your yard's sun exposure, soil type, drainage, and the existing structures. We ask what you actually want to do in that space. Then we recommend the right structure, not the most expensive one. We build pergolas that are engineered for wind loads and winter snow. We build arbors that will hold a mature wisteria without collapsing. We install trellises that attach securely to your house without damaging the siding.
We also handle the permits, the material sourcing, and the cleanup. A typical pergola project takes three to five weeks from initial consultation to completion, depending on weather and material availability. We use only pressure-treated lumber that is rated for ground contact, stainless steel or coated fasteners, and concrete that meets the local frost depth requirements.
If you are not sure what you need, we can help you figure it out. That is the part of the job I enjoy most, solving the puzzle of your yard.
Frequently Asked Questions
Do I need a permit for a pergola in Cary?
Yes, if the pergola is over 200 square feet or attached to your house. Cary requires a building permit for any structure that is anchored to a foundation or attached to the primary residence. Burns Carpentry handles the permit application for every project we build, so you do not have to deal with village paperwork.
Can I attach a pergola to my existing deck?
Yes, but the deck must be structurally capable of supporting the additional load. If your deck was built without a ledger board or with undersized footings, attaching a pergola can cause sagging or failure. We always inspect the deck first and reinforce it if needed before building the pergola.
What is the best wood for a pergola in Illinois?
Western red cedar is the best choice for longevity and appearance. It resists rot and insect damage naturally. Pressure-treated pine is more affordable but requires staining or sealing every two to three years. Avoid using untreated pine for any part that touches the ground.
How long does a Burns Carpentry pergola take to build?
Most pergola projects take three to five weeks from the first consultation to completion. That includes the site visit, design, permit, material ordering, and construction. The actual build time is four to seven days, but we pad the schedule for weather delays and material availability.
If you are tired of guessing which structure fits your yard, give Burns Carpentry a call. We will come out, walk your property, and give you a straight answer. No upselling. No pressure. Just honest advice and a free estimate. Whether you need a custom pergola, a garden arbor, or a simple trellis, we handle it all in Cary and the surrounding areas.
