Pergola mistakes – an outdoor structure specialist reveals 9 pergola errors that can cause big problems, and how to avoid them

Pergolas are the perfect way to create a covered social space in the garden. They provide structure and cover without creating a claustrophobic nook that boxes you into a patio.

However, there are a few mistakes that can turn even the prettiest pergola into a problem. Poor planning, placement, and maintenance can make for a weak pergola that ruins your whole garden aesthetic.

I spoke to a pergola expert about the worst mistakes she's seen when installing these garden structures – and found out how to avoid these pergola mistakes.

1. Poor material choice

A common perogla mistake is using the wrong material. By far the worst choice is untreated wood.

Pergola expert Leslie Chapus says: 'The worst material for a pergola is untreated wood, especially softwoods like pine that are prone to rot, warping, and insect damage.'

Pine can still be a good choice for a pergola because it's cheap and widely available. However, if you use pine, opt for pressure-treated pine. This wood is placed in a vacuum chamber alongside a chemical preservative; the vacuum sucks the preservative deep into the wood fibres and prevents rot and insect damage. You can also use wood like cedar, which has natural rot resistance, but these woods still need a lot of maintenance.

The lowest-effort material is aluminum, which won't rust in the rain and needs little maintenance. However, it's a sleek material best suited to contemporary and minimalist yards and won't work for more traditional spaces.

Leslie Chapus 

Leslie leads Azenco Outdoor's global expansion and international strategy. Azenco Outdoor is a specialty manufacturer of made-to-measure high-quality aluminum outdoor structures, including pergolas, cabanas and pool covers.

2. Poor placement of a pergola

Another common pergola mistake is poor placement. Sometimes, a spot that seems like the perfect place for a pergola won't quite work because of the ground conditions, especially at the bottom of a slope. Leslie Chapus explains that: 'Placing a pergola in a low-lying area with poor drainage is a mistake, as it can lead to water pooling and potential damage to the structure's base.'

You also need to consider the direction your garden faces and the shade from nearby trees. Leslie adds: 'Additionally, positioning a pergola without considering sun patterns can result in insufficient shade or excessive heat. Ideally, a pergola should be sited to optimize shade and airflow while enhancing the surrounding landscape.'

3. Not gaining a permit where necessary

It varies by location, but most people need a permit to build a pergola, especially if it's attached to your home. Leslie Chapus explains: 'In most cases, a permit is required for a pergola, but regulation s vary by location. Factors such as the size, height, and whether the structure is attached to a home can influence permitting requirements.

Failure to comply with local laws can mean expensive alterations to your pergola or even fines, so it's best to check the rules before you start installation. Leslie says: 'Homeowners should consult their local building authority to ensure compliance with zoning laws and codes before installation.'

4. Exceeding height laws

While you may not need a permit to build a pergola, you could still fall foul of local regulations. Even if you don't need permission, a tall pergola could break local height restrictions.

Leslie Chapus says: 'Many municipalities impose height restrictions for pergolas, typically ranging from 8 to 12 feet. Exceeding these limits without proper permits can lead to fines or a mandate to modify the structure. Checking local regulations beforehand is essential to avoid these pitfalls.'

5. Building a pergola too close to a fence

One of the most common pergola mistakes is putting it too close to a fence. A quiet corner of a yard seems like the perfect place for a social space like a pergola, but placing it too close to a fence can cause complaints from neighbors and potential fines.

A pergola that works for you could cast shade over a neighbor's patio or pool, creating cold patches that disrupt their hosting or limit sunlight on their plants. It can also be a privacy issue, and it can cause safety issues with the structure of their fence. All of these problems can cause arguments with neighbors that can even become litigious.

On top of that, most counties have zoning laws about how far away a structure should be from shared property lines. In most cases, it's at least five feet, but it may be as far away as 20.

Moreover, it can make the space feel claustrophobic. Leslie Chapus says: 'Placing a pergola too close to a fence can restrict airflow and create a cramped appearance. A recommended approach is to allow sufficient space for air circulation and maintenance access.'

6. Forgetting maintenance

Maintenance is vital for a safe, sturdy pergola, especially if you build with wood. Whichever wood species you choose, your pergola needs regular staining and sealing to keep it looking good and preventing rot and damage. You need to maintain a wood pergola every two or three years, as neglecting it can be a safety issue.

Leslie Chapus warns that: 'Neglecting maintenance can lead to rust, fading, or structural weakening, especially for wood or metal pergolas. Regular cleaning, inspections, and touch-ups on protective coatings are essential to extend the lifespan of a pergola.'

7. Shallow foundations

Another mistake - one especially common with DIY pergolas - is shallow foundations. Leslie Chapus warns that: 'A frequent mistake is insufficiently deep post foundations, leading to instability. Posts should be anchored securely in concrete, ideally extending below the frost line to prevent shifting.'

The usual rule of thumb for pergola posts is to bury them at least 1/3 of their length and deeper if the frost line is lower than this.

8. Using thin beams

Strong, sturdy beams are vital for a safe pergola. Many people overlook this area because they think of the beams as aesthetic. However, pergola beams need to hold a lot of weight. They need to be able to support shades, snow, or the weight of climbing plants.

Leslie says: 'Improper beam sizing and spacing are common mistakes that can cause sagging or reduce load-bearing capacity. Using beams that lack adequate thickness or failing to secure them properly to the posts can also lead to structural issues. Ensuring beams are level and reinforced as necessary is crucial for a sturdy pergola.'

9. Failing to plan ahead

Finally, make sure you plan ahead for utilities. They may not be a part of your design now, but you may find in later years that you want to add wired utilities like pergola lights or fans.

Leslie says a common mistake is 'Overlooking wiring for lighting or motorized elements like louvers. This can limit functionality later on.'

So, if you can, make sure to plan your placement around the wiring in your yard, and have power outlets built into the pergola that can support lights or other appliances.

Before you buy a pergola, you should consider if it's the right choice for your yard. Weighing up the benefits of a gazebo vs a pergola can help you find the best structure for your yard.