What is the Purpose of a Pergola on a Deck?

A pergola is an eye-catching structure that covers your deck or patio, with rafters and slats crossing across them, making it the first noticeable feature in your yard.

The purpose of a pergola is to enhance the appearance of your deck or patio area while providing protection from the elements. The shade that a pergola provides can increase the enjoyability of your outdoor space, even in the heat of the summer.

While shade and aesthetics are the main reasons for a deck pergola, there are many others.

Pergolas provide various benefits to homeowners beyond just increasing their options for outdoor leisure activities.

Let’s discover some of these advantages.

Increase Privacy

There is a certain level of comfort created by having a roof over our heads.

Often a pergola can provide privacy for your deck or patio, making it a more comfortable place to relax.

Pergolas can also offer increased privacy, and its posts help to define the area further.

The slats of the pergolas provide some level of seclusion from outside eyes, which is especially ideal for homes facing public areas and busy streets.

The surround rafter can also limit overhead sounds from planes flying over. Helping you to relax just a little bit more.

Defining Space

A pergola is a great way to visually define your outdoor deck space and create a more organized look. Its open walls and roof provide just enough protection from the elements while still allowing you to enjoy the outdoors.

Not only can it define the area, but it can also create an attractive backdrop for your outdoor furniture.

Pergolas can also help create different areas in your yard, such as a sitting area or an entertainment space. This can be great for larger groups looking for multiple areas to relax and enjoy their outdoor spaces.

You can go even further. Adding some twinkle lights or other decorative elements makes the area under your pergola even more inviting.

However, you do it. A pergola on your deck or patio area, can create an attractive and comfortable spot for entertaining guests or simply enjoying some peace and quiet in your own backyard.

Celebrating Outdoor Parties

Pergolas are an ideal place for decoration.

You can hang decorations from the rafters or posts.

Remember the last outdoor wedding you attended? With beautifully decorated arbour or pergola. Enhancing the festive atmosphere.

The option for decorating are endless, but hanging lights, ornaments, wreaths, and streamers are a good start.

A decorated pergola can even be enjoyed when you are not outside.

Often the lights glowing in the night can bring peace through your window from inside your house.

Hanging Garden

Probably the most common decorating is also the oldest one.

Pergolas originated by the Mediterranean Sea and continue to be popular. Where they are often covered with vines or hanging flower pots.

Bringing nature to your deck, creates a plant-filled environment to enjoy being outdoors.

If you have an adjoining garden. Pergolas can be the perfect addition to your garden creating a beautiful backdrop and adding visual height to your outdoor space,

Adding climbing plants further enhances the pergola’s appearance by adding greenery and colour to the structure.

Yard Aesthetics

As I mentioned before, pergolas are visually appealing structures that tend to catch your attention. When you enter any backyard, the first thing you will notice is usually the pergola.

Adding some charm to a simple deck or patio area with its unique design of slats and rafter casting dancing light below.

Decorative cuts on the ends of rafters and beams or creative purlin patterns further increase its aesthetic appeal.

Decorative knee braces go even further to improve the look and strength of the pergola.


A major reason for having a pergola is to provide shade.

The shade helps protect you from the hot sun while being outdoors. With a comfortable space for you to relax.

Free from the beating midday sun.

Taking the edge of the sun’s glare by reducing the intensity of the sun’s rays.

All while lower the temperature of your deck by a few degrees. Making it much more pleasant to use during hot summer days.

Like having air conditioning for your deck.

If you want to increase the amount of shade even more. You can stretch a fabric shade cloth over the rafter of your pergola.

Increase Shade with Fabric Over a Pergola

Now that you have your reasons for a pergola on your deck.

How should it be constructed?

How far apart should pergola rafters be spaced?

The larger rafters of the pergola are typically placed at regular intervals of 16″ or 24″. A common spacing for framing roof rafters.

To ensure a consistent and aesthetically pleasing look, adjust the spacing of the rafters so they are equally spaced along the larger beams.

For example, if you have a beam 11’ (132”) and you want close to 16” on centre spacing.

132” divided by 16” equals 8.25. Round up to 9 and divide again.

132” divided by 9 equals 14.66” or 14 21/32” (8’ high, we can fug this number a little to 14 5/8”

Adding one rafter to start, and we need ten rafters at 14 5/8” on centre.

This is a question about how much shade.

If the purlins are closer together, more shade will be created. Cooling your deck more.

However, if the spacing is too close together, it will be more like having a roof.

Spacing often ranges anywhere between 24 inches to as close as 4 inches.

Cedar Pergola with Purlins

24-inch spacing is more for aesthetics. Providing minimal shade.

At 4″ spacing, maximum shade is created but still allows sun through the slats.

For the purposes of decoration and shade, 12-16” spacing is generally ideal.

This allows for maximum shade. While still allowing enough light through to enjoy the outdoors without being too dark.

But again consistent spacing will look better.

Which direction should the pergola purlins be oriented with respect to the sun?

Pergola purlins should run east to west to create the most shade. Assuming you’re in the northern hemisphere.

This will help block out the sun’s rays when they are most intense, around midday. When the sun is setting in the west, it’ll be less of an issue as your shaded area increases.

Orienting purlins east to west also maximizes shade while still allowing morning and afternoon light through, which creates a pleasant atmosphere for enjoying your deck.

How large should a deck pergola be?

The purpose of pergolas is to provide shade, add visual appeal, and create a comfortable outdoor space for relaxing. The size of the pergola will depend on the dimensions of your deck or patio area as well as how much shade you want.

Generally speaking, most people opt for a larger pergola that covers the entire deck or patio area. Large enough to comfortably set up a table with chairs for guests.

Often a 16′ by 12′ area under the pergola is needed for a table for six Opens in a new tab.with room to move.

Material options for a Pergola

There are many different material options for a pergola. Some of the more common are

  • Pressure-treated wood
  • Cedarwood
  • Redwood
  • Vinyl or Composite
  • Fibreglass

I prefer cedar pergolas due to their cost-effectiveness and low maintenance.

Unlike pressure-treated wooden structures with numerous hard-to-reach parts, cedar pergolas are easier to refresh paint or stain.

Moreover, cedar pergolas are more resistant to the damaging effects of sun and rain and are naturally resistant to insects. Cedar pergolas can last for many years without needing regular staining. But it can improve their appearance.

Vinyl, composite or Fiberglass are good requiring no maintenance but are more expensive upfront. 

Low Maintence Composite Pergola


When planning a pergola for your deck, consider the purpose of the structure. The size and shape should be tailored to fit your needs; from providing extra shade to giving an inviting ambiance for your outdoor space.

Also, make sure to properly space out rafters and purlins for a consistent and aesthetically pleasing look. And when deciding on the material for your pergola, keep in mind the balance between cost and durability.

Cedar is a popular choice due to its affordability and low maintenance requirements while vinyl, composite or fibreglass are long-lasting with no need for regular staining but may be more expensive upfront.

No matter which material you choose, a pergola can add character to your outdoor space and provide much-needed shade from the sun.

Enjoy your deck.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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