how much shade can I expect if I build a pergola on my deck
by Miriam Kearney
(Tweed, Ontario, Canada)
Our house faces south east and gets a ton of sun most of the day. It's not until about 3 pm in the afternoon that I can venture out. I've been using a big-box bought gazebo for a few years but I'd like something more permanent and that looks like it belongs there. But I do need shade, lots of it and I need a way underneath during bug season to hang bug drapes.
The deck is built of pressure treat pine and I can see how to build the pergola be either replacing some of the uprights or sistering them. What I don't know is what to expect or how far apart to put my rafters in order to have enough sun protection. I can hang lightweight fabric drapes if needed to block the lower sun.
There are a few things that effect the amount of shade provided by a pergola. The height of it should be such that a lot of unwanted sunlight doesn't come in on the sides. You want it to be tall enough to be comfortable to walk under. My typical pergola is 8 feet tall. If there is an architectural reason like tying into an existing roof line, the height may change. Since you are willing to use a shade cloth to hang from the pergola to screen sun that might come in through the sides, make the height comfortable for you and consider how it looks in proportion to any surrounding structures.
The top members do most of the shading. I usually use 2" x 6" lumber on end no farther apart than 8 inches. The closer you space these members, the more shade you will get. I have spaced them as close as 4 inches. Since you want dense shade, I would put at least 2 layers of top members. The top layer is a repeat of the first layer. I did one pergola by a pool for a client that wanted even denser shade, and on the second top layer I used 1" x 4" lumber laid flat with only a small space between each piece. This created a pergola look with almost a solid cover. There was enough space to allow rain water to get through.
Good luck with your project! If you'd like to see the detail of the pergola with the 1" x 4" top members, go to http://www.landscape-design-expert.com/pergolas.html.
Thanks so much for submitting your question!
All the best,
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