designing a fancy pergola

March 8, 2012 9:17 AM

I would like to build a pergola in my backyard. With a hanging bed under part of it. I have no idea what I'm doing. Please help.

My backyard is just a weed-filled patch of dirt right now, but we have big plans for it.

Part of what I'd like to do is build a pergola along the narrow back part along the house, about 20'x7'. I want it to look simple, like the one in this picture, with either 6x6 or 8x8 posts and beams.

I also want to have a hanging bed somehow. Something like this, I guess. I'm worried about how to make sure the hanging bed can support the weight of a couple adults, or several kids jumping around like crazy monkeys on top of it.

What's the best method for giving the posts a secure foundation and how do I figure out how far apart they can be placed? How do I securely attach the bed (rope or chain?) to the structure? Anything else I should know?

posted by logic vs love to home & garden (9 answers total)

The bigger the support posts, the better.
Cement footers for the posts.
6-7ft between each post.
Lag bolts to secure the main supports.
Lag screws with eyelets for the ropes.
Drill holes in the bed frame, drop rope through, tie knot with a washer on the bottom side.

Seems very doable, even if you don't know what you are doing. Seems like a great project. Good luck!
posted by LeanGreen at 9:34 AM on March 8, 2012 [1 favorite]

I love the picture you found; I want that in my backyard, too. So let me ask a few extra questions on top of yours: what kind of wood should we be using, and (assuming a 7'x10' size) does it matter whether the roof beams are running parallel to the long dimension or the short dimension?
posted by davejay at 9:52 AM on March 8, 2012

This is also a project of mine (well, kind of)!
You should look at Anna White's website to give you some ideas for the model and construction techniques. You could combine this pergola with this hanging bed for example...
posted by ddaavviidd at 10:15 AM on March 8, 2012 [1 favorite]

Yes on all that LeanGreen mentions. We had a similar pergola added on to our house just last summer. I don't know where in the hell our contractor found 10" (yes) solid cedar posts, but that's what he used for the support members. And they're attached to cement footers.

The whole thing, in fact, is cedar. We opted for that over pressure-treated wood and are letting it weather naturally. In just a year, it's fading to a greyish hue, but it still turns cedar-red when it rains.
posted by jquinby at 10:17 AM on March 8, 2012

(on posting)

davejay - on ours, the main support pieces run longways and parallel to the house to which it's attached. The 'roof' pieces (casting most of the shadows) run perpendicular to them. One thing I learned by watching is that many of these decisions come down to dealing with the standard sizes of boards and whatnot. Fewer cuts, faster work, etc. This is elementary stuff to a woodworker type, but not to me, which is why we paid someone to build it.
posted by jquinby at 10:21 AM on March 8, 2012

Do check with your municipality about any setback and/or permit requirements.
posted by dhartung at 12:40 PM on March 8, 2012

My suggestion would be buy a book on pole building to see how the loads are carried. Or use plans from an outdoor structures book, most DIY publishers have one (such as tuanton or black and decker).

On a practical advice level, pay attention to how the weight reaches the ground. Don't put fasteners (screws and nails) in tension where the weight is pulling them apart. This means boards should rest on boards and if you undid the screws/nails the structure wouldn't just fall down. The fasteners only serve to keep stuff from moving, not carry any load (unless they are designed to such as lag bolts-which you shouldn't need) The only part of your structure in tension (being pulled apart by the weight of the structure) should be the ropes that hold the platform that hold the bed. This stuff isn't hard, people have been building this since, well there have been people (meaning Homo-Sapiens). Gobekli Tepe uses this basic building technology, as does stonehenge and all the greek temples.
posted by bartonlong at 1:40 PM on March 8, 2012

If you're in San Francisco you will need a permit for something that size.
posted by oneirodynia at 7:43 PM on March 8, 2012

If all the wood is nice and big, it's pretty hard to get this wrong by just winging it.

For longevity, use galvanized steel stirrups embedded in concrete footings to hold the bottoms of the posts; if you cheap out and embed the posts themselves in concrete, the bottoms will rot out in a decade or so. Oil the crap out of everything every few years. Laying galvanized steel capping along the tops of all the beams will keep sun and rain off the top surfaces and likely give them an extra ten years of life.

For joining beams to posts, you can either lay the beams straight over the tops of the posts and use angle-steel brackets and batten screws to fix them together, or cut inch-deep chunks out of the side of the posts and hold the beams into those with great big bolts.

Some diagonal bracing will go a long way toward making your pergola feel reassuringly sturdy. Ours has 8mm stainless steel cable run diagonally through the beams between screw-eyes in the corners, with turnbuckles to tension it. That makes the "roof" grid quite rigid, and since one side of the pergola is attached to the house, the rigid roof is enough to keep the poles at the other side firmly vertical.
posted by flabdablet at 10:57 PM on March 8, 2012