How NOT to build a curved deck. (revised 1.25.2017)
This deck existed in Richmond Hill ON, and at the time of this revision I am sure it is long gone. There was a lot wrong with this deck ranging from footings to the way it was built. In searching for something complimentary to say, in an effort to engage in positivity, the railing guy didn’t do a bad job! The patios were collapsing, the stairs were scary, oh, wait, that was the metal guy too! He didn’t do so well on that !
Judging by the reaction of the homeowner, he likely tried to build it himself and didn’t appreciate me criticising it
harshly. That is one of my character flaws, when I see something dangerous or poorly done I have to open up with both barrels–it is what I do! Lets take a closer look!
A perfect example of how NOT to build a curved deck. I know this is how they do it on TV, however, I visited this one when it was 5 years old, and it wiggled like a cobbled together scaffold. It had nice strong support posts but this deck was flimsy. That said, my God, what a beautiful deck it was! Brilliant design, just badly, badly, terribly orchestrated. I love the concept, I love the look, but when you see the mistakes made you just have to shake your head.
A Curved Deck with Structural Concerns Everywhere!
Where’s the Meat? As you can see kerf cuts only leave 1/4″ or so of solid wood to nail through . Not quite enough to keep the deck straight, and furthermore, the kerfs expose end grain and cause what is left to rot prematurely.
So Graceful and flowing, this deck is gorgeous, but walking up these stairs is akin to the kids obstacle course at the carnival with the steps moving under foot! Kind of fun, sure, but will it impress your guests? What will your Architect friends think?
Kerf Cuts, Don’t do it Outdoors!
Kerf Cuts, so clever, so fun, piles of sawdust, and when you are doing them there is so much noise, and dust, but for outside applications, please don’t.
Tragic flaws on this deck–No lateral bracing, the steel stairs project the weight outward causing them to spring. The deck has no rim joist to speak of which means the joists all move independently. The joists are held in place by the fasteners in the decking. Some of the footings moved, which means they were poured on disturbed soil or were too small for the deck. There was evidence of water infiltration into the stucco finish of the home as well.
The owner of the home asked me if he could add a 3 season room with pergola on top of the deck. He didn’t like what I had to say and might have been upset when I giggled. I let him know that I wouldn’t erect a big box umbrella on the existing structure, and that it should be removed and rebuilt properly.As you can see, the rim joist has released and failed completely. Even if you clad it in composite decking, it will surely fail in a short time using this method.
Kerf Cuts are often used in construction, however these should NEVER be exposed to the elements. When they are used in interior work they are usually filled with glue and then bonded to something. Anything you build outdoors needs to have the end grains sealed to prevent rot–and it should be built twice as strong , to be safe after the structure starts to rot.
When nails are driven through this kerfed rim into joists, only about 3/8″ of solid materials is secured–which doesn’t take long to rot. The nails will pull through and if stressed all the fasteners will release. The load is also supported by a nail that has 1″ of space to flex, which means it will carry even less load. Can you imagine what would happen to this deck during an earthquake?
Details for building curved decks shown here was published in a book by Black and Decker, “The Complete Guide to Decks”. The information inside is deeply flawed. The book is so bad that a carpenter likely wasn’t even consulted during production.
Among the numerous bad details, they instruct you to countersink all lag bolts into beams and framing. That has the effect of making the beams break away under load. It weakens the connection by half. Your 2×8 becomes a 1×8. Rot sets in quickly to weaken the lag or carriage bolt connection. Please do not build any deck from this book! 400,000 copies have been sold, so if 1 in 4 actually built decks there are at least 100,000 dangerous decks out there if they followed instructions by Black and Decker!
I jumped on line to see what information was available on curved decks. There is actually some guy making 2 1/2″ rim joists out of exterior plywood–another temporary method. Exterior plywood is not made to be exposed to the elements. It is made of thin layers or spruce, pine and fir, and a water resistant adhesive. The voids in the adhesive allow moisture to infiltrate. I wouldn’t expect those to last longer than a few years either.
The steel stringers would have worked but they needed to be much stronger and or braced because of the weight deflecting outward on the curve. They sprung badly under my 220 lb frame. It felt unsafe to me.
This article was originally published in 2011, but the information is relevant so it has been revived and re-edited. What kinds of disaster decks have you run across?
By Lawrence Winterburn
If you want to see how curved decks should be built… check out the following links: