Creating Curves Part 1 of 2

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A curved deck is created by cutting joists to match the curved profile, then attaching a curved rim joist, which can be shaped in one of two ways (see Construction Options). Braces attached to the tops of the joists hold them in place as the rim joist is installed.

 

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Continue to Step 1

Overview

By their nature, curved shapes lend a feeling of tranquility to a landscape. A deck with curved sides tends to encourage quiet relaxation. A curved deck can also provide an effective visual transition between the sharp architectural angles of the house and the more sweeping natural lines of the surrounding landscape.
Curved decks nearly always use a cantilevered design, in which the curved portion of the deck overhangs a beam that is set back from the edge of the deck. This setback distance generally should be no more than one-third of the total length of the deck joists, but longer cantilevers are possible if you use a combination of thicker joists, closer joist spacing, and stronger wood species, such as southern yellow pine.
Note: The curved deck shown on the following pages was built using primarily 4 x 4" posts. Recent changes to some building codes indicate a preference for 6 x 6" posts. Always check with your local building department to learn applicable codes for your deck.
If your curved deck will be high enough to require a railing, we recommend a design that incorporates a circular curve rather than an elliptical or irregular curve. Adding a curved railing is much easier if the deck curve is based on a circular shape.
Curves and Deck Design

Adding curves to your deck is not something you should do on the spur of the moment. Consider the pros and cons carefully before you commit to curves. Here are some to think about:

Pros:
• Curves can add visual appeal and uniqueness to your deck.
• Curves soften the overall feeling.
• Used wisely, curves have a natural, organic visual quality.
• A curve can be used to work around an obstacle in a pleasing way.
• A curved corner can preserve space below the deck.

Cons:
• Decks that incorporate curves almost always require more posts and beams, and they make less efficient use of building materials.
• A deck with curves takes at least twice as long to build as a square or rectangular one.
• Curved railings are tricky to make.
• Impact is lessened if curves are overused.
• Curves reduce and constrict deck floorspace.

What You'll Need

Tools:

Circular Saw
joists
drill
1 1⁄2" deck screws
belt sander

Materials:

Circular Saw
joists
drill
1 1⁄2" deck screws
belt sander

 

Step 1

Design Options for Curved Decks - Option 1

Circular designs are the best choice for curved decks that require railings. However, circular curves require a fairly long cantilever, a limitation that may limit the overall size of your deck. Circular decks are laid out using simple geometry and a long compass tool, called a trammel, which you can make yourself.


Step 2

Design Options for Curved Decks - Option 2

Irregular or elliptical curves should be used only on relatively low decks, since railings are quite difficult to construct for this kind of curve. These designs also work well for large decks, since the amount of overhang on the cantilever is relatively short compared to that for a circular curve.


Step 3

Construction Options - Option 1

Kerfed rim joist is formed by making a series of thin vertical cuts (kerfs) across the inside face of the board, making it flexible enough to wrap around the curve. A kerfed rim joist made from 2"-thick dimension lumber is sufficiently strong, but if you are kerfing a 1"-thick redwood or cedar fascia board, it should be backed with a laminated rim joist (next photo).


Step 4

Construction Options - Option 2

Laminated rim joist is made by bending several layers of flexible 1⁄4"- or 3⁄8"-thick exterior-grade plywood around the curve, joining each layer to the preceding layer with glue and screws. A laminated rim joist can stand alone, or it can provide backing for a more decorative fascia, such as a kerfed redwood or cedar board.


Step 5

How to Lay Out a Curved Deck

Install posts and beam for a cantilivered deck. Cut joists slightly longer than their final length, and attach them to the ledger and the beam. Add cross-blocking between the two outside joists to ensure that they remain plumb.


Step 6

How to Lay Out a Curved Deck

Mark the joist spacing on a 1 x 4 brace, and tack it across the tops of the joists at the point where the deck curve will begin. Measure the distance between the inside edges of the outer joists at each end of the beam, then divide this measurement in half to determine the radius of the circular curve. Mark the 1 x 4 brace to indicate the midpoint of the curve.


Step 7

How to Lay Out a Curved Deck

Build a trammel by anchoring one end of a long, straight 1 x 2 to the centerpoint of the curve, using a nail. (If the centerpoint lies between joists, attach a 1 x 4 brace across the joists to provide an anchor.) Measure out along the arm of the trammel a distance equal to the curve radius, and drill a hole. Insert a pencil in the hole, and pivot the trammel around the centerpoint, marking the joists for angled cuts.


Step 8

How to Lay Out a Curved Deck

Variation: For elliptical or irregular curves, temporarily nail vertical anchor boards to the outside joists at the start of the curve. Position a long strip of flexible material, such as hardboard or paneling, inside the anchor boards, then push the strip to create the desired bow. Drive nails into the joists to hold the bow in position, then scribe cutting lines on the tops of the joists.


Step 9

How to Lay Out a Curved Deck

Use a speed square or protractor to determine the bevel angles you will use to cut the joists. Position the square so the top is aligned with the layout mark on the joist, then find the degree measurement by following the edge of the joist down from the pivot point and reading where it intersects the degree scale on the square.


Step 10

How to Lay Out a Curved Deck

Use a combination square to extend the cutting lines down the front and back faces of the joists. At the outside joists where the curve begins, mark square cutting lines at the point where the circular curve touches the inside edge of the joists.


 
 

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