Building a Round or Curved Deck

Why Curved Decks Need a Plan

Curved decks are visually appealing and distinctive, but they are also more difficult to build because deck framing materials tend to be straight and rigid. It is usually preferable, to begin with a well-thought-out strategy. In the actual world, it's much easier to draw curved decks on paper than it is to build them. To get the center of the circle and the length of the radius(the distance from the center of the circle to any point along the edge of the circle), you will need to use an Auto CAD application or graph paper to make the calculations. Alternatively, we can suggest you use our deck design tool.

Using an array of right-angled dropped beams, posts, and footings to support cantilevered joists that will span across the curved or round section of the arc, you can construct your own curved deck. Without the assistance of an engineer, joists are typically permitted to cantilever a beam by 2'. Because you will be cutting them all at once, you can let the ends of the joists run wild past the beam until they meet the beam. Read more: How to Design and Build and Above-Ground Pool Deck You will then lay out and mark the radius of your joists across the ends of their lengths. A deck board can be used as a compass to guide you. Using your plan, determine the pivot position, then screw your compass to the center point with a screwdriver to secure it. Leave a small amount of play in the screw to allow the compass board to revolve. If the pivot point of the compass is located between joists, you will need to install cross blocking to secure the pivot point to the joists. A construction pencil should be used to mark the radius on either side of the joists after you have arced the compass across the front ends of the joists. Following that, you will need to cut the joists to the proper lengths and prepare the front rim board, which will be used to cover the ends of the joists as they meet the curved edge of the deck's perimeter. If the pivot point is placed inside the home, you will need to plan out the circle in the yard to accommodate the pivot point. Pieces of plywood should be laid out around the diameter of the circle. You can trace and cut these plywood pieces into templates, which you can then lay out on top of the deck to draw the radius of your decking post holes. It is always a good idea to add blocking between joists around the curving ends of the deck to prevent the deck from sagging. This will help to reinforce the frame and provide a strong clamping surface for bending your fascia board across the curved radius of the frame.

Forming the Curved Rim: Kerf Cuts, Laminations & Soaking

Kerfed cuts can be used to bend the rim board to the desired shape. This entails slicing the 2x material with a circular saw to allow it to bend over the radius of the bend radius. Alternatively, 1/2" plywood can be used in layers up to 1.5" thick, with each layer increasing in thickness. Alternatively, you can soak strips of pressure-treated plywood in hot water for about an hour before adding a curved rim or header board to increase the flexibility of the material. Finally, bend the pressure-treated plywood strips in a cross-over fashion across the front of the joists and screw them into place. 

Decking & Railings for Curves

Composite decking is sufficiently flexible to allow it to be twisted across curved areas of a decking structure. Because it is hot, it will be considerably easier to bend the decking to achieve the proper shape. This versatile board can be fitted over the rim board to smooth the edges and make them more attractive. A number of composite and aluminum railing manufacturers provide curved railing that may be custom ordered to meet the radius of your deck.

FAQs about Building a Round or Curved Deck

Can you build a curved deck with standard straight framing?

• Yes. Frame with straight joists that cantilever past the beam, then scribe and cut the arc. Add blocking at the curve to stiffen the edge and to fasten fascia/decking cleanly. 

How do you form the curved rim/edge?

• Common methods: laminate thin, weather-resistant plywood strips into a curved rim, or kerf-cut a rim board so it bends, then cover with fascia. Heavier blocking + flashing at the edge keeps fasteners bite-solid and moisture out. 

How far may joists cantilever for a curved edge?

• Per the IRC, max cantilever = 1/4 of the joist’s backspan (see your local code/version). Example: a 12-ft span can cantilever up to ~3 ft when allowed by tables/species/spacing.

What railing height applies on a curved deck?

• Residential decks >30 in above grade typically need 36 in guards; commercial/multifamily decks require 42 in (IBC). Curved geometry doesn’t change the height rules.

Can composite/PVC decking be bent for curves? What radius?

• Yes—by heating and forming on a jig. Minimum radius depends on brand, board, and tools. Trex’s CustomCurve system advertises radii down to ~25 cm for certain components; always follow your product’s guide to stay in warranty.

What joist spacing should I use under curved decking or picture-frame borders?

• Follow the board’s install guide. Many composites call for 16 in on-center max, tightening to 12 in on-center for diagonal layouts, borders, or designs that need extra stiffness.

Best way to lay out the curve accurately?

• Use a beam compass (pivot point + straight board/tape equal to the desired radius) to swing the arc across joist tops; when the pivot lands between joists, add cross-blocking for the pivot screw. Templates/jigs help reproduce the radius.

What should I use for curved fascia/trim?

• Heat-formed cellular PVC (e.g., AZEK) or bendable composite fascia shaped on a jig works well; manufacturers publish heat-forming temps and handling (e.g., ~290–300 °F for certain AZEK profiles with heat blankets).
  
  

Does a curved deck cost more than straight/angled designs? Why?

• Usually yes. Curves need more blocking, custom jigs, heat-forming, and often curved railings—all of which add labor and lead time; some builders estimate roughly 2× the labor vs. a straight edge.

Any inspection/code details people forget on curved decks?

• Two big ones: (a) ledger attachment & lateral-load hold-downs per your IRC cycle; and (b) guard compliance along the entire curve (height, openings, loads). Curves don’t waive these requirements.

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