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Build a Curved Rafter Cedar Pergola

By February 27, 2020 No Comments

Build your own Curved Rafter Cedar Pergola.  Plans available for download in PDF Format.

See the How to Video.

For this blog post I’d like to go back and revisit a curved pergola I built with my friend Doug a few years ago.

Build the Pergola

The Sketchup Model
Pergola sits on lib of cistern

Pergola sits on lid of cistern

Cistern lid

The pergola is made from rough sawn Western Red Cedar and sits on the lid of an underground 2800 gallon concrete cistern. The homeowners collect rainwater in the cistern for use on their gardens in the summer months.

Overall size of pergola

Overall size of pergola

The six posts are spaced 8′ apart across the front, and about 6’6″ on the sides.

Overall height of pergola

Overall height of pergola

The overall height of the curved pergola is 9’5″ with a head clearance of 7’3″.

Max head clearance

Max head clearance

The posts are 6×6 and, in this particular installation, simply are held in place by weight and galvanized alignment rods that are set in shallow holes in the concrete lid and up into the bottom of each post.

Pergola sits on lid with alignment pins

Pergola sits on lid with alignment pins

Alternatively the posts could be attached to concrete footings with galvanized saddles.

Alternative footings for pergola

Alternative footings for pergola

Two 6×6 beams are bolted to the posts and run North to South.

Curved pergola beams

Curved pergola beams

Fourteen curved rafters are attached to a 6×6 beam and a 2 by 9-1/2″ ridge beam.

Curved pergola rafters

Curved pergola rafters

Along the sides of the pergola are 8 curved corner braces.

Curved side braces

Curved side braces

There are 6 slightly larger curved braces that stiffen the structure side to side and add support to the rafters.

Slightly larger curved braces for from view

Slightly larger curved braces for from view

Topping the structure are three 2×4 louvers.

Simple cedar louvers add shade

Simple cedar louvers add shade

The number and spacing of the louvers can be changed to increase the shade under the pergola.

The POSTS

The posts, and all other parts, are full dimension.

True 6" x 6" posts and beams

True 6″ x 6″ posts and beams

The posts are 6″ x 6″ and cut to length with a circular saw.

Using a circular saw to cut beams

Using a circular saw to cut beams

For this video I have enough lumber around from other projects to show the steps to make each part of the curved pergola

Hand saw to finish the cut

Hand saw to finish the cut

I draw a pencil line around the post with a speed square. If the post is square and true then the lines will meet.

I make 4 cuts with a circular saw. Rotating the post a quarter turn each time. Then finish the cut with a hand saw.

They are then chamfered using a power plane. A sanding disc on an angle grinder will work for this as well.

Drill guide used for galvanized alignment rod hole

Drill guide used for galvanized alignment rod hole

A hole is drilled in the center of the bottom of each post for the galvanized rod.

Post ready to be installed

Post ready to be installed

This rod will keep the post in position. I use a drill guide for this to ensure the hole is square to the end of the post.

If you want to see how to lay out the post locations for pouring concrete footings have a look at my previous pergola video.

A shingle is added between the concrete and post as a moisture barrier.

Shingle used as moisture barrier between bottom of post and concrete cistern lid

Shingle used as moisture barrier between bottom of post and concrete cistern lid

Stakes are driven in and temporary braces are added as we set each post in place, then plumbed with a spirit level.

Posts in place held with temporary bracing

Posts in place held with temporary bracing

The layout and size of this pergola was determined by the size and dimensions of the concrete cistern lid.

Pic of the site during assembly

Pic of the site during assembly

The lid was found to be square and level so this made everything easier.

The BEAMS

6×6 beams sit on the posts.

The beams have a point

The beams have a point

On each end they have a 30 degree bevel to form a point. Like the posts, I mark a line around each beam with a square.

Setting circular saw to 30 degrees

Setting circular saw to 30 degrees

I set my circular saw at 30 degrees and make four cuts.

Point of beams can be cut with a miter saw as well

Point of beams can be cut with a miter saw as well

The plans include a cut list for the saw mill. Every part of this build was cut at Doug’s workshop ahead of assembly so we were pretty fussy with tolerances and lumber selection from the mill.

This could also be done with a large miter saw.

Saw cut cleaned up with sharp chisel

Saw cut cleaned up with sharp chisel

If the beam is square then you are left with a nice point. I cleaned up the handsaw cuts with a chisel.

Making "bread" on the beam

Making “bread” on the beam

These beams sit down on the posts an inch. I cut this dado with a series of close saw cuts across the beam.

Knocking off thin wafers to form a dado

Knocking off thin wafers to form a dado

Then break off the pieces with a mallet. And finish up the groove with a chisel.

Cleaning up dado with a chisel

Cleaning up dado with a chisel

Each 6×6 beam has three of these dados. One for each post.

Drilling for the large lag bolt that will attach the beams to the top of the posts

Drilling for the large lag bolt that will attach the beams to the top of the posts

The beam is flipped over and a counterbore and hole drilled for the lag bolt that will secure the beam to the top of each post.

Marking the ridge beam end

Marking the ridge beam end

The ridge beam is 2″ x 9.5″. 30 degree angle cuts are made on each end of this beam. When complete, the beams are also chamfered with a power plane.

Chamfering the beams and posts with a power plane

Chamfering the beams and posts with a power plane

The beams are lifted onto the posts and the lag bolts run in with a socket wrench.

The beams in place

The beams in place

A temporary bridge is set in place across the beams to hold the ridge beam in place at the proper height.

Pic of the site with my old dodge in the driveway

Pic of the site with my old dodge in the driveway

The rafter locations are marked on the underside of the ridge beam and galvanized strapping is screwed on. This strapping will make setting the rafters easier and will also add strength to the roof of the pergola and prevent sagging.

The Curved RAFTERS

I start by making a pattern for the curved shape of the rafters.

Cutting the pattern blank for the rafters

Cutting the pattern blank for the rafters

The pattern will be cut from thin plywood. I lay out a grid with tape measure, pencil, and straight edge.

Marking a grid on the rafter blank

Marking a grid on the rafter blank

Then I mark points where the curve intersects the grid.

Marking the points for the rafter pattern curves

Marking the points for the rafter pattern curves

I tap in a nail at these points then bend a thin strip of metal across them to form the upper and lower curve of the rafter.

Flexing a metal strip against the nails to draw a curve

Flexing a metal strip against the nails to draw a curve

I used a strip of linoleum edge metal for this.

Lower curve drawing

Lower curve drawing

I trace the curve on the plywood with a sharpie.

On the plans I also show the radius values for the two curves that make up the shape of the rafter. The curves could also be struck with a long straight piece of trim like a compass.

Rough some meat off the pattern for the next step

Rough some meat off the pattern for the next step

Over sawhorses I rough off a piece of the pattern to make the next step easier.

Small jigsaw rips through the thin plywood

Small jigsaw rips through the thin plywood

Then cut the upper profile of the pattern with a jigsaw. Then use a belt sander to smooth and shape.

Belt sander is very fast at smoothing the curves

Belt sander is very fast at smoothing the curves

I reposition the pattern to cut the other curve.

Curved Pergola. Nice!!

Nice!!

The location of the beam is also marked on the pattern then this birds mouth is cut.

The birds mouth is also cut in the pattern

The birds mouth is also cut in the pattern

We had our sawyer mill boards just over 12″ wide for these rafters. Alternatively, thinner boards could be glued up to get the width required but, it’s a lot easier to just have them cut to what you need.

The pattern is done! Yess!!!

The pattern is done! Yess!!!

The pattern is traced on the rafter blank.

Laying the pattern over the rafter blank

Laying the pattern over the rafter blank

We cut the 12 degree angle in the upper and lower ends of the rafter with a circular saw.

Tracing the pattern on the cedar rafter blank

Tracing the pattern on the cedar rafter blank

We cut the curved sections of all our rafters on a large bandsaw.

Cutting each end of the rafter

Cutting each end of the rafter

But, if working alone a jigsaw cuts almost as well. I use a heavy, stiff blade on my jigsaw for this 2″ thick Western Red cedar.

A powerful jigsaw with a heavy blade works well at cutting the rafters

A powerful jigsaw with a heavy blade works well at cutting the rafters

My friend Doug is a very artistic and skilled carpenter. We worked on quite a few design ideas for the curved rafters. We wanted the most elegant curve with the minimal waste of material. We decided on the idea of pairs of rafters that were supported with a ridge beam. And that each rafter tapered down from the center top to the sides. This was done by using two different radius curves. The homeowners approved the design and we all thought it looked a bit like an upside down wooden boat hull.

Bosch jigsaw burns through the cut. Nice!!

Bosch jigsaw burns through the cut. Nice!!

Each rafter was then chamfered with a sanding attachment on an angle grinder.

Belt sanding the edge smooth

Belt sanding the edge smooth

Angle grinder with flexible sanding disc attachment for chamfering the rafter edges

Angle grinder with flexible sanding disc attachment for chamfering the rafter edges

Rafters finished and ready to be hung

Rafters finished and ready to be hung

These rafters were set in place and toe screwed to the beams. And also screwed to the galvanized strapping attached to the ridge beam.

Dropped in place on the beams

Dropped in place on the beams

Then the temporary supports for the ridge beam can be removed. Or left there until all the braces are added.

All rafters in place. A sight to be seen

All rafters in place. A sight to be seen

The BRACES

A pattern is also cut for the two brace shapes. Again I use 1/4″ plywood for the two patterns.

Ripping the thin plywood to make brace patterns

Ripping the thin plywood to make brace patterns

The curves will be scored with nails through a yardstick-size piece of plywood with a pivot laid out on my workbench.

Making a compass from a yardstick-like strip

Making a compass from a yardstick-like strip

I mark the pivot and two curve radii then drill pilot holes. Then tap in finishing nails.

Marking the 45's on the brace pattern blank

Marking the 45’s on the brace pattern blank

On the small brace pattern I mark the two 45 degree angles first. Then I nail the blank to the workbench.

Sweeping the curves on the plywood

Sweeping the curves on the plywood

Along a pencil line on the bench I tap in the pivot point nail then sweep the yardstick along the blank to scratch the curve on the plywood. Then draw a pencil line along this scratch. I darkened it with a sharpie as well.

Darkening the scratch with a sharpie. (mainly so it shows better on video)

Darkening the scratch with a sharpie. (mainly so it shows better on video)

The 45 degree angles were cut on the miter saw.

Miter saw used to cut 45's

Miter saw used to cut 45’s

The second, slightly larger brace pattern was made in the same way.

The large brace needs its own compass

The large brace needs its own compass

The plywood blank is bigger and the radii that I need to scratch in the wood is also greater.

Setting the compass stick in place

Setting the compass stick in place

As before I make a compass for striking the arcs from a thin strip of plywood, measure and drill pilot holes, and tap in some finishing nails.

Darkening large brace curves

Darkening large brace curves

I mark the points for the 45 degree cuts then secure the blank and the compass pivot to the bench. Then scratch the arcs on the wood. Then darken the curves and take the blank to the miter saw.

Cutting 45 degree angles on large brace pattern blank

Cutting 45 degree angles on large brace pattern blank

I use a bandsaw to cut the brace pattern curves. A jigsaw would also work just fine.

A jigsaw is the best way to cut these curves. I have a small table top model that does the job well

A jigsaw is the best way to cut these curves. I have a small table top model that does the job well

Then I sand these curves smooth on a small belt sander.

A small hobby belt sander is super handy. How do I get by without one?

A small hobby belt sander is super handy. How do I get by without one?

Both patterns only took a few minutes to finish. This little sander is so handy, I use it a lot.

Setting the brace patterns in place on a board

Setting the brace patterns in place on a board

The pattern was copied to the cedar brace blank referencing one straight edge on the board.

Tracing the patterns

Tracing the patterns

The 45 degree edge of the speed square is used to align the pattern before tracing. This is repeated for the second larger brace. To save material I nest the braces into each other on the board. Alternating them if possible depending on any rough sections or large knots in the red cedar.

And just like the patterns, the braces are cut on the miter saw then the bandsaw.

Cutting 45's on the miter saw

Cutting 45’s on the miter saw

This could also be done with a speed square, circular saw, then jigsaw.

And cutting the brace curves on the bandsaw

And cutting the brace curves on the bandsaw

Cedar Curved Pergola Outdoor Structure

After sanding the curves smooth on a hobby belt sander I bevel the edges with a sanding disc on my angle grinder.

Braces at chamfered with the angle grinder

Braces at chamfered with the angle grinder

The last step in prepping the braces is to drill holes for the lag bolts.

The lag bolt hole locations are laid out on the patterns

The lag bolt hole locations are laid out on the patterns

I mark a point half way along the flat section of the brace where it mates to a post, beam, or rafter. I draw a line 90 degrees to that point, then another 20 degrees off that.

And marked on the braces

And marked on the braces

This way the lag bolts will pull the brace into the corner.

Now I copy this mark to the brace. Then mark the center of that location.

Setting the table of my drill press at a 20 degree tilt

Setting the table of my drill press at a 20 degree tilt

I tilt the table of my drill press to 20 degrees.

Counterbore using a forstner bit

Counterbore using a forstner bit

And clamps some stops to the table to help hold the brace. With a forstner bit in the chuck I counterbore a hole on each end of the brace.

And a drill bit swapped in to finish the lag bolt hole

And a drill bit swapped in to finish the lag bolt hole

Swap the bit, then drill through for the shank of the lag bolt and washer.

Stack of small braces ready for installation

Stack of small braces ready for installation

These larger braces had one additional cut that was done on site. The brace was laid in place against the rafter and scribed. This piece was then removed so the brace would fit tightly to the shape of the rafter.

A similar brace being installed on my woodshed

A similar brace being installed on my woodshed

To attach the small braces I hold them in place and drill into a post then beam. Then with an impact driver I run in the galvanized lag bolt. This is a clip from my woodshed build where I used a similar curved brace.

Side view of the pergola with bracing flying in

Side view of the pergola with bracing flying in

Eight of these braces are required for the sides of the pergola and attach to the posts and 6×6 beams.

Front view with the larger braces flying in

Front view with the larger braces flying in

This process was repeated for the larger braces that are secured to the posts and rafters.

Now all the temporary bracing is removed.

The LOUVERS

The three louvers, or more if needed, are made from 2×4 stock. They are simply cut to length then chamfered. They are positioned over the rafters and screwed in place.

Louvers beside the main beams and ridge beam

Louvers beside the main beams and ridge beam

And that is it. The curved pergola is done. Let me know what you think by dropping a note in the comment section. I try to reply to as many questions as I can.

Louvers being dropped in

Louvers being dropped in

Thank you so much for reading.

Cedar Curved Pergola Outdoor Structure is done!

Cedar Curved Pergola Outdoor Structure is done!

And thanks to everyone who has supported our channel through Patreon. It’s very much appreciated.

I have a full set of plans available for download.

If you have any questions, please leave them in the comments below. Thanks for reading

See also:  Shed Style Garden Pavilion

Pictures after 5 Years

Here’s some pictures taken last November to show how the pergola has aged. I think it’s holding up very well. It’s the worse time of year for any flattering photos but maybe that’s okay.

a5 P1050328

a5 P1050327

a5 P1050325

There’s a long crack in one beam but that’s all I could find of any significance.

a5 P1050324

a5 P1050321

a5 P1050320

And that’s all. Thanks!

 

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