Build a Post and Beam Greenhouse


Making the Long 6×6 Beams

Now I’ll make the North South beams. And these would be 16 feet long.

Cutting a square end in a 6x6 cedar beam
Cutting the beams square before laying out scarf joint

I didn’t have any 6×6’s that long so I’d have to make them from two pieces. And I decided to make a simple scarf joint in the end of each and bolt them together into one.

As there’s a stud wall under these beams the scarf joint would not be under much load (if any). But I built them as if there would be and then I could count on them holding up well when I set them across the posts.

Shoulder cut into 6x6 beam with circular saw
Making the shoulder cut into the beam fir the scarf joint

After squaring this end of a 6×6 I made a shoulder cut and then a rip cut on opposite sides with my circular saw.

A circular saw ripping into a cedar 6x6 beam
Circular saw cutting opposite sides of the beam to start the scarf joint cut

Then I finished the cuts with a handsaw.

handsaw finishing the lap or scarf joint in a 6x6 cedar beam
Using a handsaw to connect the circular saw cuts in the beam

I countersunk and drilled holes for the bolts in one end of the scarf cut. Then clamped on the other scarf end and drilled through it.

Using a drill guide for pilot holes in a beam scarf joint
Using a drill guide for the pilot holes in the beam scarf joint
Making a scarf joint in the end of a 6x6 cedar beam
The pilot and recess holes drilled in the scarf joint

Attaching Beams at Scarf Joint

Don’t get too judgemental here but, I did add some construction adhesive in this joint before I clamped it back together and tightened the bolts. And I liked how it sealed the slightly rough edges of my not-so-perfect joinery. Did I say I wasn’t a timber framer?

Adding construction adhesive to 6x6 cedar scarf joint
Adding a generous amount of construction adhesive to the beam scarf joint
Assembling the scarf joint in a 6x6 cedar timber with bolts and clamps
Assembling the scarf joint in the 6×6 cedar beam using carriage bolts and clamps

But I think these joins ended up working out well. And now I have two 6×6’s long enough to make the next cuts.

Bolted scarf joint in 6x6 cedar beams for timber frame greenhouse
Scarf joint in cedar beam joined with galvanized carriage bolts and washers

Cut Quarter Ellipse Profile of Greenhouse Beams

Copy end profile to cedar beam
Copy the quarter ellipse end profile to the 6×6 cedar beam

And that will be squaring up an end and marking and cutting the quarter ellipse profile.

Cutting a 6x6 beam end profile with a jigsaw
Cutting a 6×6 beam end profile with a jigsaw and crazy long blade

I have a long blade for my jigsaw for this. I can’t push it too hard though.

It’s western red cedar but I’m basically ripping with the grain and it’s a 6″ deep cut.

Cut Dados in Greenhouse Beams

These beams sit down on the post an inch. So I can now cut that shallow dado with my circular saw.

Making wafer cuts with a circular saw in a 6x6 cedar beam 051
Making wafer cuts for a shallow dado in a 6×6 cedar beam

I’ll rotate that beam 90 degrees toward me then cut another deeper dado that will accept the end of the cross tie.

Making wafer cuts with a circular saw in a 6x6 cedar beam
Making wafer cuts for a dado with a circular saw in a 6×6 cedar beam

At this joint there’s two holes required for the lag bolts that will hold the beam to the post — then the beam to the cross tie.

Cleaning up dado in 6x6 cedar beam with chisel
Finishing the rough dado in a cedar beam with a chisel
A greenhouse beam with dados and pilot holes
A greenhouse North-South beam with dados and pilot holes for lag bolts

The cross ties are cut to length and a lap cut in each end. That’s so the cross tie will sit down on the post an inch. And the front cross tie also needs two dados in it’s underside to accept the 4x4s that form the doorway.

Cutting dado in cross tie beam with chisel
Finishing the dado in a Grand Fir cross tie beam with a chisel

The North South beams are stained and ready to be lifted into place but, I decided to install the East and West stud walls first. That way we can drop the drilled bottom sill plate over the anchor bolts.

Install Greenhouse Stud Walls

Lifting a greenhouse stud wall into place
Lifting the west side stud wall into place over the anchor bolts

And Marilyn came to help me carry and drop these in.

And with those two walls in place my neighbour Calvin came over to help me set the beams on the posts.

A beam lifted over posts and a stud wall for a greenhouse
Lifting a beam and placing it over the stud wall and onto the top of the corner posts

I’ll drill a pilot hole through the beam and into the top of the post. Then run in a lag bolt.

Drilling through a cedar beam
Drilling through the cedar beam into the end of the post below
Head of a lag bolt holding a cedar beam to a fir post
The head of the lag bolt is recessed into the beam

And we then set the rear stud wall in place.

Installing a cedar stud wall in a greenhouse
Dropping the rear stud wall over the anchor bolts

Then the rear cross tie can be dropped in over the wall.

Post and beam greenhouse cross tie drops into place over stud wall
Dropping the rear cross tie over the rear stud wall

Followed by the front cross tie.

Post and beam greenhouse cross tie drops into place
Dropping the front cross tie into dados in the North-South beams

Bolt the Greenhouse Posts and Beams Together

And I’ll drill horizontally now through the beam and into the end of the cross tie. And run in a lag bolt.

Drilling through beam into horizontal cross tie
Horizontal drilling through beam into cross tie for lag bolt

The four curved corner braces are held in place and pilot holes drilled into the post and the beam. And lag screws secure them and the angle of the pilot holes tighten it toward the corner. These braces are flush mounted and I have used this design on a few other structures.

Curved cedar flat mount corner braces
Curved cedar flat mount corner braces attached with lag bolts to posts and beams

The 4×4 door frame posts are then set in place and plumbed. And screwed to the front cross tie and the post saddles.

Cedar 4x4 posts to front wall of greenhouse
Cedar 4×4 posts added to front wall of greenhouse with screws into post saddles and cross tie above

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