Build a Post and Beam Greenhouse


Finish Framing the Front Wall

And the last two wall sections are set in over the anchor bolts. The pilot holes for the bolts were angled so I could set them in then rotate the top of the wall up under the cross tie.

Stud walls between posts  in greenhouse timber frame 069
Front stud walls angled into place between posts

Ridge Beam Temporary Supports

Like the North South beams, the ridge beam is also made in two pieces. I cut a lap in the end of each of the 2×8’s then glued and screwed them together. I used some angle brackets and mending plates here.

The 2x8 ridge beam is built in two pieces
The 2×8 ridge beam is built in two pieces with a scarf joint

Here’s the first temporary brace I made to hold the ridge beam in place. These were carefully lined up in the center of the cross ties. And an additional angled support running to a 2×6 rafter tie that connects the two north south beams mid span.

Ridge beam temporary support brackets screwed to cross tie
Ridge beam temporary support brackets are aligned and screwed to a cross tie

The ridge beam is cut to length, stained, then lifted and slid into these temporary supports.

Ridge beam temporary support brackets and bracing
The ridge beam temporary support brackets require extra bracing to the rafter tie beam
Sliding a ridge beam into temporary braces in a greenhouse roof
Sliding the ridge beam into the temporary braces

Make the Greenhouse Roof Rafters

With that ridge beam secured to the temporary braces I now can start to work on the rafters. And I went back and checked some dimensions of the structure and compared it to the Sketchup model.

Checking the distance between beams during greenhouse construction
Checking the distance between beams with a measuring tape

And that helped me fabricate a template so I could copy this onto the 2×6 blanks I had selected for the rafters.

Laying a rafter pattern over the greenhouse beams
Laying the first rafter pattern over the greenhouse beams to check the fit

And that looked like it fit well enough so I started to copy the ellipse profile and the peak angle on the cedar 2×6’s.

Tracing a tail pattern on a cedar greenhouse rafter
Tracing the quarter ellipse tail pattern on a rafter blank

And I can cut the rafter to length on my miter saw. Then cut the tail profile with a jigsaw.

Cutting a rafter tail profile with a jigsaw
Cutting one of the many rafter tail profiles with a jigsaw

And I can chamfer the edges while holding it in this improvised slot jig.

Chamfering the edge of a cedar rafter with a power plane
Chamfering the edge of one cedar rafter with a power plane held in a slot jig

Then I stained each rafter and let them dry.

A pile of cut cedar rafters ready for staining
My pile of cut cedar rafters ready for staining

Then I reconsidered the birds mouth depth of my first pattern. I thought it might be a bit too deep. So I cut a new rafter pattern with a shallower notch and checked it’s fit.

A pattern for a sculpted roof rafter
Test fitting a rafter pattern over the beams

I like it better so I went ahead and copied the birds mouth cuts on the rafters and cut them.

Cutting a notch in roof rafters
Cutting a birds mouth notch in a roof rafters

And they fit well so I attached all the rafters to the beams that afternoon.

in the Timberframe Style Greenhouse
Adding cedar roof rafters to the greenhouse with screws
Adding cedar roof rafters to the greenhouse
Adding cedar roof rafters to the greenhouse with screws

Greenhouse Roof Rafter Blocking

The next day I cut and installed the 2×4 blocking between the rafters at the midway point between the ridge beam and North South beam.

Roof rafters and blocking on a greenhouse roof
Blocking added between roof rafters

Then some 2×6 blocking at the top of the North South beams. And these ones had an angle ripped to match the slope of the roof.

Inside Corner Braces

Next I added some flat mounted corner braces to the inside of the stud walls. These are the same shape as the outside braces but they are cut from 1″ thick stock.

Flat mounted cedar curved corner braces
attaching flat mounted cedar curved corner braces with GRK washer head screws

Next I added some 1x4s for the facia boards ant they’re attached to the rafter tails with trim screws.

Installing cedar 1x4 facia to ends of roof rafter tails
Installing cedar 1×4 facia to the ends of the roof rafter tails with trim screws

Next I removed the temporary braces supporting the ridge beam as they are not needed anymore.

Removing a temporary ridge beam support from a cross tie beam
Removing the front temporary ridge beam support from the cross tie beam

Frame the Greenhouse Gable Ends

And I’ll add some framing at each gable end. These 2x4s will support the glazing and the square opening will be used for a vent at the front and a fan in the rear.

Gable framing details in a Timberframe Style Greenhouse
Gable 2×4 framing complete with opening for a vent or fan

Build the Greenhouse Door

The door is made from 2×4 and 2×6 cedar. I cut lap joints at the corners that are glued and screwed together. And the mid rail has a lap that fits into two dados.

Assembling a cedar greenhouse door
Assembling the cedar greenhouse door with glue and screws and pipe clamp

And I’ll cut a relief with my router for the polycarbonate glazing that will be added after the door is hung.

Router cutting glazing relief in cedar greenhouse door
Using a router to cut a glazing relief in cedar greenhouse door
A cedar greenhouse door with plastic glazing panels
A custom built cedar greenhouse door with plastic glazing panels for our greenhouse

Cutting the Greenhouse Polycarbonate Sheets

Each polycarbonate panel is cut to size with a fine tooth blade on my circular saw. I use an aluminum straight edge clamped to the glazing and to my improvised work table. I screwed some 2×4’s to sawhorses to make a surface big enough for the 4×8 foot panels.

Cutting Polycarbonate Glazing for the Timber frame Style Greenhouse
Cutting Polycarbonate Glazing for our greenhouse

And I marked and drilled pilot holes (with an oversized bit) for the roofing screws I’ll be using to attach the panels. You need to make allowances for expansion and contraction of the polycarbonate.

Drilling pilot holes for screws in the greenhouse glazing panel
Drilling pilot holes for screws in the greenhouse glazing panel

After cutting and drilling I blew out any chips within the wall with an air compressor.

Twin Wall Clear Polycarbonate with chips in wall
Chips from cutting and drilling inside polycarbonate wall
Air compressor air blast to blow out chips
Air compressor blast to blow out chips in panel wall

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