Build a Post and Beam Greenhouse


Install the Greenhouse Glazing Panels

The bottom and top of the glazing panels are sealed with plastic J channel. The bottom channel has holes spaced every 12 inches or so to allow condensation to drain.

Sliding J channel to cut end of twin wall polycarbonate glazing panel
Sliding J channel to the cut end of a twin wall polycarbonate glazing panel

And these wall panels are held in place and roofing screws run into the studs.

Sliding J channel to cut end of twin wall polycarbonate glazing panel
Sliding J channel to the cut end of a twin wall polycarbonate glazing panel

I left a small expansion gap between panels that I covered with cedar strips.

Adding polycarbonate panels to wall of a greenhouse
Adding polycarbonate panels to the East wall of the greenhouse

And that’s the east facing wall done. I repeated all that for the identical west wall.

Finished glazing on greenhouse wall
Finished glazing on greenhouse wall

Add the Greenhouse Roof Glazing Panels

I clamped some stops to the facia to hold the roof panels in place. And I also used some thin spacing strips attached to rafters for the expansion gap.

Installing Polycarbonate Panels on Greenhouse Roof
Installing polycarbonate panels on our greenhouse roof with rubber washer roofing screws

I’ll add the bottom J channel to the roofing panels later once the entire side is complete. Between the panels on the roof I will slide in an H channel to seal this edge.

Completed roof on East facing side of greenhouse
Completed roof on East facing side of greenhouse

And there’s the east facing roof done. That lower J channel bridges across panels and it has some clear silicone added to keep snow from pulling it off in the winter.

Sliding in greenhouse roof H channel
Sliding in greenhouse roof H channel

And the next day I added my stops to the west side facia, cut, drilled, then slid the panels up into place. Then ran in screws through the pilot holes like before. And slid in and attached the H channel. And the H channel is also screwed to a rafter.

Make the Greenhouse Ridge Cap

The galvanized ridge cap I selected will be lifted higher by a wood cap I made from ripping down some concrete form lumber.

Greenhouse roof wood and metal ridge cap combination
Greenhouse roof wood and metal ridge cap combination

This will keep the metal cap separate from the polycarbonate to ward off any heat damage in the summer sun. This wood cap also has a strip of 3/8’s plywood to mimic the shape of the metal cap.

Safe Access to The Greenhouse Roof

To install these cap sections I made a ladder to lay over the polycarbonate panels. So I could crawl up there without causing any damage. I made a sturdy rail attached to the rafter tails to hold the bottom of the ladder.

Greenhouse roof protection
Greenhouse roof protection

So I can screw on the wood cap sections.

Installing a metal ridge cap to greenhouse roof
Installing a metal ridge cap to the greenhouse roof with screws
Installing a metal ridge cap to greenhouse roof
Installing the metal ridge cap sections to our greenhouse roof

Then add the metal cap over top. And this looked pretty good I thought.

Complete the Greenhouse Glazing

I have glazing panels to add to each side of the doorway.

Installing glazing in greenhouse wall
Installing glazing on our greenhouse wall

And I used the same cedar strips at the edges of the panels as I did to bridge the gaps on the side walls.

Adding cedar trim to polycarbonate glazing
Adding cedar trim to the polycarbonate glazing edges

I cut some triangle shaped polycarbonate to fill in the gable ends.

Polycarbonate glazing on a greenhouse wall
Polycarbonate glazing on our greenhouse wall

And to finish the glazing, I’ll add panels and cedar strips to the back wall.

Back wall of greenhouse
Back wall of greenhouse with glazing and cedar strips

Add a Thermostat Controlled Greenhouse Fan

A thermostat controlled louvered fan is installed in the opening in the north facing gable end.

Installing a gable thermostat controlled greenhouse fan
Installing a gable thermostat controlled greenhouse fan
A greenhouse fan louvers in a gable
The greenhouse fan louvers in a gable end

Cedar Louvered Greenhouse Vents

I made three wooden louvers from red cedar. I glued and tacked them together with and air nailer.

Building a cedar louvered gable vent
Building a cedar louvered gable vent

And a few trim screws here and there. Then a light sanding and finished them with several coats of stain.

Install the Cedar Lightweight Greenhouse Door

I installed the door with three gate hinges screwed to the 4×4 posts.

Installing a cedar door in a greenhouse
Installing our cedar door in the greenhouse

I tacked on some spacers to the cross tie and the posts to center the door and hold it flush to the inside face of the posts while I ran in screws.

Installing a cedar door in a greenhouse with galvanized hinges
Installing the custom cedar door in the greenhouse with galvanized hinges

Later I’d come back and add a simple gate handle plus a spring loaded screen door latch.

I made a door threshold from 2×6 treated lumber and attached it with screws into plastic anchors that I drilled and tapped into the concrete foundation.

Installing polycarbonate glazing in the door of a greenhouse
Installing polycarbonate glazing in the door of the greenhouse

A bead of clear silicon is added to the routed inside edge of the door. And the rectangle glazing pieces are secured with washer head screws.

Install the Greenhouse Vents

The gable louver vent is installed in the opening and held with screws.

Installing cedar louvered vents in the front gable of a greenhouse
Installing cedar louvered vents in the front gable of our greenhouse

And here’s the lower side wall vents going in.

Installing cedar louvered vents in the sidewall of a greenhouse
Installing cedar louvered vents in the sidewall of our greenhouse

And then some hardware cloth was stapled on.

Hardware cloth stapled to inside of greenhouse vent
Hardware cloth stapled to inside of one greenhouse vent for critter protection

Later I’ll come up with a way to control the air flow through these vents when the temperature in the greenhouse increases.

Post and Beam Greenhouse with polycarbonate glazing in a garden
Post and Beam Greenhouse with polycarbonate glazing in our garden

And that is about it. The greenhouse is done.


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