Greenhouse Roof Replacement 2024

In the fall of 2024, after years of becoming increasingly leaky, the glass roof of the greenhouse was replaced with a twin wall polycarbonate roof. It took two months, not counting the years I spent figuring out how to actually do it (and wishing it were possible to keep the glass roof).

The caulk and butyl tape that kept the glass panes of the original roof in place made the roof difficult to maintain. The panes would slip a quarter of an inch, an inch, or a foot, leaving gaps for rain to pour into the greenhouse. To fix one slipped pane required unsealing and resealing not just one pane but between two and eight panes. One would think that if they are slipping it would be easy to get them off to reseal, but NO, that was not the case. While the caulk and butyl tape did lose their sealing powers after a few decades, it was only in a few spots. The rest of the caulk and tape stuck so well to the wood and glass that it was very hard to move the glass without breaking it. I decided that the only way to keep the greenhouse functional and prevent it from falling apart was to get rid of the glass roof.

Twin wall polycarbonate panels are used often on greenhouses now. They do not require caulk and are long-lasting. (Too long, if you don’t want to be contributing to the world’s microplastic problem.) The trick for me was figuring out how exactly to cut the polycarbonate panels for my particular roof that had specifically been made to hold glass panes and that had two different slopes and also six large, openable windows.

The good news is that once the glass, caulk, and butyl tape were removed, the rest of the roof — the wood frame — was in nearly perfect condition and very sturdy. I’m sure the frame breathed a sigh of relief to have the much lighter-weight polycarbonate on it instead of the heavier glass panes.

During most rains now, there are no leaks at all inside the greenhouse. It’s completely dry! During very heavy rains with wind, a small amount of water splashes into the greenhouse in a few places, not enough to be a problem. It is a greenhouse after all — I splash more water around when I water my plants.

Here are photos from the roof work:

Greenhouse roof in 2014, freshly painted. Unfortunately in the subsequent 10 years, the paint and wood condition deteriorated with age and weather. Worse, many of the glass panes slipped, causing leaks everywhere inside the greenhouse when it rained.

Sept 8, 2024. Official start of roof replacement. In this photo one of the six roof windows has been taken off and one pane has been removed. The other pane slipped out on its own a couple of years ago.

Some of the wood was in bad condition.

Another view of the roof before it was replaced. The missing pane half slipped out many years ago. I managed to pull it the rest of the way out a year or so ago.

Two slipped panes. There were 8-10 slipped panes by 2024.

One of the windows/vents. The wood has seen better days.

The same window, closer up.

Two strips of wood on the upper slope removed. The glass panes are still well-seated in butyl tape and caulk. Most of the time it was a struggle to get them out -- but much easier if you didn't mind if they broke during the process. Only 20% of the panes came off unbroken.

This is one of the 2x2s that makes up the roof rafters and that supported the glass. The glass was attached on its bottom side to the 2x2 with butyl tape and caulk, and on the top with more butyl tape and caulk to the thin strips of wood.

One of the piles of butyl tape, caulk, and broken glass from the old roof.

Some of the nails from the old roof. I finally got my tetanus booster while working on this roof replacement -- it had been 24 years since my last one.

Piles of broken glass and wood from the roof.

Removing glass from the old roof.

Glass removal in progress.

A lot of caulk and glass fell to the floor while removing the roof.

Glass removal in progress.

One half of the old roof completely removed.

Half of the old roof gone.

The windows were cleaned up in the garage. Some wood was replaced and quite a few pieces were patched with two part wood epoxy.

Bending the window flashing without a brake (tool for bending metal) was tricky but I got it done.

Cutting the twin wall polycarbonate. The cat is helping.

The polycarbonate for the windows was the first to be cut and attached. Note that the rafters have also been painted, at least the parts that would be difficult or impossible to paint once the roof is on.

Measure measure measure. Even after dark.

The twin wall polycarbonate panels drying after being cut with the jigsaw and then hosed to remove little bits of plastic.

The first half of the roof is half done.

Half the roof is done.

View of the polycarbonate roof from inside the greenhouse.

The completed first side. I did have to take the three windows off one more time later to put on the metal flashing and add more screws. Also, the metal flashing that goes on the peak is not attached yet -- that had to wait until everything was done.

One side done.

The second side now has all the glass, caulk, and butyl tape removed.

The second side has been painted.

View from inside the greenhouse. One side of the roof is completely open; the other side has the new polycarbonate roof.

Putting on the last panels.

Finally it's finished! The metal peak is back on. Metal flashing has been attached to each of the six windows. New vent openers were installed and the windows all open on their own on warm days.

Close-up of one of the windows in the open position.

Close-up of one of the windows. The metal flashing made all the difference with rain not getting in on stormy days.

Windows open on a warm day.

Part of the floor was brick until now. I reused the old bricks and added new ones to cover the whole floor. Note the dirty walls on the left. This is from when the roof leaked and rain splashed down on the dirt and splattered mud on the walls.

The new floor is finished. The walls have been cleaned up.

The rest of the wood making up the roof support is painted now. The next photos show views of the newly-painted rafters.

Newly painted roof rafters.

Another view of the roof rafters.

Another view of the roof rafters.

Another view of the roof rafters.

Everything complete... aside from some leaks in the vertical glass panes which will no doubt keep me busy for the rest of my life.

Greenhouse with new roof. Roof windows partially open.

More of the crazy rafters.

New twin wall polycarbonate roof with old rafters freshly painted.

More of the crazy rafters, different lighting than before.

Greenhouse roof replacement finished.

Inside the greenhouse with the lights on and cat looking out a lower window.

The Greenhouse Roof Repair Goddess. She keeps in our memories broken glass, old butyl tape and caulk, rusty screws, and rotting wood. Also twin wall polycarbonate, vent tape and U-profiles, metal flashing, and bricks.