After the silicone dried, we used a roll of weather barrier material to cover the aluminum channels. This added a second level of protection against any moisture penetrating down through the center of our roofline.
Step 6 : Sealing the Roof Line
To attach the plastic to our frame, we used aluminum extrusions available for this purpose instead of the polycarbonate styles also available. A single splice was used to hold the plastic along the outside edges, around the fan and door cutouts and along the top of the arched walls. The double splice extrusion was needed between the plastic sheets on the side and end walls. One of the challenges we faced was finding a way to seal at the very peak of the greenhouse where the arched walls join together.
We first added the aluminum channels along the very top of our greenhouse. These would be used to hold the top of the polycarbonate sheets that form our side walls. We then sealed the gap between the aluminum channels with a silicone caulk. As you can see here, this work would not be possible to complete if we waited until the plastic was up and in place.
This material had a sticky back that adhered nicely to the aluminum channels. Here you can see how this tape formed a leak proof seal between the two sides of our greenhouse. Any moisture penetrating down to this area will now be directed over the top of the aluminum channels and down onto the exterior walls..
We then used wide pieces of aluminum flashing to help construct a nice looking roof line. We first screwed the flashing along the top, taking care to maintain a nice straight line along the peak of the greenhouse. Once the flashing was in place, we used silicone caulk to also seal between these pieces along the very top. As a final level of protection, we used a wide roll of roofing construction material to form one more leak proof seal between the sides of our greenhouse . This material has a shiny surface on the outside and a sticky tar coating on the underside. Once heated from the sunshine, it formed an even tighter waterproof seal onto the top of the flashing.
As the side walls were constructed, we screwed the bottom of the flashing down onto the arches. The last photo shows our finished roof line. It took a little bit of brainstorming and a few trips to the local building supply store before we finished. But we were happy with the completed look and even happier to survive our first winter without any difficulties. Another benefit of the arched design is that snow simply slides down from the top, helping to prevent any buildup of ice or snow that might otherwise accumulate and cause problems.