The goal of the insulation is to get a barrier between the top of the glass and the cold outside air. This barrier will retard heat loss from the interior of the cold frame.
The cheapest choice for me was 3 1/2 inch fiberglass insulation intended for use in wall cavities between studs. I bought it on sale from a local building supply store. I chose insulation with paper facing on one side.
I began with a blue plastic tarp approximately 5 feet by 7 feet which I laid flat on my driveway. Next, I cut 3 strips of insulation and laid them side by side on the tarp leaving a few inches at the sides and ends of the tarp. I also laid two additional strips of insulation over the two seams created by the three original strips of insulation. The lower 3 strips of insulation had the paper facing on the bottom. The upper 2 strips had their paper facing on the top. In this way, the bare fiberglass of the lower and upper layers faced each other and tended to hold each other in place.
I used a simple desk stapler to go around the perimeter and staple the paper backing of the insulation to the tarp. I made ample use of my stapler. Finally, I placed another blue tarp on top of the insulation and went around the perimeter once again, folding the edges of the two tarps down over each other and stapling them together.
One would think that a brand new plastic tarp would be water proof and would protect fiberglass insulation sandwiched inside. At least that's what I imagined to be true until the next rain taught me an important lesson and set me to work figuring out how to dry insulation sealed between two plastic, not waterproof tarps. Once the insulation was dry and the blankets reassembled, I enclosed the blankets in plastic sheets of house wrap, again purchases at my local building materials retailer. I also used simple staples with the edges of the plastic house wrap folded downward so that water running off the blankets would not seep inside.
I made four blankets so they would each be a manageable size to move about and also completely cover the top of the winter garden. When I cover the blankets with a large blue tarp and secure it to the ground around the edges of the winter garden, the blankets remain in place despite wind gusts. Snow that accumulates on top can be brushed off or the tarp can be pealed off and carry the snow with it.
I would like to report that this design works perfectly, but I can not. Fiberglass insulation has a remarkable attraction to moisture, and I can not always figure out just exactly how moisture is getting inside, but it is a continuing problem, and I am still working to solve it.
Table of Contents
Back to home page
