The Forestry Forum

What is the best place to buy the roof material? Lowes had 8' sheets for 13 bucks but the price went up to over 21 bucks!. i did check at a metal roofing place they call it sky light which is more costly. would that be a better option?

Mine came from Lowe's, but that was several years ago. Whatever you use, it needs to be infra-red transparent, in other words greenhouse quality. It's the infra-red that makes heat, not visible light. Be aware that some acrylic sealing compounds may attack polycarbonate plastics, use silicone to be safe..

The best product determination is based on three energy related characteristics.  The best cover is one that 1) admits close to 100% of the incoming solar; 2) reflects nearly 100% of the infrared that is inside the kiln, keeping the heat inside; and 3) is a good heat insulator, to minimize convection losses. 

Although two layers reduce the solar transmission into the kiln, the two layers do an excellent job of acting as an insulator.  So, two layers are pretty much essential; some commercial collectors will even use three.

Another characteristic to look at is the durability of the material to rocks and hail.  Further, the best covers will not deteriorate much on exposure to uv light.  Of course, weight and cost are also important, along with ease of installing.

So, what does all this mean?  The plastic sheets that we find at the lumber yard, polyethylene, get brittle quickly.  Fiberglass corrugated material has lower transmission of solar, but is positive in all other respects, except I recently saw it at $2 per sq ft.  Glass that does not have a greenish color on the edge is excellent from an energy standpoint, but is heavy and may break; oftentimes the glass is available from a building supply resale shop at a low price.  Plastic films (oftentimes called greenhouse films) that have been treated to absorb uv are pretty good and are inexpensive ($.20 per sq ft if you buy a 2000 sq ft roll) but last for four years; snow load and high wind can be an issue.  A rigid polycarb product (two  layers in one sheet with air channels), is really good in all respects and will last for many years ($1.50 per square foot).  All in all, I like this last product.