Something to keep in mind when using cinder block/concrete block (or the new name - concrete masonry unit (CMU) - a name that rolls right off the tongue) - they are very porous and present a minimal barrier to the penetration of water and moisture (unless you're talking about solid concrete block). I learned the hard way. Since I rebuilt the north wall (4ft, or 1.2m high) of my custom greenhouse with CMUs (on a poured concrete foundation) the humidity level in the greenhouse has elevated to the point where it's a real problem, even with a circulation fan running 24/7. During our frequent rainy periods the wall can be saturated for long periods. As a result, trying to keep Botrytis under control is a major issue during coolish conditions, at least in my climate. This was not much of a problem when that wall was plastic. I plan on sealing the exterior side of the wall this summer to see if that will help ameliorate the problem. Afraid I don't know what a better building material would be. Maybe poured concrete stem walls? Or another type of block that's not porous? This is just something to consider when building or upgrading a greenhouse. Thank you, Jim, for all your practical advice and experience. Mike Western Washington zn 7, cool mediterranean > > _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/… Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net>