Jim, I would still try to find cedar. I lived in Arkansas for 4 years, and
treated landscape timbers started getting termites after about 3 to 4 years
anyway. Cedar is the lumber of choice of builders to put on the wall
between a house and an attached greenhouse or room containing a sauna or hot
tub. I guess they feel it withstands the additional moisture better. Do
you have access to Lowes or Sutherlands? If they don't have it, maybe they
can order it.

Good luck. Dwayne


"Jim" wrote in message
...
On Thu, 20 Mar 2003 15:39:24 -0600, B.Server wrote:

On Thu, 20 Mar 2003 19:06:12 GMT,
(Jim) wrote:

I'm building an 8' x 16' greenhouse. The foundation will be cinder
block between posts. I'm going to put a 2 x 8 bottom plate on top of
the cinder blocks. I want to avoid pressure treated lumber because of
the chemicles used. Anybody have a recommendation for a preservative
to use on the wood?

Without knowing where you are located, what sort of use you will make
of your greenhouse, (seasonal, drainage, type of floor, etc) it is
pretty difficult to guess what would work.

NE Washington state, probably not used Dec - Feb, dirt floor, will
grow driectly in ground & off benches.

Basically, pressure treated wood has the clear advantage that it works
and will prevent or diminish rot for quite some time. If you are growing
food in soil
into which the materials in the wood might leach, that can be a good
reason to either not use it or move the food-growing beds. A
greenhouse is just about the worst possible combination of heat,
light, humidity, and enriched diet for wood decay.

Agreed.

Anything that you can put on the wood to accomplish the same ends as
pressure treatment is likely to (1) be at least as toxic, (2) offer more
exposure
because you will have to apply it, (3) leach even more rapidly because
it is
on the surface, (4) fail more quickly because it is on the surface.

Good points. I may resort to pressure treatment as the lesser of
evils. There is the 'red stuff' and the 'green stuff'. Your best
guess as to which is 'less toxic'?

You could begin by using some of the more rot resistant woods, cypress
for example.

My options here are cedar & redwood. The local building supply
doesn't have cedar in 2x, no redwood available locally, hence the
question if I have to do it myself.

Being careful to avoid a way for water to wick to the
wood or pool on it will help.

Agreed. It will be on top of cinder blocks, so that will help keep it
off the soil & reduce leaching, but water will occasionally run over
the lumber onto the soil at the perimeter.

Unfortunately, even with careful flashing, the weeping of GH
sheathing will keep the sill plate wet much of the time,

? Not sure what you mean, but my last GH did not have that problem
(but that was many years ago).

not to mention your own watering.

Yes, though I'm careful when I water.

If you GH is framed in aluminum,

wood

you might consider sinking bolts into concrete filled holes in the block
and attaching the metal to the block without a sillplate.

Sounds like I need to look around more for cedar or redwood....


Thanks for your input & time. Much appreciated.

Jim