Hi - We have a wood-frame lean-to style greenhouse. Before we cut an opening where it attaches to the house, a lot of moisture accumulated and I'm sure it would have been a problem. I think using treated wood is a good idea unless you plan to paint it. Good luck!

Although the chemical companies say it's safe. If youÂre growing veggies I would think twice about using ACQ treated lumber. But the jury is still out on how safe it is. Just an opinion and we didn't.

No...In my state they found that treated lumber can cause
health problems in the future because of the man made chem.
in the treated lumber. This is the soil samples they tested
on and near our children play ground it show high levels of
this chemicals.
If you want to use wood then why not use oak, redwood,
cedar and other types then treated lumber. You can make
it out of PVC or GH kit sold on the internet.

According to the Wolmanized website:

As long as the treated lumber is "Wolmanized®" then you will be fine and environmentally responsible. You are most likely going to purchase the wood from Home Depot or Lowes and both carry the Wolmanized® lumber. The lumber is treated with a copper preservative and an organic fungicide.

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My 10x10 GH is made 100% of treated lumber. I'm not worried. Red meat and beer will kill ya too! Just my 2 cents.

Personally I think it's just too darn early to tell.
Wasn't asbestos safe, What about DDT?
Just better safe then sorry.
Red meat and beer do not kill. The over consumption does..

Even though we have covered this topic several times before, here is the info again:

ACQ treated wood ("AC2" and "ACQ" are brands) contains:

Copper oxide
Ammonia (some types)
ethanolamine

CAB treated wood ("Wolmanized" is one brand) contains:

Amine copper
Tebucoazole (a fungicide and termicide)
Formaldehyde (in "Wolmanized" plywood)
Ammonia (for treating refractory species such as Douglas Fir)

In the good old days before December of 2000, CCA treated lumber could be used and sold. This lumber contains an arsenic compound. Arsenic has been shown to be a strong carcinogen and easily leached from the wood. CCA treated lumber can still be used in "commercial" settings such as utility poles and supports for road signs

The constituent components in the newer treatments are not listed as suspected carcinogens. However, Tebucoazole is being investigated as a possible carcinogen. This fungicide is currently used on some food crops and as a sanitizing agent in processing plants that do food processing.

In a greenhouse, for anything other than the foundation elements (i.e. "structures in constant contact with water") it is not necessary to use treated lumber. Good old regular lumber with a couple of coats of latex paint will last as long as the paint is rated for, although using a mold inhibiting additive to the paint is probably not a bad idea.

Cottage farmer,

You make a great case. I think I will go with plain ol' lumber and give it a splash of exterior paint. since I have to buy some anyway, whats a bit more? I would think the key lumber to paint would be any that comes in contact with condensation and likely the end-grain in these areas which would be the most suseptable to wicking moisture.

Sail,
I think you'll find painting only part of the frame is going to look strange. Bet you end up painting it all.
In our wood frame g/h I cant think of any part of the frame that hasn't come into contact with moisture.

Paint the lumber before you build with it. At least give it a base coat or two and then one more when you finish the structure.

Believe me, painting a wood framed greenhouse is not a fun job.

Amen to Chris' suggestion about painting before you construct, if you can. I did paint four coats of paint on a wood framed 9x14 and it was a Pain...literally.

As I said last time this came up, you should investigate penetrating oils such as linseed, tung and lanolin. These actually soak into the wood and stablise the top 5mm or more from moisture penetration stopping fungii from getting a hold. creosote is another popular option, although I believe there may be some issues with it healthwise.

/me who is repairing a garage where the previous owner just covered up wood rot with cheap cladding. grrrr.

I can give you a personal experience reason not to use it.
My best friend has a 2000 sq ft greenhouse that her husband built for her over 10 years ago using treated lumber. They leave it open in summer and cover it with poly film in winter. When water hits the wood and drips off, if it consistently drips directly onto plants, it ruins them. Especially sensitive plants like bromeliads, ferns and orchids. She has lost many plants because of this damage from the chemicals in the wood. I have seen them, they are sad. Of course with that size GH she can't just start over.

Good point bihai. Why would anyone think they could save money with a wood frame greenhouse? That treated wood is expensive. And untreated is a waste of time and energy. Even painted the expected life is going to be quite short whereas a galvanized structure will last a lifetime. Use treated wood elsewhere in the structure for the same reason. If you are concerned about your health avoid fried foods, especially bacon. PVC is about as shortlived for different reasons. It can't take the freezing and heat of greenhouse conditions. All you need to do is take a ride in the country and look at what the commercial people are using.

bmoser, sorry but I cant disagree more.
The main reason is looks. Most folks on this forum don't want a commercial greenhouse in their back yard. There just not that darn pretty. Now they do make really nice steel and aluminum prefab g/h's but they can run into the 10's on thousands of dollars for just the frame.
Untreated wood is a very good alternative to the expensive prefab g/h frames. If maintained correctly will last as long as any steel frame house. Steel fasteners do eventually rust.
Coming from one who owns both and I love bacon....especially when you slaughter your own pig.

Just recently i bough a pre-fab from shedsusa through a local unfinished furniture place in the boston area.... 8x10 (optional) cedar, PT 3/4" floor.. best money i ever spent

For what I wanted (almost 2000 sq ft with a 20 ft roof) I think I got a great deal. I had my greenhouse built by a company frm Apopka FL. They build all sizes, commercial and residential. Here in this part of Florida (the cold, Arctic north central part) we do actually get a "winter". We have several drops to freezing between November and April, and usually have a few hard frezes in the low to mid-20's as well. So if you want to grow the plants I want to grow (tropicals like heliconias, etlingeras, orchids, etc) you need something you can heat efficiently. But the larger problem in all of Florida and the south is summer heat. Its much harder to cool the greenhouse in summer than it is to heat it up in winter. After watching the work it takes my friend with her wood frame to cover it in poly film in winter and uncover it again in spring, and seeing the damage to her plants from treated wood, I decided to use a metal frame.

For us in this part of the country, its not just the issue of water/damp damage to the wood. Its the issue of termites and wood destroying insects and fungi as well. Untreated wood structures here may as well have a sign on them that says "Free dinner for termites and wood boring beetles, while supply lasts!" And using "repellant" woods like cedar is good, but termites do infest cedar (my house is sided with cedar, and we have had termite damage in the past even though all of the siding is cut well above the soil line)

My greenhouse is almost 3 years old now. It is 1728 sq ft, glazing is single thickness corrugated Lexan, it came all inclusive with two 36" exhaust fans, 4 HAF circulating fans, a 36 ft vent on a motor that opens automatically, a 36 ft swamp cooler over that vent, motor to open vent, pump to wet down the cooling pad, Wadsworth step controller to automate the heat and cooling system, 200,000 BTU Modine propane heater, sprinkler system for watering, 2 water hose taps, plugs, floodlights. Its rated to withstand winds of 120 mph. I am very happy with it. It was about $25K to build. I didn't need a building permit because it has no concrete foundation.

I have seen much smaller greenhouses in catalogs and on websites that cost almost as much, and they don't come with the equipment.

Hello,

I am going through the same deliberation as to the treatment of wood in my GH. After much reading and web research, I decided to buy a copper-naphthenate product. This treatment kept reappearing everywhere and was touted as considered safe by "most experts". I found a product called "Copper Green" at my local hardware store. The only problem is that it leaves a kind of green tinge on the wood. Some of the posts in my GH are gorgeous and I hate to slather this stuff all over them, so I am torn. My husband told me to use polyurethane instead???? I have no idea of the effects of polyurethane in the greenhouse. Has anyone used copper-naphthenate or poly and if they have used the copper product, is the green coloring permanent? Could I use the copper product and then cover it with poly?

Thanks!

I'm using copper napthenate to treat wood rot in my 40 year old garage. It seems like a good product. However, I wouldn't use it to treat wood that is as yet unrotted. My prefered treatment there is to use a penetrating oil like tung oil. The chinese made wood ships that survived hundreds of years at sea by using tung oil, so it does work.

Polyurethane is just a skin, like paint. If it gets a scratch the water gets in under the surface and can't get out. A penetrating oil goes into the wood so it is far more scratch resistant, and water will not move through the wood. Wood rot happens when the wood gets more than 20% water.

Perhaps if you are really concerned you could use Copper napthalate on the hard to see parts (where the rot is most likely) and tung oil on exposed parts. I haven't looked, but I presume that the two are readily mixable (as they are both penetrating oils) so just paint the tung oil over the top.

I made an outdoor greenhouse bench for hardening off seedlings using hardwood and tung oil. It survived being watered every morning for 3 years with its feet in wet sand, before I moved house (It's still in good condition, just dismantled).

Another approach, even with cedar materials, is to use a non-toxic wood sealer. Quoted from another post:

"Protecting the wood is probably not as important as it seems where the wood is not in contact with soil. Avoid wood sealers that contain preservatives such as pentachlorophenol (a now restricted pesticide). Many "deck sealers" and outdoor wood stains contain gross carcinogenic poisons. You probably don't want these materials in your greenhouse. The best protection against humidity is a single coat of melted paraffin wax (a penetrating wood pore sealer), brushed on the surface. This is a little messy, sticky and somewhat difficult to apply. You could rub it out with lint free rags and give it a couple of coats of shellac to reduce the stick. The next best (non-high tech i.e. two part epoxy finish) would be 2 or preferably 3 coats of two-part polyurethane gloss varnish or 3 to 6 coats of marine spar varnish. Deck furniture is coated with several coats of marine spar varnish. Varnishes need to be renewed every year with a single coat or they will crack, eliminating the moisture barrier effectiveness. 3 coats of shellac will provide some protection. Shellac needs regular maintanance, too. For all finishes, lightly sand with 120 grit sandpaper between each coat but not after the final coat. Obviously, these suggestions are an attempt to provide as complete protection against humidity and fungus growth as possible. If you can live with your wood aging "gracefully", you can relax your finishing techniques. Don't finish the wood if it has high internal moisture. Wait until it is dry. Much information is available on the US Forest Products Laboratory website at http://www.fpl.fs.fed.us";

If you are building a GH as an objet d'art, go with the cedar, mahogony, or teak and marine spar varnish. This is the classic wood GH finish (and yachts, deck chairs, etc.).

For the situations where there are termites and other agressive wood borers, you need to work with them. Use baited termite stakes like Norm and Co. on TOH. These traps give the termites some wood (actually cellulose) that they can get to more easily around the perimeter of the GH that is laced with a little poison.

Here is a link that might be useful: Forest Products Laboratory

Or, you could use tung oil, as I suggested, which is an easy to apply, cheap and readily available, non-toxic (indeed edible), clear penetrating oil. People use it for finishing wood art. It's certainly adequate for framing timber.

Fungus will not attack wood with less than 20% moisture, perhaps the framing wood should be stacked in an empty greenhouse for 6 months first to really dry it out :)