Repurposing a Greenhouse to Dry Wood

[Kent Adams]

I've got a large, permanent structure glass greenhouse on my property. Originally, I planned to renovate it when I purchased the house. However, after getting several estimates, the cost of renovation doesn't make any sense.

The greenhouse gets sun all day and the temperatures, even in the winter time, will get as high as 130 to 140 degrees F. The addition of airflow will bring it down maybe 20 degrees on the hottest day. If it's 80F outside with the sun shining, it will be near 100F in the greenhouse.

There is no way to control the humidity in the structure. Right now its serving as storage and I use it occassionally to apply paint or stain on a project that doesn't require a finishing booth. Its great to do this in the winter when humidity is low and the temps are warm to hot in the greenhouse. At night, the temps match the outdoor temps so it can't be regulated at night, without running a heater which would be expensive because it has no insulation and it leaks air everywhere.

I put several boards of 3/4 maple in the greenhouse this spring and they were fine sitting in there, with only a few of the boards bowing after a week or so. This wood was already in the 10% moisture range, so that may be the reason they've been fine. I also have about 200 bdf of landscape timbers in there, waiting to be used that have done fine (borg bought). I'm trying to figure out what I can use this thing for, because I can't use it as a greenhouse. Renovation costs are simply too high.

I'm thinking I could use the building to dry wood. During the day, the heat would speed the process up and there is no air circulation problem (I can hook up large fans). My concern would be that I have no way of controlling humidity, the heat might dry out the wood too fast and I'm not sure about the UV rays and what damage if any they would cause. I'd think that if greenhouses were great for drying wood, commercial lumber processors would use them?

I could not put large trunks in the building because it has just standard 36" doors. But, I could put in some wood that could be milled and laminated.

Here are my questions:

• Could I use this structure to dry wood?
• What other use could I get out of this structure?
• Is there a type of hardwood that could be used on the flooring system that could handle the humidity from the ground and the heat above it? I've thought about turning it into an outdoor living room.

Thanks in advance.

P.S. I've never milled or dried my own lumber before. Also, all the plants you can see in that picture were not grown in the greenhouse, but under metal hallide and sodium lamps in my basement.

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[Allan Speers]

Kent,

First, you are the luckiest man I know !


Second, re the ground moisture, here's one very workable solution:

Lay down thick pavers over the entire surface, and use a concrete mix in-between them, so there are no gaps.

Next, buy 5 gallons or so of Radonseal, or Xpex, or whatever, and apply several coats. I used Radonseal in my basement, which used to get massively humid in the summer. Now it's dry as a desert. Any water spilled on the floor just beads up & rolls around - even three years after my application. I'm planning on doing my garage/shop now, as I'm realizing that this is causing my tools to rust, and causing my dehumidifier to run way tooo much.

Oh, and of course, when you lay the pavers try to end up with as level a surface as possible. This should make it slightly easier to construct proper drying racks.

[David Nelson1]

Kent,

First, you are the luckiest man I know !


Second, re the ground moisture, here's one very workable solution:

Lay down thick pavers over the entire surface, and use a concrete mix in-between them, so there are no gaps.

Next, buy 5 gallons or so of Radonseal, or Xpex, or whatever, and apply several coats. I used Radonseal in my basement, which used to get massively humid in the summer. Now it's dry as a desert. Any water spilled on the floor just beads up & rolls around - even three years after my application. I'm planning on doing my garage/shop now, as I'm realizing that this is causing my tools to rust, and causing my dehumidifier to run way tooo much.

Now that's the best idea I have heard all week! I have the same problem in my shop even with a moisture barrier.

[Keith Outten]

I ran a small dehumidification kiln for about 15 years. The key to drying high quality lumber is controlling the temperature first and then having a means to remove the moisture. My kiln was a super insulated box with an EBAC dehumidification unit inside. The unit kept a constant temperature via a small heating coil and in accordance with a drying schedule and at the same time removed the moisture in the box, when the moisture inside the box was lower then the moisture in the wood the wood would give up its moisture. The unit was similar to an air conditioner extracting the water via condensation and it was collected by a tube to an exterior storage bucket so it could be measured each day.

If you cannot control the temperature reliably 24 hours per day in your greenhouse it isn't a good candidate for drying lumber IMO. The fact that you get free heat is not much of an advantage as it doesn't take a lot of heat for a lumber kiln unless you prefer the brute force system such as the steam dryers but then you have to have a means to produce that at night without a temperature drop. If the greenhouse isn't air tight you don't have control over the moisture inside.
.

[Allan Speers]

Keith, that's very interesting.


If you have your lumber properly stickered, with a lot of weight on top, what is the problem with wide temperature swings? Does this somehow make the lumber twist more?

[Yonak Hawkins]

It's important to be able to remove moisture, even if it's as simple as a fan expelling air to the outside. That said, unless you want a very efficient kiln, it doesn't need to be air tight. The heated air, during the day, even only on some days, will accelerate the drying much more than simple air drying, plus staying above 130° for periods of time, will help to control any powder post beetles. I have a passive solar-kiln-type set-up that is quite inefficient as far as air control but I can still dry wood in a third of the time of air drying.

[John TenEyck]

As Yonak said, solar lumber dryers inherently have wide temperature swings - by design, and the lumber that comes out of them is as good as wood dried any other way as long as they are run properly. In a solar dryer the temps. are 130 F or more during the day and the wood gets stressed as it dries at the low RH associated with that condition, but at night the humidity goes way up and the wood reconditions and the stress is relieved. Rinse and repeat daily as the moisture content in the wood goes down.

I think your green house could be used as a wood dryer if you shield the wood from direct sunlight. That's easy enough to do by putting plywood or corrugated roofing on top of your stacks. Then you have to figure out how much air to let in and out of the green house, which is how you will control the RH. If the greenhouse is leaky as far as air you may just want to leave it closed up. Put a couple of RH meters in there and see how much the RH changes day to night and let that be your guide.

Read up on solar wood dryers and decide for yourself whether or not to give it go. I vote yes.

That's a really nice looking greenhouse. I'm surprised it can't be rehabbed at reasonable cost for that use. Nice looking garden, too.

John

[Kent Adams]

Yonak, I'd never heard of solar kiln's before so I looked them up. Basically, my greenhouse could be used as a massive solar kiln from what I've been able to read. Thank you so much for the help!

[Kent Adams]

John, I'd never heard of these solar kiln's but looked them up after your and Yonak's recommendation. I think my greenhouse would work perfectly for one of these. I can regulate the air flow not only with fans, but the top of my roof also open's up which really helps with the build up of heat and trapped air.

I've had some luck with tarps preventing UV damage in the greenhouse. I imagine I could use those in place of plywood. I've also tried to monitor the RH in the greenhouse. But, in the hot summer climate, the plastic RH wireless monitors I put in there melt on a hot summer day unless they are shaded, and I'm not too sure I'm getting an accurate reading with them being shaded. The floor of the greenhouse is 1x4's spaced about an inch apart with a gravel substrate underneath to the ground. Allan's idea to control humidity maybe the way to go for the flooring.

In regards to the renovation costs, its complicated. The greenhouse was built in 1977. It's a Lord and Burnam model. The curved glass is now only being specially produced by one manufacturer and they charge $200 per panel. There are several sections of flat and curved glass that have broken and the prior owner replaced them with poly which is now warped from the sun. The greenhouse has 2 heaters and an evaporative cooling system, none of which are working any longer. The copper sprinkling system is trashed and the roof motor is no longer working. I had someone who refurbishes greenhouses come out to give me an estimate and it was going to run about $20-$25k to replace all the glass to code, the heaters, the plumbing, the gas line and the evaporative system. In perfect working order, the greenhouse could only be used in the winter. I couldn't justify that expense for what would just be a hobby for 1 season. This is the reason I turned to my 2nd hobby, woodworking. I can cool and heat my shop with no problem and I can use it throughout the year, which makes me and the wife happy. I'd love to fix that greenhouse, but I can't quite get over the cost factor to only be able to use it 1 season during the year.

[Kent Adams]

Kent,

First, you are the luckiest man I know !


Second, re the ground moisture, here's one very workable solution:

Lay down thick pavers over the entire surface, and use a concrete mix in-between them, so there are no gaps.

Next, buy 5 gallons or so of Radonseal, or Xpex, or whatever, and apply several coats. I used Radonseal in my basement, which used to get massively humid in the summer. Now it's dry as a desert. Any water spilled on the floor just beads up & rolls around - even three years after my application. I'm planning on doing my garage/shop now, as I'm realizing that this is causing my tools to rust, and causing my dehumidifier to run way tooo much.

Oh, and of course, when you lay the pavers try to end up with as level a surface as possible. This should make it slightly easier to construct proper drying racks.

Thanks Alan, I may just do this. Currently, I have 1x4s as flooring over a gravel substrate. The flooring would need to be taken out and the substrate leveled for the pavers, not really a huge deal to do that. I've never heard of that Radonseal, sounds like a solution to several problems. Thanks for your feedback.

[Kent Adams]

Keith, moisture at night is a real problem to be sure. As John suggested in the thread, I'm going to run an RH meter in there for a few days. The heat in there I suspect gets rid of most of the moisture during the day. The swing at night would probably replace some of the moisture lost during the day, but I'm not sure it's 1 for 1 so to speak. I'm going to set up an experiment with some fresh cut oak logs to see what happens before I start to renovate the structure. Thanks for your input!

[John TenEyck]

Kent, for drying wood you could take up your 1 x 4 flooring, put heavy poly on top of the gravel, and then put the 1 x 4's back down. You don't have to seal off the ground moisture completely, just reduce how much comes up to an acceptable level. Put your RH meters in the shade, in the same condition your wood would be, and see what the swing is from night to day. You want it to be high at night; that's why the floor doesn't need to be absolutely impervious.

Spend some time and read some of this, especially the chapter on Solar Kilns: http://www.fpl.fs.fed.us/documnts/fp...ardwood-lumber

John

[Kent Adams]

Kent, for drying wood you could take up your 1 x 4 flooring, put heavy poly on top of the gravel, and then put the 1 x 4's back down. You don't have to seal off the ground moisture completely, just reduce how much comes up to an acceptable level. Put your RH meters in the shade, in the same condition your wood would be, and see what the swing is from night to day. You want it to be high at night; that's why the floor doesn't need to be absolutely impervious.

Spend some time and read some of this, especially the chapter on Solar Kilns: http://www.fpl.fs.fed.us/documnts/fp...ardwood-lumber

John

John, that is an excellent recommendation. I could use something like 6 mil below the floor. I'll look at the link tonight. Thanks for you input, lots of good ideas and guidance.

[Cody Colston]

A passive solar kiln is actually a lot like a greenhouse. As was said, cover the lumber to protect it from direct sunlight and provide sufficient air flow. There are formulas to determine the amount of air flow needed, depending on the size of the lumber charge. Google the Virginia Tech Solar Kiln and you will find loads of information.

The drop in temperature at night is actually beneficial. When the temperature drops, the RH rises and conditions the wood, relieving drying stresses that are introduced during the day. That means you don't have to introduce moisture at the end of the drying cycle to relieve the stress. Don't worry about controlling the RH in the greenhouse. Just make sure you provide a way for moisture to escape. It will be a trade-off between maintaining heat and letting moisture escape. As the wood dries and releases less moisture, the RH will decrease.

[Keith Outten]

Keith, that's very interesting.


If you have your lumber properly stickered, with a lot of weight on top, what is the problem with wide temperature swings? Does this somehow make the lumber twist more?

Allan,

Controlling the temperature is definitely about lumber quality not so much about drying speed. A very slow drying schedule and controlled temperatures is the key to perfect lumber that won't twist, stain or warp. I used to get my lumber right off the sawmill and put it in my kiln soaking wet. This extended the time but provided perfect lumber that people paid handsomely to purchase. Not once did I ever have a board twist when running it through my table saw, this is the real challenge. Its not enough to just put weight on a lumber pile and keep it flat, its all for nothing when it twists on the out-feed side of the saw blade. You can air dry lumber if thats all you want but it won't ever be high quality wood and there will be some loss from every load you dry.

My kiln worked so well that two of my friends purchased EBAC systems and built identical kilns to mine, theirs were both larger but the same principles applied.
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