Storing dry lumber in an unconditioned metal building

[Phillip Mitchell]

I want to re-arrange some of my wood storage a bit to free up some room in my shop. I’ve had mostly the same stack of maple, cherry, and little bit of mahogany on my horizontal wood racks for years taking up space, while all the wood that has actually gotten used for projects comes in and never makes it to the racks because it gets used quickly (and the racks are full...) There’s probably 200-300 bd ft of assorted hardwood on the racks and double or triple that again in other places on my property.

Im exaggerating a bit, but I do want to move some of my lumber stash out of the shop and keep my in shop wood rack more for in progress or only next on deck project wood. The horizontal racks are terrible for sorting through boards for selection...you typically need to unload the entire rack to at least see the bottom boards. Not an optimal use of space and I’m trying to reclaim as much usable space in my small shop as possible.

My shop is a dehumidified walkout basement. I also have a 20x20 uninsulated metal building - 2 car garage with roll up doors and a concrete slab. I have stored some lumber and less precious building materials in there in the past, but always wondered if there was any downside to using it for more long term lumber storage. Of course, being uninsulated there is no humidity control. It also gets pretty hot in there with the doors closed with little air flow...compared to the loft of my barn where I have more long term lumber storage with good air flow. The garage is way more convenient than the barn loft, especially for big and long stuff. In theory, I would prefer to keep long term lumber storage in the barn loft because I know it will get proper air flow and not mold, however, in practice, it’s a pain to get stuff up and down and it’s a bit rough and has developed some roof leaks that need to be addressed before expanding lumber storage there.

I am talking about fully dried lumber (both air and kiln dried.) I typically try and bring wood into my shop a week or so ahead of time to acclimate to the lower and more constant humidity before milling anyway. Just wondering if there is potential for damage, mold, excessive warping/twisting/etc by storing lumber long term in a place like a hot metal building without a lot of cross breeze air flow.

Thoughts? Thanks!

[Steve Rozmiarek]

I had a similar situation with a previous shop. My outbuilding was an old garage, a bit drafty, roof leaked a little, not ideal. Wood stored fine, as long as I kept it from getting wet. I stored a average of around 500bf of various things in there. I did notice that the moisture content reached a lower level after a while in there than it went in at. I suppose all locations are different, but the lumber will reach equilibrium for your location. The temp swings never bothered the stacks unless they got wet from a roof leak or something. I'm still using some quarter sawn white oak from there, still good stuff.

[Scott Winners]

I don't know the weather data for Boone, NC; up in the hilly end of the state I think. The forest service will know. You might poke around a little on the US Forest Service website a little bit.

What you are facing is EMC - Equillibrium Moisture Content. If you know the temperature and humidity of a space, there are tables where you can look up what the EMC of your stored lumber will be when it has acclimated to the temp and humidity. Some species acclimate faster than others, blah blah.

What you will want to know is what your summer time and wintertime EMCs are and then decide if you can use that. Without a lot of airflow - you mentioned the building gets really hot in the summer - your summer time EMC out there inside the building might be, probably will be somewhat lower than what the EMC would be if your lumber was under a picnic pavillion with good airflow.

Can you do it, yes. How long you will need to bring lumber into your shop to acclimate before you make household goods from it, I don't know.

[Jim Becker]

The biggest risks are water and vermin. If the space doesn't leak and you can set things up so you're keeping it well off the ground/floor, etc., there should be no issues. I'd consider using thin stickers (.25" is fine) to allow for even air flow. But the fact that it's unconditioned space really isn't an issue...the wood will fluctuate MC to ambient conditions. If there's a great difference, just allow for some acclimation when you bring it in for a project with stickers and good airflow for a day or three.

[Curt Harms]

Bugs would probably be my biggest concern short of a leaky roof.

[Phillip Mitchell]

The roof doesn’t leak, though the underside does condense at certain times in the winter time and drips down in certain places.

What would be ideal storage for me is to have most of the lumber stored vertically against one wall on a slightly elevated platform to isolate the end grain of the boards from the raw concrete slab. There could be different “bays” to separate different species, etc.

The question is what does the platform need to be made from to properly isolate potential moisture wicking up from the concrete and prevent bugs. The roof is pitched from 10’ at the peak to about 8’ closer to the side walls and it would be nice to stand up any lumber that was 10’ and under in a rack.

I suppose my initial hesitation with the space was that it gets quite hot and still inside the building in the summer and would that have negative effects on the stability of the lumber inside, but sounds like that’s not really a concern to be worried about. I understand relative humidity, EMC, and acclimating lumber which I already do in my current arrangement.

[John K Jordan]

Whether wood is kiln dry, air dry, or wet, moisture will move towards the EMC for your area based on the temperature and relative humidity.

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The time it takes depends largely on the thickness and type of wood as well as how you have it stacked (tight or stickered).

You can find the EMC numbers for your region. Here is one, I think from the USDA publication "Air Drying of Wood" of around the country:

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and another with more data from your area. This is a piece of a table from
"Equilibrium Moisture Content of Wood in Outdoor Locations in the United States and Worldwide United States"
From the USDA Forest Products Laboratory FPL-RN-0268 and available online.

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You can find other tables with the average EMC for the year for your area.

If the wood is already mostly dry there shouldn't be any significant warping. Some people will sticker the stacks and put weight on the top, in the storage AND when moving back to the shop. The time it takes to re-acclimate depends on the wood thickness and moisture content acquired in storage. A good moisture meter might help. In East TN the EMC for outdoor storage is about 14-15%. In my shop with heat and air EMC is usually around 10=11%. (I don't heat or cool to extremes.)

There is a danger of powder post beetles getting into certain species of wood (most problem is with wet wood but some even like dry wood.) Treatment, Bora-Care, etc, might prevent infestation.

JKJ

[William Hodge]

If you aren't using the wood, you could sell it.
Stored in a rack in a conditioned space sounds good, if you have never put the wood on the floor.

I need to do the same thing. I have clear longleaf heart pine that cost $8.25/bf. I am at about the point of giving it away, because I need the room. It takes time to work around it, and not have room to store other stuff.

The extra Ash I had came in handy a few weeks ago when I needed a 14' bench top for an entablature over an entrance. I also built a table to hold my finishing planer out of Ash. Given the price of lumber, I might be using Ash tomato stakes.

[Phillip Mitchell]

Thanks all for the EMC charts. Helpful to see the science.

Yes, William, thanks. I actually just listed about 75 bd/ft of unremarkable 4/4 Cherry for sale locally and may have a buyer so that helps condense the stack a bit and prevents me from having to move and stack it yet again. It’s lumber that I have picked through for the last 5 years, built a few nice furniture projects with some of it and haven’t seen a real use for the remainder in that time. I’d rather get $200-300 for it at this point and reclaim the space than have to deal with moving and stacking and the time and effort that entails.

[Scott Winners]

I am reticent to store lumber vertically. I have a small side hobby of restoring striking tools. When an axe is left head down on the foor of a barn or shed, leaned against the wall, the handle will warp. I can't explain how, but I have observed over and over again it happens. Invariably the haft will warp towards the wall. The picutre is the most extreme one in my collection, but pretty much any axe I find leaned against a wall at a barn sale is going to need the haft replaced.

[Mel Fulks]

Well. Even though you don’t like to talk about storing lumber vertically, it’s good that you write about it. Good tip there on on handling the
handles.

[Richard Coers]

Take it from someone that lost thousands of board feet of air dried lumber in a steel sided shed to powder post beetle, DON'T DO IT. Air dried goes up enough in moisture in Central IL to make soft maple and ash appealing to PPB. I had 8/4x20"x10' that had zero untouched area. The boards were filled by tunnels. I gave a little away as firewood, but it makes a man cry to throw 2x20s of curly soft maple onto a bonfire.

[Scott Winners]

Perhaps reluctant would have been a better word choice. I do store some lumber vertically, but I know even in my conditioned shop it will warp if I leave it leaned against a wall long enough.

I also have a cat that likes to climb on rough sawn lumber. I think she finds it exciting to ride falling boards to the floor, like some kind of surf board or something.

[Curt Harms]

Take it from someone that lost thousands of board feet of air dried lumber in a steel sided shed to powder post beetle, DON'T DO IT. Air dried goes up enough in moisture in Central IL to make soft maple and ash appealing to PPB. I had 8/4x20"x10' that had zero untouched area. The boards were filled by tunnels. I gave a little away as firewood, but it makes a man cry to throw 2x20s of curly soft maple onto a bonfire.

Sorry to hear about your curly soft maple. Maybe spray with something to protect against powder post beetles when stacking?

[Richard Coers]

Sorry to hear about your curly soft maple. Maybe spray with something to protect against powder post beetles when stacking?
This was not a recent incident, but I share it in an attempt to warn others. It was my mistake for not researching storage methods more thoroughly and it was a very hard lesson. A preventative pesticide is essential unless you live in an area where there aren't any powder post beetle.