How to Store Lumber to Prevent Warping

A warped sense of humor can be funny and fun, but warped wood isn’t.  It will be either unusable or require a lot of effort to make it so. 

When it comes to lumber and its arch-enemy, water, warping is a very real problem.  If you aren’t going to be using lumber right away, storage becomes of critical importance.  There are few things worse in a woodworking shop than to find a board for your project only to see it is warped wood and no good.

Let’s look into this further.

How Long Can Lumber Be Stored?

It’s rare that you can purchase the exact amount of lumber you need for that project you are about to begin.  Or perhaps you are buying multiple lengths of dimensional lumber but won’t be using it all at once. 

Storing Lumber Outside

Sometimes a bulk purchase can be delivered wrapped or treated with a weather protective coating.  But the lumber yard where you purchase your stock may not be able to accommodate the wrapping, and weather coating lasts only for 3 and up to 6 months, depending on the conditions of its storage.

If you have the space, your best bet is to store it horizontally.  And, since you’re a woodworker, why not build yourself a lumber rack?  If it’s dimensional lumber spans you are storing, support the lumber every 18 inches along the span to keep it from bowing.  At the end of the piece, we’ve given you a video from Youtube with some ideas to consider.

Storing Lumber Outside

And, avoid layers of lumber in a stack without that support along the span.  You want good air circulation to keep the boards as dry as possible, and you want the maximum surface area exposed to that circulation.  If it is to be stored outside, elevate it so it’s not in contact with the ground; and cover it with something that will protect it from the environment.

Polyethylene or something like it is non-porous and can create a vapor barrier to its underside where moisture can condense, so make sure air can circulate to prevent that from happening.

You don’t have any control over the weather, though, and storing wood outside for any length of time can be problematic.  The old sailor’s expression “keep a weather eye on the horizon” is apt when it comes to storing lumber outside. 

Storing Lumber Inside

If storage is to be inside, and kiln-dried wood should be stored inside out of the weather, stack the wood in the same way – supported by scrap wood such as pieces of 2 x 4 every 18 inches or so, again to allow for air to circulate.  You want to control the environment and keep the humidity level steady, so the boards become acclimated to it.  The more surface exposed to that air circulation, the greater chance of keeping your boards straight.

When the moisture level in wood rises, the wood expands; when it is later dried, whether naturally or by kiln or by a more tightly controlled environment, the wood shrinks.  If it shrinks unevenly, it will twist or become cupped, or you find the lumber bowing.

If you follow these simple and fairly obvious steps, you can store your wood for quite some time.  If storing it outside (unseasoned), it can even make it through winter.  Of course, only purchasing enough lumber for the project at hand obviates the necessity of storage concerns, as does using it timely.

Is It Better to Store Wood Horizontally or Vertically?

Storing wood vertically will take up less space, and if space is at a premium, it can be stored vertically. 

Make sure it is stored off the ground to prevent water damage – – again, water is wood’s enemy.  And, be sure to support it fully at the top and bottom to avoid bowing. 

But, if space is not an issue, it’s better to stack lumber horizontally.  Follow the general rules outlined above – – supported every 18 inches or so, allowing for air to circulate, and if stored outside, covering it for protection from the elements. 

How Do You Keep Wood From Shrinking?

We’ve already noted that water is wood’s enemy.  Wood expands when it gets wet; its pores absorb the moisture and hold on to it.  Drying the wood, ridding it of that moisture, then causes the wood to shrink.

To keep wood from shrinking, either keep it completely dry by storing it well in a controlled dry environment or by letting it reach an equilibrium with its environment where the moisture content is constant and matches the environment where the wood will find its permanent place.

Again, keep in mind that it’s the process of expansion and contraction that causes wood to warp, twist, or bow.  When you can minimize that expansion and contraction, that fattening up and then shrinking, your wood will remain usable and not require extra effort with your planer and joiner to make it usable again.

Does Treated Wood Warp?

Moisture.  Wood’s enemy.  Causes warping, bowing, twisting in the entire process of absorption and depletion. 

Treated lumber is lumber that has been soaked in a vat of treating liquid, and then pressure is applied to make sure the treating liquid is forced into the wood.  The wood becomes saturated and arrives at your lumber yard wet. 

Treated wood warps easily and often.  Why?  Moisture.  The process of soaking and drying puts tremendous strain on the wood, and drying is invariably uneven.  That causes warping and twisting and bowing and all sorts of problems with the wood’s use.  If you want proof, come see the bench I built with 4 x 4s and cinder blocks.  Twisted and warped in that project, though, can be covered by outdoor cushions and pillows.

The answer to the question is yes, treated wood certainly does warp.

What Wood Is Least Likely to Warp?

Moisture causes warping in wood.  It is absorbed into the pores of the wood, and the wood expands.  In drying, wood then shrinks, and the unevenness of the shrinking causes wood to warp.

This shrinking and swelling occur at the cellular level as the moisture seeps into its pores.  Eventually, though, it reaches an equilibrium, and we call this equilibrium “seasoning the wood.” 

Fir is the most stable wood on the cellular level, dimensionally stable, meaning that once it has been “seasoned,” it is no longer easily affected by environmental changes.

It is a softwood, although its stability once seasoned makes it a good choice for uses most commonly associated with hardwoods.  These include:

  • Flooring
  • Trim and joinery
  • Boats and airplanes
  • Furniture

It’s very tough and lasts a long time, holding its shape, resisting dings and dents.  It is the wood least likely to warp.

Can You Store Lumber In The Garage?

If you’ve followed along so far, you can probably answer this question for yourself. 

Unseasoned lumber stacked and covered properly can withstand winter and be ready for use in the spring.  It should be stored outside. 

Kiln-dried lumber, though, should be stored inside.  It’s been cured and has reached the equilibrium we spoke of earlier.  It is “seasoned” needs some protection from the elements.  If you can’t store it in your basement workshop, the garage, or a shed for the purpose, it will suffice.

Make sure the roof of the garage or shed is weather-tight so the lumber will not be rained or dripped on to raise its moisture content.  If these conditions are met, you can store lumber in the garage.  Be sure to follow the other rules we mentioned earlier – – supporting every 18 inches, for example. 

What About Storing Plywood?

Storing Plywood

If plywood is what you are storing, keep it flat.  Don’t stand it up on its edge, or it will warp.

Use scrap 2 x 4 blocks to separate the plywood and keep it off the ground if it’s being stored outside.  Moisture can rise up and be absorbed by the plywood, and again, moisture is wood’s enemy.  The blocks will separate each sheet and allow air to circulate on both sides of the surface.  Keep it out of direct sunlight, too. 

The same rules apply if storing plywood in your shop or your garage.  Separate the sheets with blocks and allow air to circulate along both surfaces. 

There are numerous videos on Youtube about drying and storing wood, and we picked a few for you to watch.

With lumber prices on the rise, you’ve likely spent some good money for your stock, no matter where you are storing it.  Take the time and go to the effort of storing it properly.

The enemy is moisture.  You’re looking to avoid warping and rot during the seasoning process.  If the stock is kiln-dried and thus seasoned, find a spot inside to store it, and stack it properly.

You’ll save the lumber, and in the process, save money, too.