Woodworking in Florida: Wood Moisture and Outdoor Builds

Month-by-month outdoor wood moisture for 13 places in Florida, from 12.2% in West Palm Beach in April to 16.2% in Apalachicola in August, and what it means for buying lumber, gluing up and finishing.

Wood trades moisture with the air around it until it reaches a balance called the equilibrium moisture content (EMC). The numbers on this page are the average EMC of wood kept outdoors under cover (out of direct rain and sun) for each month, calculated by the USDA Forest Products Laboratory from at least 30 years of NOAA humidity and temperature records. Wood that gets rained on will be wetter for a while; wood inside a heated or air-conditioned house will be drier. The general advice below uses Miami as the reference city.

Outdoor wood moisture in Florida, month by month

City by city

The 6 cities whose climates differ most get their own section; the other 7 follow one of them so closely that they are listed with their numbers and the closest match. Deck board figures are for a 5½-inch flat-sawn pine board going from the wettest to the driest month.

Other Florida cities with a similar climate

These cities track one of the cities above closely, so instead of repeating the same advice, here are their own numbers and the closest match.

• Daytona Beach: 13.0% in April to 15.4% in August, averaging 14.2%. Month by month it is within 0.1 points of Vero Beach on average, so the advice there applies.
• Fort Myers: 12.5% in April to 14.2% in September, averaging 13.6%. Month by month it is within 0.2 points of Miami on average, so the advice there applies.
• Jacksonville: 12.4% in April to 15.0% in September, averaging 13.7%. Month by month it is within 0.4 points of Miami on average, so the advice there applies.
• Orlando: 12.5% in April to 14.4% in August and September, averaging 13.6%. Month by month it is within 0.2 points of Miami on average, so the advice there applies.
• Tallahassee: 12.9% in April to 15.0% in August, averaging 13.8%. Month by month it is within 0.3 points of Pensacola on average, so the advice there applies.
• Tampa: 12.7% in May to 14.7% in August, averaging 13.8%. Month by month it is within 0.4 points of Vero Beach on average, so the advice there applies.
• West Palm Beach: 12.2% in April to 14.5% in September, averaging 13.5%. Month by month it is within 0.1 points of Miami on average, so the advice there applies.

What moisture content to aim for

The Wood Handbook's rule is to install wood at the moisture content it will live at, so it moves as little as possible afterward. In Miami the year-round outdoor average is 13.5%.

• Outdoor projects (decks, benches, planters, siding and trim): the Handbook recommends an average of 12% (individual pieces 9% to 14%), the Handbook's figure for damp, warm coastal areas.
• Indoor furniture and trim: about 11% (8% to 13%), the damp, warm coastal zone on the Handbook's map.

A pin or pinless moisture meter takes the guesswork out. Check a few boards from each batch, not just one.

How much a deck board moves here

Using the Wood Handbook's shrinkage coefficient for flat-sawn loblolly pine (a common treated-lumber species; Table 13-5), a board 5½ inches wide, the width of a 2x6 or a 5/4 deck board, changes width by:

These are estimates: real boards are rarely perfectly flat-sawn, and western redcedar moves about 10% less than pine. The point is the direction. Lumber bought at 19% will shrink, so gaps between deck boards installed tight will open as it dries.

Acclimating lumber in Florida

1. Bring it home early. Buy lumber a week or more before you build.
2. Stack it with stickers. Lay straight spacer strips every couple of feet between layers so air reaches every face, and keep the pile off the ground.
3. Store it where the project will live. Outdoors under cover for outdoor projects; inside the house for indoor furniture.
4. Measure, don't guess. When moisture meter readings stop changing from one day to the next, the wood is ready.

Damp all year

Outdoor wood in Miami stays above 12% in almost every month. Kiln-dried furniture lumber (dried to 6% to 8% at the mill) stored in an unheated garage or shed will drift up toward the outdoor level. The Forest Products Laboratory notes that warming a closed storage space above the outside temperature lowers the moisture level: with an outdoor EMC of 14%, holding the space about 20°F above outside brings it to about 7%. Store furniture stock indoors or in a conditioned room, and build indoor pieces there too.

Damp weather also favors mildew on outdoor finishes. The Wood Handbook advises washing mildew off with a commercial mildew cleaner or diluted household bleach and detergent before refinishing, since new finish over mildew fails early.

Wet months

In Apalachicola, outdoor wood reaches 16.2% in August. Keep lumber covered and off the ground, with stickers (spacer strips) between layers so air can move, and plan glue-ups and finishing for the drier months.

Woods and finishes that hold up outdoors

For anything left outside, choose wood that resists decay or wood treated for it. The Wood Handbook's Table 14-1 rates the heartwood of the cedars (including western redcedar), white oaks, black locust and old-growth redwood as resistant or very resistant, Douglas-fir and young-growth redwood as moderately resistant, and most pines, spruces and firs as slightly or not resistant. Use pressure-treated lumber rated for ground contact for posts and anything touching soil.

From the Handbook's Table 16-5: a water-repellent preservative typically lasts 1 to 3 years, semitransparent stain 4 to 8 years on rough-sawn or weathered wood, solid-color stain 6 to 15 years and paint 10 to 20 years. Clear varnish is a poor choice for furniture left in the sun; it generally needs refinishing every 1 to 2 years there.

Best months for outdoor builds and finishing

In Miami, outdoor wood is driest in March, April and May and wettest in June, August and September. Lumber dries fastest, and finishes go onto dry wood, in the drier months, so plan staining and painting for then. Avoid sealing wood during the wettest stretch, when it is holding the most moisture it will hold all year. If those months are cold, check the minimum application temperature on the can before you finish. The city sections above give the driest months for each city.

Keep reading

• The actual size of a 2x4, and why it matters
• Why your woodworking project doesn't fit
• How to build an Adirondack chair

Deciding what to build this season? Start with our list of 9 things worth building instead of buying.