The three biggest problems affecting hardwood decking materials' look and performance are completely preventable: improper moisture management (draining and ventilation), improper acclimation and improper finishing.
Because high density tropical hardwood species like Ipe, Cumaru, Garapa and Machiche are so strong, hard and long lasting, many people believe that nothing should be done before installing them on a deck, siding or other outdoor structure. While it is true that these hardwood decking and siding species have some remarkable physical properties, they are still natural wood products and must be treated as such, especially initially.
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Here's Why it is a Critical Success Factor to Drain and Ventilate a Deck Properly:
In the design phase, a crucial long-term durability and sustainability factor is to find the best way to effectively manage moisture on your site. When installing decking without adequate under-deck drainage and ventilation, it is a formula for poor performance and long-term dissatisfaction with your entire deck structure.
If wood decks do not have adequate ventilation designed into the structure, how will the deck breathe? How will the moisture be minimized for the joists and framing members of the deck structure? What’s preventing mold, mildew and fungus from thriving and ruining the entire structure over time? The best solution to eliminate or at least minimize these problems is to design and build the deck with proper drainage and ventilation.
When moisture is allowed to persist in a cool, dark and improperly ventilated area (under a deck for example), the hygroscopic (water absorbing) nature of wood framing and decking will retain some of this moisture. The closer to the ground a structure is built, the more moisture the wood will retain. The less ventilation under a deck, the more moisture the wood will retain. The bottom of the wood decking boards will retain as much of this moisture as nature allows.
The worst possible combination of all is to build a deck too close to the ground without proper drainage or proper ventilation. A well designed deck, even in tough topography like this stunning Ipe deck, can effectively manage moisture because the adequate drainage and adequate ventilation were planned and built into the design.
Meanwhile, on the top of the deck, while we are happily grilling hot dogs and enjoying a hot sunny afternoon, the sun is drying out the top of the decking boards. Science teaches us that when two powerful opposing forces meet, a violent reaction will occur. When cool, moist decking board bottoms meet hot and drier deck board tops, the boards are at maximum stress and will move, often by cupping upward at their edges.
The best solution to prevent and minimize this clash of forces is to eliminate one of the forces. Since we like to enjoy sunny days on our decks, we probably don't want to put a roof or awning over our deck. So that leaves us with controlling and minimizing the amount of moisture beneath our deck.
- The first step is to adequately pitch the drainage to slope away from the home or structure.
- Many construction professionals have developed techniques to keep the soil under the deck in proper order including using either a landscape fabric, crushed stone or both.
- Landscape fabric is a great idea because it helps keep the moisture in the ground
- A layer of crushed stone helps slow the flow of rain water from rushing out too quickly from below the deck - but it still gets out
- Another option is to use a specially designed drainage system under the deck joists. They're expensive but are particularly effective for decks that have lots of usable outdoor space below.
While these are all good solutions to help remove bulk moisture and get it out from under the deck, adequate ventilation is also essential to remove the rest of the moisture. Any water or moisture under a deck needs a means to escape or it has the potential to wreak havoc with the wood deck components and decking boards and become a breeding ground for moisture and mold to create rot and and decay.
Proper drainage and ventilation minimizes moisture and reduces the potential for boards to cup and for mold to grow. Ventilate. Ventilate. Ventilate. Providing adequate under-deck ventilation on three side of your deck works best. It gives moisture vapor a place to go.
Proper Acclimation of Wood before Installation is Essential for Best Performance
It is a natural characteristic for wood to change sizes when it gains or loses moisture. Nothing can change this naturally occurring phenomena. However, once wood achieves EMC (Equilibrium Moisture Content) the movement of the wood is a lot less significant. If you allow your exterior wood decking, lumber or siding to properly acclimate (achieve EMC) before installation, you will eliminate lots of potential headaches immediately. Click here to download “Critical Tips for Proper Wood Acclimation”.
Cumaru decking installed before it was fully acclimated.
Each board expands and contract differently. Ouch.
Failure to properly acclimate wood decking and siding prior to installation can lead to different spacing between decking or siding boards and other possible problems. If you want your wood deck or structure to look its best, the best building practice is to follow the proper steps to allow the wood to adjust (acclimate) to its new site. The best decking installation practice is to choose the best deck boards to work to your best advantage after they have properly acclimated on site. Click here for additional information on proper acclimation of exterior wood.
Pre-Finishing Your Exterior Decking, Siding and Lumber is a Best Building Practice
Pre-finishing exterior hardwood lumber is not an absolute requirement, but it should be. It is generally an excellent idea and a very good construction practice. Pre-finishing exterior wood on all four sides before it is installed is the best way to ensure that the wood is evenly coated.
There are a number of benefits to pre-finishing exterior wood, including the fact that it will help the wood acclimate better by protecting it from harmful UV rays and moisture during the critical acclimation process. Putting a UV inhibiting sealer on your exterior wood also helps minimize surface checking.
Learn more about pre-finishing exterior hardwood decking and siding.
Pre-finishing your exterior hardwood decking, siding or lumber prior to installation offers many other great benefits as well. In addition to better protection, other key benefits of pre-finished exterior woods include instant beauty, better blending of grain and color of the boards, better stability of the wood, minimized surface checking and faster construction completion times.
Once your exterior hardwood decking is finished (initially), you can continue to maintain the 'like new' wood appearance over time. Or you can allow it to mellow to a silvery gray patina. Even if you want your deck to 'silver out' over the years, applying a UV preventative sealer first is a best first-step practice. After your wood seasons in place, you are free to let your deck weather as you wish.
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