Deck Ideas Above a Walkout Basement: Create a Living Space without Damaging Your Deck

Deck ideas above a walkout basement can make great use of the area beneath your basement.

Decorating a walkout basement space won’t damage the deck above it if you keep some tips in mind.

Not too long ago, a young lady bought the house behind mine. It was built on a slope with a walkout basement and a deck above the basement. One of the first modifications she made was to add lights and a ceiling fan to turn the space into an outdoor lounge. She then enclosed the underside with an aluminum soffit—something that covers the undersides of joists or rafters—to create a ceiling. She invited the neighbors and me over for a housewarming party when she was done, and we spent a fun summer afternoon sitting in cushioned chairs under her fan.

Unfortunately, as fall became winter the ceiling fell down, taking the expensive lights and fan with it, leaving her carefully chosen furniture covered in rotten wood and insect debris. The ceiling’s collapse revealed that the joists holding the deck up were rotten, and the deck boards were rotting from below. The ceiling she installed had been trapping moisture and damp leaves against the wood and had created a nice nest for insects. This misadventure explains perfectly why it’s important to find a balance between the needs of a structure and what you want in a living space. Great deck ideas for above a walkout basement will create an area you’ll want to spend time without compromising your deck.

A Deck Above a Walkout Basement Doubles Your Outdoor Space

My neighbor was trying to take advantage of one of the best parts of having a deck above a walkout basement. That’s the fact that they effectively create two outdoor living areas for the price of one. With a deck like this, there’s a temptation to treat the area below the deck as a second room. That’s not necessarily a bad thing, but there’s some background information you should know before you get started on any projects. It isn’t general knowledge, but even moisture-resistant decking requires ventilation to keep water from working into the boards and substructure, damaging the deck. When something like a ceiling is added beneath the decking, it cuts off the ventilation, creating a moisture problem. Now, there are a variety of ways to waterproof a deck in order to turn the space underneath into a sealed living area:

  • Membranes can be added that go beneath the boards and over the joists in order to catch water and carry it to the outer edge of the deck. Since water doesn’t go uphill, the joists that support this membrane will have to go on top of the beam, similar to the way rafters in pergolas are mounted above the beams. This allows the water to flow out over the beam, but it also increases the overall height of the deck. If the joists are hung in the usual manner, on the other hand, with the joists running directly into the beam, the downspouts will end up inside the inner perimeter of the deck. In practice, this method often doesn’t work very well, and the water ends up draining improperly.
  • Seals that are manufactured by a third party are placed in the grooves between the boards where hidden fasteners usually go. They may ensure that the area beneath the deck stays dry, but will invalidate warranties and may trap water against the decking surface. If the deck boards have to be specially grooved to install these seals, then they also provide a direct path for moisture into the core of the board.
  • Edge to edge installation of decking is a typical way of installing deck boards in an attempt to seal the space between them. Unfortunately, this traps water and keeps it from evaporating, all but guaranteeing the board will rot. The issue gets even worse if a ceiling of some sort is added beneath.

The unfortunate truth is that all these methods trap moisture next to the substructure and the deck boards and will speed along rot. Airflow is just as important as drainage, and short of building a roof above the deck, there is no way to seal the deck itself without creating a maintenance problem. Another, more fortunate, truth is that none of this is really necessary to turn the area beneath a deck into a complete living space.

Creating an Outdoor Living Space Doesn’t Require a Waterproofed Deck

After my neighbor’s deck collapsed, she asked for my advice and I did some research. It became clear that there wasn’t any foolproof system for creating a deck with a ceiling that didn’t either invalidate warranties or risk repeating her previous experience. However, with further research, it was clear that a ceiling wasn’t entirely necessary. Overhead electrical features that are built for the outdoors don’t actually require that level of protection. A ceiling fan or light that is approved for outdoor use is tested for wet conditions, and there are three categories of ceiling fixtures.

  • UL Listed Dry for indoor use (sometimes labeled just “UL Listed”) fixtures are strictly for use in a sealed, dry environment such as inside the home.
  • UL Listed Damp means the fixture can be used in areas exposed to condensation. These are suitable for screened-in rooms beneath roofs, but not suitable for places where they will be directly exposed to rain and other moisture.
  • UL Listed Wet fixtures are for areas exposed to outdoor rain. These are the ceiling lights and fixtures that should be used in any outdoor application. The key thing to look for if installing these beneath a deck is that the label doesn’t say “covered ceiling mounts only.” These types of fixtures are not proofed against water intrusion from above.

Once you’ve chosen the appropriate overhead fixtures, then installing them is simply a matter of using conduit or other suitable wiring to connect them to the house’s power. Visible conduit may not be appealing to everyone, but it does give an industrial chic touch. It is also far better than creating a situation in which a deck will rot into unsoundness.

Practical Deck Ideas Above a Walkout Basement

Using fans and lighting fixtures that were built to resist water intrusion from above, we easily wired up the features she wanted overhead. In this case, we used a ceiling fan with lights built-in for summer evening cooling and outdoor reading. With the addition of some wrought iron furniture and cushions made of moisture- and mildew-resistant fabric it was pretty comfortable. She also added a bowl-type firepit for entertaining once the temperature dropped.

With the decor established, she was ready to replace the deck. After her experience with rotted boards and picking insect bits out of her furnishings, she was adamantly opposed to wood this time around and went looking for composite decking that doesn’t mold. The problem that many composites have when it comes to moisture is that they are often only capped on one side. The cap is the moisture-resistant layer which also gives the boards the look of wood. Using a composite like this would mean two things: first, it would leave the underside of the decking vulnerable to moisture, and second, it would create a ceiling of unappealing beige. Fortunately, there are fully capped boards out there. These are not only more moisture resistant than partially capped boards, they also have wood grain on both sides. Using a composite with this features means that when she and her guests walk out of her basement for an evening get-together and look up, they see a finished-looking ceiling that appears to be wood.

One very high-quality capped line of composite decking is Infinity by Fortress Deck. It’s a bamboo-based composite that is co-extruded with a full cap that features a reversible grain: a smooth exotic wood grain on one side and a more weathered rustic grain on the other. Matching fascia boards that cover the deck posts create a put-together, uniform look that’s perfect for summer days reading in a hammock or ghost stories around the campfire. These thoughtful details are Fortress Building Products’ calling card, and you’ll find the same careful engineering in other Fortress products as well, such as railing and fencing.

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