Most homeowners think about what’s on top of their deck. The boards, the railing, the furniture. Far fewer think carefully about what’s underneath, and even fewer think about the two as a connected system. That’s a missed opportunity, especially in Merrimack where the climate punishes outdoor structures and where elevated decks are common thanks to the rolling lots and walkout basements that define so much New Hampshire housing.
When you combine well-designed deck skirting with an under-deck waterproofing system, you don’t just hide the underside of your deck. You create a second usable outdoor space, protect your foundation, extend the life of your deck structure, and add real square footage to how you actually live in your home. The two work better together than either does alone, but only if the design accounts for how they interact.
Here’s when this combination makes sense, when it doesn’t, and what to think through before committing.
What Each System Actually Does
Deck skirting is the material that closes off the visible gap between the bottom of your deck and the ground. It can be lattice, horizontal slats, vertical boards, stone veneer, composite panels, or custom millwork. Its primary jobs are visual (hiding posts, plumbing, and storage) and practical (keeping animals, debris, and kids’ toys from accumulating under the deck).
An under-deck waterproofing system is a drainage assembly installed below the deck boards (or sometimes below the joists) that captures water passing through the deck surface and channels it away from the area underneath. There are two main types. Above-joist systems install before the decking goes down and protect the joists themselves. Below-joist systems install after the deck is built and create a dry ceiling beneath the deck without protecting the structural members above.
On their own, each addresses one problem. Together, they transform the space below your deck from the area where stuff gets damp and forgotten into a genuinely usable second story of outdoor living.
When the Combination Makes Sense
A few specific situations make the combined approach worth serious consideration.
Walkout basements and elevated decks
If your deck sits more than four or five feet above grade, you’ve got real usable space underneath. Adding waterproofing creates a dry patio area. Adding skirting gives it walls and visual definition. Without both, the space is technically open but rarely used in any meaningful way.
Sloped lots
Merrimack has plenty of properties where the back of the house sits significantly higher than the front, or where the deck overlooks a downward grade. These lots almost always benefit from finished under-deck space because the natural slope already creates a kind of room shape. Skirting and waterproofing turn that into actual outdoor square footage.
Homes where outdoor living time matters
If you host regularly, have kids who use the yard, or just want more flexibility in how you use your outdoor space across the seasons, the combination doubles your usable deck area. The lower level stays cool in summer heat, dry during rain, and protected from the worst of the wind. In our climate, that’s genuinely valuable.
Storage and utility needs
Pool equipment, lawn tools, kayaks, firewood. Combined skirting and waterproofing creates dry, protected storage that doesn’t eat into your garage. Add a skirting panel with a discreet access door and you’ve got a functional shed without the visual clutter of one.
Foundation protection priorities
Water dripping through deck boards lands close to your foundation by definition. Over years, that constant moisture exposure contributes to foundation cracking, basement seepage, and grading erosion. A waterproofing system that channels deck runoff away from the house through a proper gutter and downspout extension is meaningful foundation protection, and skirting helps direct surface water from the grade above as well.
When It Doesn’t Make Sense
Honestly, sometimes this combination is overkill.
Low decks with no usable space underneath
If your deck is only 18 inches off the ground, there’s no room to do anything below it. Skirting still makes sense for appearance and to keep critters out, but waterproofing would be pointless.
Tight budgets where the money is better spent elsewhere
A premium under-deck waterproofing system isn’t cheap. If you’re choosing between waterproofing and, say, upgrading from pressure-treated wood to PVC decking, the decking upgrade probably delivers more visible value for most homeowners. You can always add waterproofing later, though it costs more as a retrofit than as part of original construction.
Heavily shaded lots where the space under the deck would never get used
If the area below your deck faces north, sits under tree cover, and gets minimal use anyway, investing in turning it into a room may not pay off. Skirting alone (for appearance and pest control) might be enough.
Design Decisions That Matter When Combining the Two
If the combination makes sense for your project, several design choices will determine whether it actually works the way you want.
Above-joist vs below-joist waterproofing
Above-joist systems protect the structural framing and last longer because the joists stay dry. They have to be installed as part of original construction or a full deck rebuild. Below-joist systems can be retrofitted to existing decks but leave the joists exposed to weather. For a new build in Merrimack, an above-joist system is almost always the better long-term choice.
Ceiling finish
Once you’ve got a waterproofed ceiling under your deck, you’ve got a surface you’ll actually look at. Cheap systems leave exposed white panels that scream “we waterproofed this.” Better installations integrate a finished ceiling material (vinyl beadboard, aluminum panels, or even stained tongue-and-groove) that makes the space feel like an intentional room rather than a covered afterthought.
Skirting ventilation
This is where a lot of designs go wrong. If you fully enclose the space under your deck without adequate airflow, you’ll trap moisture, encourage mold, and create the exact problem the waterproofing was supposed to prevent. Good skirting design includes ventilation, either through deliberate gaps, lattice sections, or hidden vents. The visual goal is an enclosed wall. The functional goal is a breathable enclosure.
Drainage integration
The waterproofing system collects water. Where does that water go? A proper design ties the system into a gutter that runs to a downspout that drains well away from the foundation. Skipping this step means you’ve just moved the water problem from below the deck to somewhere along its edges.
Skirting material match
Composite skirting pairs naturally with composite decking. Stone veneer can elevate a higher-end home and tie into existing masonry. Custom millwork lets you create something unique but adds cost. The right choice depends on your home’s exterior, your budget, and how visible the skirting will be from primary sightlines.
Lighting and electrical
Once you’ve created a functional outdoor room under your deck, you’ll want to use it after dark. Plan for recessed ceiling lights in the waterproofed ceiling, outlets for fans or speakers, and possibly a ceiling fan if the space is large enough. These details are dramatically easier to install during original construction than as retrofits.
Access for maintenance
Even the best waterproofing system needs occasional inspection. Even the best skirting panels need to be removable for access to anything plumbed or wired underneath the deck. Build in access panels deliberately. Don’t seal yourself out of your own structure.
Merrimack-Specific Considerations
A few things matter more here than they would in a warmer or drier climate.
Frost heave and substructure
New Hampshire winters move soil. Skirting attached directly to a frame that isn’t engineered for ground movement will crack, separate, or pull away over time. Good design either anchors skirting to a frame that floats with the seasonal soil movement or uses materials flexible enough to absorb minor shifting.
Snow load on the waterproof ceiling
An under-deck waterproofing system isn’t a roof. It’s designed to handle water, not the weight of accumulated snow if any drifts in through skirting gaps. Properly enclosed and ventilated systems don’t usually have a problem, but it’s worth thinking through how snow could enter the space during heavy storms.
Spring thaw and water volume
Merrimack springs can dump enormous amounts of water in a short time. Your under-deck drainage system needs to handle peak volumes, not just average rainfall. Undersized gutters or improperly pitched drainage lines will overflow and dump exactly where you don’t want them to.
Ice management
Where the waterproof ceiling system meets your home’s siding or foundation, ice dams can form if drainage isn’t continuous and properly insulated. This is a detail worth getting right at the design stage rather than fixing later.
Bringing It All Together
The combination of deck skirting and an under-deck waterproofing system isn’t right for every project. But when it fits, it transforms a deck from a single-use outdoor surface into a layered outdoor living space with real flexibility and real long-term value. Done well, it’s the difference between having a deck and having an outdoor wing of your house.
The two systems are most effective when designed together from the start, with attention to drainage, ventilation, material compatibility, and how the finished space will actually be used. Retrofitting is possible but always more expensive and usually delivers a less polished result.
Ready to Plan Your Combined Deck and Under-Deck Space?
Designing a deck where skirting and waterproofing work together as a single system takes some upfront planning, but the result is outdoor space that genuinely earns its keep across every season Merrimack throws at it.
Villandry Home and Outdoor Living designs and builds integrated deck systems that include skirting, under-deck waterproofing, finished ceilings, lighting, and the structural details that make it all hold up to New Hampshire weather. Call us at +1 603 437 2750 to start planning a deck that works as hard underneath as it does on top.