Building a deck on top of an existing patio is certainly possible, but there are some important considerations to keep in mind. The feasibility and process will depend on the construction and condition of the original patio. With proper planning and preparation, you can create a safe, functional deck that seamlessly incorporates with the patio below.
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Assessing the Existing Patio
The first step is to thoroughly examine the existing patio to determine if building a deck on top of it is structurally sound. Here are the key factors to assess:
- Patio Material – Concrete, pavers, flagstone, and poured concrete patio surfaces can typically support a deck. Other materials like gravel, dirt, or stone dust are not suitable foundations.
- Condition – The patio surface must be in good condition with no major cracks, crumbling areas, or signs of sinking or shifting. If there are any defects, they must be repaired prior to deck building.
- Thickness – A concrete patio should be at least 4 inches thick to handle a deck’s weight. Pavers should be at least 2 inches thick and make sure the base beneath is compacted gravel.
- Drainage – The patio must slope away from the house to prevent water pooling under the deck. Any low spots or drainage issues should be fixed.
- Footings – If there are existing footings for the patio, this is ideal as they can provide supplemental support for the deck.
In addition to the patio itself, examine where the patio connects to the home. Flashing, weatherproofing, and the condition of the wall should be checked.
Planning the Deck Design
Once you have confirmed that building on top of the patio is structurally possible, it’s time to plan the deck design. Here are some key considerations for planning:
- Decking Material – Pressure treated wood and composite decking are common deck materials that pair well with patio foundations.
- Substructure – A free-standing deck frame is recommended rather than attaching to the house. This prevents loading forces onto the walls.
- Height – The deck surface can be level with the patio or elevated. Railings may be required if over 30 inches high.
- Shape – Consider how the shape integrates with the home and patio footprint. Long rectangular or square designs work well.
- Stairs – Plan stairs for access, abiding by building code requirements for tread depth, riser height, and railing inclusion.
- Utilities – Deck footings must not disrupt any underground pipes, wires, or utilities near or beneath the patio.
In the planning phase, also make sure to acquire any necessary building permits from your local municipality.
Preparing the Patio Foundation
Once the deck design is finalized, the existing patio foundation needs to be prepared:
- Clean – Sweep or pressure wash the patio thoroughly to remove dirt, debris, and old sealer.
- Repair – Fix any cracked or crumbling areas of concrete with patching compounds.
- Level – Grind down any high spots or uneven areas to create a flat surface.
- Seal – Apply concrete sealer to protect from moisture penetration.
Proper preparation provides a clean, stable foundation for your deck substructure and helps extend the patio’s lifespan beneath the deck.
Building the Deck Frame
With the patio prepped, it’s time to build the structural skeleton of the deck. The main steps include:
- Mark post locations based on your plans, keeping posts in the interior area of the patio, not along the edges.
- Dig post footings per local building codes, typically 42-48 inches deep. The footings must extend below the frost line.
- Pour concrete into the footing holes. Use anchors or post bases to secure 4×4 or 6×6 posts.
- Allow concrete to fully cure before moving on.
- Attach beams to the tops of the posts, spanned perpendicular to the home.
- Add joists in between the beams, spaced 16-24 inches on center.
- Complete railings, stairs, and other framing components.
For proper support on a patio foundation, posts and footings are critical. Do not attach directly to the sides of the patio for support.
Adding the Deck Boards
Once the underlying frame is complete, the decking boards can be installed. Here are some tips for this stage:
- Use deck screws, not nails, for a stronger hold and to prevent squeaking.
- Space deck boards with a 1/8 inch gap to allow for drainage and expansion.
- Stagger end joints between rows for better stability.
- Use plastic or composite decking screws designed for the specific material.
- Follow a pattern for visual appeal, such as herringbone or diagonal decking.
- Secure stairs by screwing through the side of treads into stringers.
Proper gapping is extremely important with decking to prevent buckling. Take the time to space boards correctly.
Finishing Touches
The final steps complete the transformation of your patio into a functional deck:
- Attach railings with aluminum balusters or cable infill for safety and code compliance.
- Add lighting, electrical outlets, ceiling fans, and other fixtures as desired.
- Seal side edges and install trim boards for a clean finish.
- Coat decking with waterproof sealer to protect from weathering.
- Furnish with weather resistant chairs, tables, planters and other deck amenities.
Once finished, your deck creates an expanded outdoor living space right on top of the existing patio. Be sure to perform regular maintenance by cleaning, resealing, and inspecting for any structural issues.
Conclusion
Building a deck over an existing patio is a complex process that requires careful planning and preparation, but the end result can be an invaluable addition to your outdoor living space. With the proper foundation, framing techniques, and finishing, you can have a safe, durable deck seamlessly mounted on your patio. Just be sure to do thorough research and follow building codes for deck construction on top of patio foundations.
Frequently Asked Questions
Can any patio support a deck?
No, only certain patio materials like concrete, pavers, and flagstone can reliably support a deck structure. Materials like compacted gravel, dirt, or stone dust would require additional foundation work before adding a deck.
How much weight can a concrete patio hold?
A 4-inch thick slab of 2,500 psi structural concrete can typically hold 40-50 lbs per square foot. This is enough for most residential deck loads. Thicker slabs at 5-6 inches can hold up to 75 lbs per square foot.
Do you need footings for a deck on a patio?
Yes, you should dig footings for the deck posts rather than relying solely on the patio for support. Footings anchored below the frost line prevent shifting and transfer weight through the proper structural components.
Can you attach a deck ledger to a house with a patio beneath?
It’s best not to attach a ledger board directly to the house above a patio. The weight and forces of the deck should be transferred through freestanding posts into footings. Attaching to the house could cause the patio to crack over time.
How far apart should deck posts be?
Deck posts typically need to be spaced 6-8 feet apart depending on the size of beams used. Spans up to 10 feet are possible with multiple beams or larger dimensional lumber. Local building code specifies maximum allowable spans.
Example Deck Plans for Patios
Here are some example schematics to give you an idea of how to design and frame a deck on an existing rectangular patio:
Simple Square Deck
| Patio Length: 16 feet | Patio Width: 14 feet |
| Deck Length: 16 feet | Deck Width: 14 feet |
| Footings: 6 | Beams: 4×6, 16 feet |
| Joists: 2×8, 16 feet | Decking: 5/4×6 composite |
This simple square deck matches the patio footprint below. Only four footings are needed at the corners to support 4×6 beams. The 2×8 joists span the 14 foot width.
Rectangular Deck with Extended Side
| Patio Length: 12 feet | Patio Width: 10 feet |
| Deck Length: 18 feet | Deck Width: 10 feet |
| Footings: 6 | Beams: 4×6, 10 feet & 12 feet |
| Joists: 2×8, 12 feet | Decking: 5/4×6 composite |
This deck expands past the patio on one side, supported by additional footings and beams. The two different beam lengths allow the joists to span the width and attach to the house side.
Multi-Level Deck
| Patio Length: 16 feet | Patio Width: 12 feet |
| Deck 1 Length: 16 feet | Deck 1 Width: 10 feet |
| Deck 2 Length: 12 feet | Deck 2 Width: 8 feet |
| Footings: 8 | Beams: 4×6, varied lengths |
| Joists: 2×8, 12 feet | Decking: 5/4×6 composite |
A multi-level deck design allows you to take advantage of the full patio area. The upper level is narrower to accommodate stairs leading to a lower landing. Beams frame each section separately.