Can I build a deck on top of concrete?

Quick Answer

Yes, it is possible to build a deck on top of a concrete surface. The key considerations are ensuring proper drainage, allowing for movement between the deck and concrete, and selecting deck fasteners that can be secured into the concrete. With careful planning and construction, a deck can be successfully built over concrete.

Allowing for Movement Between the Deck and Concrete

One of the main challenges with building a deck on concrete is allowing for slight movements between the deck structure and the concrete below. Concrete will expand and contract slightly with changes in temperature. If the deck is rigidly attached to the concrete, this movement can cause the deck to buckle or fasteners to pull loose.

To allow for movement, use deck clip fasteners instead of screws drilled directly into the concrete. The clips secure the deck ledgers in place while still permitting normal concrete movement. Also, be sure to leave small gaps between decking boards to accommodate expansion and contraction in the decking itself. With room for movement, the deck will remain safely secured to the concrete.

Selecting Appropriate Deck Fasteners

Choosing the right type of deck fasteners is critical when building on concrete. Standard screws and nails will not secure the deck properly. Instead, you need specialty concrete deck screws or clip systems. Here are some good options:

Concrete Deck Screws

– Hex head lags: These have a hex washer head and threaded lag tip to penetrate concrete. Use 1/4″ x 3″ or longer screws.

– Wedge anchors: The screw has an outer sleeve that compresses and locks into the concrete as the screw is driven. Lengths of 1/4″ x 2 3/4″ work well.

– Tapcon screws: Hardened masonry screws designed for concrete applications. Use 1/4″ x 2 1/2″ size or larger.

Deck Clip Fasteners

– Bynerd deck clips: Galvanized steel clips that bolt to the ledger and grip the concrete. Allows ledger movement.

– Simpson Strong-Tie DTT2 deck tension ties: Black powder-coated clips that bolt through the ledger. Adjustable for various deck heights.

– TimberLOK screws and clips: A system of hardened screws and connector clips to fasten ledgers to concrete.

Preparing the Concrete Surface

For proper fastener installation, the concrete surface under the deck should be:

– Clean – Free of loose debris, dirt, oil or other substances that can interfere with installation. Sweep or pressure wash the area first.

– Structurally sound – No large cracks, crumbling areas or other deficiencies that would weaken the fastener hold.

– Level – Pitch or slope in the concrete could cause improper ledger contact and fastening. Grind down any significant high spots.

– Textured – A smooth concrete surface provides less grip for fasteners. Etch or roughen the area under the deck with a masonry grinder or chisel.

Proper prep ensures the fasteners penetrate the concrete fully and keep the deck securely anchored.

Allowing for Proper Drainage

With a deck installed over a solid concrete surface, it’s important to still allow for drainage and airflow. Pooling water can cause rot and moisture issues over time. Here are some tips:

– Slope the deck slightly to encourage water runoff. Aim for a 1/4″ drop over 12″ distance.

– Leave small gaps between deck boards rather than butting them flush. This allows water drainage and air circulation.

– Attach decking with hidden fasteners or screws/nails placed intermittently. Avoid tight board spacing and fasteners everywhere that block drainage.

– Use perforated plastic drainage mats under the decking to promote drainage while still allowing fastener attachment.

– Install the deck ledger boards slightly above the concrete level to raise the decking itself and improve runoff flow.

Proper drainage and moisture management will help the deck last longer. Monitor the concrete area under the deck periodically for any pooling issues.

Installing Railings for Safety

For both safety and aesthetics, install railings around the perimeter of the deck. On concrete, railings can be attached in a few ways:

– Use masonry sleeve anchors. Drill holes in the concrete, insert sleeves, and bolt the railing posts in place.

– Attach post anchor plates to the concrete with appropriate fasteners. Then connect railing posts to the anchored base plates.

– For metal railings, secure posts with concrete wedge anchors driven into drilled holes. Strong and secure.

– Utilize freestanding railing posts not attached to the deck surface. The posts can be anchored in concrete footings or stabilized with weighted bases.

Having sturdy railings will provide necessary fall protection according to local deck safety codes. They also give the deck a nice finished look.

Selecting Suitable Decking Materials

You can use standard decking lumber, composite boards or other quality deck materials when building over concrete:

– Pressure-treated pine is affordable and provides good traction with a textured surface. Requires periodic sealing and staining.

– Redwood, cedar or other dense hardwoods offer natural beauty, weather resistance and durability. More expensive than pine.

– Composite decking has excellent durability and requires minimal maintenance. Provides good concrete adhesion. Higher material costs.

– PVC decking is slip-resistant and doesn’t warp or rot over time. Can withstand sun exposure and concrete moisture.

– Aluminum decking is very low-maintenance and resistant to both corrosion and mold. Durable but also conducts heat.

Choose a decking material suited for use over concrete that fits your budget and required maintenance level. Composite or PVC are great low-maintenance options.

Building a Concrete Paver Deck

For a different look and feel, consider using interlocking concrete pavers on pedestals over the concrete instead of typical deck boards:

– Porcelain pavers offer durability along with a range of color and pattern options. Resistant to moisture, freezing, heat and staining.

– Natural stone pavers like bluestone, travertine or granite provide beautiful texture and appearance. Handle weather well but more expensive.

– Concrete pavers are affordable, durable, and slip-resistant. Available in many shapes, colors and patterns.

– Use self-leveling or adjustable pedestals under the pavers for easy installation over uneven concrete. Allows moisture drainage.

Concrete paver decks offer the look of stone, brick or tile while still being an affordable DIY project. The pavers distribute weight well over concrete too.

Tying Into the Existing Structure

When attaching the deck to an existing building:

– Connect the ledger board securely to the band board with lags spaced every 16″. Sealing any gaps with flashing.

– Alternatively, use galvanized steel joist hangers to connect the deck joists directly to the structure’s rim joist. Evenly distributed loads.

– If connecting to a brick or stone wall, use masonry anchors and spacers to tie in the ledger while leaving drainage gaps.

– Make sure existing walls and structures are sound enough to handle the deck loads properly. Reinforce as needed before attaching.

– Flashing and side trim should seal off all connections and gaps cleanly. Prevent moisture intrusion into walls.

Proper structural connections provide strength while neatly integrating the deck visually. Coordinate decking installation with the removal of siding, installation of flashing, etc.

Permit Requirements for Concrete Decking

Most areas require permits and inspections for concrete deck construction:

– Many municipalities require drawings showing the deck’s position on the property and attachment details.

– Permission may be needed if the deck extends over property lines or utility/access easements.

– Entry access requirements, maximum height restrictions, and minimum setbacks often apply.

– Inspections verify proper concrete preparation, secure fastening methods, railing code compliance and safe electrical integration.

– Documentation from a structural engineer may be mandated for elevated decks or special reinforcements.

Deck permits and inspections ensure code compliance for safety. Research local requirements thoroughly before deck construction begins.

Conclusion

Building a quality deck over a concrete surface is an involved but very feasible project. The keys are allowing for proper concrete and decking movement, selecting suitable fasteners, maintaining drainage, and safely integrating the deck with existing structures. With careful planning, preparation, and construction, a beautiful and functional concrete deck can be enjoyed for years to come. Be sure to obtain all required building permits and have the finished deck inspected before regular use. With the proper research and process, you can successfully build the concrete deck of your dreams.