Building A Deck Over Concrete Patio: A Step-By-Step Guide

Building a deck over a concrete patio is a great way to enhance your outdoor space. It's a more straightforward and cost-effective project than building a deck from scratch, as it uses the existing concrete patio as a foundation. This approach is ideal for homeowners who want to revitalise their outdoor area without the hassle of removing old hardscapes.

Before beginning the project, it's crucial to assess the condition of the concrete patio. Minor cracks and flaws can be repaired with concrete leveling compounds, but significant damage, such as extensive cracking or sinking, may require removing the concrete entirely.

The next step is to choose the type of decking material, such as wood or composite decking, considering factors like budget, maintenance, and aesthetics. Composite decking, made from a combination of wood fibres and PVC plastic, is more durable and requires less maintenance than wood.

When installing the deck, it's essential to use spacers or sleepers to create a gap between the concrete and decking material. This promotes proper drainage and prevents moisture-related issues. The decking boards are then securely attached to the sleepers using appropriate fasteners, ensuring all materials are weather-resistant.

Building a deck over a concrete patio is a challenging yet rewarding project that can transform your outdoor living space.

Inspect the concrete for cracks, shifting or water damage

Before building a deck over a concrete patio, it is vital to inspect the concrete for cracks, shifting, or water damage. Concrete slabs can crack for many reasons, such as repeated freezing and thawing, heavy loads, tree roots, and ground shifts. Concrete cracks can range from being non-structural and cosmetic to detrimental to the structural integrity and safety of a building. Therefore, it is important to identify the type of crack and determine the appropriate repair method.

• Check for any signs of bulging or leaning: Inspect the concrete slab and foundation walls for any signs of bulging or leaning, which indicate an uneven load on the foundation. Both the foundation and walls should be flush and level.
• Look for cracks in the concrete: Identify any cracks in the foundation, particularly those that are 1/8 inch (3mm) wide or more. Also, look for cracks that span around corners, stair-step-shaped cracks on concrete block walls, or horizontal cracks. Cracks wider than 1/4 inch (6mm) usually indicate more serious problems and may require professional repair or replacement.
• Assess the condition of the concrete: Determine if the concrete is in good condition or has structural cracks, shifting, or water damage. Exposure to the elements can cause concrete to swell and contract over time, leading to repairs.
• Evaluate the severity of the cracks: While very fine cracks or "crazing" may be cosmetic and not affect the structural integrity, wider cracks (over 0.3mm) can pose issues for durability and watertightness. If left untreated, these cracks can act as passageways for water ingress and other destructive materials, leading to corrosion and concrete deterioration.
• Inspect for water damage: Check for any signs of water damage or moisture issues, such as wet areas around cracks, rotten wood, musty odors, or efflorescence (a white powdery substance on foundation walls). Water intrusion can also attract insects and rodents.
• Check for shifting or movement: Look for any signs of shifting or movement in the concrete slab or foundation. This can include cracks that span around corners, horizontal cracks, or uneven surfaces.
• Assess the need for repair or replacement: Depending on the severity and extent of the cracks, determine if repair or replacement is necessary. Minor surface cracks can be repaired with concrete patching compounds or fillers. For larger or deeper cracks, consult a professional for effective repair methods.

By following these steps, you can thoroughly inspect the concrete for cracks, shifting, or water damage before building a deck over a concrete patio. This will help ensure the safety and structural integrity of your project.

Prepare the concrete surface by cleaning and levelling

Preparing the concrete surface for a deck installation involves cleaning and levelling. Here are the steps to achieve this:

Cleaning

Start by giving the concrete patio a thorough clean to remove any dirt, debris, mildew stains, and old sodas. A pressure washer will be effective in removing stubborn stains and giving your patio a facelift.

Patching Cracks and Pits

After cleaning, inspect the concrete surface for any cracks, pits, or spalling (surface flaking). Patch these imperfections with a concrete resurfacer like Sakrete Flo-Coat Concrete Resurfacer or an epoxy, latex, or mortar mix. If there are large cracks or extensive damage, it's best to consult a professional about repairing or replacing the concrete slab.

Levelling

Use a level to check if the concrete surface is even. If there are low spots or uneven areas, you can correct them with a self-levelling compound or a thin concrete overlay. This step is crucial to ensure your deck has a flat and stable foundation. Apply the self-levelling compound with a trowel or long-handled trowel, smoothing it out with a push broom or squeegee.

Additionally, creating a slight slope away from your home will improve water drainage. You can do this during the levelling process by ensuring the concrete surface slopes slightly in one direction, typically away from the house.

Once the concrete surface is clean, patched, and level, you're ready to move on to the next steps of building your deck.

Use spacers or sleepers to create a gap between the concrete and decking

Spacers or sleepers are essential when building a deck over a concrete patio. They are pressure-treated 2x4s used instead of traditional joists and are attached directly to the concrete slab. They slightly elevate the deck to allow water to run off the concrete and not get trapped, which could cause rot.

You could lay your sleepers directly on the concrete, but spacers let you run sleepers parallel to the house, so decking can run perpendicular to the house if that’s what you prefer. Spacers also allow sleepers to dry.

To install spacers, measure, mark and rip a PVC board into strips using a table saw or circular saw. This is the width of the sleepers. Mark and cut each strip into 2-inch sections with a miter saw. These will be your spacers. Space them every 18 inches along the sleeper edge line marked on the patio. Lay the sleeper board onto the spacers.

To install sleepers, lay them directly on the concrete pad or use spacers for added elevation. Ensure they form a single flat plane. Start at the highest point of your patio and position your first sleeper, using plastic shims to even out any low spots. Pre-drill holes through the spacers, sleepers, and into the concrete. Secure everything with concrete screws that penetrate at least 1 inch deep. Align additional sleepers using a straight edge for consistency. Finally, apply joist deck tape on the top of each sleeper to keep water out of any screw holes, safeguarding your project from moisture damage.

Attach the sleepers to the concrete with concrete screws

Attaching sleepers to a concrete surface is a crucial step in building a deck over a concrete patio. Here is a detailed, step-by-step guide on how to attach sleepers to concrete using concrete screws:

Step 1: Prepare the Concrete Surface

Before attaching the sleepers, ensure the concrete surface is clean, level, and free of any debris. Use a straight board or a level to check for any uneven areas or high spots on the concrete. If necessary, use a concrete levelling compound to correct any low spots or unevenness.

Step 2: Layout and Position the Sleepers

Determine the layout of the sleepers by marking their position on the concrete with a pencil and tape measure. Start measuring and marking from the centre of the deck, keeping a 1/2-inch distance from the house's foundation or concrete edge. Continue marking at standard joist spacings of 16 inches on centre until you reach the end of the patio. Repeat this process on both sides of the patio, 1 foot from the edge.

Step 3: Use Spacers (Optional)

Although optional, spacers are recommended to elevate the sleepers slightly and allow for water runoff. Cut spacer blocks from a 1/2-inch thick PVC trim board to a width of 3 1/2 inches using a table saw or circular saw. Place these spacers every 18 inches along the marked sleeper lines.

Step 4: Position the Sleepers

Lay the sleeper boards directly on the concrete or on the spacers. Start from the highest point of the patio and work outward, using plastic shims to level any low spots. Ensure the sleepers form a single flat plane, checking with a 4-foot level across and along each sleeper.

Step 5: Predrill Holes for Concrete Screws

Using a hammer drill with a 3/16-inch masonry drill bit, predrill holes through the sleepers, spacers, and into the concrete. Drill holes 1/4 to 1/2 inch deeper than the screw will reach to accommodate dust and grit, making it easier to drive the screws. Pull the drill bit out of the hole occasionally while drilling to clear the dust.

Step 6: Secure the Sleepers with Concrete Screws

Use a drill with a driver bit to drive in the concrete screws. Select screws that penetrate the concrete by at least one inch, such as 3-1/4-inch screws. In low spots where shims are stacked, use longer screws, such as 3-3/4-inch screws. Ensure the sleepers are securely attached to the concrete.

Step 7: Check for Level and Adjust if Necessary

Once all the sleepers are screwed down, double-check their level using a 4-foot level. If you find spots that are 1/16 inch or more out of level, adjust by loosening the screws, adding or removing shims, and retightening the screws.

Tips:

• Wear safety gear, including safety glasses, a dust mask, and hearing protection, when drilling concrete and operating power tools.
• Drill bits can get very hot, so avoid touching them with your skin until they have cooled down.
• Have extra drill bits on hand, as they can wear out over time, making it harder to drive the screws.
• Apply flashing tape to the top of the sleepers before installing the decking boards. This prevents water from soaking into the sleeper tops and promotes water runoff.
• Ensure all materials are weather-resistant and suitable for outdoor use.

By following these steps and tips, you can effectively attach sleepers to a concrete patio using concrete screws, providing a solid foundation for your decking project.

Lay the decking boards and secure with appropriate fasteners

Laying the decking boards is similar to installing them on a regular deck. You should follow the manufacturer's instructions for your chosen decking product. In general, you should start from the outside of the deck and work inwards, screwing the boards into the sleepers as you go.

For solid composite decking, you may need to pre-drill holes. However, the process for installing timber and composite decking is generally similar. You should aim for two screws per deck slat on each sleeper panel. Use deck screws to fasten the boards and ensure that all materials are weather-resistant.

If you are using wood decking, you will need to account for water seepage. Water pooling underneath the boards could soak into the wood and cause damage. To prevent this, you can use angled brackets to hold vertical sleeper planks in place.

Frequently asked questions