Building a Garden Deck and Pergola for a Hot Tub
Step-by-step guide made from DIY With Emma's YouTube video.
A comprehensive guide to demolishing an old, undersized garden deck and building a new, larger one from scratch, complete with a wooden pergola. The project covers everything from setting posts in concrete and building the frame to laying the decking and sealing the wood, resulting in a sturdy and attractive platform perfectly sized for a hot tub.
- Difficulty: intermediate
Safety
- Always wear gloves when handling old wood to protect against splinters and rusty nails.
- Wear a dust mask when mixing or pouring dry concrete or mortar to avoid inhaling the dust.
- Use appropriate eye protection when cutting wood with any type of saw.
- Be careful when handling wet cement or mortar as it can be corrosive to skin. It's best to wear gloves.
Must know before you build
- Leave slightly larger gaps between decking boards; wood expands with moisture.
- Seal all cut ends of treated timber with preservative or oil for longevity.
- Lay landscaping fabric under the entire deck frame to prevent weed growth.
- Use a spacer or offcut to ensure consistent, professional gaps between decking boards.
- Ensure robust footings like paving slabs under all joists for hot tub weight.
- Set main support posts securely in Postcrete for a stable, long-lasting foundation.
Tools
- Impact Driver (Cordless, DeWalt, 18V)
- Reciprocating Saw (Cordless, DeWalt) (optional)
- Jigsaw (Cordless, DeWalt)
- Miter Saw (Corded)
- Circular Saw (Cordless, DeWalt) (optional)
- Hammer
- Crowbar (optional)
- Tape Measure
- Speed Square
- Spirit Level
- Clamps (Irwin) (optional)
- Pressure Washer (Kärcher) (optional)
Materials
- Treated Wood Posts (4)
- Treated Wood Beams/Joists
- Decking Boards
- Postcrete (Fast-setting concrete mix)
- Decking Screws
- Landscaping Fabric (1 roll, Weed cover)
- Paving Slabs / Breeze Blocks (Concrete breeze block)
- Mortar Mix (Sand & Cement) (1 part cement to 5 parts building sand)
- Wood Glue (Weatherproof (D3), Loctite)
- Decking Oil
Step by step
Step 1: Demolish the Old Deck
First, the hot tub is drained and removed. Then, the old deck is dismantled by prying up the decking boards and using various tools to break apart the underlying frame.
- Drain and Remove the Hot Tub. Drain all the water from the hot tub. Before using the water on plants, test it to ensure it's free of chemicals like chlorine. Once empty, remove the cover and the tub itself from the deck.
- Tip: Hot tub water can be used for plants if the chlorine level is zero. Use a test strip to check before draining onto your garden.
- Remove Insulation and Start Demolition. Take up any insulation mats from under the hot tub. Begin the demolition by removing the first few decking boards, using an impact driver for accessible screws.
- Pry Up Decking Boards. If screws are stripped or driven in too deep to remove, use a crowbar and hammer to forcefully pry the decking boards off the frame.
- Common mistake: Sinking screws too deep into the decking can make future removal or repairs very difficult.
- Dismantle the Old Frame. Clear away the removed decking boards. Use a reciprocating saw to cut through stubborn sections of the old frame to break it down for removal.
Step 2: Prepare the Ground and Foundation
The old frame and concrete footings are removed, and the ground is cleared. A small, crumbling stone retaining wall is rebuilt with mortar, and the entire area is leveled for the new deck.
- Remove Old Frame and Concrete Footings. Cut and remove the remaining pieces of the old deck frame. Dig around and pry out the old concrete footings using a shovel, fork, and brute force.
- Clear the Area. Remove the old landscaping fabric and any remaining debris from the area. Clear away the old wood, which can be saved for firewood.
- Watch out: If you find evidence of pests like rats, you may need to take steps to address the issue before building your new structure.
- Rebuild the Retaining Wall. Mix mortar using a 1:5 ratio of cement to building sand. Use the mortar to rebuild the crumbling stone retaining wall, filling in the gaps to create a solid base.
- Tip: For a basic mortar mix, use a ratio of 1 part cement to 5 parts building sand.
- Tip: When rebuilding a stone wall, use a mix of large and small stones to fill gaps effectively.
- Level the Ground. Once the wall is rebuilt, rake the soil and dirt across the area to create a relatively flat and level surface for the new deck frame.
Step 3: Build the Deck Frame
New post holes are dug and the main support posts are set in postcrete. The outer frame is built around them, followed by the installation of inner joists and noggins to complete the sturdy base.
- Dig Post Holes and Set Footings. Dig holes for the new support posts, aiming for a depth of about 90cm. Place a breeze block or paving slab at the bottom of each hole to act as a solid footing.
- Set Posts in Concrete. Place the posts in the holes on top of the footings. Use temporary braces and a spirit level to ensure each post is perfectly vertical. Fill the holes with postcrete and water according to the package directions, and allow it to set.
- Tip: Postcrete sets very quickly, so have your posts braced and level before you start mixing and pouring.
- Build the Outer Frame. Measure and cut the beams for the outer frame. Attach them to the posts, using a level to establish a slight slope for water drainage away from the house. Secure the corners together with screws.
- Tip: To create a drainage slope, make one side of the frame slightly lower than the other. The creator lowered hers by 0.5cm.
- Tip: Pre-drilling pilot holes before driving in large screws can prevent the wood from splitting.
- Install Weed Barrier and Joist Supports. Lay down landscaping fabric inside the frame to prevent weeds. Place paving slabs or offcuts of wood on top of the fabric to support the middle of the joists.
- Install Joists and Noggins. Cut and install the inner joists, spacing them approximately 40cm apart. Then, cut and install noggins (smaller pieces of wood) in a staggered pattern between the joists for added rigidity.
- Tip: Space your joists no more than 40cm apart for maximum support.
- Tip: Stagger the noggins between the joists. This provides access to drive screws in from the side without them interfering with each other.
Step 4: Lay the Decking Boards
The decking boards are cut to length, with notches made to fit neatly around the pergola posts. The boards are then laid and screwed down, and fascia boards are added to the sides for a finished look.
- Prepare the Decking Boards. Cut a small piece off the end of each decking board to ensure a clean, square edge. This removes any rough factory ends.
- Tip: Always cut a small amount off the end of new decking boards to get a fresh, clean, and perfectly square edge.
- Cut Notches for Posts. For boards that will meet a post, use a speed square to mark out the section that needs to be removed. Use a jigsaw to carefully cut out the notch.
- Common mistake: Forgetting to account for the width of the next board when marking a cut. The creator cleverly uses a spare board as a guide.
- Lay and Space the Boards. Begin laying the decking boards across the frame. Use a homemade or store-bought spacer to ensure a consistent 0.5cm gap between each board for drainage and expansion.
- Screw Down the Decking. Pre-drill pilot holes and then drive two decking screws through each board into every joist it crosses. Use string lines as a guide to keep your screw lines perfectly straight.
- Attach Fascia Boards. Cut and attach decking boards to the exposed sides of the deck frame. This hides the frame and gives the deck a clean, finished edge.
Step 5: Build the Pergola Frame
The main beams of the pergola are cut and attached to the tops of the support posts, creating the top frame. The posts are then trimmed to be flush with the top of this new frame.
- Temporarily Brace the Top Frame. Temporarily attach the top beams to the posts with a single screw. Use these beams to pull the posts into a square and stable position, checking the distance between them at the top and bottom.
- Secure the Top Frame. Once the posts are square and correctly spaced, add more, longer screws to permanently secure the top beams to the posts.
- Trim the Tops of the Posts. Using a reciprocating or circular saw, cut the tops of the vertical posts so they are flush with the top of the newly installed pergola frame.
Step 6: Clean, Seal, and Finish the Deck
The new deck is pressure washed to remove all marks. Decking oil is then applied to the top, bottom, and sides of all boards to protect the wood from the weather.
- Clean the Deck Surface. Use a pressure washer or a stiff brush and water to thoroughly clean the surface of the new deck, removing any dirt, bird droppings, and pencil marks.
- Seal the Underside of Boards. Before final installation, flip over the remaining decking boards and apply a coat of decking oil to the underside and edges. This protects them from moisture coming up from the ground.
- Common mistake: Forgetting to seal the underside of the decking boards before screwing them down, leaving them vulnerable to moisture from below.
- Apply Oil to the Deck Surface. Using a small roller or a pad, apply a thin, even coat of decking oil to the entire top surface of the deck and the pergola frame. Wipe away any drips to prevent them from drying unevenly.
- Tip: Apply decking oil in thin coats for best absorption. You can use a roller, a pad, or even just a cloth.
Step 7: Install Pergola Rafters
The pergola rafters are measured, marked, and cut with decorative ends. Notches are cut so they can slot onto the top frame, and then they are screwed securely into place.
- Measure and Mark Rafter Spacing. Measure the total width of the pergola and divide it by the number of rafters you plan to install to determine the correct spacing. Mark these positions on the top beams.
- Cut Decorative Ends and Notches. Draw a decorative shape on the end of one rafter and use a jigsaw to cut it out. Use this as a template for the others. Then, measure and cut out notches on each rafter so they will sit securely on the top frame beams.
- Tip: When marking out cuts, put an 'X' on the piece of wood that will be discarded. This helps you remember which side of the line to cut on.
- Install the Rafters. Place the notched rafters onto the top frame, aligning them with your marks. Pre-drill pilot holes and then drive long screws down through the top of each rafter into the beam below to secure them.
Step 8: Final Assembly
With the construction complete, the hot tub is moved back onto the new deck, the pump is connected, and it's filled with warm water using a clever siphon from an indoor tap.
- Position and Fill the Hot Tub. Move the hot tub onto the new deck. Connect the pump and begin filling it with water. To save on heating, you can run a hose from an indoor hot water tap to fill it up.
- Tip: To save time and energy heating your hot tub, fill it with warm water from an indoor tap using a hose and a siphon system.