Replacing Hardiplank Siding Requires Removing Old Boards, Preparing the Sheathing, and Installing New Planks with Proper Fastening and Sealing
Hardiplank replacement follows the same sequence whether you are patching a damaged section or re-siding an entire wall: remove the old boards, inspect and repair the underlying sheathing, install new planks with staggered joints, and seal all seams and fastener holes. The work is physically demanding and requires climbing, but the steps themselves are straightforward. Most homeowners can handle a small repair; a full house typically takes a contractor two to four weeks depending on size and weather.
The main difference between Hardiplank and wood siding is that Hardiplank is fiber cement — heavier, more brittle, and slower to cut. It does not rot, which is why it lasts 25 to 30 years, but a dropped board can crack and a saw blade dulls fast. You will need a circular saw with a carbide blade rated for fiber cement, a caulking gun, and a level. Rent or buy a scaffolding system if you are working above the first story; ladders alone are unsafe for this job.
Key Takeaways
- Remove old siding by unzipping the nails holding each board, starting from the top and working down, and save the trim pieces if they are still sound.
- Inspect the sheathing (the plywood or OSB underneath) for rot, soft spots, or missing sections, and replace any damaged area before installing new siding.
- Install new Hardiplank with a 1/4-inch gap between boards to allow for expansion, staggering the end joints so no two boards end at the same spot on adjacent rows.
- Fasten boards with corrosion-resistant nails spaced 16 inches apart along the studs, and caulk all seams, corners, and fastener holes with paintable sealant.
- Hardiplank cuts slowly and produces silica dust; use a wet saw or a circular saw with a dust mask, and wear gloves because the cut edges are sharp.
Removing Old Hardiplank Without Damaging the Sheathing
Start at the top of the wall and work downward. Each board is nailed to the studs (the vertical framing members spaced 16 inches apart), and the nails are driven through the top edge of the board below, locking it in place. To remove a board, you must first lift the board above it slightly to unzip the nails holding it down.
Use a pry bar or a flat shovel to lift the upper board just enough to slide a shim underneath and hold it open. Then drive a flat pry bar under the nails of the board you are removing and work along the length, lifting each nail out. Do not yank sideways; pull straight up or you will split the board and damage the sheathing. If a nail bends, tap it back down and try again from a different angle. Once all nails are out, slide the board down and out.
Save the trim pieces — the J-channel that wraps corners and windows, the starter strip at the bottom, and the cap at the top — if they are not cracked or warped. Reusing them saves money and time. If any are damaged, note the profile and width so you can order matching pieces.
Inspecting and Repairing the Sheathing
Once the siding is off, look at the plywood or OSB underneath. Press on it with a screwdriver or awl; if the tip sinks in easily or the material feels soft, that section is wet or rotted and must be replaced. Mark all soft spots with chalk.
Cut out the damaged section using a circular saw, cutting along the center of the studs on either side so you have a solid nailing surface for the new piece. Remove nails and pull out the old sheathing. Cut a new piece of plywood or OSB to fit, nail it to the studs with 8-penny nails spaced 8 inches apart, and seal any gaps with caulk or foam. If the damage is extensive, call a contractor; structural issues are not a DIY repair.
Check that the sheathing is flat. Sight along the wall from the side; it should be smooth without bumps or dips. Minor waves (less than 1/4 inch) are normal and will not show through the siding. If there are larger dips, shim the studs or add furring strips to bring the surface flush.
Installing the Starter Strip and First Row
The starter strip is a metal or vinyl channel that sits at the bottom of the wall and supports the first board. It is nailed to the sheathing and must be level. Snap a chalk line 1 1/2 inches up from the bottom of the wall (or whatever height your starter strip requires — check the manufacturer's instructions), and nail the starter strip along that line with nails spaced 16 inches apart.
Measure the wall width and cut your first Hardiplank board to length. Use a circular saw with a carbide blade and wear a dust mask; fiber cement produces fine silica dust that damages lungs. Cut slowly and let the blade do the work. If you are making many cuts, consider renting a wet saw, which produces less dust and cuts faster.
Slide the first board into the starter strip from one end. It should sit flat and level. Check with a level and adjust by tapping with a rubber mallet if needed. Once it is level, nail it to each stud with two nails per stud, one near the top and one near the bottom of the board. Space the nails 1 inch from the top edge. Use corrosion-resistant nails (stainless steel or hot-dipped galvanized) rated for fiber cement; regular nails will rust and stain the siding.
Staggering Joints and Installing Subsequent Rows
The second row of boards overlaps the first by about 1 1/4 inches. Before you install it, cut the first board of the second row so that its end joint does not line up with the end joint of the first row. Stagger the joints by at least 24 inches; this prevents water from running down a continuous seam and keeps the wall stronger.
Slide the second row board into the overlap of the first row, leaving a 1/4-inch gap between the end of the first board and the start of the second. This gap allows the boards to expand and contract with temperature and humidity changes. Hardiplank expands slightly when wet and shrinks when dry; without the gap, boards will buckle or crack. Check the board for level and nail it the same way as the first row.
Continue upward, staggering the joints on every other row. When you reach a window or door, measure the opening and cut boards to fit around it. Leave a 1/4-inch gap on all sides of the opening so the trim can sit properly. Caulk these gaps after the trim is installed.
Cutting Around Windows, Doors, and Corners
Measure from the edge of the opening to the edge of the wall, and subtract 1/4 inch for the gap. Cut the board to that length. If the opening is in the middle of a board, you will need to cut a notch out of the board. Mark the notch on the board, drill a hole at each corner of the notch, and use a jigsaw to cut between the holes. Sand the cut edges smooth.
At outside corners, install corner trim (J-channel or metal corner bead) before the siding. Nail the corner trim to the sheathing, then butt the siding boards against it. At inside corners, the boards meet at an angle; caulk the joint after installation.
Around windows and doors, install the trim after the siding is done. The trim sits on top of the siding and covers the gaps. Use the same corrosion-resistant fasteners and caulk all seams.
Sealing Seams, Fasteners, and Finishing Details
Once all the boards are nailed, caulk every seam, corner, and fastener hole. Use a paintable, exterior-grade caulk rated for fiber cement (check the label). Load a caulking gun and run a bead along each seam, pressing the caulk into the gap with a wet finger or a caulk tool. Caulk should be smooth and flush with the surface, not lumpy or recessed.
Pay special attention to the seams where boards overlap and the gaps around windows and doors. These are the places water enters. Do not skimp on caulk; a thin bead will crack and fail within a year.
Once the caulk is dry (usually 24 hours), the siding is ready to paint. Use an exterior paint rated for fiber cement; some manufacturers recommend a primer first. Paint protects the siding and gives it color. Without paint, Hardiplank will weather to a dull gray over time, but it will not rot.
Tools and Materials You Will Need
| Item | Purpose | Notes |
|---|---|---|
| Circular saw with carbide blade | Cut Hardiplank boards | Rent or buy a wet saw for large jobs; produces less dust |
| Pry bar or flat shovel | Remove old nails | Work slowly to avoid damaging sheathing |
| Level (4 feet) | Check that boards are plumb and level | A laser level speeds up the work |
| Corrosion-resistant nails | Fasten boards to studs | Stainless steel or hot-dipped galvanized; use 2 1/2 inch for standard boards |
| Caulking gun and exterior caulk | Seal seams and fastener holes | Use caulk rated for fiber cement |
| Dust mask and gloves | Protect against silica dust and sharp edges | Fiber cement dust is hazardous; wear a respirator-style mask |
| Scaffolding or ladder | Safe access to upper walls | Do not work from a ladder alone on upper stories |
Frequently Asked Questions
Can I install Hardiplank over existing siding?
No. Hardiplank must be installed on solid sheathing so the nails have something to grip. Installing it over old siding creates voids underneath, and the boards will flex and crack. Remove the old siding first, even if it adds time and cost.
What is the correct fastener spacing for Hardiplank?
Nails should be spaced 16 inches apart along the studs, with two nails per stud (one near the top and one near the bottom of each board). Nails must be driven through the board into the stud; if a nail misses the stud, remove it and move it to a spot that hits solid wood.
How much gap should I leave between boards?
Leave a 1/4-inch gap between the end of one board and the start of the next, and between boards at corners and openings. This allows for expansion. Do not force boards together; they will buckle when they expand in warm, humid weather.
Do I have to paint Hardiplank after installation?
Paint is not required for the siding to function, but it protects the surface and extends the life of the caulk. Unpainted Hardiplank will weather to gray and may develop mildew in damp climates. Most manufacturers recommend painting within 90 days of installation.
What should I do if a board cracks during installation?
Remove the board and replace it. Hardiplank is brittle and cracks cannot be repaired. If a board cracks after installation, remove the nails, slide it out, and install a new one. Keep a few extra boards on hand in case of breakage.