How to Replace Fiber Cement Lap Siding Boards

Occasionally, some sort of accident or natural disaster will damage your home's fiber cement lap siding. Cracks and chips can allow moisture into the layers beneath, potentially causing bigger problems later, so it is best for you to replace the damaged siding as soon as you notice it. This multi-step process can be done successfully by do-it-yourself homeowners and can improve the look of your home while protecting your investment.

Step 1 - Preparation

Determine the amount of the siding that needs to be replaced, and order or buy the necessary pieces. Remember that many fiber cement boards are smooth on one side and faux wood grain on the other. Some brands are able to be used on both sides while others sell two different products. Make sure you get the right one for your job.

Step 2 - Remove Damaged Lap Siding

Put on protective eyewear and a face mask. Then, using a pry bar, gently lift the bottom edge of the overlapping siding. Work your way down the board, prying the bottom edge up and loosening the nails. This will allow you to remove the nails without damaging the top piece of siding. Occasionally there are stubborn nails that will require cutting with a reciprocating saw or hacksaw. Remove the nails, and countersink any nubs that might prevent your new siding from sliding up under the old. Use wood shims to hold the top board away from the wall while you continue to remove nails along the length.

Tip: If you are removing more than one level of siding in an area, start at the bottom and work your way up. When you reach the top of what you're trying to remove, perform the step above. A reciprocating saw can also be used to make a vertical cut so you can remove a partial piece of siding.

As you are removing the siding pieces, you may want to lay them down in the order you pull them off. This will help create an easy-to-follow template for the new pieces later.

Step 3 - Fix any Problems Behind the Siding

Check the area behind your siding to see if any damage has occurred there was well. Replace any compromised vapor barriers or rotting wood. If the issues extend underneath healthy pieces of siding, these will still need to be removed so the entire situation can be remedied.

Step 4 - Replace Boards

Siding is always hung starting at the bottom, which is where most repairs are needed. If your repair includes the very bottom tier of siding, add a spacer strip the thickness of your siding along the entire bottom edge, to mimic the angle of your overlap.

Fiber cement lap siding is heavier than wood and requires a special diamond-tipped blade or a tungsten-carbide saw blade to cut. Trim your replacement pieces down to size, using the old siding for reference. Then, use a chalk line to create a reference mark for the first or bottom piece of siding and start securing the siding pieces from the bottom to the top. A long piece of siding will sag in the middle, so use temporary blocks to hold it in place while you attach it. Use the nail holes on the top board to attach your very last piece, and only caulk button joints—never horizontally along with lap siding.

Tip: It's always a good idea to drill pilot nail or screw holes, although it will dull a bit very fast.

Step 5 - Paint

Purchase a high-quality acrylic latex exterior paint and primer that matches the color of your existing siding. Paint all surfaces including edges, using more than one coat as needed for a long-lasting and professional finish.