How to Side a Chimney
Old homes with masonry chimneys jutting out of the roof are classic American iconography. Chimneys have become little more than empty spaces used to provide enough clearance between prefabricated fireplaces and combustible materials. While not as iconic, these wood-clad chimneys are much more flexible when it comes to siding materials. Unlike an open masonry fireplace, which should not be sided due to the potential for direct contact between extreme heat and combustible siding materials, wooden chimneys can be sided with heat-sensitive materials such as vinyl siding.
Preparing the Chimney
Cut foam board insulation to fit the chimney's sides and bottom. Attach the foam insulation using nails, fitting each piece tightly against the next. Snug the corners. Nail the bottom piece on tightly.
Tape the joints between the pieces of foam board in order to create an effective seal. Overlap tape pieces by at least 2 inches to ensure no air can penetrate the seam. Run tape along the edges by taping one side of a corner with half the width of the tape, then folding the tape onto the other side of the corner and pressing firmly. Tape the bottom seams as well. Caulk the foam board at the chimney's connection to the house.
Install house wrap around the chimney, over the foam insulation. Cut the house wrap large enough to fold under the bottom of the chimney so there are no seams. Staple the house wrap at 12-inch to 18-inch intervals and at the joint of the chimney and the house, near the caulking. Wrap the chimney with as few pieces of house wrap as possible. Overlap any joints by at least 4 inches and tape the seams.
Siding with Vinyl
Measure the height of the corners where the chimney meets the house. Cut one inside post per corner. Cut a 45-degree angle with a downward slope at the top of the inside post for a chimney that is taller than 10 feet. Cut a corresponding angle from the second section of the inside piece (for tall chimneys only) to prevent water infiltration. Repeat for the outside corners. Nail all corners into place, overlapping any lower post sections with upper sections and caulking their joints.
Cut a section of starter strip for each side of your chimney, about 1/2 inch shorter than the actual measurement. Fit starter strips into the channels in the corner posts with the nailing slots facing up. Align the strips with the bottom of the chimney, or even slightly below, and check to make sure they are level. Nail each leveled strip into the chimney loosely, leaving about a 1/16-inch gap. Test the tightness of the strip by grasping it from the bottom and moving it from side to side. The strip should move freely, but remain snug with the chimney.
Cut the first row of vinyl siding about 1/2 inch shorter than the actual width of the section you will be siding. Fit the siding into the channels created by the posts, with the slots facing up. Bring the bottom of the siding over the lip on the starter strip and snap it into place. Check the siding's level before nailing the siding using the same method as described in Step 2. Lock each subsequent piece together and test each strip before moving upward. Repeat until you are within about 1 foot of the top of the chimney on each side.
Measure the width of the top of the chimney against the chimney cap. Cut a section of under-sill trim for each side of the chimney that is approximately 1/2 inch smaller than the actual measurement so the trim pieces will fit inside the channels properly. Nail the under-sill trim snug against the chimney cap with the nailing fins down. Continue adding siding until you reach the last piece.
Cut the last piece of siding 1/2 inch shorter than the width of the chimney top. Measure the space between the lock on the last full strip of siding and the top of the under-sill trim in several places along the length. Use the measurements you've taken and cut the top off of the final siding strip until it will fit into the remaining space. Using a crimper, place aluminum clips every 12 to 16 inches along the length of the last piece. Push the top of the piece into the under-sill trim until it clicks while hooking the bottom over the siding lock below.
Caulk the siding along the chimney cap if the cap does not fully overhang the siding. Plan to do this when the weather is dry so the silicone can cure without potential water infiltration.
Things You Will Need
- Utility knife
- Foam board insulation
- Foil tape
- Caulk gun
- Silicone caulk
- House wrap
- Construction staples
- Vinyl snips
- Vinyl inside corner posts
- Vinyl outside corner posts
- Vinyl starter strip
- Vinyl siding
- Under-sill trim
- Crimping tool
- Aluminum clips
- Insulation needs vary regionally. Check with local building codes before insulating your chimney for the best results.
- Other types of siding appropriate for chimneys include sheet metal, wood lap and cement fiber.
- Use a vinyl siding stand-off for fireplaces that are vented through the chimney wall.