James Hardie Siding Clearances: Ground, Roof and Deck

What a clearance is

A clearance is the space left between the bottom edge of the siding and whatever is below it: soil, a concrete walk, a deck, a step or a roof. James Hardie’s installation instructions set a minimum gap for each of these. The numbers are in the current instructions for your product and region, and your installer should be working from them.

Why fibre cement needs the gap

Fibre cement resists moisture very well on its face, which is sealed and painted. The bottom edge is the weak point. If that edge sits in wet soil, standing water or a snowbank that melts and refreezes all winter, it soaks up water it was never meant to hold. Over years that shows up as swelling, paint failure or crumbling along the bottom course.

Calgary makes this worse than most places. A chinook melts the snow piled against the house in the afternoon and it freezes again overnight. That cycle can repeat dozens of times in a season. Siding that is kept clear of it simply lasts longer.

Where clearances apply

• Above the ground. The largest gap is here. Soil and mulch hold moisture against anything they touch.
• Above hard surfaces. Walks, driveways, patios and steps need a smaller gap so water and meltwater can drain away.
• Above decks. Where a deck meets the wall, siding stops short of the deck boards and flashing protects the joint.
• Above roofs. Where a wall rises from a lower roof, such as over a garage or porch, siding is held up off the shingles so water and debris can run past.
• At horizontal flashing. Above windows, doors and band boards, a small gap is left over the flashing and not filled with caulking, so water that gets behind the siding can escape.

How to spot a problem on an existing house

Walk the perimeter and look at the bottom course. Trouble signs include siding touching or buried in soil or mulch, siding sitting tight on a concrete step or deck, a line of dirty, peeling or swollen board along the bottom, and siding resting directly on roof shingles at a wall.

Often the siding was installed correctly and the ground came up to meet it. New flower beds, added topsoil and extra mulch are the usual causes.

What you can do

• Keep soil and mulch pulled back and down from the bottom of the wall.
• Shovel snow away from the walls where it piles deepest, usually beside driveways and under roof valleys.
• Make sure downspouts discharge away from the house, not along the wall.
• If you’re adding a deck, patio or landscaping after the siding is done, tell the contractor the siding needs its gap.

Why this belongs in your quote conversation

Getting clearances right sometimes means extra work: adding flashing, adjusting where a deck ledger meets the wall, or starting the siding higher and covering the foundation differently. It’s better to hear about that at the estimate than discover it wasn’t done. It also matters for the product warranty, which expects the product to be installed to the manufacturer’s instructions.

Related: maintenance and the installation process.