When fibre-cement board or (Hardieboard) siding is not installed properly, it doesn’t just look bad, but it can cause real damage to your wall, sidewalks, flashing, and even the foundation wall. In this case study, I’ll walk you through a project where Hardieboard was placed too low, what problems it caused, and how we corrected it.
The Problem
At the base of this wall, the Hardieboard siding terminated directly onto the sidewalk.
- The siding had no clearance from grade.
- The metal flashing detail was flat, creating a ledge where water pooled.
- No proper waterproofing membrane tied the wall into the sidewalk.
Over time, this caused:
- Rusting and staining of the flashing.
- Deterioration of the adjacent sidewalk.
- A risk of long-term moisture damage to the wall assembly.
Before: Hardieboard siding sitting directly on the sidewalk. Rust streaks are visible where water collected and bled onto the concrete.
Why It Failed
- Clearance issue Hardie requires fibre-cement siding to be at least 6″ above grade or hard surfaces, but here it was tight to the sidewalk.
- Flashing slope Instead of sloping away from the wall, the flashing was flat, which turned it into a shelf for water.
- Membrane continuity The wall base wasn’t tied into the sidewalk with a continuous waterproofing membrane, leaving the assembly exposed.
Before: Close-up showing the flat flashing and rusting at the base. Water was trapped here with no escape path.
The Fix
To correct the detail, we:
- Removed the sidewalk to expose the cladding base and flashing.
- Installed a self-adhered waterproofing membrane and concrete-faced insulation (CFI) to create a continuous protective layer.
- Added new sloped closure flashing to shed water away from the wall.
- Re-poured the sidewalk with proper slope away from the building.
- Raised the siding so that there was a minimum of 6″ of clearance above grade, in line with Hardie installation guidelines.
Newly designed detail: includes New CFI panel installed below grade. Recommend ‘exposed’ portion be minimum 4″ (100mm) above sidewalk surface (disregard graphic representation). Base of wall flashing to overlap, Ensures positive overlaps are maintained at the flashing transitions. New sub-grade waterproofing transition lapped by wall membrane above. Henry-Bakor WP200 was recommended, but we used a blueskin alternative which was equally as effective.
Progress Photos
Remove and Reinstall: First we removed the existing concrete sidewalk, removed the hardieboard siding installing a proper membrane behind.
Waterproofing Install: Self-adhered membrane and insulation panels installed at the wall base to protect against water intrusion.
Flashing Replacement: New metal closure flashing in place, sloped to direct water away from the siding.
After : Completed repair with siding raised, sidewalk re-poured with slope, and clean water-shedding detail.
Lessons for Homeowners
If you’re planning any siding work, here are some things to keep in mind:
- Keep clearance: Siding should never touch sidewalks or soil. Maintain at least 6″ above grade.
- Flash properly: All flashings should slope away from the building, and should not be touching concrete below.
- Tie in membranes: Waterproofing should always connect from foundation to wall.
- Check concrete slope: Sidewalks and patios should slope away, not toward the house.
Takeaway
This case study shows how a small oversight in siding installation can create ongoing water damage and costs to repair but also how proper detailing fixes it. With raised siding, sloped flashing, and corrected sidewalks, the wall now drains properly and the materials will last much longer.
📥 Free Download: