Who this guide is for
- Homeowners with damp or staining at the wall base
- People planning new cladding and the base detail
- Renovators coordinating wall, foundation and grading
- Anyone briefing a builder on base-of-wall flashing
Why the wall base is vulnerable
Water sheeting down the wall arrives at the base, and the change from cladding to foundation is a junction where water can get behind or wick up. Splash-back from the ground adds to the wetting. This concentration is why the base needs deliberate detailing.
The water table detail
A water table is a projecting trim or ledge near the base that throws water clear of the foundation line, much as an overhang protects the top of the wall. It is both a visual feature and a weather detail. Plan it to shed water outward, with a drip.
Base flashing and drainage
Base flashing leads any water that gets into the wall or cavity out at the bottom, integrating with the weeps and the barrier so it sheds away rather than into the structure. This is the exit point for a drained wall. Plan the flashing with the cladding and any cavity.
- Base flashing carries cavity water out at the bottom
- It integrates with weeps and the weather barrier
- A water table throws surface water clear of the base
- The detail must shed outward, never trap water
Working with grading and splash
The base detail only works alongside ground that slopes away and manages splash-back, so the flashing, water table and grading are planned together. A perfect flashing above poorly graded ground still struggles. Coordinate the base with the surrounding grade.
Weather-critical work and professionals
Base flashing ties into the foundation, cladding and drainage and is weather-critical, so a qualified builder should detail it, and damp at the wall base should be assessed rather than sealed. Requirements vary by location and project, and the base junction is not a place to improvise.
Base flashing planning checklist
- 1Recognise the wall base concentrates water
- 2Plan a water table to throw water clear of the base
- 3Plan base flashing to lead cavity water out
- 4Integrate the flashing with weeps and the barrier
- 5Coordinate the base detail with grading away from the wall
- 6Address splash-back from the ground
- 7Have damp at the wall base assessed, not sealed
- 8Use a qualified builder for the base detailing
Common mistakes to avoid
- Ignoring the base as a concentrated water junction
- Letting the cladding wick water up from the base
- Omitting base flashing so cavity water can't exit
- Detailing a water table that doesn't shed clear
- Planning the base without the surrounding grading
- Sealing damp at the base instead of assessing it
When to involve a professional
- Have a qualified builder detail the base flashing and water table
- Treat base-of-wall flashing as weather-critical work
- Coordinate the base with grading and drainage
- Have damp at the wall base assessed by a professional
- Requirements vary by location and project; verify with your professionals
Frequently asked questions
Questions readers ask about this topic
What is a water table on a wall?
A water table is a projecting trim or ledge near the base of the wall that throws water clear of the foundation line, much as an overhang protects the top. It is both a visual feature and a weather detail, planned to shed water outward with a drip.
What does base flashing do?
Base flashing leads any water that gets into the wall or cavity out at the bottom, integrating with the weeps and the weather barrier so it sheds away rather than into the structure. It is the exit point for a drained wall.
Why is the bottom of the wall so vulnerable?
Water sheeting down the wall concentrates at the base, the change from cladding to foundation is a natural weak point, and ground splash-back adds wetting. That concentration is why the base needs deliberate detailing with a water table and flashing.
Does grading affect the base detail?
Yes. The water table and flashing only work alongside ground that slopes away and manages splash-back, so they are planned together with the grading. A good flashing above poorly graded ground still struggles, and requirements vary by location and project.
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