MS Why Do We Use Vertical DPC? Where It Goes and What It Does
Vertical DPC explained: what it is, where it is placed on a building, and the specific problem it solves that a horizontal damp proof course cannot.
Overview
Most people have heard of a damp proof course. Far fewer have heard of vertical DPC, even though it protects a different part of the house from a different kind of moisture. If your plot slopes, if the house has a basement, or if ground level outside is higher than the floor inside, this detail is likely to matter to you.
Below you will find what vertical DPC is, where it is placed and why a horizontal layer alone does not cover the job.
Horizontal and vertical: two different jobs
A horizontal DPC blocks moisture rising up from the ground into the wall above it. That is the job described in our guide to damp proof course in house construction. Vertical DPC handles moisture moving sideways, from wet soil into the face of a wall that is in contact with it.
Picture a basement wall with earth packed against its outer face. Water in that soil pushes inwards through the concrete or brick over time. A horizontal layer at the top of the wall does nothing about that. A coating on the outer face does.
Where vertical DPC is placed
It goes on the outer face of walls that sit below ground level or against retained soil: basement walls, retaining walls, the below-ground portion of boundary or foundation walls, and any wall where the earth on one side is higher than the floor level on the other.
It is usually applied from the base of the wall up to a point above finished ground level, so it overlaps with the horizontal DPC and leaves no gap between the two. That overlap is the important part. Two separate barriers that do not meet leave a path for water.
What it is made of and how it is applied
The common method is a cleaned, sound surface, a coat or two of bitumen-based waterproofing, and protection over it so the backfilling does not tear the coating. Some builders add a membrane for extra safety on deeper walls.
Application is only as good as the surface beneath it. Honeycombed concrete, loose plaster and dust all stop the coating from bonding. The preparation takes longer than the painting and is where most shortcuts are taken.
Why it is easy to skip and costly to miss
Vertical DPC is buried the day the backfill goes in, so nobody sees whether it was done. That makes it a habit-of-the-contractor question, not an inspection question. When it is missed, damp shows up on the inside face of the wall, sometimes years later, and the fix means digging out the soil.
It also sits alongside the plinth beam in the sequence of early works, and both belong in the written specification of any proper grey structure contract.
A quick example from a sloping plot
Take a plot where the street sits a metre higher than the back garden. The front wall of the house may have soil against it on the outside while the floor inside is level with the garden. That wall is now acting a little like a retaining wall, and the earth against it will send moisture inward every time it rains. Owners often overlook this because the house looks perfectly normal from inside. It is exactly the situation where a coating on the outer face, applied before backfilling, earns its cost many times over.
What to check before backfilling
Ask to see the coating applied, and ask for a photo before the soil covers it. Confirm that it overlaps with the horizontal layer and runs above ground level. These two checks cost nothing and catch most problems.
Keep Reading
Damp Proof Course in House Construction
The barrier that stops ground moisture climbing your walls, and where it goes.
Read guide →What Is a Plinth Beam?
The concrete band that ties your walls to the foundation.
Read guide →Grey Structure Mistakes to Avoid
The errors that cost most, and how to prevent each one.
Read guide →Not sure whether your plot needs it? A free site visit settles that. Learn how our construction company in Lahore works, compare it with the checklist for the best construction company in Lahore, and see where we build under the areas we serve. Further reading is in our guides.
Frequently Asked Questions
What is vertical DPC?
It is a waterproof coating applied to the vertical face of a wall that touches soil, such as a basement or retaining wall, to stop moisture moving sideways into the structure.
Where is vertical DPC placed?
On the outer face of below-ground walls and walls with earth on one side, from the base up to above finished ground level, overlapping with the horizontal DPC.
What is the purpose of vertical DPC?
Its purpose is to block lateral moisture from wet soil, which a horizontal damp proof course cannot stop because that only protects against moisture rising from below.
Is vertical DPC different from a horizontal DPC?
Yes. The horizontal type stops rising damp at plinth level. The vertical type protects walls in contact with earth. A well-built house often needs both.
Does every house need vertical DPC?
Not every one, but any house with a basement, retaining walls or ground level higher than the floor inside should have it. We confirm this at the site visit.
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