Case file — Accokeek, Prince George’s County, MD. One of the 25 jobs in our 250-home series. New here? Start with our open letter.
At a glance
| Location | Accokeek, Prince George’s County, MD |
| Crawl space | Just under 1,000 square feet |
| The problem | Water entering the crawl space persistently enough that sealing alone would not have held it |
| The fix | A perimeter drain pipe around the full footprint, five columns wrapped and sealed, then the floor and walls encapsulated and the rim joists insulated |
| Time on site | Four days |
There are three answers to crawl space water, not one
Every crawl space has some moisture. What separates a modest crawl space job from an expensive one is not the size of the space. It is how much water is arriving and in what form.
One: vapor. Moisture rising out of bare soil as a gas. This is the most common case by far, and a sealed, taped vapor barrier plus a dehumidifier handles it.
Two: occasional liquid water. Water that shows up after heavy rain, spreads across the floor and slowly goes away. Sealing alone makes this worse — you trap it. What it needs is a drainage plane underneath the barrier, so water has somewhere to run. We did exactly that on a Burke crawl space with a dimple board.
Three: persistent liquid water. Water arriving often enough, or in enough volume, that giving it a path is not sufficient. It needs to be collected and taken somewhere.
This crawl space was the third kind.
A drain around the whole perimeter
About 120 linear feet of perimeter drain pipe, set into the dirt floor around the full footprint of the crawl space.
This is the same principle as an interior French drain in a basement, adapted to a crawl space: a pipe at the lowest point of the perimeter, where the floor meets the foundation wall, because that is where water arrives. Water that gets in reaches the pipe instead of the middle of the floor, and the pipe takes it out.
The work is only possible in the right ground. The plan specifies non-rocky, dirt-floor conditions — you can trench that by hand in a space you cannot stand up in. A rocky or slab floor is a different job with different equipment and a different price, which is the sort of thing an inspection tells you and a phone call does not.
Five columns, wrapped to code
Five vertical supports, each wrapped in a 90 mil foil-faced insulated barrier and sealed at the seams.
Columns are not a detail anyone thinks about. They matter for two reasons.
The obvious one: a sealed crawl space with five bare columns standing in it has five uninsulated thermal bridges and five interruptions in the vapor barrier.
The less obvious one: wrapping them is a code requirement, not a preference. Vertical supports have to be treated in accordance with local code, and a crawl space quote that skips them is quoting a job that would not pass.
Then the encapsulation
The floor — just under 1,000 square feet of 20 mil barrier, over the completed drain.
The walls — a mechanically fastened insulated liner, sealed to the floor barrier at every seam so the two behave as one surface.
The rim joists — about 130 linear feet, insulated into each pocket.
Order matters here as much as it did in Burke. Drain first, then seal. You cannot install a perimeter drain under a finished barrier without cutting the barrier open again.
Why four days
This was the largest crawl space in this series, and the only one where the drain had to be trenched, laid and tested before anything else could start.
Four days, in a space with maybe three feet of headroom, is not four days of convenience. It is trenching 120 feet of perimeter on your knees before the part the homeowner can actually see even begins.
That is the part of a crawl space quote that is hard to compare across companies: two numbers can be a thousand dollars apart and be for completely different amounts of work happening under the plastic.