What Is a Drain Tile Test? The Whole System, Explained

Written By Vincent Matarrese

This article is for general educational purposes only and is not engineering advice for any specific property. Reading it does not create an engineer–client relationship with VM Engineering. Foundation and structural conditions vary. Have a licensed professional engineer inspect your property before making repair, purchase, or legal decisions. This is not legal or real estate advice. Questions about disclosure, contracts, or contingencies belong with your broker or a real estate attorney. Full disclaimer

In southeast Wisconsin, “drain tile test” shows up in a lot of offers. Here is what the system is, what the test checks, and how to read the results — based on the Wisconsin UBC foundation repair chapter.

Moisture staining on a basement foundation wall
Seepage means the drainage system is overloaded or not working. The test helps find which part.

The whole system

Five Parts, One Path for Water

Drain tile is one piece of a system. Water should be stopped or collected at each step before it reaches the basement.

1 · Outside

Grade and downspouts

Roof and surface water sent away from the house. Code target: soil sloped ½ in. per foot for 10 ft.

2 · Outside

Exterior drain tile

Perforated pipe outside the wall, at or on top of the footing. Common on older homes; can’t be seen without digging.

3 · Inside

Interior drain tile

Perforated pipe, 3 in. minimum, just below the floor along the walls, bedded in clean ¾ in. stone.

4 · Inside

Weep holes and wall drainage board

Holes drilled into the block cores drain the wall onto a plastic board that carries water into the tile. It stands at least 1 in. above the floor.

The fifth part is the sump crock and pump. The crock collects water from the tile, and the pump sends it out and away from the house. The crock rim should sit at least 1 in. above the floor. A dead pump makes a good tile system useless.

Post interior drain tile replacement system — section Section through a concrete block basement wall showing grade and downspout, exterior drain tile at the footing, weep holes drilled into the block cores with the wall drainage board, interior drain tile in clear stone below the slab, and the sump crock and pump. Blue arrows show water moving from the soil through the wall into the tile and out through the sump pump. POST INTERIOR DRAIN TILE REPLACEMENT SYSTEM OUTSIDE BASEMENT 1 Grade and downspouts Slope soil ½ in. per ft for 10 ft. Extend downspouts away. 2 Exterior drain tile Older homes. Often clogged or crushed; left in place. Bleeder through footing — may or may not be present. Hollow block cores Water through wall cracks runs down inside the cores. 4 Weep holes + wall drainage board Holes drilled into every block core drain the wall onto the board. The board carries water into the tile and stands 1 in. min. above the floor. Floor cut, then replaced 3 Interior drain tile 3 in. min. perforated pipe in clean ¾ in. stone, below the slab. Tile runs to the sump 5 Sump crock + pump Pumps water out and away. Rim 1 in. min. above floor. Water path Rain and groundwater soak toward the wall, leak through cracks, run down the block cores, exit the weep holes, follow the drainage board into the drain tile, and flow to the sump pump. PE-Inspect.com PE-Inspect.com
Post interior drain tile replacement system, in one section: water moves from the soil, through the block, into the interior tile and out through the sump pump. Drain tile tests open the floor along the wall, where the tile sits.

Scroll the drawing sideways on a phone

The test

How a Drain Tile Test Is Done

Where the procedure comes from

WAFRP is the Wisconsin Association of Foundation Repair Professionals, a trade group of foundation repair contractors, drain tile testers, engineers and suppliers. It formed in 2002 to bring consistency to foundation repair in Wisconsin, and in 2003 it wrote the Best Management Standards for Foundation Repair.

WI UBC is the Wisconsin Uniform Building Code, a model building code that many southeast Wisconsin municipalities adopt as their local building ordinance. It is separate from the state’s Uniform Dwelling Code. In 2017 the WAFRP standards were written into its foundation repair chapter (Chapter VI, section 30.50). Appendix A of that chapter is the drain tile test procedure.

Not every municipality uses the same version, so confirm with the local building department.

In short: open the floor along the wall, add water, find any blockage, and report it in writing with a diagram. The steps:

  1. Open test holes in the floor along the wall — at least three, each at least 12 × 12 in. Best spots are corners, areas with seepage, and under windows.
  2. Add water to the hole and see whether it drains.
  3. Run a hose into the tile in both directions, where possible, to find any blockage.
  4. Test outside if needed. A “spud test” puts water in the ground within a foot above the exterior tile, at least two spots per wall in question.
  5. Rate the blockage and report it in writing, with a diagram showing which sections need repair.
3test holes, minimum
12″minimum hole, each side
<30%blocked — marginal
>50%blocked — serious

Common causes of blockage are silt, tree roots, iron ochre (an orange sludge) and mineral deposits. Crushed tile, or tile that never connected to the sump, shows up too.

Reading results

What the Test Does Not Tell You

A drain tile test is a drainage test. It does not tell you whether a wall is bowing, sliding or settling — that is a structural question. A garden hose also cannot reproduce a spring thaw. The code itself notes that drain tile evaluation requires an opinion and “reasonable minds may differ.” That is why the tester matters.

Before the test
  • Get the seller’s permission — the holes go through the floor
  • Ask who patches the holes, and how, before the test is booked
  • Clear storage along the walls; finished walls can limit where holes go
  • Consider an independent tester who does not sell drain tile repair — WAFRP lists independent testing members
  • Ask for the written report with the diagram, not a verbal pass or fail
  • If the wall is also cracked or bowed, call an engineer before pricing drain tile
Foundations for realtors — three-part series
  1. When to Call an Engineer About a Foundation
  2. Pre-Listing Foundation Assessment: Get Ahead of the Inspection
  3. What Is a Drain Tile Test? The Whole System, Explained — you are here
The bottom line

Drain tile moves water. It does not hold up a wall. A good test tells you whether the system is working and which sections need repair. If the same wall is wet and moving, the drainage and the structure need to be looked at together.

VM Engineering LTD. We provide the plan. We do not do the repair. Contact us.

References: WI UBC Chapter VI, 30.50 Foundation Repair & Damp Proofing (WAFRP Best Management Standards), sections 30.50(3), 30.50(6)–(8) and Appendix A · WAFRP member directory, Drain Tile Testing — Independent.

Vincent Matarrese
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