French drains and waterproofing in Amarillo

When water is getting to the foundation below the surface, regrading the yard will not reach it. This is the below-grade half of the problem.

What a French drain is, and what it is not

A French drain is a trench containing perforated pipe bedded in clean, well-graded gravel and wrapped so that soil fines cannot migrate in and blind it. Water in the surrounding soil takes the path of least resistance into the gravel, enters the pipe and is carried to a discharge point. It intercepts water in the ground, which is a different job from a surface swale that intercepts water running across it.

It is not a general-purpose fix. If the water reaching your foundation is running off a roof and landing beside the wall, the answer is an extension on the downspout, not a trench. A French drain is for water already in the soil profile, moving toward the house.

Amarillo has basements, and its code has details for them

This surprises people who think of Texas as slab country. The City of Amarillo's Panhandle Residential Foundation Manual contains an unusually complete set of basement details — trenched walls, formed walls at eight and ten inches, concrete masonry walls at eight and twelve inches, perimeter conditions for siding and for brick, and window well details for egress windows.

Those details also spell out the drainage package that goes with a basement wall here: dampproofing to the residential code provision, a drainage board system against the wall, four-inch perforated PVC pipe bedded in well-graded gravel at the footing, filter fabric over the top and sides of the gravel, and a sump pump. That is a specification you can hold a proposal against.

Where below-grade water shows up around Amarillo

Three site types account for most of it. Properties on slopes receiving run-off from higher ground — which around here includes lots stepping down toward the Palo Duro Canyon rim in southern Randall County and the broken ground toward the Canadian River in northern Potter County. Properties on or near playa basins, where the closed basin has nowhere to send water except into the ground. And properties where an old utility trench or poorly compacted backfill has created a preferential path that quietly pipes water to the foundation.

The canyon-rim case deserves particular care. Ground with real relief moves laterally as well as vertically, and a drain installed without regard for the slope can simply move a problem downhill onto a neighbour. Getting the discharge point right is part of the design, not an afterthought.

Interior versus exterior systems

Exterior footing drains address water before it reaches the wall, which is the better engineering answer. They require excavating to footing depth around the affected area, which is disruptive and correspondingly expensive, and they allow the wall to be dampproofed and a drainage board fitted while it is open.

Interior perimeter drains are cut into the slab edge inside the basement, collecting water that has already arrived and routing it to a sump. Far less disruptive to landscaping and usually cheaper, but by definition they manage water at the wall rather than keeping it away.

Which is appropriate depends on the wall, the site and the budget. Both are legitimate. A contractor who only ever offers one of them is describing their preference rather than your situation.

The discharge point is the whole design

A drain is only as good as where it ends. It has to daylight somewhere lower, or reach a sump that can pump reliably, and that destination must not put water onto a neighbouring property or back into the same basin it came from. If a proposal does not name the discharge point clearly, it is not finished.

What to ask

• Where does the water come from, and how was that established rather than assumed?
• Where does the drain discharge, and what happens there in a heavy storm?
• Is filter fabric specified, and how is the gravel protected from silting up?
• If a sump is involved, what happens to it during a power cut?
• Is the wall being dampproofed and drainage board fitted while the excavation is open?

Related

Always confirm the surface work has been done first — see drainage and grading correction. Damp under a raised floor is covered on crawl space repair, and wall cracks admitting water on crack repair.

What a properly built drain looks like in section

The components matter individually. A trench is excavated to a consistent fall — a minimum of around one percent, and consistency matters more than steepness, because a drain with a low spot holds water and silts up there. The trench is lined with filter fabric, a bed of clean washed aggregate is placed, and perforated pipe is laid on it.

Pipe orientation is a genuine technical point worth asking about: with perforations facing downward, water is collected from the lowest level of the trench and the pipe drains itself completely between events. More aggregate is placed over the pipe, and the fabric is wrapped over the top before backfilling, so the stone is enclosed on all sides.

The fabric is doing the essential job. Without it, fine soil particles migrate into the aggregate over a few seasons, the voids fill, and the drain becomes a buried line of dirty gravel that conducts nothing. Most French drains that fail did not fail structurally; they silted up because the separation layer was omitted or was the wrong specification.

Amarillo's own basement drainage specification

Unusually for Texas, the city publishes complete basement detailing, and the drainage package it shows is a reasonable benchmark to hold any proposal against: dampproofing applied to the wall in accordance with the residential code, a drainage board system against the face, four-inch perforated PVC bedded in well-graded gravel at footing level, filter fabric over the top and sides of that gravel, and a sump pump.

Each element does a distinct job. The dampproofing resists moisture passing through the wall. The drainage board gives water a free path down the face rather than letting it stand against the membrane. The pipe and stone collect and carry it. The fabric keeps the stone clean. The sump removes what arrives. A proposal that drops one of them should be able to explain why.

Sump systems and the night the power goes out

A sump is only as reliable as its worst moment, and its worst moment is a heavy storm that also takes out the electricity supply. Panhandle thunderstorms are perfectly capable of doing both at once, which makes battery backup a practical consideration here rather than a luxury item.

The other components worth specifying are a sealed pit lid to stop the sump humidifying the space it is protecting, a check valve to prevent the discharge line draining back into the pit and cycling the pump unnecessarily, and a discharge line routed well clear of the building. A sump that empties beside the foundation has built a circuit rather than a drain.

Calcareous ground and long-term maintenance

Soils across this region carry substantial calcium carbonate — the Potter soils on the broken ground are calcareous throughout, and the Amarillo series carries a calcic horizon at depth. Groundwater moving through carbonate-rich material carries dissolved minerals, and mineral deposition within drainage aggregate and pipe perforations is a recognised long-term maintenance consideration in ground of this kind.

The practical implication is not that drains do not work here. It is that access for future maintenance should be designed in from the start rather than discovered to be absent in ten years. Cleanouts at the ends of runs and at any change of direction cost very little at installation and make the difference between a system that can be flushed and one that has to be dug up.

Interior or exterior, decided honestly

An exterior footing drain intercepts water before it reaches the wall and allows the wall to be dampproofed while the excavation is open. It is the better engineering answer and it costs more, because it means excavating to footing depth around the affected area and reinstating whatever was above.

An interior perimeter drain is cut into the slab edge inside, collects water that has already reached the wall, and routes it to a sump. It is far less disruptive outside and generally cheaper, and it manages the problem rather than preventing it.

Both are legitimate, and site conditions, wall construction and budget decide between them. What should raise an eyebrow is a contractor who offers only one regardless of circumstances, because that is a description of their preferred method rather than an assessment of your house.

Winter operation, and the failure that happens at the worst moment

Drainage systems in this part of Texas have to work in genuine winter conditions, and that is a design consideration rather than an afterthought. At around 3,600 feet the region gets sustained sub-freezing spells, and the components most likely to fail in them are the ones at the end of the run.

Discharge lines are the usual casualty. A pipe carrying water to a daylight point or a pop-up emitter has a short section near the surface at its far end, and that section can freeze solid while everything upstream is fine. The result is a blocked outlet at exactly the moment a thaw is delivering the most water into the system, and the water backs up to wherever it can go.

Two design choices reduce the risk substantially: burying discharge lines below the depth at which the ground reliably freezes, where site conditions allow, and giving a sump system a secondary discharge route so a single frozen outlet does not stop the whole system. Neither is expensive at installation and both are difficult to add later.

Sump pumps deserve their own winter check. Test the pump before cold weather rather than during it, confirm the check valve holds so the pit is not repeatedly cycling on the same water, and if there is battery backup, verify the battery still holds charge. Batteries fail quietly and are typically discovered to have failed during the event they were bought for.

The broader point is that a drainage system is not maintenance-free simply because it is buried. Ask at handover what the annual checks are and where the access points sit, and write it down while somebody is standing there who knows the answer.

Egress windows, wells and the below-grade opening

Any basement room used for sleeping needs an emergency escape opening, and Amarillo's details cover the assembly: an egress window not exceeding four feet in width, an approved window well system, and drainage at the well.

The window well is the detail that causes trouble, because it is a deliberate hole in the ground against your foundation wall. It collects everything that falls into it — rain, leaves, snow, whatever the wind delivers — and unless it can drain, that water sits directly against the wall and the window at a point below grade.

A properly built well drains into the footing drain system rather than relying on the soil beneath it, has a gravel base rather than compacted silt, and ideally a cover to keep out debris and precipitation while remaining openable from inside for escape. A well that has silted up over the years is a bucket held against your basement wall, and it is a recurring cause of water entry in houses whose main drainage is otherwise sound.

The city's basement details also specify dampproofing to the residential code provision across the wall, with a drainage board over it. It is worth being clear on the distinction between dampproofing and waterproofing, because the words get used interchangeably in sales conversations and mean different things. Dampproofing resists moisture in soil; it is not designed to hold back standing water under pressure. Where a wall will face genuine hydrostatic head, a waterproofing membrane is the appropriate specification and costs more.

Establishing which condition your wall actually faces is therefore part of the design. It depends on the water table, the surrounding soil's permeability and how well the exterior drainage performs, and it is a legitimate question to put to whoever is quoting.