How do I keep roof water away from my foundation?

Most water that ends up in a basement started on the roof. In Lancaster, PA, a good share of wet basements and damp walls trace back to one gutter, one downspout or one low patch of soil. Here is how to find which one, and what to do about it.

The plain answer

Roof water reaches a foundation in three ways. It spills over the gutters, it comes out of a downspout right beside the wall, or it lands on soil that slopes back toward the house. Fix those three and most of the problem goes away.

Start at the top. Gutters need to be clean, pitched toward the downspouts and big enough for the roof area they serve. Next, every downspout should carry water well away from the foundation, onto ground that falls away from the house or into a buried pipe that runs to a safe outlet. Last, the first stretch of soil around the house should slope down and away from the wall, not toward it.

None of this is complicated. The catch is that each piece depends on the others. A long downspout extension does little if it empties onto a flat spot that drains straight back to the wall. Good grading does little if an overflowing gutter sends a sheet of water over it in every storm. Most wet basements we see have at least two of these working against each other.

What changes the answer on a real property

Soil matters first. A lot of the ground around Lancaster is heavy and slow to drain. Water that sits in clay next to a wall has time to find every crack and joint, so on heavy soil the water has to be moved farther from the house than it would on sandy ground.

What lies under the soil matters too. Much of Lancaster County sits on limestone, and water dumped in the same spot year after year can slowly wash soil down into gaps in the rock. That is one more reason not to let a downspout empty against the house, and a good reason to spread or carry roof water to a sensible place.

The age of the house changes things. Older homes in the city and in towns around the county often have stone or block foundations with many joints, and downspouts that run into old clay pipes nobody has looked at in decades. Those pipes crack, fill with roots or separate at the joints, and then they leak right beside the foundation. Newer homes in subdivisions usually have poured walls, but the soil backfilled against them often settles over the first several years and leaves a low trough along the house.

The layout of the lot is the last piece. A driveway, patio or walkway that pitches toward the house will send roof water straight back to it. A neighbour's yard that sits higher than yours adds its own water. A house on a flat lot may have no natural low point to drain to, which changes what is possible.

What you can check yourself

The best check costs nothing. Put on a raincoat during a steady rain and walk all the way around the house. Look up at the gutters and see whether water is spilling over the edge, especially at inside corners and above doors. Look at where each downspout ends and follow the water. Note any puddles that form against the wall or within a few steps of it.

On a dry day, look at the soil along the foundation. If it is level or dips toward the wall, or if you can see a gap where the soil has sunk, that is a spot water collects. Mulch beds built up higher than the lawn, and plastic edging that holds water in, cause the same problem.

If you have downspouts that go into the ground, put a garden hose into the top of one and let it run. Then find where the water is meant to come out. If it never appears, or the ground near the house goes soft, the buried pipe is blocked or broken.

Finally, look inside. Damp patches, a white powdery crust on the wall, or a musty smell in the corner of the basement just below a downspout all point to roof water getting in from that side.

When it needs a professional

Some fixes are simple homeowner jobs: cleaning gutters, adding a downspout extension, or raking a little soil against the wall to restore the slope. Call someone when those steps are done and the water still comes in, or when the fix needs more than a wheelbarrow.

A buried downspout pipe that is crushed or full of roots needs to be dug up and replaced. A lot that is flat, or that drains toward the house from several sides, usually needs soil moved and reshaped over a wider area, and sometimes a buried line to carry water to an outlet. Patios and walkways that slope the wrong way may need to be lifted or worked around.

It is also worth having someone look when the water is showing up in the middle of the basement floor or along the joint where the floor meets the wall. Water that appears there is often coming up from groundwater rather than down from the roof, and that is a different problem with different repairs. The same goes for foundation cracks that are getting wider.

How this connects to the work we do

Two of our services are aimed squarely at this problem. With Downspout Drainage, we connect downspouts to solid buried pipe and run it to a point where the water can safely leave, such as a spot downhill in the yard or a pop-up outlet in the lawn. With Grading and Regrading, we reshape the soil around the house so it falls away from the foundation, and we fix low areas that hold water.

A visit starts with a walk around the property. We look at the gutters and downspouts, the slope of the ground, the hard surfaces and the basement walls, and where it helps we run water through the downspouts to see where it goes. Then we explain what we found and what we would do, starting with the simplest fix that will work. If roof water is not the main cause, we say so.

If you are in Lancaster or one of the nearby towns and water keeps reaching your foundation, you can request a drainage visit and we will come and take a look.