What exterior waterproofing means
Exterior basement waterproofing keeps water from reaching the foundation wall. It includes grading, gutters, downspouts and, in serious cases, digging down to the footing to seal the wall and install drainage. The first group is an easy DIY win. The last is heavy excavation that most owners should not try.
This guide separates the two and tells you where to start. If your basement already floods, our basement waterproofing page and sump pump page cover the interior side.
Start with the cheap fixes
| Fix | DIY? | What it does |
|---|---|---|
| Extend downspouts away from the house | Yes | Moves roof water away from the wall |
| Clean gutters and check slope | Yes | Prevents overflow at the foundation |
| Regrade soil to slope away | Yes, with care | Sends surface water away |
| Seal cracks from inside | Sometimes | Slows seepage but may not stop it |
| Excavate and seal the wall | No | Heavy work, needs engineering judgment |
| Install exterior drain tile | No | Deep excavation, outlet needed |
Most wet basements improve a lot from the first three. Try them before spending serious money.
Grading and downspouts in practice
- Walk the house in a rainstormWatch where roof water lands and where it flows.
- Extend the downspoutsRun them at least six feet from the foundation if the lot allows.
- Check the soil slopeSoil should fall away from the wall, a few inches over the first several feet.
- Clear the guttersLook for sags, leaks and clogs.
- Re-check after stormsWatch the basement for changes.
When it needs a professional
- Water enters at the floor-wall joint during moderate rain.
- Cracks widen or leak steadily.
- The wall bows or shows horizontal cracks.
- A sump pump runs constantly and still cannot keep up.
Bowing walls and wide cracks are structural, and a plumber is not the right contractor. We say so on the phone and send you to an engineer or foundation specialist.
Water coming in now?
Call the 24/7 line in Chelmsford.
What we do on the plumbing side
We handle sump pits, discharge lines, interior drains and the plumbing that ties them together. We do not do foundation repair. When water control is a drainage and pump question, we are the right call.
For emergencies where water is coming in now, see our sump pump page and call the 24/7 line.
Reading your basement for clues
| What you see | What it often means |
|---|---|
| White powder on the wall (efflorescence) | Moisture is passing through the masonry |
| Damp spot at one corner | A gutter or downspout dumping nearby |
| Water at the floor and wall joint | Groundwater pressure from below or beside |
| Vertical hairline crack with seepage | Settling crack, may be sealable |
| Horizontal crack or bowing wall | Structural, call an engineer |
Photograph the wall after every storm and note the date and rainfall. A pattern tells you more than a single wet day.
A weekend plan that costs little
- Saturday morningClean gutters, fix sags and check for leaking joints.
- Saturday afternoonExtend each downspout with a rigid pipe that discharges well away from the wall.
- Sunday morningRake soil back to slope away from the foundation. Do not bury siding or vents.
- Sunday afternoonLook for hoses, sprinklers or window wells that hold water near the wall.
- Next rainWatch what changes and record it.
If the wall stays wet after these steps, the water source is below grade, and a sump or interior drain is the next question. Our sump pump page explains the pump side.
Window wells, vents and other weak points
Window wells collect rain and funnel it straight against the basement window. A plastic cover and a small drain at the bottom of the well fix many leaks. Dryer vents, hose bibs and cracked concrete steps can also let water into the wall. Walk the outside of the house with a flashlight and look for places where water can collect against the foundation.
Keep mulch and soil several inches below the siding. Contact between soil and siding invites rot and insects as well as water.
Materials and tools for the basic fixes
- Rigid or flexible downspout extensions, sized to your downspouts.
- Clean fill soil, not topsoil, for building up the slope near the wall.
- A hand tamper or the back of a shovel to pack the soil.
- Gutter scoops, a ladder and gloves.
- A level or a long board to check the slope.
None of these require a permit or special skill, though a ladder deserves respect. If your gutters are high or the roof is steep, hire the gutter work out.
Mistakes that make water problems worse
- Piling soil against siding, which invites rot and insects.
- Grading toward a neighbor and creating a dispute.
- Sealing the inside of the wall and trapping moisture in the masonry.
- Discharging a downspout onto a driveway that slopes to the house.
- Ignoring a gutter that overflows at one corner.
Small mistakes at the surface cause most of the wet basements we are called to. They are also the cheapest to correct.
Local notes for Chelmsford homes
Before any digging in Massachusetts you must call Dig Safe on 811. Work near wetlands, streams or other protected resource areas can fall under the Wetlands Protection Act, so ask the Chelmsford Conservation Commission before digging or regrading near them.
Do not point downspouts or pumps toward a neighbor's property or into the sanitary sewer. For help nearby see Westford and Tyngsborough.
According to Massachusetts law, you must call Dig Safe on 811 before digging, and work near wetlands is regulated under the Wetlands Protection Act.
Questions Chelmsford homeowners ask
You can improve drainage and seal small cracks. Digging to the footing is a professional job.
Yes. Massachusetts requires a Dig Safe call before digging.
Interior sealant slows seepage but rarely stops water pushing from outside.
At least six feet from the foundation if you can.
If your work is near wetlands or a stream, ask the Chelmsford Conservation Commission first.
When water enters from below the floor. A pump removes water from the pit.
Not sure if DIY is enough?
We will tell you honestly.