Scott Razzino has an all-too-familiar problem. The basement of his 1,100-sq.-ft. home in Atlanta is chronically damp. He’s installed a 65-pint dehumidifier, which must be emptied every day. Surely, he wonders in this Q&A post, there must be a better way to tackle the problem.
Razzino reports that the house is about 26 years old and has a block foundation. He’s routed gutters away from the house and sealed air leaks in the walls with mortar and concrete sealant. The basement doesn’t have a sump pump.
Short of installing French drains around the house, along with a sump pump, is there anything that can be done?
The first step, says Robert Hronek, is to figure out the source of the moisture. He suggests taping foil to the wall in several spots and waiting to see whether any condensation appears.
“If the water is trapped between the wall and foil, then it is coming through,” Hronek writes. “If there is condensation on the outside of the foil, then the moisture is from air leaks.”
If moisture is migrating through the block, adds Robert Riversong, sealing the surface with two coats of UGL Drylok masonry sealer “will make a major difference.”
The manufacturer claims that Drylok’s breathable film won’t trap moisture in masonry and will withstand 10 lb. of hydrostatic pressure, “greater than a wall of water 22 ft. high.”
“Drylok is the only foundation waterproofer I will use, and it’s excellent for a capillary break between footings and foundation wall on new construction,” Riversong says. “I’ve used it to seal the interior of site-built CMU composting toilet chambers (over surface-bonding cement) as well as the exterior of exposed chimney block.”
Where is the water coming from?
“Concrete-block walls in a wet and humid climate are a recipe for disaster unless extreme attention to moisture management details are in place,” writes Armando Cobo. “Probably the only way to stop all that moisture from coming in the basement is to trench around the foundation, waterproof the walls, and install a drainage system; but I’m sure you’ll still need some dehumidification in your climate.”
James Morgan, a builder in North Carolina, thinks Cobo is “unduly pessimistic.” He’s seen plenty of concrete-block foundations that have been “totally cured” of humidity issues. “The key most often is good stormwater management on the outside,” says Morgan.
So what does good stormwater management look like?
All gutter leaders should extend at least 10 ft. from the house in buried, nonperforated pipe, to a properly drained swale, Morgan says, along with adjusting the surface grade to slope away from the house, “with special attention to the uphill side if the surrounding grade is not level.
“We have successfully dealt with many basement water ingress issues with these interventions alone,” he writes. “I have no experience with the Drylok product: I have heard good things about it, but I prefer to address the upslope issues first and have always found that to be effective.”
“To me, proper drainage keeps the pressure off the foundation as well water out of the basement,” writes Hronek. “I think many times we [treat] the symptom and not the cause. Although you may be able to keep the moisture out of the basement with Drylok, you may miss a bigger concern.
“Wet soil both pushes in on the foundation wall and does not provide adequate support to footings. I have been in many homes where the owner has tried to seal the block but in the long run ended up with bigger problems: foundation walls that need straightening and footings that have sunk.”
And now a word about inept contractors
Morgan says he doesn’t generally recommend trenching around the outside of the foundation to install a perimeter drain and apply waterproofing. How come?
“This operation is often performed incompetently with inadequately compacted and graded backfill, even by specialist contractors,” he says. “The drain performs as intended for ten years or so until it clogs with sediment, and then the problems miraculously reappear. By this time the original homeowner has moved on and the ‘specialist’ happily returns to repeat the same mistakes.”
There may be some subpar drainage contractors out there, Riversong says, but that’s “no reason to avoid installing what every foundation should have: a perimeter drain. Just because there are carpenters and builders who build substandard houses is no reason to give up on having a house built.”
While gutters, downspouts, and grading take care of surface water, a footing drain removes groundwater and relieves a rising water table, Riversong says.
“With gravel backfill as a capillary break and drainage medium to relieve hydrostatic pressure and move subsurface water to the footing drain, and a perforated drain pipe protected by filter fabric and brought either to daylight or a sump pump, such a system should not fail,” he says.
How should a perimeter drain be installed?
No one seems to dispute that in new construction, every house deserves a correctly installed footing drain. Which leaves one detail open for debate: Should the perforated pipe that picks up water at the base of the foundation be located below the footing, on top of the footing, or at some level in between?
“And, while it’s better to install the drain tile next to the footing, as long as the weir of the pipe (hole or water level) is below the top of the slab (which is often on top of the footings), the wall/footing junction is sealed with hydraulic cement, and the foundation wall waterproofed, this should work as intended,” Riversong says. “It’s not necessary to dig down to the bottom of the footings and risk undermining them.”
That’s for a retrofit. But in new construction, he adds, where the site is excavated to the bottom of the footing, perimeter drains “absolutely” should be below the top of the footing. He includes a link to a drawing showing a correctly installed drain .
Morgan isn’t buying it.
“I can only tell you from extensive personal observation that your ‘should absolutely’ location is simply not observed hereabouts,” he writes. “I have never seen any problems arise from this, nor have I seen problems with older homes in which which foundation drains have been completely absent, except those arising from poor surface water management.”
We asked GBA’s Technical Director, Peter Yost, for his opinion:
Basements are tough because we often build them as holes in the ground that we will never live in or condition — without the proper air, thermal, and water barriers we use for high-performance above-grade spaces. Then, in part because it’s so “easy and cheap,” we turn them in to family rooms or extra bedrooms.
A lot of points have been raised, I will respond to them one at a time.
1. Determine how the basement is getting wet:
I completely agree with this approach. Look first to surface water management to take the load off of foundation walls. You may be able to significantly reduce the amount of moisture the walls experience from the outside at the surface.
2. Are the walls and/or floor damp or wet?
There is a big difference here. If the walls or floor are wet, and they are still wet after completely managing surface water, then get ready to cut concrete and dig an interior perimeter French drain. If the walls or floor are damp, you may be able to simply let them continue to dry to the interior and let your dehumidifier handle the load. Even if your walls of floor don’t seem to be damp, its best to test for what you may not be able to see or feel. There is actually a test for this: ASTM D4263, or the more sophisticated ASTM F1869 calcium chloride test that allows you to calculate the rate of moisture transmission through your concrete walls or floor.
3. Using a sealer to keep bulk water at bay.
I don’t have any experience with this approach, but if Robert says his sealer works, I believe him. A note of caution, though: Unless the sealant can maintain its integrity for the life of the building even as settling and slight shifting introduces hairline cracks in the concrete, I would be concerned about burying that seal in a finished basement.
4. Location of footing perimeter drains:
GreenBuildingAdvisor Mike Guertin, GBA architect Steve Baczek, and I spent quite a bit of time talking about just where the perimeter drain should be located at the footing. Take a look at any of the GBA Construction Details for basements in the GBA Detail Library . We ended up agreeing that the pipe should be located — perforations facing down — just next to the footing.
5. Energy Star dehumidifiers:
In my own home, we open the seven small hopper windows whenever we can, and run a dehumidifier when we can’t. Dehumidifiers use a lot of electricity (ours pulls 400W when running), so make sure your unit is an Energy-Star-labeled one.
6. Building Science Corp. has a useful article on the topic
The article, Renovating Your Basement , was done as part of the Building America program. Don’t leave your above-grade space without it.