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Basement-to-Living-Space Moisture Problems

Does humid air come from water problems inside or poor storm water management outside? And what about foundation waterproofing?

Posted on Oct 8 2010 by Scott Gibson

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 capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. break between footings and foundation wall on new construction," Riversong says. "I've used it to seal the interior of site-built CMUConcrete masonry unit. Precast concrete block used to build walls. CMUs have hollow cores that can be filled with concrete onsite for additional reinforcement. The use of stronger, more lightweight types of concrete such as autoclaved aerated concrete (AAC) is becoming increasingly popular in CMU manufacture. 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: ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. 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.


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Image Credits:

  1. Green Building Advisor

1.
Oct 9, 2010 11:51 AM ET

It Depends
by Michael Chandler

There is a lot of Yankee vrs southerner stuff here. You all have very deep frost depths and gravel soil and I guess you must over-dig and form all your footings rather than cut trenches and fill them with concrete with a twelve inch frost depth in heavy clay soil like we have in the South East.

if we were to set our drains next to the footings as you suggest we would have to over dig and form or re-excavate after the footings had been poured. The simple fact is that, while it may be preferable to over-dig and form in order to place the drain adjacent to the footing it really doesn't make any difference in the soils we have in the south east. Placing the footing directly on the waterproofing where it coves out from the foundation wall onto the footing gets the bulk of the water away and relieves the pressure at very low cost. In general we see best value in proper grading at the surface and vigilance about horizontal rock formations below the soil with water lensing (moving horizontally) horizontally on top of them between the rock and the clay.

Things are just different down here. Ventilating the basement or crawl just lets in hot humid air which condenses on the cool concrete and slab floor as well as pipes and AC ducts and makes things wetter. An exhaust fan that pulls conditioned air from the house and exhausts it from the crawl makes more sense than ventilating it with outside air or running an AC supply into the crawl (and returning that air to the house through the return)

James Morgan is right, New England best practices just don't always apply in the South East.


2.
Oct 9, 2010 9:06 PM ET

Nor Vice Versa
by Riversong

In the Northeast we know how to install proper foundation perimeter drains because their purpose is NOT to evacuate surface water - that's taken care of with overhangs, gutters, leaders, grading and swales.

In much of New England, seasonal high ground water prevents the installation of in-ground septic systems. That also means that seasonal high ground water may be precariously close to the footing and basement slab level. Perimeter drains are designed to evacuate rising ground water, which is why the holes are on the bottom of the perforated pipe.

So all the above-ground mitigation may not be sufficient to alleviate a wet basement and, just as gutters are preferable to surface drains as a first line of defense, an exterior drain is far preferable to an "after-market" interior drain as the first line of defense against wet basements.

You'll notice in the image I linked to (http://www.hipspro.com/webart/footing-perimeter-french-drain.jpg), there is a relatively impermeable cap layer of soil over the course aggregate backfill so that ground water but not surface water finds its way to the perimeter drain. The course backfill also alleviates hydraulic pressure on the foundation as the soil becomes saturated.

One questionable detail in the foundation drain image at the beginning of this blog post is the transverse drain through the footing. A properly installed perimeter drain should prevent ground water from rising up under the basement slab and the 4"-6" of sub-slab stone will serve as a capillary break, assisting the sub-slab vapor barrier in keeping the concrete floor dry. But, for a radon vent at the inside perimeter of the foundation to function properly, it cannot be tied to an outside perimeter drain to daylight. The radon stack, connected to the inside perimeter piping, is designed to induce a negative pressure under the slab to draw soil gases out. A short-circuit to daylight will undermine this negative pressure zone.

If daylighting of the footing drain is impossible due to flat topography, then a transverse connector through the footing will empty the drain into a gasketed radon-proof sump, which is NOT connected to the interior radon drainpipe or to the subslab stone.

With rectification, as with new construction, the most reliable way to keep a basement dry is to dig out around the foundation to the footings, install a proper perimeter drain, cove the wall/footing joint with hydraulic cement, waterproof the exterior of the foundation, and backfill with well-drained mixed aggregate covered with a soil cap. I did this on a 1965 cape I owned and it effectively stopped what had been a spring-time stream running through the cellar.


3.
Oct 11, 2010 3:04 AM ET

"In the Northeast we know how"
by Michael Chandler

Down here we have an expression for Yankees who talk like that.


4.
Oct 11, 2010 3:31 PM ET

Retrofits vs. New Construction
by Andy Ault, CLC

Wet basement retrofits vs new construction details just aren’t a fair-fight comparison. No question, that in a perfect world with an open-ended budget, a full exterior excavation with the aforementioned detailing would be a best-case resolution. That’s what I’d want on my house if all the stars-and-moons were aligned in my favor. However, here in the mid-Atlantic, a full excavation project for an average single family home can be $20-$40k pretty commonly. On the other hand, a retro-fitted interior drain tile system can be accomplished for usually less than $10k.

Add to that the difference in safety and logistics for the two options. Our area has had 5 laborers killed in the last four years due to residential retrofit excavation cave-ins. As such, it is on every building and OSHA inspector’s radar screen as soon as they see soil coming out (and rightly so). With the tight lots many of our houses are built on, it can often be impossible to implement the four-foot step-back grading slope requirements for workers’ safety. So then instead the GC has to supply and install trench-collapse boxes. When was the last time anyone saw one of those on a residential site??

Our area also had an incident last year where workers were injured when the old rubble-stone foundation wall collapsed into the trench (not to mention damage to the house). The post-incident report said that it could have been prevented with properly engineered structural-shoring matched with geotechnical soil analysis for shoring support. But once again, how often does that ever happen in residential remodel situations?

While far from perfect, an properly detailed interior retro-fit perimeter drain system is often the best choice; financially, logistically, and time wise. In addition to being far safer, an interior system can be accomplished in 1-3 days depending on the linear footage vs weeks for an exterior project. It also isn’t weather dependent and it won’t tick-off all of your neighbors, unlike many exterior undertakings. It does a great job of relieving the hydrostatic head on the foundation wall, and it efficiently moves the water out-of and away-from the structure.

When combined with either a battery back-up system (most common) or a municipal water-pressure back-up system (my personal preference because it can still run for days during our often prolonged power outages) then it creates a proven track record of dry basements. Like anything, there are plenty of hacks putting these systems in poorly, but the better guys who take their time really get great, long-term results.

As for the UGL product, we also use it. When it’s part of the package solution including a drain system it works like a champ for us. However, in our experience with the mid-Atlantic’s super-compressive clay soils, when it is used by itself without any hydrostatic relief, we only seem to get about 3-5 years out of it before it starts bubbling and delaminating. We’ve even installed it with the factory rep looking over our shoulder just to be certain we were following the guidelines and our soil was still too much for it. We can always tell because the white paint will start turning rust color at the blister marks which is where the clay has driven through the CMU voids and is pressing into the interior. This obviously shows poor (or no) foundation wall treatment on the exterior, but that’s pretty common for a good portion of our pre-1940 housing stock.


5.
Oct 11, 2010 5:03 PM ET

Chandler's detail
by Hunter Dendy

Michael Chandler- would you mind sharing a sketch of the detail you mentioned:
"Placing the footing directly on the waterproofing where it coves out from the foundation wall onto the footing". Something about that wording isn't clear to me. I'm designing/detailing here in NC too (the western side) and would like to fully understand what you have found successful in our area.


6.
Oct 11, 2010 8:02 PM ET

that detail
by Michael Chandler

There are some photo's here that show what I'm talking about. the Footing DRAIN is placed directly on the waterproofing where it coves out from the foundation wall onto the footing.

This is that house we had to work with the appraiser so hard to get financed in this article.
http://www.greenbuildingadvisor.com/blogs/dept/business-advisor/green-bu...


8.
Oct 11, 2010 8:47 PM ET

oh boy, more ammo for my wife
by Hunter Dendy

oh boy, more ammo for my wife and friends for why i should join facebook


9.
Oct 12, 2010 5:13 PM ET

wet basements
by Gary Martin

Leaving aside retrofits for a moment, in all this back and forth no one has mentioned the elephant in the room: basements are mostly for wet spiders and stuff you don't use. Humans are not groundhogs. Why build a basement at all? Slab on grade (and radiant if you can afford it) makes a lot more sense.


10.
Oct 13, 2010 12:26 PM ET

detail drawing
by jeff medanich

just a comment/question:
I continue to see footing/foundation details drawn with a keyway cast in the top of the footing.
I have not seen that detail actually installed in over twenty years, and have never seen it in production building. This engineered connection has been replaced by cast in place rebar.
Is anyone out there including this detail or is it time to start revising these dated drawings?


11.
Oct 14, 2010 12:30 PM ET

Insulate It
by Chris Vlcek

AFTER you solve the water problem (with Drylok paint, internal drain, sump, external gutters & grading...) take the job to the next step and add insulation. For block walls you can install EPS sheets, say 3" or 6". Install w/ strapping for an attached finish wall - wood or sheet-goods. Air-seal and Insulate the band joist. Paint the slab with Drylok too, or install 1-2" XPS - but then you need a finished floor.


12.
Oct 25, 2010 9:20 AM ET

Limestone foundation walls
by Julie Kardatzke

Our 80-year-old house in Wisconsin has limestone foundation walls. Is the UGL Drylok appropriate for stone walls, or would something else work better with stone?


13.
Nov 10, 2010 1:03 AM ET

I moved to Knoxville TN
by David McNeely

I moved to Knoxville TN almost two years ago. I have looked at every house for sale in one of the most upscale neighborhoods here (about 40 by now). I can count on one hand the houses that did not have mold problems. Even newer houses with no apparent moisture problems left my wife and I with sore chests after a short time. I can only speak for Knoxville, but mold resulting from poor drainage management is a big problem here.
My solution is to build my own house. When I spoke to the head guy at the main Building Dept., he said the detail he would choose would be to have continuous gravel under both slab and footing, and locate the drain pipe even below the bottom of the footing. He suggests this will prevent excess moisture below the slab and will obviate the need for an interior drain. In my estimation, over-digging the footing will be worth the expense because it will result in a house we can live in.


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