Basement moisture question
Wc_guy
| Posted in General Questions on
We have had a four-year saga of trying to address basement watering the way to finishing our basement in Westchester NY (climate zone 4). We clearly have a high water table which we found out when our addition’s basement (addition completed in 2014) flooded in the very first rainfall. We had a basement waterproofing company come in to do the standard interior French drain system to exterior dry wells. We also had them lower the floor and replace our the slab in the older basement section (a stone wall foundation from its 1925 original build). We were able to insulate the new slab and we had the exiting walls “parged,” which involved chicken wire covered by a cement coat. Unfortunately, they did not put a vapor barrier behind so we are left with damp on the walls usually at the bottom (see pictures).
There are a few things that we intend to do for remediation. We plan to dig around the addition foundation and re-waterproof from the exterior, redirect our gutter leaders to a new dry well, and then regrade as well as we can. Finally, we plan to install a wall system from Connecticut Basements called Bright Wall, which is intended to allow any water to drain down the wall to the French drain system.
There are many questions I could ask (obviously), but my main question has to do with finishing the walls with such a wall catchment system in place. We have noticed that we have been getting wetness on the walls after a rain that does not dry out. We started using our dehumidifier again (we had readings in the 90-100% range for relative humidity) and that seems to dry out the wall. So here’s the dilemma. When we put up studs and insulate (plan is closed cell foam) with the intent to make our interior airtight, does it matter that our dehumidifier system would (I assume) not get to that area? Everyone claims that concrete does not allow mold, but as a practical matter I worry that there must be *some* organic material there and I worry that will cause mold. Am I right that the wall would not dry out in this situation and is it a concern? Should I deliberately leave the finished wall “leaky” to allow the area to dehumidify?
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Replies
Brian,
I'm sorry to hear about your frustrating situation. First, you may want to read this article: “Fixing a Wet Basement.”
The general rule is that a basement wall with signs of dampness or water entry should not be insulated from the interior. The order of business is generally (1) solve the moisture entry problem, and then (2) insulate the wall.
If you decide to insulate the basement walls from the exterior (at the same time that you will be “digging around the exterior to apply waterproofing”), you can do that at any time. It’s worth considering the installation of an exterior dimple mat when you get this work done. For more information on dimple mats, see “Using a Dimple Mat to Keep a Basement Wall Dry.”
If you have a functioning exterior footing drain, and some type of exterior dampproofing or dimple mat, your walls shouldn’t be displaying the type of dampness shown in your photos. That raises the question, “Are your footing drains functioning?”
Two more points:
1. Closed-cell spray polyurethane foam doesn’t really care if it gets wet. (Remember, it’s possible to use closed-cell spray foam as roofing.) So there really isn’t any risk if you decide to go ahead and insulate your interior of your basement wall with closed-cell spray foam, even if the wall is damp — except for the obvious risk of interior puddles in a rainstorm. (If that issue worries you, you really need to verify that you’ve got a well-installed footing drain system, either on the exterior or the interior.)
2. Foundation walls, whether made of concrete, stone, or stone-and-mortar, don’t mind being damp or wet, even for 100 years. Once your wall is insulated with closed-cell spray foam, the moisture level behind the spray foam is no longer a concern. You don’t have to worry about mold — the foam is an air barrier as well as a vapor barrier, after all — and you don’t have to worry about the integrity of the foundation. All you have to worry about is liquid water entry.
Martin,
Thanks for the detailed response. As you can imagine, I have been reading your basement series with great interest as this saga has progressed. It is often surprisingly hard to get contractors, particularly basement “specialists”, to do things a different way, based on building science versus rules of thumb but I press on.
On the specifics, one of the concerns we would have about doing anything on the outside of the 1925 foundation is that we have been told that the dirt is a key part of holding it up and that if we dig around, we might undermine it. Of course, that’s exactly what we did when we put on the addition and the house didn’t fall down (picture below) so maybe that concern is overblown. We also underpinned the original basement to lower the floor and it didn’t collapse, so these foundations may be more resilient than given credit for.
I will say that we have had the hardest time stopping the water from coming in when it rains, even with doing gutter caulking and some regrading. The great irony is that while the pictures I showed before are all of the old basement, the worst problems have been in the block foundation basement addition from 2014 (other pictures). Portions have been re-waterproofed from the outside and while there is an improvement, we still get significant damp.
With regards to the working of the exterior footing drains, I assume we don’t have any in the 1925 section; I’m also assuming, perhaps incorrectly, that it is impractical to install a footing drain on such an old foundation if it didn’t exist? One of the oddest design elements of the basement addition was that we originally had the gutters go to the footing drain at which point a buried sump pump (at footer level) sent the water back up to our town-mandated dry well. As that seemed a recipe for several disasters (why send roof water to footers, what happens when pump fails), we eventually had the gutters go by gravity to the dry well, reducing the journey of water against the foundation. We also have gutters around the original house that lead straight into the ground but appear to go nowhere, so our hope is that by taking all these to a dry well on a portion of the property that drains away from the house that we solve the bulk of our water issues. But to your point, it seems like we should have the footing drains re-evaluated if we dig around the foundation.
Either way, we’re well into the sunk cost irrational stage where we are determined to get a finished basement at this point by hook or by crook!
Brian,
You're correct that the water from roof gutters should never be directed to the footing drain system, so your decision to re-route the roof water was a good one.
Q. "I’m also assuming, perhaps incorrectly, that it is impractical to install a footing drain on such an old foundation if it didn’t exist?"
A. Installing new exterior footing drains on an old house isn't impractical -- it is simply expensive. But if you are already planning to dig up the exterior of your foundation walls to install some type of waterproofing system, it's an ideal time to also install (a) footing drains, (b) exterior insulation, and (c) dimple mat. There may be valid reasons why you don't want some of these elements, but if the hard part -- the excavation -- has already been done, it's worth considering all three steps.
If it can't be solved on the exterior, a dimple mat in the interior between the insulation and foundation to allow bulk water to drain toward a (new) interior perimeter drain can work. But managing the bulk water on the exterior is usually best.