Question for Worthy on Seattle 1920's Basement Waterproofing

kimhojAugust 18, 2013

I have thoroughly enjoyed reading and researching all the prior posts on this question of which system to go with- interior vs exterior waterproofing and it seems quite clear to me that exterior waterproofing is the clear winner in terms of actual "water-proofing".

The biggest disadvantage of course is cost so that is why I am even remotely considering an interior system as an option. I have a couple of questions for Worthy and for others.

I have a 1920's Seattle home that has poured concrete foundation walls. The east wall of the basement tends to have water leaking through the walls about 4 feet from the floor. I can see salt marks left over. Last winter after a terrible thunderstorm (more than usual for Seattle), our basement literally flooded with 5 inches of water. The East wall also has a Landscape Grade problem- The backyard SLOPES down towards the East wall. Additionally, our neighbor's garage does not have any gutters and all that rain literally just falls right into our lawn and down the slope. The slope differential height is about 18 inches. We have gutters that all drain into the main sewer line and have been inspected recently.

Question #1:
Would Re-Sloping the backyard and doing proper drainage planning be sufficient to avoid any exterior drainage system? Is it worth it to do this first and wait and see what happens before investing into an expensive exterior system?

Question #2:
Does an exterior waterproofing retrofit properly done prevent water from seeping up from the floor (assuming no cracks in the floor foundation)? If not, would an interior waterproofing system prevent water from seeping up from the floor?

Question #3:
On the East wall, the wall/floor junction is not a straight 90 degree angle but curved. One of the bidders told me that this may be a "monolithic" pour. If so, wouldn't it be a bad idea to cut through the concrete floor to install an interior french drain system since it may compromise the structural integrity of the foundation system?

Question #4:
Is it common for homes built in the 1920's to have Concrete footers that were poured separately from the walls and floors? Does it matter when choosing between an exterior vs internal system?

Question #5:
Is it legal to drain the sump-pump into my sewer line (where my rain gutters also tie into)?

I'm leaning towards an exterior system but the cost is killing me. One guy gave me an estimate that was the cost of a new honda civic. It blew me away. Another guy however gave me an estimate for an exterior system for the cost of a used 2003 honda civic. Makes me wonder and very frustrated.

Thanks for any tips and sorry for the long post!

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Grading and drainage are the first things to look at in reducing the chance of basement flooding. On new builds, I must file a grading plan by a surveyor or other accepted independent expert to show how I'm keeping all water that falls on my property on my property and out of the basement. That means proper sloping away from the building and the use of swales and/or ditches to keep it off the neighbour's lot. In older properties, a complaint to the municipality may be effective or a legal action taken. (Though about 99% of us won't take that route to neighbour war!) So you should consider regrading as your first step.

When it's pouring, go outside and see exactly what's going on.

I don't have much use for interior systems either, unless you have a rubble foundation, which may fall down if you expose it on the outside; or there is simply no way to access the foundation from the exterior. The incoming water is still at work undermining the foundation.

3) I'm not sure there is such a thing as a monolithic pour of a slab and full foundation. The often stated purpose of a monolithic pour is to eliminate the cold joint that may leak. But since concrete is a pretty porous material to begin with, I've have never understood that rationale.

4) In my area, solid brick homes of that era often had brick foundations with footings simply the same brick set perpendicular to the wall.

5) It is evidently still legal to leave downspouts and sump pumps connected to the municipal sewer systems in Seattle and King County, though discouraged.

In many municipalities in the US and Canada, new connections have been banned for many years and old connections have to be removed. In fact, just last month my neighbourhood was targeted for smoke and dye testing to detect illegal connections.

This post was edited by worthy on Sun, Aug 18, 13 at 11:38

    Bookmark   August 18, 2013 at 10:03AM
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Thanks a bunch Worthy!

Just a couple of followup questions.

Since our backyard is hard to access, if we do the re-grading/landscaping of the backyard first, we may want to try to do a more finished landscaping project as opposed to a simple regrading of the lawn. If so, if simply regrading the landscaping does not work, the work on the previously paid landscape would have to be torn up near the house and then the exterior French drain put in.

My question is this- in most cases, do you think that most cases of basement waterproofing is solved by just regrading the landscape or that eventually most of the time some form of French drain system will need to be installed?

Also I know costs vary from country to country and city to city but is there a rough estimate per square area for an exterior French drain system? We have about 25-30 linear feet of wall and about 6 feet deep before the footings are reached. This would assume a connection to a sump pump with a battery back-up. Thanks for all your expert advice!

    Bookmark   August 20, 2013 at 12:54AM
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I'd try the least expensive fix first, especially when it's part of a good water management anyway. Once I "fixed" a leaky basement simply by tamping down a bag of coldpack (asphalt) between the concrete walk and the foundation. Not permanent, not pretty, but it worked for the few years more I owned the property.

I have no idea if altering surface drainage will be the whole answer. It depends on the soil and the condition of the foundation.

If you do go to an exterior weeper system, be sure that it is done in conjunction with a good waterproofing system most commonly a plastic membrane on the wall such as Platon and/or granular backfill.

I guess you're suggesting $6-$9k for the job. Labour and overhead is the biggest cost and that's too local to guess from three time zones away. As with everything else, comparison shop.

One last note: double check the operation of the eaves and downspouts in action in the rain.

Hope this helps.

    Bookmark   August 20, 2013 at 3:12PM
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Hi kimhoj--

I'm also in Seattle and have a 1919 house. We do not have footings under our foundation -- as I understand it, the use of footings was not a widespread practice until much later. We had to have new footings put in to support the main beam of the house when we replaced part of it.

We're fortunate in that we've never had water issues in our basement, probably because it's a daylight basement and we're at the top of a hill so the water has somewhere else to go. Our downspouts are also tied into the sewer system like yours. We are remodeling the basement right now and had to take out part of those pipes on one side of the house. We replaced with new piping that discharges into a buried cistern that gradually allows the water to seep through a leach field and into the soil. We haven't had any significant rain to test that solution yet, but by all accounts it should work. There is some more information from the city about this kind of system in the link below. There are even a few areas of Seattle where you can get rebates for installing cisterns or rain gardens. I wonder if regrading the east side of your yard and installing a rock trench/rain garden where the neighbor's garage roof water falls into your yard would solve most if not all of your problems. If you're not getting flooding at other walls, it seems to me it's most likely the grading issue and that's definitely where I would start.

On your question #5, we were looking into replacing our driveway and in discussing drainage solutions for that our contractor said that the city will not allow NEW tie-ins to the sewer system, so I don't think you could discharge a sump pump that way. You could call and ask though.

Hope that's helpful!

Here is a link that might be useful: Managing storm water in Seattle

    Bookmark   August 26, 2013 at 3:03PM
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