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wet basement

I have 60 year old house. I want to finish the basement to use as living space.

The basement walls are concrete blocks which have been painted with dryloc. The gutters have been checked and the downspouts direct water at least 10 feet from the house into a drywell. I still get water inside the basement where the back wall meets the floor. Part of that wall has an 8 foot extension to the house build over it so no rain ever reaches that area. My contractor broke the floor near that wall and said it is only 1/2 inch thick concrete. He recommends breacking the floor all around the back of the house, putting gravel in the trench then a pipe to a sump pump.

Three questions:
1. Is the thin floor going to be a problem?
2. Is that (expensive) trench system the correct was to dry my basement?
3. Is there a web page that shows in detail exactly how he is supposed to do this trench system - I want to be sure, if I spend all this money it is being done correct, not wasting my time and money.

I have had several contractors give me estimates. It seems every contractor that comes into my house tries to sell what they do - not necessarily what I need - at costs ranging from $3000 all the way to $35,000.



Re: wet basement

Boy, 1/2 inch thick floor is way to thin.

Here a site that has some explanation along with both a description of exterior and interior drain systems.

Usually there should be an exterior drain system located at the footings of the foundation. If these are nonexistant or not working , water will build up in the soil which can be forced into the basement. This is known as hyrostatic pressure , the moisture in the soil is forced by the pressure of the soil.
Also if the exterior drains aren't functioning this can allow a buildup of water under the basement floor which will have the similar thing of hydrostatic pressure.
I believe the proper way to resolve the problem is doing it from the exterior. It's the most expensive and disruptive way since the foundation needs to be dug all the way around the house.
The other way is trenching the basement floor on the inside around the foundation. This is the easiest for the contractors and the least expensive, but I don't believe it's the best way.

Either way the new drain system should go into a sump pit with a sump pump.

Re: wet basement

I agree with bsum1---the best way to drain a basement is from the exterior---it's usually more expensive to do it that way, but you may be able to get by with doing just the one wall that's leaking---you might also find some old drain tiles that are clogged up that can be cleaned out & made to work again using just a garden hose.

Some contractors have a trenching machine that can bore a 6" hole along the outside foundation to get a drain tile in there without digging everything up.

The site below demonstrates how a sump is placed when the inside of the foundation is done---note the little white perforated drain tile located on the outside of the foundation wall.


Re: wet basement

An exterior drain probably never existed on my property and installing one would be very difficult without damaging my neighbor's property. Houses here are between 5 and 8 feet apart. My contractor recommended the interior french drain system which we are going to do.

Most web sites I read seem to recommend putting a hole in each of the cement blocks so they drain into the french drain. My contractor does not want to do this saying it will just increase the amount of water the pump will have to deal with. Is this correct?

Also, is it better to drain the pump into a drain in my house or out to the street via a long pipe?

Thank you again - AKB

Re: wet basement


Posting a few photos would help a lot---it's hard to imagine the layout of your property when you say there is only 8' between property lines/buildings.

Sight unseen, I would tend to agree with the contractor on avoiding holes in the concrete block---the sump has to be emptied by pipe to a lower spot on the property, to the street, if allowed, or into its own drywell---it is NOT allowed to be emptied into a city sewage drain, a septic system, or adjacent to the property line so it flows onto someone else's land.

Re: wet basement

Thanks for all the help. I am attaching a photo of my house. My property line is at the concrete path on the side of the house that is visible on the picture. On that side my property is 4 feet from the house (8 feet between the houses). On the other side I have less than 3 feet (5.5 between the houses). I actually have a rather large lot for this area. Some houses near here only have 2 feet between houses (less than 1 foot from the house to the property line). Again - THANKS

Re: wet basement

I had problems with water in the basement in my first house. I had the interior drain tile system installed. It took care of the problem just fine. I agree with bsum1 that the exterior system would be preferable but with your tight quarters that looks like it would be very difficult.

One thing I don’t understand about what your contractor said --- if you don’t drill a hole into each block cavity then how is the water going to get out (quickly) to the drain system? You will probably get some water collecting in those cavities. Unless it has somewhere to go I think your cement blocks will be damp until the water slowly leaches through the wall. I watched a local home improvement show where the whole show was on waterproofing a basement. They drilled holes in the concrete block cavities and in some places the water just poured out.

If you do have the contractor drill the holes then make sure they also drill the holes in the cavity formed where two blocks are put together. This was a large cause of the water problems in my first house. The basement did have a drain tile system. However, they did not drill the holes in the cavity between the two blocks. Also, some of the holes were choked with debris. Once the water was provided an easy way to get out of the blocks and into the drainage pipe my basement stayed dry.

Re: wet basement

ok, now I am really confused. If he does not drill the holes at the base of each concrete block column will my basement stay damp???

Thank you

Re: wet basement

Hopefully someone can help us. My contractor apparently is learning on my house. He is installing an interior perimeter drain. He dug the trench all around the inside of the foundation, put gravel and perforated pipe in it which runs to a sump pump draining out of the house.

When researching the design of this kind of drain system I found a web site by the University of Minnesota Extension Service that recommends placing a dimpled membrane over the trench and up the inside of the wall before re-pouring the concrete for the floor. As a mater of fact they say: "A critical component of this approach is the dimpled plastic sheeting placed at the base of the wall and beneath the slab edge." Does anyone know where such a membrane can be bought? Our local Lowes and Home Depot do not have a clue as to what the stuff is.


Re: wet basement

I firmly believe and agree with the other posters ...... the best approach to dealing with basement water issues in the is from the outside .... that's usually the main source of the moisture.
If the secondary inside approach of dealing with this issue is used then it needs be done properly.


My contractor does not want to do this saying it will just increase the amount of water the pump will have to deal with.

It's scarey when you mention the contractor seems to be learning on your project ... and franky the comment above is scarey.

The lower course of block is going to accumulate water if the foundation isn't water proofed along with proper drains on the exterior.

You definately need to relieve this water build up in those lower course of blocks by providing weep holes to the interior drain. If he's worried about too much water overwhelming the interior drain then you have big problems.

I believe the weep holes in the lower course of blocks along with the dimpled drainage membrane should be employed.

Here's a link to Platon one manufacturer of a dimpled memebrane along with a "where to buy" locator : http://www.systemplaton.com/foundations.html

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