First, I apologize if my question has already been answered in another thread.

My yard has an extremely high water table. The soil is like clay and I sit lower than the properties surounding my house.

I have 2 sump pumps in my basement (not sure why there are 2 - I bought the house this way) that work very well. In 6 years and several Noreasters, I have NEVER had any sort of obvious standing/puddeling or leaking water in my basement.

Unfortunately, I assumed that meant my basement was dry and stupidly installed carpet (I have since removed the carpet). As I am sure you can predict, it appears that moisture still permeates my foundation through the walls and floor even though it is not noticible.

My question: will an interior floor trench system be suitible for eliminating this moisture or do I need to dig outside?

Thanks.

Interior systems, water control, should never be a consideration to eliminate dampness. Interior systems allow the water to enter, in order to pump it back out. Often these interior methods increase the moisture levels in a home.

Waterproofing, which requires exterior excavation to the footer, repairing and treating the walls, installing new drain tiles, and backfilling with gravel, is always the best course of action to eliminate dampness through the walls. If your floor is in decent shape, and not poured on the thin side it should also eliminate the dampness through the floor.

You should make sure the source of dampness is from the outside, and not being created fron within. A simple test is to place a square of tin foil, 12"/12" to the wall and floor. Completely seal with tape. After a good rain check to see if there is moisture on the inside or outside of the foil. If the inside is dry, then possibly all you need is a good dehumidifier.

How old is the house? The reason I ask is that newer homes, bult since maybe the 1950s, will have a vapor retarder under the basement floor slab, while older homes, built before that, will not. The test wtrprfr1 suggests will work on walls as well as floors, so do it on both.

Is your foundation built of blocks or poured concrete? Either could have cracks or holes or a failure of the dampproofing outside the walls which are not discernable from inside. You could try a hose test during a period of dry weather, to see if it reveals exactly where water is entering. It may or may not work, since you have not had standing water. The rate that water enters may be too slow to show up in a reasonable amount of time.

Thanks to both of you for your responses. The house was built in the early 60's. Both the floor and the walls are poured concrete.

At some point in time, a previous owner attempted to seal the walls with some sort of dry-lock..but it has since started to crumble away towards the bottom half of the walls, sometimes taking tiny pieces of the concrete with it. This is what makes me think the water is coming from the outside.

Additionally, the floor was once painted grey - now it has started to peal off.

Most of the time, the basement "feels" dry, yet smells damp.

Lastly, when I finally pulled up the carpet - which was dry on the surface, the padding and underlying concrete were damp.

Next question: do you have any way of knowing whether foundation/footing drains were installed outside the foundation? On second thought, if they were, they probably were not done right, and the backfill is probably an insufficient amount of stone, so that ground water in the soil above can't ever get to the drains. The stone should extend all the way up to within 8 to 12 inches of finished grade. Almost no builders do that.

Hard to say whether stopping water entry through the wall will also prevent it from coming up through the floor, but it often, maybe even usually, does. Was your carpet underlayment uniformly wet all over, or wetter near the walls?

If your floor and footings were poured monolithically (meaning "at the same time and as one piece"), the the joint between floor and wall becomes very very critical, and that could be where water is entering. Also, since the advent of spray "dampproofing", the dampproofing compound is usually applied too thin, and can easily fail, allowing moisture to enter the wall.

That floor-wall joint can be waterproofed by extending the waterproofing all the way down over the top and side of the footing. The same waterproofing will also take care of dampness entering through the wall. I would bet that a careful waterproofing job will end your moisture problems forever.

Ok - so at the risk of sounding stuipd, how exactly do you define "waterproofing"?

Never never place a carpet in a basement floor. Unless its one you can pick up and clean.

I have seen more mold in carpets in basements then I care to. Even if the basement was totally dry, moisture always seeks a lower level. Meaning any humidity within a home will find its way down there. Raising the moisture level on the carpet. With all the stuff that finds it way into carpet and add this dampness. Dust mites and a whole host of goodies will appear. Ever wonder why kids end up with ear infections? They play on this carpet that we clean with water, spray cleaning chemicals on, and walk all over with shoes that were just on the freshly chemical covered lawn.

The peeling and crumbly wall your talking about is a perfect example of why we here keep telling people NOT to install these so called water proofing systems on the inside of a home. Sure the stuff stops the water entry, but it also traps it just behind the surface of the finish. The end result is vapor pressure combined with the chemicals within the block or cement reacting with the moisture causing the masonary surface to crumble. And when it does more times then not the problem is even worse then it was before it was painted. Personally I would rather see the dampness coming through then trap it within the wall where it can do hidden damage.
Follow the advice found here and do the system on the outside of the house. Read the warranty carefully of those who claim to install water proofing system in home. Most warranties only cover a few feet on each side of the new system and not the entire basement, which is what you thought you were paying for, but they forgot to tell you about this fine print.

"Dampproofing" is applied to a foundation to attempt to limit moisture migration through it. Period. It will not bridge cracks or cover holes.

"Waterproofing" is applied to a foundation to SEAL it and prevent water entry and moisture migration. It usually consists of a membrane of some sort, and an adhesive. The membrane is such that no water will penetrate it. Waterproofing in commercial work goes far beyond that, and I am surprised that some of the technology used in commercial work has not found its way into residential construction. Things like waterstops and gaskets, for example.