It was explained to me on another forum about the fallicy of paint over masonry or concrete as a moisture barrier as paint still allows water to penetrate.The exteriors need to be waterproofed with coatings such as rub-r-wall, or with membranes adhered to the exterior, On existing homes like yours it means excavation,worst because of your deck. To do it right also involves the installation of a drainage system at the base of the footings of your basement.I have heard of cases where this is done on the inside where a ditch is dug around the perimeter,removing the concrete , digging down the required depth, and installing an interior drain.The interior walls are waterproofed, and the water behind this membrane is directed down and out through the drainage system, some involving pumps.High dollar im sure, but you'll have a dry basement and peace of mind from mold.Im not sure what to call a contractor who specializes in basement work(maybe mole man?), but most or all give free estimates, and if you find a reputable one that is willing to give you references, they will have the right advise for you,im sure.Im reading that people jumping in and finishing off their basements without considering moisture problems are running into mold, and rot issues.

The painted walls are fine, they are not leaking. The problem is on the back wall, where the small washroom is.

The toilet and sink were installed by a previous owners and a small drywall/panelling cubicle was erected around it for privacy. The leak is behind the drywall wall at the very back (the ONLY closed in area of the basement) GRRRRR.

Is it possible to waterproof the basement AND renovate together? Drop the floor and install some kind of waterproofing at the same time?

Lowering your floor will give you the opportunity to install the inside drain, since you'll have it all dug out anyways. I dont believe an internal drain system would be that great of an expense,but will have to drain out the exterior at some point unless a pump system is used.Not knowing your situation completely, where to run the water out and how could get expensive. Im not sure what to reccomend for an inside waterproofer/membrane. Hopefully someone else can advise, but i would waterproof to save any future hassles both the existing as well as the dug out portion.The leak behind the drywall will more than likely cause mold problems.

First, you need to determine the cause of the leak....once determined, it may require a simple fix, and all this waterproofing and trench digging may not be neccessary.

Since it is in an area where plumbing is present, have you had a plumber come and take a look as of yet?
Obviously, the drywall would need to be removed in order to do so.

IMO, that should be your first step..... trying to determine the actual source and then rectify the leak itself if at all possible.....as opposed to allowing it to continue...and then spending beaucoup bucks drain and/or channel the water when it may be possible to stop it at the source.

Logic, if you read the original post, they feel the leak is due to water seeping in from the outside after it had rained. I would never suggest anyone leave a plumbing problem or leak to leave it alone and just install a drain. That would be assnine. I simply stated that since they want to lower their floor, it might be wise to install an inside drain system while they were at it, since the concrete will be removed anyhow.This could help eliminate any future moisture and water problems they might have in the future, waterproofing from the inside. This is done when people dont or cant go to the expense of having the exterior excavated and waterproofed and drain system installed there.You might want to read the whole posts before commenting.

Sierraeast: Logic, if you read the original post, they feel the leak is due to water seeping in from the outside after it had rained....You might want to read the whole posts before commenting."

Hmmm. Sierraeast, perhaps you might want to read the OP's posts..and my response once again.

Let's review.

The only statements made by the OP specifically describing the water intrusion are as follows:

"Lots of rain today, and the back wall is leaking AGAIN!!"

then:

"The problem is on the back wall, where the small washroom is.
The toilet and sink were installed by a previous owners and a small drywall/panelling cubicle was erected around it for privacy. The leak is behind the drywall wall at the very back (the ONLY closed in area of the basement) GRRRRR."

From those two statements you, Sierraeast, infer that the OP "feels" that the leak is due to water seeping in from the outside after it rained. However, the OP never stated that water ONLY seeps in during heavy rain.

In addition, since it seems as if the OP still has the drywall intact, it would be difficult for the OP to know for certain if indeed heavy rain is the sole cause, or if there is also other issues at play here...such as plumbing leaks, grading issues, etc.

Bear in mind that according to the OP, this is the ONLY area of the back wall where water intrusion is seen; the fact that it is also the area that involves plumbing indicates that the plumbing should not be ignored as part of the problem. In addition, there may also be other simple explanations such as a down spout draining directly into the foundation base at that point, and/or improper grading sloped toward that point of the foundation....both of which would cause a problem in havy rain..and both easily rectified...for almost zero cost.

Now..granted, the problem may indeed be one that is more complex...and may require further remediation..such as drains, waterproofing, etc. However, the bottom line is that in accordance with the info provided by the OP, the actual cause of the water intrusion has clearly not yet been determined. Therefore, the OP would be better served by FIRST being advised to find out for certain the real cause and/or causes of the water intrusion, and THEN deciding upon a remedy based upon actual fact...as opposed to what they or anyone else may "think" might be the case.

As the expression goes, when one assumes...

I stand corrected. Any leak takes priority regardless of plumbing,water intrusion,roof,window,etc.Sorry for the misunderstanding on my part!

Taking logics advise and concentrating on the leak and seeing where that takes you cost wise ould be a good start.If you want to go ahead with the rest of the project, ask co- workers,friends, or family for a contractor that has a crew that basically jumps in on a project like this and does it all from start to finish, not subbing everything out.Someone that is willing to excavate, re pour the concrete,take care of any framing, drywall,etc.,but that is willing to work with you on the projects that you want to tackle yourselves.This will probably save you some money compared to a contractor who subs everything ,and is not willing to work with you. As always, get references and more than one estimate, but best if you find one that has been refered to you by someone you know and are happy with their work.I dont think anyone out there can give you a ballpark without seeing what you have going,taking measurements, and labor/material costs differ in different regions as well. Best of luck!

Sierraeast: Sorry for the misunderstanding on my part!

No apology needed...but, thanks anyway. :-)

This may not be of any help, but since you are in Toronto
you could call Holmes on homes, he may not fix it, but would know who would do the job right the first time.
www.wetbasements.com
www.dampbasements.com
www.advancedcoatings.on.ca

Here is a link that might be useful: Holmes on homes

I'm in Toronto too, and I want to dig down my basement. An extra 18 inches or so would make an incredible difference. Let me know if you get a price.

Homemaker, if you are still hanging in there, our experience has been as follows: water through the wall after a rain storm has been the result of a clogged gutter or downspout or downspout drain (which takes the H2O away from the house to a dry well), which allows water to accumulate against the house, or a diversion of water against the house (like the paving of a drive). So during the next deluge do go and look at what is going on, even if you have to crawl under the deck. We found clogs in the most unlikely places. The joys of an old house. We also found that water through the floor was the result of a rise in the water table or undergroud diversion. Not all basement floors are built the same way. If you have a "monolith" type, the floor was poured first and the block was set on that using the floor as a footing. You can't dig up a monolith type floor or even trench around the wall, without compormising the foundation so do have a really good inspector look at it before a contractor has a go. Finally, can you see where the water is coming in though the wall? If not, do take the dry (or not so dry) wall away and, again, watch through a rain storm, you may have a crack or hole that wants hydrolic cement.

I had the same problem, my basement was leaking for years until I contacted the Europa Touch Renovations. They found out the problem with my basement and fixed it. If you still need help just visite these guys. They have a website if you want more info. Its http://www.europatouch.com

Only a thought here and a remote chance/ cause could have happened whenever that deck was installed. You would think that would keep the rain away but if they did any excavating or trenching they may have disturbed a gradient that before caused water to run off away from the house.

I'm 18 months late to this dance.

If there any wallflowers out there, you might try your search for contractors at Renomark
a part of the Greater Toronto Homebuilder's Association.

There are a number of contractors who specialize in lowering and underpinning. I've lowered and buttressed basement walls, a bit cheaper, but still costly. Unless you're in a hot area where the payback will be worth it, I'd be very cautious about spending the money. Waterproofing is another matter, and may be as simple, as other posters have suggested, as changing the grade. I'm a Tarion licenced new home builder.