Too much rain in too short a time will overwhelm many measures to prevent basement flooding. That's why the best materials to use below grade are those that are water resistant.

If the sump is not overflowing, the pump is doing its job.

If that kind of rainfall is not unusual, exterior waterproofing would have been the preferred approach.

Here's what 20" of rain in an hour looked like in Pensacola , Florida last week.

IMAGE: MARIANNA MASSEY/GETTY IMAGES

This post was edited by worthy on Mon, May 5, 14 at 13:46

Thanks for your response

Thank god we didn't have that kind of rain.... in NJ we can have one of those drenching 5 inch + rains one or twice a year.

By exterior waterproofing, do you mean checking the drainage around the house? Or something bigger...At this point I don't think it is feasibe to dig out the foundation.....

I also wonder too if the act of lowering the basement significantly increased the risk. Our sump well always has water in it (sometimes more, somestimes less depending on time of year). Pump will run at least once a day even in good weather.

By exterior waterproofing, do you mean checking the drainage around the house?

I was referring to measures taken on the exterior of the foundation. But, of course, diverting water well away from the foundation should help too. That could mean regrading. And the often overlooked movement of downspout water far away from the foundation--not just a couple of feet away on a splashpad.

I also wonder too if the act of lowering the basement significantly increased the risk.

Oh yes!

The worst I ever personally saw was when renovators lowered a basement in a century home by less than two feet. Water started pouring in and before they could find and install heavy duty sump pumps, there was five feet of water in the basement. They had hit one of the many underground streams in a city (Toronto) basically built between two rivers running into Lake Ontario.

Well, I can't these guys hit a stream (the basement was perfectly dry until the major rain), but just decreased the 'margin of error' when a big rain hit.

I am inclined to think it is the water table given that all the water seemed to come up from the bottom. Walls completely dry. Which makes me even more frustrated that the french drain just got overwhelmed.

Hello. Just wanted to re post this and look for further insight as I am about to do some costly repairs. Again, basement was perfectly dry until the major rain event. Am I to assume that my drain system has a limit, or could there really be something wrong that it can't handle such a torrential 5 inch rain?

One contractor says a French drain should be able to handle everything. Says my outside drainage is fine, but prob have a high water table. So drain must me wrong and must be dug up.

Is he BSing me? Or do I really have a problem?

Why not get a second/third opinion and estimate? The more you learn the more assured you will be when making your decision.