new house's runoff draining onto our property

A new house was built and is in the final inspection stages with the City. It was built on the 50’ x 100’ corner lot behind our 50’ x 100’ corner lot. Both houses’ driveways run along the rear property line, accessible from the side street. Our 1920s home’s masonry garage rests on the property line, so the side of the garage spans a portion of the shared property line. The rest of the shared line is a wooden fence.

The new home’s garage is set back approximately 30" from the rear lot line. But its slab was poured more than 12" higher than the existing grade. I flagged this to the builder as soon as I saw the slab, which was months ago. He said to give them time and it would be all right.

Fast forward to now, the garage is built and the grading done, and their grade is at least 9" higher than ours. Water and dirt are visibly entering our garage’s weep holes. So not only are they obstructed and not allowed to vent. But we are actually getting mud and moisture in our garage.

We hired a civil engineer who prepared a report that called for an excavated, lower-than-grade swale to be run along the property line, with their new, higher elevation resuming closer to their garage. It also calls for their downspout to tie into a French drain.

They indicated they did not plan to implement this. Instead, they placed Hardi-plank along the fence. Then they installed sod and a sprinkler system along the stretch in front of the garage. When activated, the runoff from the sprinkler floods our driveway proving that the Hardi-plank is not cutting it. The weight of the earth on the fence is also causing it to bow. Lastly, the Hardi-plank does nothing to address the higher grade along our masonry garage.

While the neighbors do seem to now agree that there is a problem, they are suggesting they will install a French drain and the problem will be solved. All the French drain will do is route the downspout water to the street. It will not address the other issues.

And they are now asking us to point to where it is in “the code” that says this is necessary. I have contacted our City’s (Houston, TX) Storm Dept. to ask this questions. He explained that “all water must drain towards the sewer. Period.” He also suggested I contact the Structural Inspection Dept. and ask for a Senior Inspector to come out. And that this is in the IRC and IBC. We are trying not to escalate this and keep things on good terms. But it is becoming more difficult. My thought is that they should implement our professional, stamped plan (and reimburse us for the cost!) or provide their own plan.

In the end, though, the reason I am posting here is that the only references I can find in the IBC and IRC are not EXACTLY what I’m looking for. They seem designed mainly to address the need to slope the grade away from one’s own foundation, versus designed to communicate what NOT to do a neighbor’s foundation and/or property.

Can anyone direct me to something codified that would be helpful so that we hopefully don’t have to get the City, or heaven forbid an attorney, involved?

Thanks in advance.

You should read up on the Texas Water Code § 11.086.