French drain design

[MSGulf]

 I recently acquired a house that has some drainage issues and have received some conflicting advice from excavation and landscape contractors. The black line is the storm drain runs to the back of the property to a culvert with 2 large square drains. The green is low area of the yard. The 2 blue rectangles are where water pools along the house. The yard above in the picture slops down into mine. The neighborhood is mostly flat and my yard is always soggy. The worst case was 5 years ago where the X's were over 2 feet deep. 

 The house has no gutters yet since I just replaced the roof. I am planning on fixing some minor cracks in the concrete slab (no basement), installing a drainage system , grading the yard and putting in a fence. In photo you can see where concrete cracked and the bricks nearby. One of my contractors has suggested french drains from the front to the back emptying out into the culvert area but I'm worried about the earth under the house where its cracked already.

Before I jump in I would like to seek counsel and I am waiting for 2 home inspectors to return my calls here in Mississippi. What license and training should a home inspector have, how much should I pay. I prefer to pay extra for a professional especially for something this important. I would to thank all for your consideration and advice.

 

 

 

 

 

 

 

 

 

[Marc]

If the tree isn't in the way, build a swale from the backyard sloping down to the street on the left side of the house. This assumes the street is lower than the areas that are flooding. If the tree IS in the way, start the swale near the left front wall of the house, ending at the street.

A swale is a sort of ditch, just much wider and much shallower.  It facilitates rainwater drainage without sacrificing curb appeal. Constructed properly, you'll hardly notice it when the grass has returned.

The best litmus test for inspector expertise is the reports the inspector has written. Nothing else comes even close. Download and do a 3 minute review of a few dozen sample reports from anywhere in the country. That'll teach you what a good report, and good inspector, looks like. Then look locally for your inspector. Good luck..the good ones are few and far between, like...fewer than one in thirty.

Edited May 9, 2021 by Marc

[MSGulf]

Thank you for your response, this is an excellent option considering this is a modest neighborhood .

[Steve M]

That swale suggestion by Marc coupled with a solid gutter system connected to an underground yard drain are probably going to be your best option based on the limited information those photos provide. Obviously with a yard drain the issue is where to dump the water, and without having a first-hand view of the property, this is all speculation.

Should you opt for a yard drain, make sure the pop-up emitter contains a 12" diameter turf restrictor plate at the surface - it does wonders in preventing the grass from growing over the emitter and impeding its performance. There should also be at least 1 inline catch basin in EACH underground run (since you have a shingled roof). I typically like to see these located in all systems somewhere at 10-15 ft from the house, removable grates are usually the best "cover" option but solid covers work as well, both should have turf restrictor plates to keep grass from growing over them. The grates provide a great visual "indicator" to monitor performance as well as maintenance use and ventilation.

Where the downspouts meet the corrugated pipe entering the ground, there should be a Wye fitting with a grated cover, or if you have a lot of leaves, you can install a downspout clean-out with filter to facilitate easy maintenance (see photo below). The Wye or (DCF) not only provides maintenance access, without disturbing the above ground gutter components, it also provides an "air gap" as well as an emergency overflow in case the drain gets clogged for some reason. What you don't want, and what I have a seen a lot of, is a major separation from your downspout and the underground drain components. Those surface grates typically installed 2 or more inches just below the downspout usually get clogged with debris, ultimately turning the immediate area into a pool from the runoff coming out of the downspout and defeating the whole purpose of the drain.

Velocity is your friend when it comes to maintenance, the faster you can allow the runoff from the roof to get to its discharge destination, the cleaner your system will remain, so if you can go with a 3" pipe, that usually works well.

One more thing, don't use the black corrugated pipe from the big box stores and absolutely do not use PVC or SDR35 pipe underground for this type of system, there are locations in the system where they may be useful (such as providing for a freeze drain before the emitter, knife cut corrugated does a better job in my opinion, but you want the flex of the corrugated as much as possible. And that corrugated should be virgin pipe. The black pipe from the BB stores is always "regrind" which might last 10 or 15 years underground, but it is subject to rapid deterioration because it is recycled and contains "binders" to keep everything together - the binders are the problem as they breakdown, even underground. A virgin corrugated pipe can last up to 500 years underground and will almost certainly last a minimum of 100 years if installed correctly.

These are the Downspout Clean-outs (with Filter) (DCF) connectors that I use to connect the downspout to the drain... You may find something similar, as long it still provides access to the drain itself to run an inspection camera or a hydro-jet should the system become clogged for some reason, such as an animal getting trapped in the system, usually because of an emitter fault - which could be caused by excessively high grass - especially without a turf restrictor, or some child removing a grate or cap and stuffing it with debris.

IF you run into a contractor that uses recycled corrugated (I believe all of the big box stuff is recycled), or believes there MUST be a turf grate under the downspout (to satisfy the air gap requirement)... WALK AWAY and find another contractor, because while they may have been doing this for 40 years, they aren't keeping current with the science behind the design or construction of these systems - and any project they do for you has an expiration date attached to the system before the first piece of sod is ever cut (many don't do this) or the first shovel of dirt is ever moved.

So a couple of quick things to look for:
1) There is almost never a place in an underground downspout that you want a T fitting - Wye fittings (or combis) should be the only connector installed underground, to facilitate water flow, unless there is a need for a catch basin (because you have a shingled roof).

2) Use 3in corrugated if you can (not always available) especially in a yard such as yours where it does not appear you have a good slope. If the corrugated is yellow or blue, it is definitely not recycled, if it is black, make sure it is not recycled.

3) The downspout connectors I presented above act as a vent to the system and facilitate keeping leaf debris out of the system. While there is a possibility that they may "overflow" (Ice or Debris usually) they are a crucial component as they don't get clogged very often, or may never get clogged depending on tree debris and climate. Just don't let the contractor use the air gap vent requirement to justify separating the downspout from the drain. If you do use a leaf deflector, make sure it doesn't spill out more water than passes into the drain line - that will defeat the purpose entirely. I've seen large and small, open-grated "leaf deflector" units that put a considerable amount of water right where they are located during severe storms, just the time you don't want that to happen. If you can't tell whether they keep the water flowing into the drain, better to just use a wye fitting with a grate cap on the side piece and check your clean-outs or catch basins regularly.

Hope this helps.

PS: I know this is a late response, but sometimes these projects can take awhile to put together for some folks. So I'm offering this reply in the event you haven't completed your project yet, or the results did not produce the desired outcome. I'm new to the forum here and consider drainage to be one of my specialties, so hopefully sharing some of that knowledge will help someone.

Edited January 29, 2023 by Steve M
time explanation