Foundation Drip Line Advanced Settings - What's working for me

Schedules & Zones
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North Texas has clay soils, slab foundations, a “monsoon” season in the spring, and extreme heat in the summer. This combination leads to expanding soils that quickly retract in the summer, causing foundation settling. Preventative measures involve drip lines around the foundation to keep the soil moist and applying pressure to the foundation year round, holding the foundation in place. Unfortunately, Rachio’s advanced settings are a bit confusing when it comes to drip lines, so I thought I’d share how I set my settings to get a working flex schedule.

The installation and recommended schedule:
The crew that installed the lines used 0.4 GPH, 18" emitter spacing check valve drip lines. They buried 12-18" off the foundation at 4-6" depth. The recommended schedule they provided is twice daily 22 min per drip line, reducing the days you water in the cooler months. They provided a 4’ T rod to push into the soil so you can gauge whether you’re watering too much (gurgles when you pull up) or too little (no soil stuck to the rod).

The Zone Settings:
Spray Head: I set to rotary nozzle to allow for flow measurements. It shouldn’t matter otherwise

Soil type: In most cases where you’ll use these foundation lines, clay will be right but I’d set what you have. The guide listed here can help!

Exposure: I set to mostly shade

Slope: Shouldn’t matter

Area: I measured the length of the hose and multiplied by 3 feet, assuming the drip line would be equally wetting 18" to either side of the line.

Available Water: Set to my soil’s available water, 0.12, determined using the guide at the link above.

Root Depth: I set to 5", assuming I always wanted the soil above the drip line to be moist and the water will work its way down under the foundation over time regardless.

Allowed Depletion: We want the soil to stay moist so this should be pretty low. I have mine set to 5.5% but played with it to get my schedule watering time right.

Efficiency: I set to 100%. Since the lines are buried, all the water is making it to the soil.

Crop Coefficient: I set this to 20%, as low as it could go. We don’t have any plants perspiring that would drive it up and most of our water isn’t making it to the surface to evaporate. It would be handy if we could lower it further but Rachio hard limits us at 20% minimum, unfortunately.

Nozzle Inches per Hour: We can’t use catch cups for underground drip lines so we need to go about this a bit differently than you would for your lawn. I measured the drip zones using my city water meter in cubic feet per minute and converted to cubic inches per hour of water. Convert the square footage you found above to square inches. Divide your cubic inches of water per hour by your square inches and you’ll have the inches per hour for your zone.

Tweaking the Zone Settings to Hit the Schedule:
I created two flex monthly schedules and aimed to hit ~22 minutes run time for my zone on each schedule. Allowed Depletion was adjusted until the duration was correct and Crop Coefficient was tweaked until January scheduled dates were about once or twice a week. This link here tells you how adjusting the parameters effects your schedule.. I set one flex schedule to run in the morning and the other in the evening and turned off wind skips for both.

Hopefully this helps someone else with their foundation watering needs!

3 Likes
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This great info. Awesome work! I’ve always seen multiple Fixed schedules for each season to water foundation. I would never have thought that you could fine tune Flex Monthly enough to achieve Seasonal Foundation watering. I’m really impressed. I’m interested in what other users in your region who have posted about this think about this solution.

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Thanks Dane, I’d love to hear as well.

I’ve actually made some amendments for a single flex daily schedule that I’ll be trying out. It looks like it’ll wet the soil about the same but should adjust frequency for weird temps a little more dynamically.

Changes from the dual monthly flex schedule to the single flex daily schedule:
Allowed Depletion: 11%
Crop Coefficient: 25%
Schedule soak settings: manual 22 min cycle, 12 hour soak

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I still find it so funny to hear/see posts about watering the foundation.

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My daughter who lives in the Austin area had to deal with this a couple of years ago — she had not been watering her foundation (grew up in the DC area where it’s not a problem) — when doors started not closing in her house, she had somebody come out and look at it and she had to put in large metal beams under her slab house, to the tune of $15K which insurance doesn’t cover! And most of the houses in her neighborhood had to make the same fix.

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I learned the hard way too, Linn but happened to catch it before piers were needed. It’s unfortunately an expensive lesson to learn through experience. I’m glad she’s sorted now.

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Do you guys not have stem walls? What part of the slab has the issues?

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It’s mostly monolithic slabs and the occasional pier and beam. I’m not sure why stem wall slabs aren’t used here, but I’m sure there’s structural or geological reasons for it above my pay grade. I’d wager the lack of basements here is probably related to the same reasoning, whatever it is.

The soil is expansive so when wet, it expands and when dry it contracts. When it contracts, it leaves part of your slab unsupported so the slab sinks and your framing bends. When the soil gets wet, it expands against the foundation and applies pressure, supporting it. A lot of expand/contract cycles puts a lot of stress on the foundation and the rest of the structure. In my case, I’ll need to redo most of my indoor sheetrock, bathroom wall tiling, and a few door frames because I didn’t know I needed to water my foundation the first year I moved in, a few years past.

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That’s brutal. In Phoenix we are dominated by slab built homes with very few basements (makes no sense not to go underground in the desert, but whatever), but majority are stem wall construction, with more recent additions of post tension slabs, but still utilizing stem walls. We have a cabin up in northern Arizona that has a basement that had some drainage issues (thanks to the neighbor running his gutter right into the back of the house) that caused the clay under the slab to heave and crack. Structurally, it didn’t affect the house at all, and once we were able to stabilize the moisture content of the soil, stitched the cracks, ground and leveled it. All is good! Still not cheap, but, I don’t remember it being $15k.