How much stone over a footing drain line?
Just posting this as the only way I can finish answering the OP named “mindgap”. For reasons unknown the thread has evaporated.
In my opinion the amount of stone to place around your drain lines will be driven by a couple of factors not least of which is the cost of the stone and the effort required to place it. I believe you asked if 10″ over the pipe is a good amount. I think that is a bit overboard for your situation, which I recall involves a hill. However, it is your money and your back.
Your soil type and grades both local and adjacent will largely control how much rain makes it down to your footing drains. I cautiously suggest that fifteen to eighteen inches of width adjacent to the footing would be enough to accommodate the fabric for burrito-ing the pipe, the fabric wrapped pipe and the stone to a depth of 4- 6″ over the pipe. There really shouldn’t be a river running through the system. The drain line is there to relieve excess water dropping down from the soil above and any dimple mats if used. This removes pooling against the footing and wall. The burrito wrap around the stone provides the square footage needed to pass water over the long haul as soil fines eventually accumulate against the fabric. The depth of the stone over the pipe could be less than 6″ as the pipe should be flowing faster than any pooling of water. I would go wider over deeper. Then again, California has shown us some extraordinary rainfall levels. And remember the larger stone will have bigger interstitial spaces and flow faster.
Do not attach your downspouts to the footing drain. Keep those exit points at the surface and directed away from the foundation. Do be mindful of your neighbors and mind any local codes regarding runoff. I moved from a region where quite aggressive run-off mitigation was required. One home near mine practically had a moat around it.
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Replies
onslow,
Our code requires a minimum of 150mm (6") above the pipe. I believe the IRC calls for the same.
Malcolm is correct, the IRC requires crushed stone 6" above the footing and 12" beyond the edge of the footing. The drain itself must be placed lower than the top of the footing. There is an exception if you have very well-drained soil. That is the minimum required; as with most things code-related, going beyond the minimum is usually beneficial.
https://codes.iccsafe.org/content/IRC2018/chapter-4-foundations#IRC2018_Pt03_Ch04_SecR405.1.
Note that it's best practice to have the bottom of the drain at, or slightly below, the level of the bottom of the footing. The idea is to collect excess water so that the footing isn't "sitting in wetness" all the time.
Bill
That's true, but can be hard to achieve in practice. Adding a capillary break on top of the footing, such as Masterseal (formerly Thoroseal) should be just as effective.
I would try to do both if possible. Belt and suspenders. This is one of those things that can cause a lot of problems down the road if it's done incorrectly, and it's very difficult to fix once everything is closed up.
Bill
Gentlemen,
The OP had asked about what kind of stone would be best for setting his drainage lines and then if 10" over the top was okay. I did note that he was free to go above and beyond my suggestion and that he needed to conform to local code requirements. If he needs 6" over top then he will need to comply. I also noted that the purpose of drainage is to prevent pooling of water against the footing and wall base. Since the original question was about the stone used I didn't get into the next to footing placement or capillary breaks. The post seemed to indicated that part of the work was done. I mentioned the downspouts to head off any bright ideas.
I concede that I have erred by not quoting the most current code available. It is good that wherever all of you live and/or build are under newer better code. Unfortunately, there are still many localities that don't subscribe. I checked some of the older code books and 2015 seems to be the first that I find specific depth of stone codified. Some references (not code books) call for stone to be flush to top of footing, which in many cases would be 4" over top of pipe if set in bedding. I would argue that a wider bed of stone is more useful than height over pipe as one hopefully is not experiencing 10-12" of water depth along the footing. Relieving soil saturation adjacent to the foundation wall to my mind is better achieved by a wider bed of stone than the code 12" from footing side. Gravity does pull down even if the hydrostatic side pressure on the wall is there dimple mat or not. The flow rates of a 4" pipe should be keeping up with infiltration such that the pipe is never full.