I wonder if anyone out there can help me. I am a custom builder in Raleigh and I am trying to figure out the best and most proper way to install a foundation drain. I have gotten lots of different opinions as to placing the drain pipe on top of the footing or down beside the footing. Any Ideas?
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Learn how to fight wood-boring beetles and prevent home infestations with expert advice from Richard D. Kramer, an authority in pest control.
Featured Video
Builder’s Advocate: An Interview With ViewrailHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
You want the water to drain away before it has a chance to enter the seam between footing and foundation wall. So the bottom of the tile would have to be at least below the top surface of the footing (down beside). I've seen a few houses where the tile was on top of the footing and there is at least one wet spot on the slab after rain.
Are you assuming the water is coming up from below the footing?I've been thinking about water and foundations lately, since I seem to have at least three in my life that aren't up to snuff.If I were building new, I'm pretty sure I know enough to build a dry basement....sump pumps, footing drains,drainage mat behind the back-fill, downspouts to daylight, and so forth.....but one house I'm trimming now is brand new, poured walls,in a high water table area but not poorly sited, and it leaks like a sieve in one corner at the slab to wall joint....sump pump runs constantly, which would drive me nuts from an energy usage standpoint....so I've been thinking about what might be "best practice" and if there is any more improvement possible. We've come a long way from block walls with a splash of parging & tar, but maybe there is more we can do....anyone for a complete continuous membrane under the slab & up the walls?
Could it even be done, given all the chance for damage in the course of the foundation work?
>Are you assuming the water is coming up from below the footing?<
No but subterranean water is not really an issue where I'm at. In our case the soils is clay/high in clay and water rolls off the undisturbed soil too well, (ie, doesn't absorb deeply before it becomes somewhat impermeable). Any of the disturbed soil around the foundation lets the water flow down from the top quite easily. Now, there shouldn't be much water gathering near a foundation at grade but that leads to the next problem I see and that's poor grading (either by the builder or the HO) and/or siting the house an inch or two too low.
Although it wasn't asked originally I should mention that I've laid in by hand concrete & tar on different occasions at the seam between footing & wall to help shed water to the drain tile I was installing post facto. I had more faith in the tar since it tends to stay pliable and will flex with any of the foundation movements whereas the 'crete I troweled on will probably release from the two pieces (footing & wall) eventually. In these cases I was just fixing what was broke (flips) but don't see a reason why it wouldn't work on new construction.
j
You may know how to water proof a baseman, but it sounds as if the one with the leak in the corner was built by someone else who either didn't know or didn't care.
oh yeah...
they definitely screwed something up....but my feeling is that with the current practice, if you have a basement in a high water table area you will either have leaks, or a very busy sump pump.
There's something to be said for building slab on grade when you live in a swampy area
Yes, designing for the specific site is always a good thing. There is no "cookie cutter" answer for individual site issues .
Its seems logical to most of us that should be several inches below the finished slab. But a lot of Architectural drawings shows the pipe to be on top of the slab where the cement blocks are started. I have seen a bad situation made worse by the Building Inspector requiring slope (which made the pipe several inches above the slab).
I live in the coast range of Or. Soils type vary but predominantly clay to weathered volcanic rock in a clay matrix.
High water table and lots of percolating water and seasonal springs.
On crawl space houses it is usual to spread 6" of graded gravel across the site for the house foundation then pour the foundation. Drain rock to the top of footing then Drain tiles for these crawler homes are usually placed on top of the footings, and wired tight . Drain rock covers the tile and the rest is back filled. Keeps the drain tile level until the beginning of slope to drain, this is especially important if using the ADS (flexible) drain pipe. I prefer the more expensive rigid pipes, easier to keep to grade. . Too often site cuts have low spots and the tile laid against the side of the footing actually acts as a low point drain, constantly leaking water to the low spot instead of carrying it away. Sump pump only if needed to pump to city drain. We do not grade foundation drains until they are exiting the footprint of the building, then depending on the pipe size it is 1/8", 1/4" ft.
Basements are quite often done the same way , with either foundation tar, (sometimes sprayed on ) or foundation water proof membrane (my preference) applied to the outside of the wall. The seam between wall pour and footer has to be sealed, as do any penetrations, especially those from "snap ties". Slabs, (with 6 mil. plastic or similar beneath) here are usually are poured above the footing top so the drain tile at that juncture (Top of Footing/Wall) will carry water away as long as it has slope after leaving the foundation area. Drains are often "socked" with a filter fabric , and buried with washed drain rock. All down spouts, french drains etc. utilize a separate "daylight" exit. They are never tied into the foundation drain.
Springs aren't at all unusual here so if I suspect one I always lay in extra drain tile where I suspect one to be, usually using ADS for the extra lines, and be sure it is held level when back filling. I use either drain mats against the poured wall or a "gravel curtain". Large slabs will get a drain line under them as well, or maybe more than one depending on site conditions.
I did my first basement pour here probably 35 yrs. ago and to my knowledge have never had a leak or problem with any that I have done.
This is my studied opinion of a Best Practices model.
The footing should be level across the wall. A 6" stubwall should be monolithic with the footing. The slab should sit on the inner footing above a waterproof membrane.
A waterproofing agent should be applied to the outside of the basement walls. All cold joints should be covered with a flexible waterproofing agent or a waterproofing joint $eal should be incorporated.
The Drain plane, whether a membrane or just gravel, should extend up to the water resistant perimeter cap, that expanding clay/mineral product, (CRS,) clay, visqueen, or a waterproof foam.
The cap should slope 1/4"/foot in moderate precipitaion zones and 3/8"/foot in extreme precip zones. It should be 1 to 1 1/2 times as wide as the footing is deep depending on precipitation.
In high water tables, there should be a tile drainage grid under the slab and the exterior tiles should be at the same elevation. Other wise the exterior drains can sit on the exterior footings.
There should be a drain line for the gutters.
All drain lines should slope to open air. Otherwise sump pits should be open and easily accessable.
If water flow may occur on the landscaping, swales and berms should be used to keep the main flow away from the perimeter cap.
SamT
Now if I could just remember that I am a businessman with a hammer and not a craftsman with a business....."anonymous". . .segundo
Sam,
Much clearer than what I tried to write. Well Done!