Foundation Drain and Waterproofing Best Practices
BrunoF
| Posted in General Questions on
I am looking for references on best practices for the design and installation of a foundation drain for new construction. We have not yet broken ground on this house which will be built on footings with CMU blocks to form the foundation walls and crawlspace piers.
There are several companies in the area that do foundation and basement waterproofing and they all seem to have different preferred methods but none of them seem to be ideal.
Any suggestions, section details, or reference material on this topic will be appreciated.
Thx
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Replies
The first question is how well drained is your lot?
Will your perimeter drainage system be able to drain to daylight on your lot?
The way I see it the waterproofing companies offer an important service but nothing they apply can really keep the water out if the perimeter drainage system is not working and generally that is not their job.
The important tings are getting the drain pipes several inches lower than the crawlspace floor and sloping the pipe to daylight.
Did you find this article?
https://www.greenbuildingadvisor.com/article/how-to-install-a-foundation-drain
Walta
So far, the waterproofing companies are the ones quoting the drains as well as the waterproofing coatings / systems on the foundation wall itself.
The site is sloping; 24" of fall from front to back and 24" of fall from left to right but I am flanked by wetlands. The house site seems to drain well and never holds water (i've already cleared it and removed the topsoil) but I have not dug any holes in it to see what happens then.
BrunoF,
A good resource are the articles on the subject here on GBA. Use the search engine for look for French Drains.
Thanks! Lots of ideas and options discussed under articles found with that search!
BrunoF,
GBA's search engine is hit or miss. We were lucky this time!
24 inches above the swamp in the middle of a drought (where I am we are in a drought but maybe not where you are). Is your frost line above your water table?
Will the house be above FEMAs 100year flood line?
Everyone sees risk differently but this ground is sounding too scarry for my tastes.
Walta
In my mind planning for just 100 year flood levels is risky. We are having too many extreme weather events.
I never said anything about a swamp and nothing resembling a swamp is anywhere near me. The 100-year flood line is far away, well below the house elevation and no factor based on topography.
Help me understand in your mind what is the difference between a “wet land” and a swamp?
I thought “wet lands” was government speak for swamp.
Did you see the FEMA map with your own eyes?
Get a free quote for flood insurance if you are on as high a ground as you think it will costs almost nothing.
Is sounded like you said you were 24 inches higher than the wet lands.
Walt
Wetlands are defined by the army core of engineers and identified by folks who core the soil and look for certain characteristics. In my area (central NC Triassic basin), they are often isolated as are intermittent streams. On my property, the identified wetlands are in the valleys and only wet half the year…they are basically the areas where the high spots drain to.
Here is a good article about the differences between wetlands and swamps.
https://www.reconnectwithnature.org/news-events/the-buzz/what-the-difference-marsh-vs-swamp-vs-wetland/
Some of the important factors of foundation drainage seem to get missed or confused even by experienced builders. I still see guys installing drain tile that is not drained anywhere, just sitting there beside the footings. Drives me nuts.
The water needs somewhere to go. If you drain to an adjacent wetland, what happens when the water table rises? Will you still have enough grade for the water to drain away, or will it back up into your system?
Drain rock (no fines) is great material. Place a thin layer at the level of the bottom of your footing, and then your perf drain pipes, and then backfill with drain rock. I like to fill all the way to grade with rock, it simplifies drainage and is not a hospitable habitat for most pests.
On the inside, fill the entire area with drain rock to the top of footing level. This should put your drain tile 8" of so below the top of your slab (depending on footing thickness).
Do not pipe your rain leaders directly down to the footings as this creates a large surge of water directly to your foundation during rains.
For damp proofing I like the self adhering sheets (peel and stick) as the sheets will span over any incidental cracks in the foundation. These sheets should wrap right down over the footings.
Unless the site conditions allowed for very efficient and trouble free site drainage, I would opt out of a basement altogether. Too many headaches.
Plumb_bob. Thx! Just a few clarification points and questions for you…the house will not have a slab in the crawlspace and will not have a basement. When you mention the gravel located on either side of the footing; I assume that you have excavated to the bottom of the footing and used forms to pour them: is that correct? I’ve for plenty of fall to daylight the drains so that is good.
Thx!