Basement drainage plan
Trying to decide on basement drainage plan in zone 6b (quite dry but decent amount of snowfall accumulating in the winter). Everyone I have talked to out here (including engineer) says soil is extremely well draining (excavation looks like we dug up a river bed…tons of river rock) and everyone ive asked has done nothing but tar the exterior walls and I haven’t heard of any basement moisture problems. This makes me a bit nervous but I don’t want to waste money and time unnecessarily as I will be doing install myself. At the same time this is obviously the time to add drainage features (I was thinking french drain to dry well as my soil is well draining. I can’t daylight as its a flat site and I don’t believe I can drain to sewer). Basement will have 9′ walls but 4′ above grade so not fully underground which should help relieve pressure I would think. Thoughts? Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
In my opinion any basement without a daylight drain is at the mercy of Mother Nature and sooner or later she gets mad at everyone.
Real-estate is about location I buy near the top of the hill I want to know any water is going away quickly. Lots of people like living next to the creek/river and are happy to redo their house every so often.
I lived in a place where a hills were where the road crosses over the interstate. Very few had basements and they needed a sub pump to keep the floor mostly dry.
Where you live may be different but every place I have lived water would fall from the sky faster than the ground could absorb the water from time to time. If the water can’t run away I would build in above ground on piers taller than the water is likely to puddle up.
Walta
If you already have the ground open for foundation work, it should be relatively minimal cost to add a perimeter drain at this time. Most of the cost of drainage systems is usually the excavation work, and in this case you don’t have to worry about that.
I would go on the principle of “better to have it and not need it than to need it and not have it here” in your case. If you never need it, you’re out the cost of the French drain material, which isn’t all that much. If you don’t have it and need it some day for whatever reason, you’ll find out when you have flooding problems and it will be VERY expensive to add at that point.
You usually can’t drain runoff water to the sanitary sewer, cities typically require that to go to a storm sewer. You can also drain to a drainage ditch or a low spot on your propert away from your home (usually). If you think there is minimal chance of water issues, you could install the French drain and sump, but no sump pump. If you ever see any water in that sump, add the pump then. The sump pump isn’t very expensive though, so you may just want to put the entire system in at once.
Bill
Bill I agree that adding an interior drains to an empty pit is cheap now make sure you have several inches of gravel under your basement slab.
Walta
Hi Jacob.
Have you read this: Best Practices for Dry, Healthy Basements?
I have. I will be going for perimeter drains as described. Are there any resources you can recommend for detailing the walls specifically. I am thinking of just going the whole 9 and doing a liquid applied membrane on the walls and then a dimple mat over the footer. My one question I guess is about how to choose what to apply under the dimplemat. Also, my basement walls are already poured over the footer and we did not do a capillary break. Should I apply some kind of peele and stick between the bottom of the wall and footer before putting on the dimplemat?
Jacob,
Not to nag, but make sure the perimeter drain is lower than your slab at minimum. Best to be at the side of the footing, but many will fuss and insist on putting the drain along the top of the footing in the corner made with the wall. If your slab bottom is higher than this point, it is passable if not preferred. If you can, make them put it down next to the footing. I would recommend fabric wrapped pipe embedded in washed stone that is protected with filter fabric. And not to get Walta cross, but I do hope he means washed stone when he says gravel. I grew up in an abandoned gravel pit, which offered three grades of gravel. None of them would be good directly under a slab, but they sure made dynamite sandboxes. You don't want capillary acting soils in contact with the slab, even if you have plastic. Plastic is never perfect and water is patient and insistent.
Do be aware that if your soil looks like a river bed, then remember rivers extend for some distance in both directions. What is the terrain like in the neighborhood. Any chance others will be saturating the river with their runoff? Draining well to where is a good thing to ponder.
Also, a third vote for do the work now. It is crazy expensive and messy to do later. Have you thought about putting radon pipes in the washed stone bed under your slab? Another thing that is super cheap to do before the slab goes in.
Thanks for the response. I will be putting radon in now as well. I'm going to go for the perimeter drains and install as you describe. The terrain is very flat so I don't think i'll be getting runoff from anywhere.
> french drain to dry well... flat site
Note that this is most reliable when below the slab level (no electricity needed). So skip the trouble and use the area under the slab as your dry well. Add a sump and a pipe to the surface in case its storage capacity is ever exceeded.
Prevention is usually better than cure - consider an "underground roof" to help keep surface water away from the basement.
Something you don't see anymore on newer houses is a 2 ft paved or concrete shelf installed against the foundation pitched accordingly to direct runoff from roofs away from the foundation. These "mini sidewalks" can be easily shoveled in the winter and promotes faster melting of the snow around the perimeter of the house once cleared. Installing french drains and such up against the foundation invites water. Sometimes the old ideas are better than the new.
Hi Jacob,
Just to add some more thought in this, most contractors and people you talk to locally will tell you all sorts of shit, doesn't mean it's right or wrong. I like to think most people are oblivious to conditions until it's a problem. Ie, you could have high moisture coming into a basement, but no one will notice unless it's enough to create mould. No one keeps hygrometers in their house for fun (well, I do). In the vein of good practice, we want to eliminate variables like this completely, so we can more easily control our interior space.
So to give some advice on the strategy, I believe you should apply a fluid applied waterproofing membrane on the exterior of your foundation, and then dimple sheeting over the entire wall down to a drain system beside your footing. All this you can do yourself, or based on site conditions maybe a hand from someone else. It's not rocket surgery and not too expensive.
I agree with others in that you should do a sump pit for your drainage system, and prepipe a 2" abs piping for a sump pump. You can keep an eye on this and add a pump later if needed.
Regarding the no capillary break, I personally have dextered the interior side of foundation walls with poly sheeting which drains to the sub slab gravel layer and is under the slab as well. I used a radon rated sheeting by Stega to make it radon resistant as well. Basically I made a bathtub keeping the outside conditions out.
Hope that helps
Jamie