Ask Your Question

Angie's List Answers is the trusted spot to ask home improvement and health questions and get answers from service companies, health providers and consumers. For ratings and reviews on companies in your area, search Angie's List.

 
 
or
Submit
Top 30 Days Experts
Rank Leader Points*
1 kstreett 240
2 Guest_9020487 110
3 Guest_9190926 105
4 GoldenKid 100
5 ahowell 95
6 KnowledgeBase 95
7 skbloom 80
8 Guest_98024861 70
9 Guest_9311297 70
10 Guest_9400529 70

*Updates every 4 hours

Browse Projects By Category

Question DetailsAsked on 8/22/2017

how should a walkup basement exterior stairwell drain be constructed?

putting in an exterior stairwell for basement access, have hole dug and slope for stairs completed. how should i go about the drainage part? dig another couple of feet down and fill with drain rock and cover with filter fabric before bedding w sand to place pavers?

Do you have the same question? Follow this Question


1 Answer

0
Votes

Sorry - that is too complex a question - too dependent on a large number of factors, so you should talk to your architect or engineer about this so it matches your specific conditions. Factors which come into play include:

1) soil type/permeability (ability to drain the water away)

2) groundwater level (highest seasonal)

3) total contributing area to the drain relative to the drain size (more or wider stairs collect more water than just one or two steps out)

4) type of foundation

5) whether you have foundation perimeter french drain passing through that area

6) whether you have access for a buried drain pipe to daylight to drain the stairwell sump to free surface (and not subject to seasonal flooding which can back up through it)

7) highest seasonal water level in adjacent area

8) whether there is any awning or roof over it to reduce the precipitation entering the area

9) risk of overtopping of the walls/top stair during storms/hurricane/etc (a jkey thing to design against, cometimes requiring additional step and wall heights to provide a protective floodwall around the stairwell

10) if in area with significant frost penetration or not (see article below on the damage an exterior stairwell can cause if the foundation footer is not locally deepened to handle the deeper frost depth

11) frost penetration expected in sump (both with respect to freezing solid, and with respect to possible surface freezing of water entering the frozen gravel or stone

12) maximum precipitation expected for design purposes (to determine volume of water drain sump will have to handle in any one event - and in areas with frequent rainfall during stormy or rainy season, totoal seasonal rainfall to design for (if sump will not drain out totally between events)

13) climatic conditions - will sump be conducive to stagnation and odor formation (like in typically hot, humid or long rainy season areas)


As you can see, there are a lot of factors - and areas with very high precipitation events or surface flooding (possibly requiring a full entrance structure or bulkhead door over the stairs), high adjacent water levels from local or general area flooding which might flood stairwell by overflowing or thorugh cracks in walls/under steps or by backing up through drain pipe, freezing conditions, ability of the soil to accept drainage wastre relative to amount expected in stairwell, interior slab drainage (will stairwell pit end up wetting basement), etc all have to be considered - some designs work well in some areas/cases, totally different approaches are appropriate.


Here is a an article link which starts to address the various factors involved:


http://www.ashireporter.org/HomeInspe...


One specific on your suggested solution - the last thing you want is filter fabric and sand over the top - because that will trap sediment and tree debris and such and block off the infiltration, possibly long before the pit has filled with water. Generally the coarsest material (gravel or clean - no fines - cobbles or river stone) would be at the top (possibly covered with a grating to keep large materials like twigs and branches out), with sand and filter fabric possibly needed at the native soil interface to prevent it from working its way into the gravel (assuming this is a drywell design rather than leading to the preferred drain pipe from the pit, which with pipe drainage would usually be an open concrete pit with grating over the top).


One other thing - some people connect the sump to a basement sump pump - BAAAAD idea - if you get unexpected inflow from overflow, record rainfall, blockage of drainage, etc you can get basement flooding. There are cases where due to high ground/surface water conditions or poor topography preventing gravity drainage, unexpected gutter overflow into the stairwell, that the sump at the stairs has to be a wetwell, drained by a dedicated sump pump - though of course due to risk of power failure statistically coinciding with major storm events as well as increased debris blockage or icing up risk due to outdoor location this is generally considered a last resort.

Answered 1 year ago by LCD




Related Questions


Terms Of Use
|
Privacy Policy