Residential Foundation Drain

[Rmc14]

Hello. I have read a number of threads here on this topic. Great conversations.

I am hoping that some of you may offer feedback on a proposed foundation drain I am working on. Details as such:

Drain is exterior to a ~4ft foundation stem wall (~3ft wall on a~1ft footing). Surrounding soil is clay (Buffalo NY area) - when wet it will stick to your boots inches thick and can be wadded into balls like play doh.

4" SDR35 perforated pipe will be laid so that it's invert lies along the top half of the footing (putting it well below the top edge of the interior slab). The pipe sits in a trench ~12" wide. The pipe will be encased with Cariff Drain-Sleeve, a knitted polyester fabric sleeve. The pipe will be bedded in 1-2" of concrete sand, then backfilled with ~1ft of addtl concrete sand. ~6" of native clay soil will cap the sand in the trench, with some organic topsoil on top of that.

A couple of questions:
1) Should geotex fabric (I currently have Mirafi 140N) be placed over the top of the sand, separating it from the clay cap? I currently have this fabric covering the opening on a 4" pipe stub where the drain water enters a sump pit, and the fabric clogs quickly when runoff in the trench accumulates around the pipe opening. This concerns me that the fabric is not a good match for my soil and will clog over time if installed as part of the drainage system.

2) Could Mason Sand be used for any part of this design? I have a ton of it but don't know if it would perform adequately in this drainage situation.

Much obliged for any feedback offered.

Mike

 

[oldestguy]

Ole guy here and perhaps you have read some of my past comments on this subject. I presume the fabric on yur pipe is a filter of sorts at least keeping the sand out of the pipe. The filter geotex fabric you may be considering for separating the top of the sand backfill from earth fill on top of that, likely will serve no purpose. Concrete sand by itself is a perfect filter for most earth that weeps water. My observations show practically no intrusion of "mud" into the voids of the sand. Ideally it is best to have as large an area of contact between weeping earth nearby or earth backfill and the concrete sand backfill because also of that plugging potential there. However, that's the best you can do. I have never seen a case where that possible plugging is of consequence. The permeability of the sand most always is larger than the nearby "earth". Now to comment on your plan details. Keeping in mind trying to have the area of contact between the nearby beside and above the sand, why not run the sand all the way up until added topsoil, etc. is needed? On the question of mortar sand as the filtering medium, as long as the grain size distribution is at least roughly the same as concrete sand, it will work fine. If water passes significantly slower in mortar sand than for concrete sand, maybe some effect, but unlikely of importance.
It is refreshing to see drain system proposed that didn't call for clean stone backfill and explains also all the features planned.

 

[Rmc14]

Thanks, oldestguy. Was hoping you'd chime in. Yes, the fabric sleeve around the pipe is just to keep the sand out of it. I would consider corrugated plastic pipe with smaller perforations but like the smooth wall pipe option in case it ever needs to be cleaned out.

Thanks for the thoughts on use of the filter fabric vs. not, as well as the usage of mason sand.

 

[dik]

OG: I still use 'clean' stone in the backfill zone and a geotextile to separate it from the clay native soil. Capillary rise and lateral pressures are less with clean stone than saturated sand. Even with a dampproof membrane on the OF of the concrete wall I've never experienced a damp foundation wall. Frost penetration in the southern part of the province is 6' typically. Also often use Miradrain adjacent to the concrete wall for added thermal improvement.

Water goes to a sump pit within generally.

Dik

 

[Rmc14]

Thanks for sharing your experience, Dik. I should add that I am also installing a rubberized asphalt waterproof membrane then rigid EPS foam on the exterior of the foundation wall. The foam will be covered with AWS's SiteDrain drainage mat. So the drainage aggregate will be able to drain laterally as well as vertically down to the perf pipe.

As an alternative drain design, I considered putting clean stone around the perf pipe, wrapped in geotex (Mirafi 140N), then covered with ~6" of concrete sand (as a prefilter for the geotex).

 

[dik]

I've used 'Blue Stuf' by Penkote for decades and it works really well. There may be similar products in your locale. Extruded polystyrene with cement board works well. Only occasionally work on houses... and generally higher quality for clients and others.

Dik

 

[oldestguy]

OG once again. Clear stone wrapped with geotech fabric does work. No question. However, I have seen too many construction situations where well meaning or lazy workmen screw things up. In the case of working in a trench and with saturated ground, cave-in can occur on top of partly covered stone, etc. With the concrete sand it is darn hard to do it wrong. Takes less labor also.

 

[dik]

OG: agreed... my way is more costly.

Dik