Building Subfloor Drainage

[GoldDredger]

I am designing the subfloor drainage for pier and beam building, with a 6-foot crawlspace. Groundwater is not an issue.

It is a fairly large and geometrically irregular structure, approximately 6.4 acres in area of crawlspace.

The subfloor drainage is only intended to pick up 'emergency' flows, such as a plumbing break in the future. Storm flows are not expected.

Does anyone have an opinion on how I should size these drainage lines? The subfloor drainage will connect to the site storm drain system with gravity flow.

 

[bimr]

First off, you should consult with a plumbing engineer so that your setup meets the building code. One specific aspect that you should address is moisture coming up through the ground and possibly entering the building.

You may get a copy of Architectural Graphic Standards for details. This book shows a detail for non-waterproofed basement walls and floors. The details show 6” perforated drain tile installed at the center line of bottom of footing running under the concrete floor with a min. pitch of 1/8” per foot. Gravel is used to cover the tile.

The drainage opening is a groove in slab or wedge replaced with gravel. The building also has a foundation drain.

You do not mention the shape of your building. The drainage should run across the width of the building to keep the drains at reasonable depth.

 

[Hoagie]

Adding to Bimr's tip: Check code for mold/mildew control in that space.

 

[civilperson]

Use 4" perforated PVC in fabric wrapped gravel at 3' below the plumbing and at 2' on both sides of all plumbing.