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June 18, 2014


Hope the neighbors don't mind this in the street for a few days.
This rather large pile of drain-rock has just arrived, ready for distribution around the building site.

All about this rock and where it goes below.

Seems like a bit much, doesn't it?  Everywhere that goes, it means dirt that was there has to be removed.

So where does it all go?
(3) places:
- around the footing drainpipes
- behind the east retaining wall
- and, most of all, in the Soakage Trench.

Its purpose is to provide a path for water to easily move (if it has nowhere to go it can build up enormous pressure). The rounded shapes leave lots of voids between the rocks.  To keep those voids from filling in with dirt and other fines, the drain rock installations are usually wrapped with landscape fabric - which acts as a filter cloth.

Footing Detail at Lower Slab
Above is our footing detail at the lower slab.  You can see the drain pipe with fabric-wrapped drain rock that runs around the entire building, and drains to the soakage trench.

Not marked on this drawing is the waterproofing applied to the concrete below grade as another measure of protection.

This east retaining wall has a similar but much simplified detail where the water drains through the rock to weep holes in the wall.  It is better to let the water through than allow it to build up and eventually push the wall over.

The soakage trench is by far the largest installation of drain rock.  It is essentially a large trench filled with drainage rock designed to contain water, away from the house, long enough to allow it to soak into the ground naturally.

Image from City of Portland
Gone are the days (in Portland) when you could just dump the water coming off your roof onto the ground (there are still exceptions for small roofs), or worse dump it into the street.  Now all water is required to be collected and retained on your property to keep from overwhelming the city sewers.

This can turn out to be a difficult thing to accomplish.

Our soakage trench is 56 feet long!  Hard to fit it all on the property.

There are a number of different approaches one can take, if a long trench doesn't fit on your property.  The Portland Stormwater Manual is an impressive document that is sure to induce sleep and/or panic attacks to those who are trying to figure out their own solutions.  That's where Architects can help - we read things like this so you don't have to.

What I like about the soakage trench is the simplicity, and the ability to hide it away underground where you don't have to look at it.  You can have lawn or plantings or hardscape covering it.

We have also designed in an extra stormwater management system that we will add down the road a bit:  a green roof.  The carport and entry canopy is structured to support the weight of the plants and lightweight soil.  This will be pretty as well as serve to reduce and delay water runoff from the roof during a storm.

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