Landscape Grading and Drainage

This summer has been focused on the landscape and exterior of Tandem House.  We have two open permits that have yet to be closed pending Zoning and SUDP (Sewer Use and Drainage Permits) final inspection and approval.  Once these permits are closed then we will finally have our Certificate of Occupancy.

Zoning has already confirmed that the building fits within the bulk plane and setback requirements (among other things), but a few items have yet to be done.  In order to get our Zoning permit closed the City wants to see that all landscaping be complete, that no lingering construction material be on-site and that they approve all exterior lighting.

The Sewer Use and Drainage Inspection ensure that the flow of water is away from the house and handled either on-site or directed properly towards the alley.  It also dictates that sump pump discharge is handled on-site and inspected per the City’s detail.

A good landscape design understands that both subjects go hand-in-hand.  A successful landscape design acknowledges grading and drainage from the very start because it dictates cut and fill, site retaining, steps, access points, circulation and the flow of water.  A major factor in our landscape design was dictated by the final Finish Floor Elevation of the house which is 3.5′ lower than what was existing.  Hense excavation and the hauling of dirt off-site was a huge endeavor and a major cost.  This was a big learning experience for myself as a landscape designer.  From this personal experience as the homeowner, I now understand the importance of limiting the amount of cut on-site by finding creative and resourceful grading solutions that limit the need to haul dirt away.  In the middle of a construction boom in Denver, hauling dirt away is more expensive than ever because everyone is building basements and underground parking.  Most construction sites are getting rid of dirt (cutting) not filling.  Hence the problem.  Dirt has to be loaded one truck at a time and hauled away 40 miles north.

This Spring we prepped the site for landscape.  All major excavation was complete so we began by installing a wood retaining wall at the south property line.  The wall now holds back the 3.5′ of dirt from our neighbor’s yard; preventing it from eroding or collapsing onto our site.  With the wall up, it allowed us to prepare for what would become a large rain garden.

Step 1:  The Rain Garden

The rain garden is the foundation for site drainage and a major landscape component.  To build the 200 SF rain garden we had to excavate another 2.5′; that’s on top of the 3.5′ that was originally excavated.  Once the garden was dug, we directed roof run-off via downspouts.  As the water exits the downspout it enters a catch basin and that leads under the now sidewalk and into a dry rock well at the bottom of the rain garden.  We also directed the sump-pump water to the rain garden.  If there is ever excessive groundwater from a rain event, the sump will pump the water up and away from the house foundation into a second dry rock well at the bottom of the rain garden.

Once the water was directed to the rain garden we filled it with a soil mix that promotes drainage.   The mix is made up of 30% sand, 25% compost, 25% topsoil, and 20% clay.  To complete the rain garden we planted two Rocky Mountain Glow Maples and a mix of Colorado native grasses (little bluestem, blue grama, and switchgrasses among the ten different species).  This rain garden is not irrigated and once established it will be fully supported by natural rainwater events.

Step 2:  Fine Grading & Artificial Turf Prep

Below is our SUDP plan.  This is subsequent to the more detailed grading plan and shows where water is flowing.  The ‘infiltration swale’ is the rain garden.  Downspouts and flowlines (FL) show where water is being directed away from the house foundation.

SUDP

Below are images that show the aggregate base for the artificial turf detail and the sloping landscape away from the house with french drains that lead runoff towards the rain garden.

We chose not to irrigate our landscape and to make that come to fruition we installed an artificial turf lawn.  The manufacturer is synlawn which is a great product.  The proper foundation for artificial turf is crucial for efficient drainage.  To prep for the lawn, we removed 4″ of earth where the turf is installed, filled the area with 3″ of 3/4″ aggregate, compacted that and added 1″ of pea gravel.  We lined the area with a steel edger which completed the prep work.  To install the lawn we rolled it out in place, made a few cuts and seams and pinned the lawn down with 6″ non-galvanized steel nails.

The lawn is now a fantastic place for our one-year-old daughter to play.  We completed it just in time for her first birthday!

 

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