Building the Practical Oasis

by Jane Gates, Gates and Croft Horticultural Design?EUR??,,????'??+garden designer, artist, horticulturist and landscape contractor

The rock shapes on the upper deck are being formed. Below is a view of the tallest retaining wall (10 feet) that shores up the pool and surrounding area. The plantings include palms that can handle desert temperatures: windmill, Mediterranean fan, pindo and queen palms. Other trees are mesquites (Prosopis), palo verdes (Parkinsonia), acacias (A. bailyana) and purple hopseed (Dodonaea aus. purpurea) bushes. Groundcovers and flowering plants must deal with fast drainage and dry summers, yet offer the maximum in bloom. To receive a little extra water washing off from the lawn above, carpet roses formed a segue into the slopes. Colorful shrubs like the desert bird of paradise (Caesalpinia gilessii), various germanders, rockroses, and rosemaries will offer lush-looking flowers and greenery despite their water-wise needs. There is tough ornamental grasses with colorful foliage like red fountain grass (Penisetum rubrum), blue oat grass (Avena) and deer grass (Muhlenbergia rigens). The plantings are kept moist via drip irrigation. Photos by Jane Gates and Velvet Heller.

Jeff Davis, contractor and owner of Davis Construction, and I, Jane Gates of Gates and Croft Horticultural Design, are creating a practical oasis in the middle of the hot, dry desert chaparral country of the Antelope Valley on the northern edge of Los Angeles for Davis?EUR??,,????'???s home. The challenge is to create a deck, grotto and pool on a steep hill in a bone dry climate where the structures would relate to the surrounding rocky hills. I wanted to design something that would echo the natural rock, fulfill the client?EUR??,,????'???s desire for lots of tumbling water, use the available space for maximum practicality, yet pay back for the water usage by imbedding the construction in water-wise planting.

The first step was to work up a design to use the difficult space efficiently. I worked with Davis?EUR??,,????'???s ideas to design a roofed grotto (with shower, sink and toilet?EUR??,,????'??+all neatly tucked away in the back) camouflaged by a waterfall?EUR??,,????'??+a waterfall created by a deck with a running river accessed right from the yard. The deck area would display a decorative fountain and a convenient entry for sunning and reading, surrounded by plants and the sound of a gurgling stream. The stream would flow down a subtle decline to spill as a waterfall into the pool below, creating a sheeting window of water viewable from the Jacuzzi inside the grotto.

A series of terraces were necessary to hold back the hillside.

To hold back the hillside, terracing was necessary. But to make it blend with the general environment yet create a segue to the large cement structure, I designed curved, natural flowing walls that were stamped to look like they were formed of local rock. We painted out a general layout of the design and marked all the retaining wall footings. Davis measured off the terraced hillside in three elevations, flattening them and digging footings for the different retaining walls. The main retaining wall, roughly 10 feet tall, needed a 6?EUR??,,????'??? x 2?EUR??,,????'??? deep footing with a keyway at the bottom directly under the 12?EUR??,,????'????EUR??,,????'??? concrete masonry unit (CMU) wall.

As February offered ideal weather for construction, all the footings, including the step footings that would terrace down alongside the stairs, were quickly completed. We installed wood stakes in the center of each footing approximately every three feet to strike a laser level and mark the stakes to pour the concrete to the marked footing top. A 2???4 horizontal was then installed with the bottom of the grade form on the mark to create a straight edge for pouring the concrete. Marking the grade form every 16?EUR??,,????'????EUR??,,????'??? created the layout for the retaining wall CMU block with a vertical bar in each block. Rebar was installed horizontally at 3?EUR??,,????'????EUR??,,????'??? off of the bottom of each footing, using #6 rebar (5/8?EUR??,,????'????EUR??,,????'??? ) vertically and wire-tied to grade form on every mark.

Gates worked with Davis?EUR??,,????'???s ideas to design a grotto beneath the deck, complete with a cozy hot tub, shower, sink and toilet neatly tucked away in the back, camouflaged by a waterfall. The slide from the upper deck will conduct fun-lovers past the waterfall and into the future pool.

As per California law, Davis had the footings and rebar inspected so the pouring of the footings could go forward. The columns for supporting the upper deck were also inspected and poured at this time so the CMU retaining wall could now begin. To create interest, the retaining walls varied from 18?EUR??,,????'????EUR??,,????'??? to 10?EUR??,,????'??? in height employing three sizes of blocks: 6???8x16, 8???8x16, and 12???8x16. The block was installed with horizontal rebar as per specs and the mortar joints filled with plastic cement and sand. With the walls at the desired height, vertical rebar could be set in every other cell right up to the rebar extending from the footings. Just in made it time for another inspection! By March, the rains made work intermittent and dampened hopes of finishing by the end of May. Still, before too long, the pea gravel mix and pump were back for grouting the wall. The occasional dark sky encouraged speed in waterproofing the back of the walls. Once grouted, we installed the perforated drain pipe and gravel necessary to assure good drainage. Finally, backfilling and compacting the soil behind the walls completed this aspect of the retaining wall work.

How it should look. The upper waterfall is sculpted out of Perform Wall, a type of Styrofoam block impregnated with concrete. After shaping, it can be sprayed with concrete plaster, overlaid with Flex-C-Ment, stamped to the proper texture and stained.

Davis tackled installing the form boards for the outer slab and stairs between the step wall leading down from the upper deck. Once the rebar steel in the stair forms and the Robertson Steel Deck were inspected, it was time to pour concrete for the flat areas and stairs. But first, the electrical (for lighting) and the drains and pipes for the planters that would be on the upper deck had to be imbedded in and below the steel deck. Once again it was inspection time, then more rain. Now the concrete could be poured to form the deck with all utilities and provisions for the future riverbed and plantings in place. The concrete itself was given a rough broom finish that would later have a stamped overlay.

To give the walls a hewn rock look, Flex-C-Ment was mixed and sprayed through a stucco pump and toweled onto the walls. Rock textures were impressed into the Flex-C-Ment with a floppy stamp and a block pattern lightly marked into the stamped surface. Adding white cement over those joint areas completed the illusion of stacked stones. Once dry, the surface color was stained.

To terrace off extensive slope areas, Davis hauled out the Bobcat to remove the vegetation?EUR??,,????'??+mostly weedy materials, but also a few struggling fruit trees. To support the upper deck, the backhoe cut into the hillside to remove about 60 cubic yards of soil. The soil went to fill and extend the pad to accommodate the swimming pool.

Irrigation and electrical installation followed sealing the stained walls, and the planter areas could now be filled with mixed local soil and added topsoil. The softscape was marked and placed out. Trees and larger shrubs went in first; the smaller plants followed. The drip irrigation system was carefully laid and hooked up to timers. Although the planting would normally be left for later after the hardscape was finished, this geographical area tends to have a very short and uncertain springtime and it is possible for temperatures to suddenly soar into triple-digit heat, so the time schedule was pushed up a bit to let the plantings get established for as long as possible while the weather remained hospitable.

Plants were very important to establish a low-maintenance sense of comfort. They softened the heavy concrete structures, hid construction edges, added color and naturalized the water features while roots worked to hold the hillside soil in place. I sought out tough desert varieties that looked lush and flowered well, while softened hard edges of walls and hiding utilities. Graceful grasses and cascading flowers were designed to fill planters on the upper deck so they would tumble over the edges and mask the rim of the artificial lawn and naturalize the ?EUR??,,????'??banks?EUR??,,????'?? of the stream down to the waterfall.

Gates designed curved, natural flowing, stamped concrete walls to create a natural rock texture. Davis measured off the terraced hillside into three elevations, flattening them and digging footings for the different retaining walls, including the step footings that would terrace down. Rebar was installed horizontally at 3'' off of the bottom of each footing, using #6 rebar (5/8'') vertically and wire-tied to grade form on every mark.

As we?EUR??,,????'???ve only pictured construction of the ?EUR??,,????'??Oasis?EUR??,,????'?? project, we wanted to show you a finished water feature by Gates and Croft Horticultural Design, also in the Antelope Valley. For the Stobie residence, waterfalls cascade in three tiers into the pool. A koi pond with water lilies is set below pool level. ?EUR??,,????'??The swimming pool is surrounded by drought-tolerant plantings that offer colored foliage, bright flowers, low water usage yet blend with the surrounding chaparral,?EUR??,,????'?? explains Jane Gates.

A late rainy April was delaying construction of the structural deck, upper waterfall, pool and spa installation. Fortunately, time was not a critical issue. So in breaks between storms, the toilet and shower room under the upper deck in the back of the grotto/spa area was plumbed down to the septic tank and water supply. After another inspection, it was back to forming and pouring the slab for the restroom. The walls were framed with galvanized steel studs, then the plumbing, electrical and wiring for stereo and satellite TV systems completed. Inspection time, again. Then the steel studs and Robertson Steel Deck were covered with diamond lath, screwed in with self-tapping hex screws. This brought the walls and ceiling ready for a scratch coat of plastic cement and sand and the Flex-C-Ment overlay was applied to match the retaining walls.

To use the upper deck for seating and for viewing the waterfall and pool, it needed to give the feeling of being an outcrop of stone feeding the lower waterfall with continuous water. The upper waterfall was sculpted out of Perform Wall, a type of Styrofoam block impregnated with concrete. It is light and can be stacked, glued together with spray foam and cut into virtually any shape with a sawzall.

To create interest, the retaining walls vary in height from 18?EUR??,,????'?? to 10?EUR??,,????'??? in height. Davis used three sizes of blocks (6 x 8 x16, 8 x 8 x16 and 12 x 8 x16) installed with horizontal rebar as per specs and the mortar joints filled with plastic cement and sand. The main retaining wall (pictured), roughly 10 feet tall, needed a 6' x 2' deep footing with a keyway at the bottom directly under the 12'' concrete masonry unit. A grouting of pea gravel mix waterproofed the retaining walls. A wall overlay of Flex-C-Ment was sprayed through a stucco pump and troweled onto the walls, then rock textures impressed with a floppy stamp. The block pattern was lightly marked into the stamped surface before the material hardened, creating the appearance of joints. By adding white cement over those joint areas the next day, the illusion of real stacked stones was complete.

Like most projects, the illusion that construction would flow in a fast, smooth, predictable fashion without interruption remained an illusion. Due to weather and the demands of other work projects the spa and pool still remain to be done at this writing. They will be dug with an excavator and skip loader, plumbed and tied into the waterfall PVC pipes and the rebar steel and form board for the gunite bond beam will follow. Guniting the spa and pool will come next, along with installing the deck flat slab rebar and outside forms. The deck and flat work will be poured around the pool and spa, tile and pool edge coping will go in and the hook up for all the pool equipment and electrical will follow. With the pool and spa plastered and filled, we will be ready to dive into this desert oasis. In the meantime, however, the plants are thriving and many have come into bloom as the weather warms. With a bit of luck, this practical desert oasis will be up and running to greet the hot summer weather, just when it will be needed most!