The challenges we faced on this pre-war rooftop's garden design were weight restrictions of 35 pounds per square foot and no elevator in the building. We designed around the weight restrictions by using lightweight potting soil, rather than heavy garden soil, and putting a false bottom inside the planters to reduce total soil volume.
Hundreds of bags of potting soil, dozens of plants, the furniture, and all of the wood materials that went into the deck and planters had to be carried up five flights of stairs by hand. Who needs a gym membership when you've got roof gardens to install? Here's how we did it:
STEP 1 - Installation of Deck
This deck was installed using composite Trex decking for optimum fire safety. The deck is raised somewhat above the roof to allow water to flow beneath it and make its way to the drain. This sort of system works really well for decks on rooftops, which need to be kept clear of obstructions. It also enables easy access to the drain for cleaning and allows sections of the patio to be taken up for cleaning and maintenance as needed.
STEP 2 - Build Planters and put weed barrier fabric in all pots
The planters were built out of red cedar and are around 2' tall from the outside, with an inside shelf built in around the halfway point, allowing us to use half the soil we would have otherwise, which keeps the soil load nice and light. A layer of weed barrier fabric at the bottom of your pots will let the water out but keep the soil in the planter from leaching out onto the deck. Choose a thin weave weed barrier fabric, as the thicker cloths tend to not drain as well.
STEP 3 - Installation of Lighting and Irrigation Lines
We left a 1-inch gap around the entire perimeter of the deck to run all of our irrigation and lighting lines discreetly up into drainage holes drilled into the backs of the planters. If you've never installed irrigation or lighting lines before, check out my Instructables on how to do both of these. Drip irrigation actually ends up saving people money over the long-run on having to replace plants because it waters the plants for you automatically just the right amount. Low-voltage up-lighting can be placed into the soil around the plants using metal stakes.
STEP 4 - Mulch
A 1-2 inch layer of mulch at the top of your pots will help hide irrigation and lighting lines for a more attractive surface appearance.
STEP 5 - Relax and Enjoy your New Garden!
Read more about our NYC roof garden projects on my blog, www.amberfreda.com