How to Install a Green Roof

Is the flat roof next to your raised porch an thorn in the side and an expensive heat island? Does the sight of pumps and filters obscure the view of your pool and garden from your second floor window? Is rainwater causing problems draining from your roof? Installing a green roof is a do-it-yourself project that improves visibility, lowers energy costs for homes, and has many eco-friendly benefits. Here is a guide on how to do it.

What is a green roof?

Green roofs are roofs that are wholly or partially covered with vegetation that grows over waterproof layers of various materials. A roof with plants growing in containers is not a green roof. There are two types of green roofs: extensive (soil layer six inches or less) and intense (soil layer greater than six inches).

Select location

An ideal location for a green roof is under a higher roof with lines of sight from the house and access from a porch or window for maintenance. The strategic placement of the green roof under the higher roof can slow down and filter the runoff of rain from the higher roof as well as rain falling on the green roof. Catching the runoff can be achieved by hanging a “rain chain” from a gutter to the green roof. Rain chains come in a variety of designs and can be purchased from online sites and some garden centers. Other placement considerations include setting up a green roof on which system equipment such as pool pumps and filters are hidden.

Flat or sloping?

Green roofs are easiest to install and maintain on a flat roof. They can be installed on low pitch roofs with a pitch of up to three feet per 12 feet of length without the need for stabilization. A reinforcement system may be required for steeper slopes, e.g. B. a planting or patio system to keep the soil in place.

What about weight?

The ideal depth for the bottom layer of a green roof without special structural design is 4 to 6 inches. According to Meg Needle, a commercial architect at Lord, Aeck & Sargent Architecture in Atlanta, a fully mixed floor with the expanded slate formula below weighs about 27 pounds per square foot when fully saturated. One bowel check for robustness, she said, is walking on the roof. There shouldn’t be any bounce or wobble, she advised. If you have any doubts about the roof design, reach out to someone with trustworthy structural expertise to suggest reinforcement options. In seismic zones, depending on the height of the roof, special consideration may be required for additional bracing. In any case, follow the local building regulations.

Install a green roof

Green roofs can be installed using a series of planters or by creating an angular rooftop area.

Here are the steps for installing a landscaping area on a level surface using a multi-layer waterproof protective barrier between the ground and the roof deck, such as plywood. The various layers available at landscapers or stores not only prevent water from seeping into the deck and rotting it, but also preventing roots from seeping into the deck and weakening it or rotting it.

With the paving in place, do the following to install a green roof:

  1. Install a waterproof monolithic membrane (rubber or plastic) on the roof terrace.
  2. Place a 6 millimeter plastic sheet on top of the waterproof membrane (this will act as a root barrier).
  3. Cover the first two layers with one or more thin layers of three-quarter inch foam insulation suitable for contact with damp soil. (Insulation is only required if the R-value for the roof needs to be increased over air-conditioned rooms. If the space under the green roof is not conditioned – over a gazebo or shed – there is no need to offer more than some protection for the waterproof membrane, such as a thin foam fan board insulation or maybe a layer of building felt.)
  4. Place a drainage mat (also called a dimple mat) with capillary spaces on top of the insulation. To prevent the floor from clogging the mat, place the mat with the felt side facing up.
  5. Frame the sides for the roof with gutter protection, wood, or other edging so that the drainage keeps the soil in place. Intermediate angle brackets may be required to keep the vertical edge stable. The horizontal leg of the supports can be pushed under the drainage mat and weighted down with the covering to prevent it from tipping over. It is best to design supports so that they do not penetrate the waterproof membrane surface to prevent leaks.
  6. Add soil.
  7. Set up the plants.
  8. Water to settle the soil around the plants.

If using trays, only the membrane and 6 mil plastic wrap are required in the following steps. Make sure you create a roof that accommodates the width and length of the trays with no gaps. The trays can be planted with the same plants as a roof without a container, or purchased pre-grown from a nursery. No edge is required with a tray system.

Another option for green roofs is to purchase vegetation mats. These are mats of succulents or other plants that are grown on the ground in the same way that some nurseries grow lawns. In areas of the country where summers are hot and dry, installing matted plants in fall is recommended because mild climates allow the plants to acclimate and establish themselves best, said Robin Andrews of the Greenbuild division of Saul Nurseries and ItSaul Plants in Alpharetta, Georgia A mat system requires a thin layer of soil because most of the soil comes with the mat.

Choose soil

Homeowners can easily create a light soil mix by mixing an aggregate such as slate, slate, or volcanic rock with an organic potting soil. A mixture of 85 percent aggregate and 15 percent potting soil has been shown to be effective. Lightweight aggregates are available from landscapers in bags or in bulk. premixed or by itself. If you don’t have a truck or access to one, it may be easiest to have the unit delivered. The advantages of an expanded slate soil mix are that it absorbs water, drains well, does not compact and is light. Commercial green roof soil mixes are great if you can find a point of sale but find a mix with locally available materials to avoid unnecessary shipping costs.

Select plants

Keep in mind that roof temperatures can reach 150 degrees F or higher. Plants that are ideal for surviving the summer heat are those that are “bulletproof” against climate extremes, pests and diseases. Fortunately, a wide variety of plants make very good roof gardens. These include many regional aborigines, perennials, ground cover, succulents, sedums, herbs, and some foods. Only use plants from these groups that are low-maintenance, shallow-rooted and drought-resistant. Some grasses may be included but will require winter deadheading. Plants that stay green all year round are good choices as the roof stays green in winter when lots of plants are dormant.

Advantages of a green roof

Green roofs over living spaces are not only a pleasant sight and a topic of conversation, they also ensure more efficient house insulation, as they reduce heating and cooling costs. They also reduce rainwater runoff, create a sound barrier in high-traffic areas, and provide habitat for wildlife. Installing a green roof over pool equipment or a pump house will reduce the noise of the equipment.

Plants for an extensive green roof

An extensive green roof is three to six inches deep. This list contains a selection of plants that are available in many parts of the country. It is not intended to be an exhaustive list. Check with local tree nurseries or other trusted sources about the suitability of the plant material in your location.

Succulents

  • Trillium garlic
  • Allium schoenoprasum *
  • Allium senescens glaucum
  • Delosperma ashtonii
  • Delosperma basuticum ‘Gold Nugget’
  • Delosperma Cooperi *
  • Delosperma dyeri
  • Delosperma keladis ‘Mesa Verde’
  • Delosperma nubigenum *
  • Delosperma ‘Osberg’
  • Graptosedum ‘Bronze’
  • Jovibarba mixed
  • Opuntia humifusa
  • Phedimus takeimensis ‘Golden Carpet’ Syn. * Green Takesimensis
  • Sedum
  • Sedum ‘golden’
  • Sedum aizoon ‘Sweet & Sour’
  • Sedum album ‘Coral Carpet’
  • Sedum album ‘France’ *
  • Sedum ‘Green Ice’ Syn.Sedum mioranthum ssp. Mioranthum
  • Sedum album ‘Jelly Bean’ *
  • Sedum Murale ‘
  • Sedum ‘Bertram Anderson’
  • Green Emarginatum ‘Eco-Mt.Emei’
  • Sedum grisebachii
  • Green evergreen
  • Sedum kamtschaticum *
  • Sedum kamtschaticum ellacombianum *
  • Sedum kamtschaticum ellacombianum ‘Akebono’
  • Sedum kamtschaticum var. Floriferium ‘Weihenstephaner Gold’ *
  • Sedum makinoi ‘spotlight’
  • Green burmannii
  • Sedum mexicanum ‘Lemon Ball’
  • Green Moranense
  • Green reflex ‘blue spruce’
  • Sedum ‘Angelina’
  • * Green sex angulars
  • Green Sichotense
  • Sedum Sieboldii ‘October Daphne’
  • Sedum ‘White Pride’ Syn. White Form ‘
  • Sedum ‘Fuldaglut “
  • Sedum ‘John Creech’
  • Sedum ‘Voodoo’
  • Sedum Stefco ‘
  • Sedum ternatum ‘Chestatee
  • Green tetractinum
  • Sempervivum green
  • Sempervivum ‘Strangeness’
  • Sempervivum red
  • Talinum calycinum *

Different perennials

  • Achillea, different varieties **
  • Agastache, different types **
  • Aster, different species / varieties *
  • Coreopsis, different species / varieties **
  • Dianthus deltoides ‘Brilliant’ **
  • Echinacea, different varieties **
  • Gaillardia grandiflora, different varieties **
  • Heuchera villosa, sorted. Sorts **
  • Liatris, different types / varieties **
  • Malphora lutea
  • Monarda, different types / varieties **
  • Penstemon digitalis **
  • Portulaca pilosa
  • Phlox, different species / sorts **
  • Rudbeckia, various species **
  • Solidago sempervirens
  • Sysrinchium angustifolium, different varieties
  • Thymus, different types
  • Tennuisect Vervain **

Different grasses

  • Bouteloua, different types **
  • Carex, different types **
  • Schizachyrium scoparium ‘The Blues’ **
  • Sporobolus heterolepis **
  • Stipa tennuisima **

These plants are considered “bulletproof,” which means they are likely to withstand extreme climates anywhere in the United States.

** These plants require a minimum soil depth of 6 inches.

Plant List Source: Robin Andrews, Greenbuild Division of Saul Nurseries and ItSaul Plants in Alpharetta, Ga.

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