The Sky Garden Intensive Green Roof system is designed to use a soil-base that will compliment the plants selected for the Green Roof.  This means that several different soil mixes may be appropriate for a Sky Garden depending on the plants selted.  However, G-SKY has developed a lightweight soil mix that will support 95% of all plants on the roof environment for decades.  Roof Soil™ is a lightweight specially-mixed soil with a saturated weight of only 44~50 lbs/ft³ (specific gravity = 0.7~0.8)! It is almost half the weight of traditional landscape soil or naturally-occurring soil.

The G-SKY Extensive Green Roof System is designed to use Roof Soil™ 2, a lightweight specially-mixed soil.  

 


Roof Soil™ products are comprised of completely natural 100% organic materials.  They consist of naturally-derived pumice, USGA well-graded sand and aged composted bark mulch.  Because of their natural states, none of these materials require the use of fossil-fuels in their production.  Because of their lightweights, use of fuels in derivation, transport and mixing is very low, resulting in the CO₂ production volume to install Roof Soil™ products on roofs or the ground much less than to install traditional landscaping soils or naturally occuring soils.


Roof Soil™ products are approximately one half the weight of regular landscaping or naturally-occurring soils which significantly reduces their burden on a building.


EPA Clean Water Act: 30mm and 100mm rain storms were simulated onto beds of Roof Soil™ products.  The quality of the drained water was well above the water quality standards dictated by the EPA's Clean Water Act for all contaminants in surface waters. 

Skin Abrasion Test: Due to the increase in Green Roof and balcony popularity, the number of people coming into contact with soil products is increasing.  Several of the soils used for Green Roofs contain substances such as artificial fertilizers or mycorrihizae inoculants to produce a healthy growth environment for plants, but are toxic or harmful to humans.  Roof Soil™ products were tested for these substances and its toxicity towards humans in several skin stimulus tests.  In dry and wet condition soil to skin tests, Roof Soil™ products produced no sign of erythema (redness of the skin caused by dilation and congestion of the capillaries), scabbing or anasarca (accumulation of fluids in the skin tissue).  Roof Soil™ products are considered safe for general handling without the need for further protection. 

Toxicity Report:  Roof Soil™ products were tested on mice to identify toxicity if ingested.  In all cases, no abnormal weight, movement ability or breathing ability changes were noted.  All internal organs were in perfect health and there was no sign of toxicity in the internal organs of the mice.  Roof Soil™ products are not harmful to humans if ingested.


Roof Soil™ products have a good water holding capacity without compromising permeability.  In addition, it is a very structurally stable soil.  If properly blown and compacted into place,  it can be safely installed on 30~35° slopes with little to no additional soil support structures installed.


Installing soil onto a building requires careful planning and established installation/safety protocols.  During installation, soil can easily be scattered by the wind causing damage or annoyances to neighboring buildings and the streets below.  Roof Soil™ products are delivered slightly damp in order to prevent scattering in the wind.  Furthermore, Roof Soil™ is unlike natural soil in that it does not become muddy in the rain, therefore making installation in the rain possible.    


Roof Soil™ used on Sky Garden Green Roofs is designed to suit the growth conditions of 95% of all plants while still being lightweight.  If particularily odd plants are used, a specially designed soil mix may need to be employed.

The soil used on a G-SKY Green Roof, which employs a thin soil-base, must be designed to provide drought tolerant/shallow rooted plants a healthy growth environment, has an adequate available moisture content for the plants (when used in conjunction with G-SKY Drain) and drains quickly enough to prevent root rot.

Presented below is a summary of the differences between Roof Soil™, Roof Soil™ 2 and naturally-occurring soils.

Roof Soil™ Products Compositions:
                   1)  Roof Soil™     :  Pumice, USGA Well-Graded Sand, Aged Bark Compost
                   2)  Roof Soil™ 2  :  Pumice, Aged Bark Compost


Chart Description

1)  What is the Fully-saturated Weight (pF 1.8) value?
	This value, pF 1.8, represents the weight of the soil when the soil is has reached the water saturation point where it can no longer hold water within its structure withstanding the force of gravity.  A pF curve defines soils moisture characteristics: {a} amount of water available for plants and {b} available water capacity of the soil. A value of ‘pF 1.8’ is a soils “field capacity”, the maximum amount of water a soil can hold withstanding gravity. ‘pF 4.2’ is the “permanent wilting point”, which is when the soil is so dry that plants roots can no longer generate sufficient suction to obtain further water from the soil, and therefore begin to wilt.  See the chart in question 3 for more details.
2) What is the Three-Phase Distribution Ratio?
	Soil is a three-phase, porous media, composed of solids, liquids, and voids (empty spaces between the solids). This ratio describes the structure of the soil quantitatively.  It exposes the soils compaction ratio, provides a method by which to calculate the water holding capacity, and water/air permeability.  The typical amount of total porosity (ratio of void volume to total volume) in a mineral soil ranges from about 40% to 60%. This means approximately 40 to 60% of the volume of a mineral soil is actually empty space between the solid particles (voids).  These voids are filled with air and/or water. The air of soil is quite different that that in the atmosphere.  In the atmosphere, oxygen comprises about 21% and carbon dioxide comprises about 0.36%. However, in the soil, the oxygen levels are generally less than atmospheric levels and the carbon dioxide levels are generally greater than atmospheric levels (with the major of the air consisting of nitrogen gas, ~78%).  Furthermore, the air in soil has a relative humidity of almost 100% all of the time (relative humidity is the amount of water vapor actually in the air relative to the amount air can hold at a given temperature). Below is a description of each phases: (1)  Solid Phase: If the solid phase ratio is too high then space for roots to grow become limited and growth is stunted. (2)  Void:  If the void phase ratio is high the roots cannot absorb oxygen due to excess moisture and root rot occurs. (3)  Liquid:  If the liquid phase ratio is high, the soil will easily dry out, and the plants will wither. Roof Soil products are closest in its physical characteristics to Volcanic Ash Soil, the most fertile soil in the world.  Sand-based soils have little moisture and a great deal of air making them unsuitable.  Alluvial and Diluvial soils consist of far too much solid material to support healthy root growth making them also unsuitable.
3) What is the Available Moisture Capacity of soil?
	What does it mean to measure the soils fully-saturated weight at pF 1.8?  The moisture state of soil between being wet and dry is described by this chart: It is important to keep the soils moisture above its wilting point, pF 1.8~3.0, in order to not place stress on the plants.  Capillary action of water stops around pF 2.7~3.0 providing little benefits to the roots of the plants unless they are in direct contact with the water in its stopped state.  Water is actively moving by capillary action in soil around pF 1.8~3.0, and therefore when an adequate volume of water exists in the soil to allow for movement by capillary action, it is referred to as the soil's "effective water content". It is important to note that the moisture characteristics of soil are effected by several factors: - Rock Fragments: reduce capacity in direct proportion to their size (i.e. gravel), unless the rocks are porous (i.e. pumice or lava rock) - Organic Matter: increases water capacity.  The type dictates how much will be increased by the quantity added, however, approximately 1% of organic matter increases the available water capacity by 1.5%  - Bulk Density:  dictates pore space available to hold water.  High bulk densities tend to lower available water capacity. - Osmotic Pressure: equal to 0.3~0.4 times the electrical conductivity in mmhos/cm.  Reduces the available water capacity when the electrical conductivity is 8 mmhos/cm or more. - Texture: different types of soil textures effect available water capacity.  Sandy soils have a low capacity, but as silts and clays are added to the soil the capacity increases significantly.
4) What is the Permeability Coefficient of soil?
	The permeability coefficient of soil represents the speed at which water can travel through the soil, expressed in metric as centimeters per second, this value is never expressed in imperial inch/sec units.  Permeability rates allows us to calculate irrigation system requirements and drainage.  The relation between the permeability coefficient and a soil's water permeability is as follows: Permeability Coefficient (cm/s) Soil's Water Permeability Comparable To: 10-2 Excellent Clean Sand 10-3 Good Clean Sand 10-4 Good Mixed Sand 10-5 Low Dirty Sand 10-6 Almost Impervious Heavy Silts 10-7 Impervious Hard Clay Natural soil and traditional landscaping soil permeability changes drastically from soil to soil, however, Roof Soil™ products have consistent permeability coefficients of 10-2 and 10-4.
5) pH (H2O)?
	pH of soil is measured by passing a distilled water through soil to expose the soils pH(H2O).  It is also often measured using a potassium chloride solution and in these cases is expressed as pH(KCl). The effect of soil pH is great on the solubility of minerals or nutrients. Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil+water solution. Most minerals and nutrients are more soluble or available in slightly acid (5.0~7.0) soils than in neutral (7.0) or slightly alkaline (>7.0) soils. Phosphorus is never readily soluble in the soil but is most available in soil with a pH range centered around 6.5. Extremely and strongly acid soils (pH 4.0~5.0) can have high concentrations of soluble aluminum, iron and manganese which may be toxic to the growth of some plants. A pH range of approximately 6.0~7.0 promotes the most readily availability of plant nutrients.  Roof Soil™ products have a pH of 6.0~7.0.
6) What is the Cation Exchange Capacity?
	Represents a soils ability to hold nutrients. The CEC of a soil is not easily adjusted and therefore must be designed into the soil mix.  If this value is high, the ability for plants to absorb nutrients increases. If it is low, adding fertilizer may be a wasted exercise and plant growth, flowering and seeding will be very low.  A good value for Green Roof soil is 6me+.