recommended readings


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Books are reviewed by Publisher Linda S. Velazquez unless otherwise noted.

April 2008
guest recommended readings

The NRCA Green Roof Systems Manual—2007 Edition

The NRCA Green Roof Systems Manual 2007 Edition
A green roofing resource

By James R. Kirby, AIA
Graphics Courtesy Professional Roofing Magazine

Publisher's Note:  This article was originally printed in the April 2008 issue of Professional Roofing Magazine, published by the NRCA.
Reprinted with Permission, © Copyright 2008 National Roofing Contractors Association

With the proliferation of the sustainability movement within the construction industry, green roofing is touted as one of the ways to make roof systems more environmentally friendly. Recognizing this trend, NRCA began developing a green roofing manual in 2004. And in 2007, NRCA published The NRCA Green Roof Systems Manual—2007 Edition.

The manual provides in-depth information about green roof system projects. The information contained in the manual was developed by NRCA member contractors and applies to roofing contractors, designers, manufacturers, and third-party individuals involved with green roof system design and installation.

Although some information is provided about green roof system components, such as drainage layers, moisture-retention layers and filter fabric, if you use the manual, you primarily will find specific information about selection, design and installation of waterproofing membranes appropriate for green roof systems.

The manual

The manual is divided into four main sections: General Green Roof Project Considerations, Green Roof System Guidelines, Green Roof System Construction Details and Glossary.


The General Green Roof Project Considerations section provides an overview of general information concerning the design and installation of quality green roof systems. The information is intended to complement The NRCA Roofing Manual series and should be used as a guideline to prepare proper specifications.

The manual defines a green roof system as "a roof area of plantings/landscaping installed above a waterproofed substrate at any building level that is separated from the ground beneath it by a man-made structure. A green roof system consists of a waterproofing system and its associated components—such as protection course, root barrier, drainage layer, thermal insulation and aeration layer—and an overburden of growth medium and plantings."

As with all roof system types, proper design, quality materials and quality workmanship are needed to achieve a green roof system that will perform satisfactorily for its anticipated service life. Appropriate maintenance during a green roof system's service life also is necessary to ensure its success.

Also provided in the General Green Roof Project Considerations section is information about pre-bid and pre-job conferences; material storage and handling; temporary green roof waterproofing systems; weather considerations (such as high- and low-temperature installation, wind and precipitation); deck and structural design considerations; surface inspection; slope and drainage; expansion joints and control joints; curbs and penetrations; flashings (such as membrane base flashings, sheet-metal counterflashings and terminations); quality assurance and water testing; overburden; warranties; and recommendations for building owners.


The Green Roof System Guidelines section provides in-depth technical information about green roof systems' design and installation; however, NRCA recognizes green roof system practices vary considerably throughout the U.S. because of the variety of conditions that exist and various roofing materials available.

Selected plant varieties commonly dictate a green roof system's necessary depth of growth medium. This also helps guide the specific component design.

Of course, when reroofing with a green roof system, a roof deck's structural capacity should be considered. Because of the varying depths of growth medium, NRCA's manual divides green roof systems into the following three primary categories:

  • Extensive (shallow): a green roof system with an engineered soil-based growth medium approximately 2 to 6 inches deep
  • Semi-intensive (moderate depth): a green roof system with an engineered soil-based growth medium approximately 6 to 10 inches deep
  • Intensive (deep): a green roof system with an engineered soil-based growth medium greater than 10 inches deep

A fundamental idea behind the manual's development is that a green roof system is a combination of waterproofing and roofing concepts. Because a green roof system is likely to have moisture present within the system most or all the time, NRCA considers a waterproofing membrane appropriate. And because green roof systems include detailing similar to all other roof system types (parapet walls and roof drains, for example), construction details for green roof system waterproofing membranes are based on termination concepts NRCA considers appropriate for all roof system types.

Graphic Courtesy of Professional Roofing Magazine

A semi-intensive (moderate depth) green roof system

Performance attributes, environmental features and common system components for green roof systems are included in the manual, as well. Possible performance attributes include increased thermal efficiency, noise reduction and extended membrane service life. Likely performance attributes are stormwater management, increased efficiency of roof-mounted photovoltaic panels and aesthetic benefits. Economic benefits, as well as LEED® (Leadership in Energy and Environmental Design) benefits, also may be realized.

The manual's green roof system details provide design and installation information for:

  • Hot-fluid-applied polymer-modified asphalt membranes
  • APP and SBS polymer-modified bitumen sheet membranes
  • EPDM membranes
  • Polyvinyl chloride membranes
  • One- and two-component fluid-applied elastomeric membranes

Specific installation parameters, including minimum membrane thickness and ambient temperature recommendations, are provided for each recommended green roof system waterproofing membrane type. ASTM International standards for materials and application are provided where appropriate.

NRCA recommends membranes be adhered to decks to provide the most stable substrate for green roof system waterproofing membranes. Therefore, thermal insulation used in a green roof system is installed above the membrane or below the roof deck. Positive drainage should be provided by sloping the structural deck.

Construction details

The manual's Green Roof System Construction Details section provides technical information and construction details concerning the design and installation of quality green roof systems. The section's introduction is intended to supplement the special notes on the individual construction details by providing additional information about green roof system components and deck types.

For each membrane type, construction details are provided for eight common conditions. The details are arranged according to membrane type to assist roofing contractors with the submittal process. Additionally, details are provided for substrate crack preparation, nonmoving cold joints, cementitious board joints, sidewall penetrations, area dividers and paver edges.

Graphic Courtesy of Professional Roofing Magazine

Low parapet flashing for thermoplastic waterproofing membrane—extensive (shallow) green roof system

Construction detail concepts for green roof waterproofing membranes are similar to those pertaining to common roof system types. Some similarities follow:

  • Membrane base flashings are recommended to be a minimum of 8 inches above the surface of the membrane and 4 inches above the overburden's top surface. For green roof systems, mechanical protection is recommended.
  • Sheet-metal rain collars are recommended for penetration details, and soft-metal pipe flashing is recommended for vent stacks.
  • Sheet-metal counterflashing is recommended for membrane terminations at skylights, scuttles and smoke vents.
  • Sheet-metal expansion joint covers that provide movement capability are recommended; however, for green roof systems, expansion joints should be formed of concrete.
  • Drain details include membrane compressed between the drain bowl and clamping ring.
  • Sheet-metal copings are recommended to include a continuous front cleat and appropriate fastening in the back face. The coping's uplift resistance should meet building code requirements.

NRCA believes an important part of a green roof system project is the verification of the integrity of the system's waterproofing membrane. Before subsequent application of necessary components—from root barrier to growth medium—NRCA strongly recommends a water test be performed.

A water test may consist of a flood test or flowing water test depending on the structural capacity of the deck and slope; each typically lasts a minimum of 24 hours. A water test documents the performance of a green roof system's waterproofing membrane before placement of system components. A water-test verification form is provided in the manual.

A valuable resource

I encourage specifiers, manufacturers and installers of green roof systems to reference The NRCA Green Roof Systems Manual—2007 Edition when designing and constructing green roof systems.

The manual also is available on CD-ROM. The CD-ROM version contains CAD-formatted construction details intended to be altered to meet specific project parameters. To purchase the manual, log on to or call NRCA's Customer Service Department at (866) ASK-NRCA (275-6722).
James R. Kirby, AIA, is NRCA's associate executive director of technical communications.

Publisher's Note: You can reach Jim at:  See this article online at Professional Roofing Magazine here.

March 2008

BUILDING GREENer - Guidance on the use of green roofs, green walls and complementary features on buildings


BUILDING GREENer - Guidance on the use of green roofs, green walls and complementary features on buildings (C644), by Paul Early, Dusty Gedge, John Newton, and Steve Wilson, 2007 from CIRIA, London, England.

Once again from the United Kingdom comes another must-have advice and guide book to be added to our green building reference arsenal.  Published by CIRIA, the Construction Industry Research and Information Association - a not for profit UK organization which "manages collaborative research and produces information aimed at providing best practice solutions to industry problems" - the book is written by well known and respected environmental design leaders.  John Newton hails from Ecology Consultancy, Dusty Gedge and Paul Early from, and Steve Wilson from the Environmental Protection Group (EPG).

Condensed Research
The authors jointly present BUILDING GREENer - Guidance on the use of green roofs, green walls and complementary features on buildings as a comprehensive assessment of published research and information on living roofs and walls, and how such low tech features as nesting boxes can easily be incorporated to encourage greater biodiversity in our building construction practices.

Complexities & Considerations, Policies & Legislation
The 197-page book is cleanly and well-organized, and the style is formatted quasi-scientifically, ie. divided into sections, and is extremely easy to follow.  Divided into four parts consisting of Introduction and Background, Green Roofs, Green Walls, and Nestboxes and other Complementary Features, BUILDING GREENer offers readers many learning tools along the way.  Figures and tables, boxes, and full-color international case studies for illustration highlight each area of learning, and icons alert the reader to case study/examples, regulations or policy, and to cross references with other important guidances.  At the end of each section, a highlighted green "Key Points" box lists the main concepts, bullet style.  And the guide further includes numerous appendices, a glossary, and a list of references.

In Part A we are introduced to the various concepts and contexts.  Challenges of acceptance and integration are addressed as well as the importance of biodiversity and stormwater to urban areas; climate change, mitigation, and adaptation, and the rationality - referring specifically to the various UK climates, but of course the message is clear that this approach can be applied universally.  The unique, special attributes of a site must always be taken into consideration, and the authors emphasize the advantages of hiring a local ecologist as part of the design team.

UK policy and legislation pertaining to the greening of roofs and walls is discussed in relation to wildlife protection, the water framework directive, planning policy framework, biodiversity action planning, building regulations and standards, as well as other initiatives.  But the meat of BUILDING GREENer, a full 105 pages, is dedicated to understanding the complexities and considerations of planning and design, development, and construction, and maintenance of these living vegetated structures.

Impressive in scope is Part B on greenroofs.  Critical issues of greenroof operation are pointed out in seven chapters along with review of the history, advantages, and an informative comparison of conventional roofs to different types of greenroofs.  Graphics in this section are particularly helpful and descriptive, and allow for easy reference.  It is interesting to note that window boxes, balconies, and planters are included as important elements for greening a building.  Along with all the segments touting the great benefits and potential of greenroofs, certain limitations are also discussed.  "Sustainable Drainage Systems," or SUDS, is a UK term for surface water drainage systems that follow principles of sustainable development.  A whole chapter is devoted to showing how greenroofs can contribute to the control of runoff near its source through reducing the peak rate as well as total volume.

Biodiversity is a Key Factor
A key focus of the book's green development aspect is the biodiversity factor for both flora and fauna.  Detailed overviews of current research is provided through case studies, the appendices as well as in the Key Points boxes at the end of the sub-chapters.  The authors point out that considerable research on the subject is underway to further evaluate which greenroof plant ecologies will benefit various communities.  Mosses, plant species for dry meadows and Alpine environments, and even rare species of orchids are touched upon.  On the fauna side, the research of rare invertebrates include bees, spiders, wasps, and beetles is cited, alongside nine bird species.

Although only two chapters in Part C are devoted to green walls, the same attention to detail to the subject is covered as with living roofs, with overviews of history, benefits, the various types of vegetated walls, applications, appropriate plant species, design considerations, how-to's, etc.  And I found it very refreshing to read about some of the complementary features available to further enhance the biodiversity factor in green buildings.  I would bet that most architects and designers, let alone city planners, ever consider the habitats of our flying friends in the design of a building.  Part D discusses how birds, bats, insects, and other invertebrates are an essential element of the natural environment, and how we can easily integrate low cost nesting and roosting structures in our designs.  Many of these are displaced through development, and we can help sustain their habitats by attaching various types of small boxes to existing buildings, or even incorporate them as nest "bricks" or bat voids during construction.  Nestboxes and other roosting habitats are truly complementary to both greenroofs and green walls in that they will further encourage the species designed to attract greater biodiversity to the site.

As a designer, I found Chapter 10 "Green Roof Design Considerations," section 10.2, Design for Biodiversity, particularly useful for breaking down feasibility and constraints, types of substrates and vegetation, and other landscape features, as these were presented as questions the designer must ask him or herself.  Equally beneficial is Chapter 13 "Green Wall Design and Maintenance Considerations," section 13.1, Standards and Regulations to the designers.  Clear design objectives and design criteria should always inform the design process!  Overall, the message for both greenroofs and green walls is that designing to encourage biodiversity or to meet specific community or species objectives must be site specific and relative to local habitats.  And adding nest boxes as complementary features is a simple way to mitigate just a bit of our ever increasing destruction of habitat through construction practices.

A Must-Have for Ecological Designers
BUILDING GREENer - Guidance on the use of green roofs, green walls and complementary features on buildings
is really a wonderful example of the term "guidance."  The meticulous attention to research and care that went into the preparation and execution of this book by authors Newton, Gedge, Early, and Wilson is evident throughout.  And the importance of the excellent reference material cannot be overstated!  Who should read it and why?  CIRIA's website, see below, answers, "The guidance is intended for use by those who require independent advice on the planning, design, construction and maintenance of green roofs, green walls and other biodiversity features.  In particular the document aims to dispel myths for clients and designers and to enable planners to maximise the benefit of design options."

I highly recommend BUILDING GREENer to readers across the board as it offers pertinent information with an inspirational bent to the UK market as well as the worldwide.  Make sure to stay up to date at the website,, where you can also purchase BUILDING GREENer - Guidance on the use of green roofs, green walls and complementary features on buildings (C644).

Enjoy ~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant

January 2008

Click here to purchase for the Sale Price: $23.07

Rain Gardens: Managing water sustainably in the garden and designed landscape, by Nigel Dunnett and Andy Clayden, 2007 from Timber Press, Portland, OR.

In our changing global climate, water is increasingly becoming a limited world resource, and ecologically-informed designers, government officials and homeowners are imperative in order to promote and protect the health and lasting beauty of our landscapes.  Although large scale planning is necessary, we can also create small scale solutions to slow down, capture, divert, and channel rainfall to meet our needs.  Sustainable design is responsible design, and as we continue exploring ways to lessen our developmental impacts on Earth, it is especially important to celebrate those methods which are relatively low-tech and affordable to maximize their implementation.

With low impact development (LID) techniques and environmental education on the rise among city planners, architects, landscape architects, and other design professionals, Nigel Dunnett and Andy Clayden have written a timely, no-nonsense practical offering to enlighten and satisfy both the domestic and public sectors about how to make the most of rainwater with Rain Gardens – Managing water sustainably in the garden and designed landscape.

Rain Gardens are Much More than Planted Depressions
Rain Gardens enhances the traditional notion of a planted depression to include a wider ranging definition, concentrating on elements and techniques which mimic natural lake or wetland dynamics.  Nigel and Andy have produced an easy to understand, informative, and authoritative book on the design and function of rain gardens, through all their many forms ~ from various depressed, sunken planted areas for rainwater infiltration and storage at ground level to living vegetated roofs at roofscape level.  We are introduced to basic engineering details and landscape design principles, technique options, plant lists, and maintenance advice for home gardeners and designers alike, with numerous sketches and graphics, color photos, terminology, examples and case studies from the United States and northern Europe, including Portland, OR, Illinois, Malmo, Berlin, and the UK.

Plants as a Low Impact Development Management Technique
The authors present rain gardens as an opportunity to manage and optimize rainwater as an environmentally friendly LID in an environmentally beneficial manner – through the water absorption/retention capabilities of vegetation.  Vegetation is the essential element to slow down the path of stormwater and to filter contaminants running off from impervious surfaces, and the beauty is that rain gardens can be incorporated in most settings with a basic understanding of the site topography, available options, appropriate plantings and local materials, all at little cost.  Some of the additional benefits of making the flow of water visible through planting rain gardens are enhanced pride of ownership, increased visual and sensory pleasure, opportunities for lush naturalistic plantings, as well as habitats for a greater diversity of wildlife.  See more reasons for the case for rain gardens in the green box below, from the authors themselves.

Organized into three main chapters, Section 1 of Rain Gardens introduces us to the history and concept of rain gardens, the interconnectivity of site features, and the flow of water: Water and Sustainable Landscapes, Water in a Changing Climate, Bioretention, and includes an introduction to The Stormwater Chain.

Section 2 delves deeper into The Stormwater Chain as its own subject and explores the following in-depth: General Design Principles for Bioretention Facilities, Green Roofs, Capturing Water Run-off: disconnecting Downpipes, Designing Your Rain Garden, Site Survey, and Setting Out a Design.

A full 23 pages of Rain Gardens is devoted to greenroofs, and they are one of the more high-tech solutions offered.  The authors note that living roofs are usually found on larger commercial buildings, but emphasize the huge opportunity for greening our smaller structures, such as garden sheds, summer houses, etc.  Engineering/roof loading and waterproofing
guidance is encouraged before proceeding, but design is presented in a simple fashion.  Advice is given on modifying a commercial system and small do-it yourself projects offering material options, including planting options for domestic applications.  Overall, greenroofs are highlighted as one underused element in the stormwater chain.

Section 3 is a Plant Directory for rain gardens and other rainwater infiltration features and the authors emphasize that many plants are potential candidates but all must be able to withstand periodic swings between wet and dry, and therefore detailed information pertaining to each particular site must be sensitively researched.  Presented in chart form, the plant types include: Herbaceous Plants, Grasses, Shrubs, and Trees, and each species lists the common name, origin, height, color, bloom time, moisture tolerance and notes.

Advocating Further Education of the Stormwater Chain
Although rain gardens can be applied at a wide range of scales, they are becoming ever popular as simple, small scale garden solutions that can readily affect our neighborhood environments and benefit people, flora and fauna.  I think it would be highly beneficial to emphasize these principles of The Stormwater Chain and how our landscapes are interconnected and affected by development to educators and parents of our elementary and middle school students, not to mention to developers and others in the construction industry.

Kudos and Praise
I just have to say that I love this book!  It comes across clean and simple, not self-important or preachy.  Kudos to Nigel and Andy for creating such a detailed and comprehensive guide, and for crediting Tom Liptan of the City of Portland as not only their inspiration, but as a leader in promoting rain gardens, ecoroofs, and all forms of sustainable stormwater design.  Tom has done more than just about anyone out there to personally affect how we see stormwater and how we can collaborate with nature to manage it.

And the personal observations of the writers’ experience as designers themselves and fathers of young children regarding the importance of designing secure but fun, interactive water design is refreshing.  The attention to detail and expertise level of Nigel Dunnett and Andy Clayden is clearly evident from how they guide the reader through informed decision-making and with each thoughtfully explained case study, definition, and photo credit and graphic illustration.  And I must say that Andy’s illustrations are great - talented and keen.

I believe the Rain Gardens Plant Directory is excellent, and really builds on the success and example of Nigel Dunnett and Noël Kingsbury’s 2004 Planting Green Roofs and Living Walls (see review below) plant list for greenroofs.  The Plant Directory chart is extremely well organized and highly useful in a wide range of rain garden schemes and will prove to be an immeasurable success as a resource in its own right.

Rain Gardens are Practical, Pleasurable and Sustainable
Nigel and Andy emphasize that although rain gardens are a relatively new concept, they follow the natural water cycle and any design element which encourages greater diversity of vegetation and less impervious cover is simply great responsible design. When we design gardens, landscapes, or green roofscapes for that matter, appealing to our inner nature responds to our connection with the natural world and our sense of place becomes greater - we derive more pleasure from taking care of these spaces, and therefore we create sustainable places, too.  I found Rain Gardens: Managing water sustainably in the garden and designed landscape to be inspirational and educational, and recommend it wholeheartedly to students, gardeners, and designers of all ages and all levels of sophistication.

~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant


Rain Gardens: Managing water sustainably in the garden and designed landscape, by Nigel Dunnett and Andy Clayden (Timber Press 2007,, ISBN-13: 978-0-88192-826-6, $34.95).


Small scale actions have impact too! Creating your own rain garden is relatively simple to do and beneficial to both the environment, people and wildlife.

Reasons to create your own rain garden:

1.  Rain gardens are good for wildlife and biodiversity:

-- Rain gardens are largely composed of flowering perennials and grasses-and ideal mix for encouraging a great diversity of wildlife.
--They support microorganisms we can't always see, allowing the larger components of wildlife to thrive.

2.  Rain gardens provide visual and sensory pleasure:

--There is a theory that our fascination with water is a result of our evolutionary history-that we have been left with an instinctive attraction to all types of water.
--Rain gardens cultivate a landscape's maximum growth potential and allow a garden's visually pleasing elements to prosper.

3.  Rain gardens are good for play:

--From waterfalls to fountains, water used to create a coherent design also creates opportunity for interactions and play.
--One of the most important aspects of designing with water is its huge potential to both animate and bring life to a landscape.

4.  Rain gardens are beneficial to a garden's microclimate and the environment:

--Any approach that substitutes plants and vegetation for hard paved surfaces has a cooling effect on the summer landscape.
--Rain gardens capture and re-direct water run-off, reducing flooding, pollution problems, and environmental damage.



March 2007

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Green Roof Plants: A Resource and Planting Guide, by Edmund C. Snodgrass and Lucie L. Snodgrass, 2006 from Timber Press, Portland, OR.

Ed and Lucie Snodgrass have successfully taken on the daunting task of researching and compiling a North American climatic-wide palette of proven greenroof plants encompassing USDA hardiness zones 2 - 9, now sharing their expertise with this wonderful compilation from personal experience. As co-owners of Emory Knoll Farms, a wholesale nursery devoted to none-other than extensive greenroof plants, they speak from a first hand working understanding and through years of species trial and error, with hundreds of greenroof projects specified and planted with their nursery stock.

Yet Green Roof Plants is not just about the plants; although they remain the focus, the book serves as an insightful historic and design resource as well as greenroof planting guide for beginners and experts alike.  The authors point out that roofs are one critical source of climatic problems in our highly developed cities and in terms of greenroof infrastructure, their sheer mass offers us a viable and attractive mitigation solution on a grand scale.

Practical and Insightful Background Information
Comprehensive in scope, a considerable amount of effort has been placed on examining greenroof fundamentals and prior to delving into plant types, colors, selection, forms, root systems and other vegetative specifics, necessary background information is discussed, specifically the benefits, challenges, construction considerations, various system components and types, and the often times overlooked site-specific concerns.

We are urged to alter our misplaced ideas that greenroofs are similar to gardens at grade and numerous site factors must influence the design including issues pertaining to roof microclimates, irrigation needs, inorganic engineered soils, and both native and introduced species whose cultural requirements must be taken into account.  To name but a few other topics, growing media composition and depth, plant nutrition, and installation methods and complete proper plant establishment methods are elegantly presented.

Function Follows Design, and Let the Site Inform the Designers
From the design side, the authors emphasize the need to articulate the greenroof’s primary use and purpose prior to planning and design, which in turn will drive the entire design process.  For example, are you designing for stormwater retention, or for pure aesthetics?  The two may not be necessarily at odds but they can be, and hence it is important to know the appropriate plants which can perform all the required and desired functions, without sacrificing one for the other.

Proven Successes and Trial and Error
As relatively young an industry as we still are, the North American greenroof community has been studying and utilizing a great variety of suitable plants on roofs, with varying degrees of success for the last decade or so.  Through trial test greenroofs we have come to rely on certain proven European plant types to ensure a high degree of success, and the Snodgrass’s build on this established research by encompassing their own experience plus some new  species and tailor it to our needs by expanding our vegetative horizons with new plants for our consideration.

The authors also open a dialogue for consideration into further plant studies among native North American communities which might fare well under the harsh climactic extremes necessary to survive on a decidedly unnatural greenroof environment.

The "Extensive Greenroof Plant Bible"
The beauty of Green Roof Plants lies in its concise, clear, and extensive (no pun intended!) coverage of the authors’ years of knowledge.  Chapters 3 and 4 hold the true golden worth of this thorough plant resource guide, full of complete plant profiles and color photos.  Alphabetically listed by genus, the authors have provided a wealth of information on more than 200 naturalized and native plants, including xeric, herbaceous perennials, and hardy succulents, especially the extremely tolerant Sedums and Delospermas.

Each plant description assists the user by listing the following:  Flower color and bloom time; foliage color; hardiness zone; category type - groundcover or accent; the plant's ability to self seed; origin and/or North American naturalization; height; spread; planting medium minimum; sun requirements, plus comments regarding other pertinent or particular characteristics of interest.  At the back of the book there is a very useful Directory of Plants by Color and Type, listed by botanical names - great when in the midst of designing!

Green Roof Plants: A Resource and Planting Guide should be considered the "Extensive Greenroof Plant Bible"; simply put, Green Roof Plants is an easy, reliable reference and a practical must-have handbook for all of us in the greenroof industry, weathered professionals or novice do-it-your-selfers.

~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant

Publisher's NOTE: Make sure to read Ed Snodgrass' Q & A column "Ask Ed" here on - and send him your plant and horticulture questions to:

Read what Timber Press has to say:

"Green Roof Plants: A Resource and Planting Guide," by Edmund C. Snodgrass and Lucie L. Snodgrass, 2006. "Despite the high level of interest in green roofs, until now there has been no reliable reference devoted exclusively to the various species of drought-tolerant plants that are suitable for use on extensive green roofs.  Green Roof Plants: A Resource and Planting Guide fills that void.  The book contains photographs and cultural information for more than 220 species and cultivars of plants.  Although many of the plants might be expected to tolerate rooftop conditions, such as the low-growing sedums, others will come as a pleasant surprise, such as dwarf alliums and campanulas..."

Download the Timber Press Promo Flyer here. You can order it from Timber Press or save some money and order it here from at the discounted price of only $19.77.

Click here to buy on

June 2004

Planting Green Roofs and Living Walls, by Nigel Dunnett and Noël Kingsbury.  2004, revised and updated 2008, from Timber Press, Portland, OR.

Greenroof professionals and enthusiasts alike will be delighted with the easy reading and scope of content offered in “Planting Green Roofs and Living Walls” by Nigel Dunnett and Noël Kingsbury.  Very well organized, the book’s forte and major value is as an essential resource - especially in terms of plant description, characteristics and specification.  It’s also a great bargain in that the book is filled with color photos, drawings, charts and reference material.  This indispensable hard cover reference guide contains a truly massive collection of appropriate plant information, and perhaps most importantly, extensive plant directories are provided for both greenroofs and façade greening.

Organic Architecture with Plants
Greenroofs, living walls, and various other bio-engineering techniques are introduced and the authors cite the associated benefits and reasons why we should be integrating these measures of organic architecture into our built environments.  The authors refer to current international research and technology; background and history are touched on; and benefits and applications of these “ecotechnologies” are discussed at length.  Yet, a “How-To Build” book this is not; basic principles are set out and tools for further research are provided.

Benefits at a Range of Scales
The section “Why Build Green Roofs?” explores hard evidence and the various benefits operating at a range of scales from amenity and aesthetic values to economic and environmental aspects.  Increased roof life, insulation and energy efficiency, green building assessment and public relations, biodiversity and wildlife value, water management, air pollution, and fire prevention and risks are discussed with supporting evidence.

Although previously well known, the biodiversity and wildlife value of greenroofs is expanded upon here, including the new British models of ”brown” or “rubble” greenroofs – those which recreate the thin, infertile landscapes of disturbed brownfield sites.  Spontaneous colonization is presented as an important natural occurrence.

A Vast Array of Planting Opportunities
The authors rightly note that “The majority of guides to green roofs and roof greening concentrate on the technical and construction aspects but have relatively little to say about planting opportunities – mainly because most authors are not plant specialists.”  Well, Noël – a well known writer of plants and gardens, and Nigel – a senior lecturer in the Department of Landscape at the University of Sheffield, most certainly are plant experts, and an entire 47-page chapter is devoted to the wide range of planting opportunities for extensive greenroofs, beyond the ubiquitous albeit hugely successful use of Sedum species.

Prevailing site conditions will always dictate the plant selection, so designers need to know what plant species will not only survive but thrive in extreme local conditions.  Desirable physical attributes of plants and how they may be established and managed are presented.  Considerations of monocultures, single plant combinations and mixtures, and plant communities are useful as planting design tools. The form and physiology of suitable greenroof plants are nicely covered from a botanical as well as functional and aesthetic perspective.  Issues of viewing considerations are pondered and design solutions are offered relating to the roof function and visual criteria.  “Methods of vegetation establishment” is particularly detailed and thus extremely valuable.   The authors point out, however, that current research is insufficient to show how long each species will live and how each species will interact over the years atop roofs.

The very important aspect of different growing medium properties and functions is addressed in-depth, and comments are provided about particular types of materials, substrate depths, and accompanying vegetative possibilities.  Maintenance issues and requirements are briefly noted, touching on feeding, plant protection, drainage, and weeding.

Considerations of Natives and Introduced Species
The unexploited opportunities of testing and using native vegetation are explored, in terms of increasing biodiversity and aesthetic benefits. Regionally native plants should be tested for many reasons, including ecological restoration.  Non-native plant species with invasive tendencies can be a problem, therefore careful selection is critical to maintain healthy ecosystems.  Yet many introduced species are appropriate, and there are many circumstances where non-natives offer considerable local wildlife value.

Certain natural plant communities and their soil types are explained and presented as an argument for further study as suitable models for successful roof plantings. Trialing of appropriate local plant communities is therefore recommended and encouraged so as ultimately to be able to introduce more natives into the greenroof matrix of plant species.

 “The natural habitats of potential roof-greening plants” explores the potential to discover and trial the world’s flora found in similar harsh habitats.  Mountain, high latitude, coastal, limestone, sclerophyllous woody vegetation, semi-desert environments, and species whose plants are exposed to climatic extremes are regions with potential for testing of new roof greening plants.

The Task Has Just Begun
Philosophy and advice to greenroof plant enthusiasts can be summed up with these reflections by the authors: “With roof greening becoming an important part of the new built environment, it is increasingly important that more attention is paid to sourcing new plant material from habitats in the wild where conditions approximate those on rooftops and other problem urban situations…The task of selecting suitable plant species for roof greening has arguably just begun, and it offers potentially enormous rewards.”

They are quick to point out that the globalization of our knowledge base and the ready availability of certain aggressive species can threaten entire ecosystems, and care must be provided to the selection of greenroof environments (just as at ground level) so as to avoid invasive and potentially destructive non-natives or introduced species.

Façade Greening and Living Wall Structures and Surfaces are the final two chapters of the book, offering both visual and ecological climbers, clingers, ramblers and scramblers.  New support structures, materials, technologies and details provide practical and interesting information for this older yet equally fascinating design element of green architecture.  The authors examine how the design of façade greening can equally disguise unattractive features while at the same time enhance existing surfaces.  In either case, education and care are necessary to promote vigorous growth that is supported by a variety of vertical and/or horizontal structures.

At the end of the book, 49 pages are devoted to the Roof-Greening and Façade-Greening Plant Directories, listed by botanical names, common names, cultivars and related species. The horticultural and cultural aspects are presented with definitions and listings of many specific plant characteristics.

A minor grumbling on my part about the book is the absence of identifying greenroof project photo captions for the geographic locations and the building application types.  It would be beneficial to know not only where each is located, but also whether the project is commercial, industrial, residential, etc.

A Dovetailing of Living Plants, the Building, and Its Human Users
Whereas Ted Osmundson’s excellent 1999 “Roof Gardens: History, Design, and Construction” is considered the bible for the intensive greenroof crowd, Nigel Dunnett and Noel Kingsbury’s “Planting Green Roofs and Living Walls” is simply a must have for extensive and intensive greenroofers worldwide.

Planting Green Roofs and Living Walls” is a comprehensive argument for integrating nature and architecture, and I highly recommend it.  It’s obvious that Kingsbury and Dunnett are first and foremost dedicated, ecologically minded plantspeople; here, then, is a very important work for those of us in the greenroof industry. Buy it here on for only $24.46.

 Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant

NOTE:  Author/speaker Nigel Dunnett held the extremely successful book launch and signing for Planting Green Roofs and Living Walls at the Greening Rooftops for Sustainable Communities 2004 in Portland OR on June 4.  Congratulations Nigel, Noël, and Timber Press!

Click here to order through!

September 2003

Cradle to Cradle: Remaking the Way We Make Things, by William McDonough & Michael Braungart.  2002 from North Point Press, New York, NY. 

Here, the noted architect McDonough and environmental chemist Braungart have collaborated on a thoughtful and insightful holistic view of how Man designs things, or better yet, how we can design better.  Inspiring and eye-opening, if this book were required reading for teenagers, we might yet have a whole new generation eager to rethink design and engineering theory and practice.

"Form Follows Evolution"

The old environmental paradigm of "reduce, reuse, recycle" is rethought as "form follows evolution" - so we must optimize design by reinventing how we think of design to nourish rather than deplete the Earth: Imagine and design for a future of prosperity and health, now.  First, let's stop using obvious toxic materials and those that off-gas harmful substances.

Instead of designing products with minimal or zero harm to people and the environment, and being "less bad," we should design things with positive attributes that can actually nurture the Earth after its planned use - "being good."

Eco-Effective Design

Greenroofs are presented as one way to take an eco-effective approach towards the negative effects of a building's footprint, and point out how a building can give back to nature.

Why are we designing technology at the expense of our health and ecology?  The authors contend that if we modeled technology on natural systems, we would design our products to be restorative from the beginning to end for their intended biological and technical purposes.  The 'cradle to grave' manufacturing model needs to be challenged and replaced with a new philosophy.

"If humans are truly going to prosper, we will have to learn to imitate nature's highly effective cradle-to-cradle system of nutrient flow and metabolism, in which the very concept of waste does not exist," say the authors.

Even the book itself is eco-effective in that it is made of a plastic resin and inorganic fillers - it's also waterproof, durable and  widely recyclable, providing a prototype for the book as a "technical nutrient."

Cradle to Cradle is certainly recommended reading for students, environmentalists, leaders of business and industry, manufacturers, designers and visionaries alike.

~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant

Wrightscapes by Charles E. Aguar & Berdeana Aguar

July 2003
student book review by Jessten Murphy, UGA

W R I G H T S C A P E S - Frank Lloyd Wright's Landscape Designs, by Charles E. Aguar and Berdeana Aguar, 2002 from McGraw-Hill, New York, NY.

(Originally published in The Georgia Landscape 2003, Reprinted with Permission.)

The just-published book Wrightscapes documents the environmental designs of Frank Lloyd Wright. Authors Charles and Berdeana Aguar chronicle the life of this talented icon from his childhood in the harsh climates of Wisconsin through to his adult life in the warmer temperatures at Taliesin West in the Arizona desert.

The authors show Wright as having been extremely sensitive to site planning and other landscape-related issues. The Aguars detail how Frederick Law Olmsted, the Columbian Exposition, and the rebuilding of Chicago after the great fire of 1871 had a profound impact on the career of America's most famous architect.

Wrightscapes clearly delineates Wright's life into understandable stages and tackles each phase with a level of detail that is impressive since Wright's life has already been so well researched. To obtain their wealth of Wright knowledge, the authors conducted extensive site visits and studies, established personal relationships with former and present owners of Wright projects and created a productive relationship with the people of the Frank Lloyd Wright Foundation.

Wrightscapes will benefit those who believe landscape architects should strongly influence a site's design before the structural architecture is created. This book makes it clear that Wright took the landscape into consideration and consulted landscape architects, including the notable Jens Jensen, before designing houses and other buildings.

Wright's interest in innovative landscape design can be seen early on in his career with the design of his Oak Park home and studio, which he sited to take advantage of views, privacy, trees, vegetation and microclimates. He was also an ardent proponent of the Prairie School, a modern architectural design style that promoted the use of native plants and creating a sense of place within designed landscapes.

Taliesin, Frank Lloyd Wright's estate in Spring Green, Wisconsin, was one of his most mature landscape designs and upheld his Organic Architecture design principals. Wright took great pains to design the house and land into one element that combined American, Italian, and Japanese components of landscape design into one cohesive whole. The book points out that although Falling Water was his most famous design, it went against his Organic Architecture strategies. These design guidelines stated that architecture should be sited in a manner that lets the occupants enjoy the most prominent features of the site, instead of building on top of them. The in-depth study done on many of Wright's Organic Architecture design sites will benefit landscape architects because they show the importance that the sun, seasons, wind, and other natural parameters of the place play into designing our environment.

Wrightscapes may never have come to fruition without the persistence and dedication of Charles Aguar's wife Berdeana after the untimely death of her husband. Wright fans and landscape architects owe a great debt to her for this because without her diligence this important book may have never been published. Thanks to Berdeana, the world can enjoy a new book about Frank Lloyd Wright that is progressive and forward thinking, an extremely difficult feat to accomplish.

Unlike Wright, an architectural genius who realized fame and critical acclaim while living, it is sometimes difficult to assess a person's true accomplishments until after they have passed away. The extent a person impacts their community, profession and family can sometimes only be fully realized once they are gone. Such is the case with Charles Aguar who passed away before Wrightscapes was published. I have learned from many sources of Aguar's extreme devotion to his students, peers and his wife Berdeana, a bond that was undividable. Aguar also greatly impacted his community as seen through his contribution to the creation of Athens (GA) greenway.

He also contributed a great deal of research to the profession of landscape architecture including an in-depth study into the life and works of landscape designer Earle S. Draper, whom Aguar dubbed "the unsung hero of Southern (U.S.) landscape architecture." Aguar's most significant research legacy nevertheless will most likely be the work that he and Berdeana compiled into Wrightscapes.

Louisa May Allcat's 'A Trellis for Mr. Ellis'

September, 2002

A Trellis for Mr. Ellis, or How I Saved the World from Global Warming, by E. G. Ellis, 2002 from Allcat Press, San Diego, CA. Review:  Greening the planet and saving the world from global warming are the dreams of an abandoned cat in the delightful tale for children seven years and up, A Trellis for Mr. Ellis.

Louisa May Allcat decides she and her new owner, Mr. Ellis, need plants to clean and cool the air on their hot apartment balcony.  Soon, the entire neighborhood follows and a huge rainbow of flowers connects the community.  Louisa then dreams about greening the entire Earth by gardening in schools, on balconies, terraces, patios and rooftops.

Greening the Cityscape in 'A Trellis for Mr. Ellis'

Self-worth, responsibility, and empowerment are the enlightening attributes shared by the ecologically aware cat through colorful multi-media illustrations and simple earth friendly messages.  Truly a joy and inspiration, A Trellis for Mr. Ellis is an ideal opportunity for parents and teachers to introduce kids to the concept of global warming and the many benefits of plants and gardening.

~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant

Retail price is $8.95.  For ordering information and to learn more about plans for further adventures of Louisa May Allcat, please visit


December, 2001
Roof Gardens: History, Design, and Construction,
by Theodore Osmundson, FASLA. 1999 from W.W. Norton & Company, Inc., New York, London. inaugurates our new Recommended Readings column with this highly informative reference standard for roof garden aficionados and design professionals alike.  While Roof Gardens is clearly focused on the more traditional concept and practice of creating aesthetically pleasing garden space on flat roofs, Mr. Osmundson does address greenroof technology and the industry's advances in the field.  In particular, the German market is credited for testing and developing highly effective yet lightweight greenroof components and systems, and case studies are presented.

The veteran landscape architect shares his practical expertise of roof garden design, research and travel, and the richly illustrated hardcover book is full of photos, plans and construction details of sixty projects in North America, Europe, Australia and Japan.  Roof Gardens also offers a historical perspective and advice on site considerations, design elements, maintenance, and appendices of useful data and sources of supply and information.

Rooftop landscape architecture promises to greatly beautify our environment by greening our buildings.  We highly recommend this easy to understand, invaluable reference for anyone interested learning about in-depth roof garden design and construction, from homeowner to city planner.

~ Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant


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