Wednesday, July 20, 2011

Department of Interior and Native Plants on Green Roofs, Guidance for Historic Structures

I am proud the U.S Park Service, Department of the Interior's (DOI) headquarter building has a green roof.  This fact alone is an amazing statement towards the Department's commitment to sustainability.

On the other hand I am amused with their choice of plants, non-native species.

In defense of non-native landscape plants, many such as Sedum are extremely well behaved and proven to survive in harsh conditions.  Sedum is beautiful and Sedum is economically important to many green roof plant growers.

I am not bashing Sedum, lets get that out of the way up front.  Once this discussion gets started,  Sedum proponents immediately change the conversation from "Sedum is not a native" to "Sedum is not invasive and has been used for years".

The underlying issue here lies not even in the fact that the U.S. National Park Department of Interior's main headquarters building in our Capital possesses a green roof with a non-U.S. native (though there are a few native Sedum species in the U.S. they are not used on the roof) plant selection.

National Park Service, Dept. of Interior Headquarters Green Roof
Sedum is native to Europe and Asia.  We have exotic European landscape plants on top of our National Park Service's headquarters, so what?

The real point here is the photo of of the DOI's green roof is used on a publication entitled "Illustrated Guidelines on Sustainability for Rehabilitating Historic Structures".  These guidelines are what every local Preservation Appropriateness Review Committee use as a standard for renovation projects.

The document states very plainly under the Recommended approach column, "Selecting sustainable native plants that are drought resistant and will not require excessive watering of a green roof".

The document then goes on to post several photographs portraying the Sedum as U.S. native plant species.
Illustrated Guidelines on Sustainability for Rehabilitating Historic Structures
 The material as presented is not accurate.

I am working on a project now proposing to incorporate a green roof onto a non-original additional to a structure in a Preservation District and every reviewer is looking to the Illustrated Guidelines on Sustainability for Rehabilitating Historic Structures for guidance.

We have been extremely careful during plant design phase to use only low growing native plant species, those found growing not just in the U.S. but those plants native to the specific area where the green roof is being proposed.

How then does our government publish guidelines and not abide by them themselves?  I suspect the U.S. Park Service and Department of Interior really do want to encourage the use of native plants and their efforts are visible with all the references to wildflowers and native plant research they support, making this issue all the more confusing.

DOI should then start by being the example everyone looks too.

I would suggest either replacing the non-native rooftop plants with drought tolerant natives on the DOI green roof or change the language in the Illustrated Guidelines on Sustainability for Rehabilitating Historic Structures to allow for use of exotic, foreign plants.

Two levels of standards, one for the government and one for us regulated is not equitable or fair.

The question is really about native plants and exotic plants.

The question is not really about exotic invasive plants.

Yet there is another even more bizarre twist to the situation.

Exotic invasive plants are typically those plants non-native to an area AND exhibiting tendencies to displace native wildflowers and plants.

Certainly there are levels of invasivity.  Sedum and kudzu cannot be fairly compared as to damage caused.

Interestingly though, the Sedum shown on the DOI's green roof in the above photographs appear to be S. acre, and other Sedum species now listed on many U.S. and worldwide invasive species lists.

I did confirm the plants shown in the photograph on the DOI building are in fact Sedum, through a project description located on the manufacturer's website.

Included below is a brief excerpt from a previous post concerning invasive species issues on green roofs:

Here in the US there are many red flags and concerns now being raised concerning Sedum use and the potential for invasive activity.

For example;

Other Countries too, view Sedum species as an invasive plant, including;
Many Not-For-Profit organizations and preserves also consider Sedum to be potentially invasive. A few include;

Truly there may be places for Sedum use.

Yet to confuse potential project applicants with photos and guidance language speaking to the use of native plants yet portraying and using a plant native not to America when referring to historic structures does not seem logical.

In fact, it is lack of consistency in guidance and procedure that can lead to expensive and time consuming litigation.

Thee is an easy solution.  Either recommend native plants and use native plants or don't recommend native plants if DOI wishes to continue to use exotic landscape plants on their green roofs.

All the Department of Interior had to do was consult with their own plant experts.  A monoculture of only a few genera never is optimum for biodiversity support.

On the other hand, a green roof filled with many different native wildflower families, genera and species could make a powerful statement about America's heritage at the headquarters of the Department of Interior.

Monday, July 18, 2011

Green Roofs and Historic Structures

We are involved in a small green roof project now in a historic neighborhood and on an addition to a historic structure.
U.S. Department of Interior's Guidance for Rehabilitation of Historic Structures

What could be moe historic than plants used in the same manner as those in the Hanging gardens of Babylon or any other number of historic structures?  Apparently the U.S. Department of interior has reservations concerning Green Roofs.

And green roofs and rooftop gardens may be an issue for concern to local ro municipal regulators when reviewing a project for compliance to code, typically due to the infrequency of green roof installations on historic structures.

The latest guidance to renovation of historic structures issued by the U.S. Secretary of Interior can be downloaded here.  Interestingly, the cover page to the document has a photo of a green roof planted with sedum.

Sedum certainly is an appropriate historical plant for some areas of the world and history has shown us of her use in portions of Europe.  Because certain species of sedum may now be added to watch lists for aggressive and invasive species lists, I think a green roof depicting native wildflowers would have been more appropriate.

After reviewing the document I offer the following comments;
  • The document recommends against the use of non-natives that may displace native species yet the document has a photo of a roof with, unless I am mistaken, Sedum acre being used.  Sedum acre is listed across Canada and in some U.S. jurisdictions as potentially invasive, including listings by the U.S. National Park Service. Though I do believe Sedum is appropriate for select green roof projects, monoculture type projects with oen or two genus should not grace the cover of our Nation's Park Service stewards (epic fail).  You can read more of my Sedum rantings here from previous posts.
  • Under the guidance round ugly satellite dishes are easier to approve on historic buildings than green roofs.
  • Green roofs are not afforded the same treatment as window boxes.  The guidance recommends a green roof be not visible from the street.
  • and more...
Download the document and keep for future reference!

I'll be doing a post once we complete the historic building review process to share what we learn.

Saturday, July 16, 2011

Green Roofs over Sloped Metal Roofs

Green and Vegetated Mat Roof systems can easily be adapted to metal standing seam roofs.

Because vegetated mats are monolithic - an integral unit - and not comprised of individualized smaller modules, the system offers considerable "uni-body type" strength.

Vegetated mat systems are attached to the standing seam metal roof with roofing screws and washers but can also be cantilevered over the peak of a sloped roof depending upon the architect's or engineer's design requirements.

MetroVerde Vegetated Mat Design for Standing Metal Seam Roof
Included here is a typical design sheet for a standing seam metal roof with a vegetated mat overlay component - designed for Florida's 5 H's - Hurricanes, High Humidity, heat, Hard Freezes and High Winds!

A membrane/liner is used to separate the vegetated roof system from the standing seam roof panels.

Low VOC adhesives are used when necessary and the standing seam roof ridge-cap and end trim cover any loose mat ends.

With advances in sealant and adhesive technologies sloped green roof systems and vertical living wall systems can be installed across the Urban Core.

Finally, as the plants grow - the plant root systems criss-cross through the mat, interweaving themselves into the mat and with other roots, creating a strong panel of plants and locked into place soil.

Thursday, July 14, 2011

Green Roof Weeds, Maintenance and Taking Care of Plants on the Roof

This is an update of a post I wrote about two years ago.

I was asked to contribute towards a new municipality green roof regulatory policy, one where there was considerable incentive given developers towards site entitlements if the project would include a green/vegetated roof.

One of the committee members also invited was an accomplished technical/construction specialist - one with multiple graduate degrees in technical and mechanical fields.  But she did not understand plants.

Her past green roof projects had been designed around available landscape plants.  Choose the typical on-the-ground landscape plant and design irrigation and fertilizer and other accessory design criteria to support the landscape plants - was the motto.

Whenever we'd discuss native species or volunteer species showing up on the roof, she'd immediately try to quash the discussion by shouting 'WEEDS!  NO ONE WANTS WEEDS ON THE ROOF!'

I think it was because she felt uncomfortable trying to work with the organic, dynamic complexities of nature.  Obviously she wanted no part of having native wildflowers or grasses on the roof.  Moreover, I've seen some of her 'landscaped' green roofs and they quickly revert back to natives, or as she calls them 'weeds'.  I am sure the selective herbicides are used quite often.

We must stop seeing masses of green and train ourselves to look at the plant.  There are few if any true weeds in nature and on green roofs.

Each plant has its own beauty and purpose, even those obnoxious ones.

I've often quoted Lydia Cabrera in saying "there are more spirits in the plants/forests than in the sky'.

The vegetated roof in Sanford I toured this week was full and vibrant due to volunteer plants.

There are no weeds.

I learned this from my daughter, today.  Though I knew it long ago.

She showed me her photos of one of the most obnoxious plants in my book - Bidens alba (Hairy Beggar's-tick).  Just try walking through a mass of Bidens and wait till you come out the other end of the patch....

I love their masses of white flowers but distrust their desire to bestow me with masses of aggravating seeds.

I almost at this time of the year agreed with the self-centered technocrat who probably couldn't tell bamboo from horsetail or coral honeysuckle from trumpet vine.  I almost shouted WEEDS!

But Jincy showed me her pictures from today.  Ones she and Ruairi took out back.  The Bidens are growing on the roof too.

And Lydia Cabrera is right about more spirits in plants.  And I am right about 'there really are no weeds'....

No need to weed green roofs.  Just step back and admire the Bidens.

Green Roof Beauty - Not Weeds - Bidens alba providing habitat and foraging
Green Roof Wonders - Not weeds, Bidens alba provides nectar

Happy Green Roofing!


Wednesday, July 13, 2011

Green Roof Plant, Sesbania herbacea, Danglepod

Danglepod is a great native green roof plant for many reasons, including habitat, forage, food for Lepidoptera, nectar provider, nitrogen fixer, shade producer, wind break plant, native species and so much more.
Sesbania herbacea, Danglepod flowers ont he Green Roof
Sure to catch anyone's attention Danglepod is also known by its scientific name Sesbania herbacea.  Danglepod grows wild across Florida and many of you may remember seeing broad patches alongside road and highways blooming during the summer.
Sesbania herbacea growing on the Breaking Ground Contracting Green Roof
I like Danglepod as a green roof plant for a number of reasons, including all of those listed above.  Very resilient to wind Danglepod makes a great permaculture type windbreak and provides shade, so though welcome anywhere on the green roof I especially like to see the plant grow around the perimeter.

Danglepod is a summer annual, however the hot tropical desiccating winds are what I most like to protect against.

Moreover, Danglepod is a fertilizer plant for green roofs.  A member of the Fabaceae family, Danglepod fixes nitrogen into the soil and has been listed in many permaculture and biodiversity online databases, including international sites such as EcoCrop.  The USDA NRCS plant website refers to Danglepod as being native across the southern US.
Danglepod's Seeds
Research is presently being conducted across the world on the economic and ecological potential of the plant, including fiber utilization and biofuel production.  The Atlas of Florida Vascular Plants has several great photos of Danglepod along with considerable botanical data.

Danglepod and other Sesbania are used by numerous Lepidoptera for food sources.  The Orange Sulfur,  Gray Hairstreak, Zarucco Duskywing and others use the plant as larval food.

The plant reseeds itself prolifically and is considered a 'weed' by many.  In fact, many herbicide companies and 'weed' organizations recommend applying chemicals to this plant to kill it (along with the butterflies and pollinators using the species).

Being a native weed I consider Danglepod a wildflower with benefits and the plant is welcome on all green roofs I work on.  If too many appear it is easy to pull a few up.

As to the free nitrogen, shade, wind protection and wildlife habitat, Danglepod packs a powerful and beneficial punch!

Sunday, July 10, 2011

Green Roofs Teach Us About Plants

We are always very focused on learning about how plants do on the ground and then using compiled data to determine what plants works best on green roofs.

Yet the reverse is true also!  We can take what we learn from green roofs and apply to ground level landscapes with stunning results!

Really cool when we learn from the Green Roof experiences about those plants who do well without irrigation and in extreme heat & desiccating winds.  Roofs are magnitudes more hostile than ground level planting areas.
Native Plants provide beautiful non-irrigated landscape
Species who have proved themselves on the roof are solid choices for most ground level landscapes.

And there are cost savings too!  
Here this planting is non-irrigated (the city approved zero irrigation) yet we have a tropical, lush look from two great native plants, Adam's needle and Little Bluestem. The soil prep was special and heavy pine straw mulch applied. Very green in many ways!  For more on this native plant install click here.

Understanding Green Roofs and Green Roof plants pays many dividends.

Friday, July 8, 2011

Brown Green Roofs, Green Roof Forensics

Any green roof designer has had plants die from time to time.  Roofs are one of the most harshest places to grow across and good green roof design involves much more than basic landscaping.

Here in the tropics an understanding of environmental factors is crucial to ensuring green roof survival, beginning with a solid knowledge of plant selection. Importantly, long-tern survival depends not only on appropriate underlying green roof support systems, but soil media and 'Right Plant Right Place' issues also.

The tropics, for instance possess finicky climates with wild temperature swings, horrendous humidity, extreme temperatures, desiccating winds, salt spray, stealth-like killer fungi, hurricanes and more.

This doesn't mean green roofs do not work in the tropics, they do!

Unfortunately, the attached photos depict what can go wrong with a green roof here.
Struggling Green Roof

Sedum is not generally considered a plant suitable for the tropics.  Note I say generally as I am sure there may be exceptions.  Southern Blight fungus and hot, sticky humidity overwhelm sedum during the hot summer months.  The same applies to many Delosperma also.  

Rainfall quantity distribution here is unusual.  In many places receiving 150 cm rainfall each year the majority of that amount may come in only a series of heavy downpours.  Green roof system drainage must be designed to handle extreme water flows, otherwise failure may occur.  Apparently some of the soil media here has ended up in the swimming pool below.

The example shown here did not possess additional irrigation.  Instead as the plants withered, a rotary sprinkler was pulled up to the roof in a futile attempt to save the plants.  Im not sure how long the sprinkler ran, but it did run long enough to erode grooves in the soil media.
Irrigation erosion from sprinkler

A green roof system without irrigation is a environmentally friendly approach, and can work.   However other factors, including appropriate plant selection must be considered.

Soil media must reflect site specific drainage requirements.  Soil media high in fines may blind geosynthetic fabrics which comprise portions of the green roof drainage system, restricting vertical permeability and causing soil media to wash off the roof.

In this case it appears a lack of vertical drainage has caused rainfall to rush across the sloped roof soil media surface, scouring the grit and producing serious erosion.  It is entirely possible that during a tropical storm, such as TS Fay in 2008 where 600mm+ rainfall dropped in some places, the soil media here would end up in the gutters or on the ground unless appropriately stabilized.  Moreover, damp water retention pads and even the smallest of pooled water depressions can lead to hoards of pesky mosquitos.

Green Roof design involves much more than planting inexpensive fertilizer pumped up plants on a roof platform.

Appropriate green roof design takes into account wind, light levels, available daylight intensities, temperatures, invasive aspects, native plant considerations, nutrients, air quality including NOx levels, pests, adjacent potential allelopathic influences, air water vapor and much more.

Investing in a Green Roof Professional's time up front will save significant costs in the long-term.

Thursday, July 7, 2011

Green Roof Irrigation Opportunities, Exploring Water Vapor

Fortunately, there are many ways green roof plants can be provided irrigation water.  First we should utilize native rainfall amounts, second water vapor in the form of dew, fog and air humidity.   Air conditioning condensate can provide a significant amount of irrigation as well.  Finally, rainfall captured in rain barrels or underground storage and cistern systems may be utilized to support plant water requirements.  Grey water too may be used if local or state regulations permit.

I've always been amazed at how much water the air holds.

Several of our past blog posts have addressed dew, fog and water vapor (biomimicry).

This morning as I inspected a recent green roof project, I was awestruck at just how much water was rolling off the solar panels, dripping to the single ply roofing, running across the roof to the drip edge and into the gutters.  Alot of water!
Dew Stream Dripping from Solar Panels

So when we think of green roof design we need to visualize the advantages elevated vegetated plantings have over ground level plants from water laden air exposure.

Nature has provided many plants with fine hairs, such as one of my favorite green roof plants, Yucca filamentosa, a physiological attribute allowing for water collection.

Before we immediately specify irrigation systems with potable water for either primary or backup supply,  lets seriously look at what nature provides.

We may be surprised at just how much water nature is making available.

Green Roof at Dawn

This morning's photo of the Breaking Ground Green Roof at dawn.  What a way to start the day!
MetroVerde Green Roof at Breaking Ground Contracting, Jacksonville, FL

Tuesday, July 5, 2011

Prostrate Rosemary on BGC Green Roof

Green Roof Rosemary
Yellowing of prostrate rosemary can be caused by three factors we've found on green roofs.  First is water stress, second is Iron deficiency and the third is Nitrogen deficiency.  In a highly inorganic material you should check the pH.  Calciferous soils with higher pH will bind iron and promote the yellowing.  We add dry pine needles and oak leaves as a mulch around the root ball before we plant and then add the same to the soil around the plants.  The organic matter provides micronutrients in ways, we've seen, industrially manufactured fertilizers can't.  In fact, smart leaf compost application has allowed us to create thriving rosemary plantings.
The attached photo is of prostrate rosemary growing on a green roof in 50mm of a soil media with sharp sand for drainage and heavy leaf usage.  Once the plant becomes established the leaf requirements diminish.  I prefer to only plant rosemary where it can 'cascade' over the side of a sidewall or edging.
Finally, cow peas interspersed with the rosemary really helps from a NH4 availability perspective.