Mission Valley Roofing, Inc.
The German Experience
1960s West Germany was 60% the size of California with a
population of 60 million
Due to rapid population growth, economic expansion and
industrialized agricultural production open natural space was
dwindling and green roofs were installed to replace these spaces.
Green roofs were not necessarily looked at as usable space.
covered green roof
installed in 1962
The German Experience cont.
1974 The large Green Roof on the Karlsruhe Hospital was used in a
scientific study about climatological consequences of vegetated
roofs. Stormwater retention and filtering was the largest benefit.
1979 Established Green Roof Supply Companies were present and
very extensive systems developed.
W & M Roofing
over SBS Torch
The German Experience cont.
1982 The FLL (German Landscaping Research
Association) published their first guidelines for green
roofs which were adopted as industry and test
standards and are still the leading source of info today.
In the 80s local governments started to mandate green
roofs and grant incentives. One incentive were reduced
waste- and storm water fees.
The German Experience cont.
1990 The FBB (German association for all professions
related vegetation on buildings) was founded.
To date an estimated 160 million sq. ft. of roofs are
vegetated, 95% of which is “Extensive”
The most extensive lighweight systems in Germany are
1 ½” thin
Extensive Green Roof
Example: Haseco-Zoger Bremen Germany
General Types of Roofs
SLOPED and LOW SLOPE ROOFS
We do not call them flat and steep roofs because all roofs should have slope!
A sloped roof is any roof with a slope of 3” per 12” or more or 14
degrees. Sometimes 2” in 12” is still considered sloped.
Roofing is installed under the assumption that water sheds off the
Common roofing materials are: Shingles, Tile, Slate, Metal
Low Slope Roof
A slope of less than 3” in 12” but no less than ¼” in 12”
Roofing or Waterproofing is installed assuming that water may
“stand” on the roof for a while
Roofing Materials are installed in a manner that results in a
“Membrane” and associated flashings that should be able to
tolerate standing water for a limited time. (48 hours)
Example of S-Tile, Flat Tile and Solar Tile
Roof Membrane Types
In the roofing industry we speak of roof systems.
The waterproofing component of the system is the
roof membrane. There are three basic types of
membranes currently used for Green Roofs:
1. Bituminous (or Asphalt)
2. Thermoplastic Single Ply
3. Cold applied liquid
Bitumen is the correct name for asphalt, a byproduct of
Oil refinement. It succeeded coal based “TAR” as the
most widely used roofing product in the 1950s.
Conventional Asphalt (non-modified) Built-Up Roofs
are not suitable for Green Roofs due to insufficient
density, flexibility and their support of organic
Single Ply installation of modified bitumen membrane
(one layer of APP or SBS) is not recommended.
Need root barrier and/or root growth inhibitors. E.G.
copper reinforcement or chemical fillers
SEBS Hot applied rubberized asphalt is the most widely
used and proven bitumen based system for green roofs
(American Hydrotech, Monsey Bakor)
Modified Bitumen roof if more than one layer and with root inhibitors
Cold Applied Liquid Membranes
Solvent based waterproofing coatings
usually with a reinforcement of fabric.
Most common are polyurethanes.
Well proven in below grade waterproofing
VOC emissions and environmental
conditions during installation can be
Thermoplastic Single Ply
Thermoplastic Single-Ply membranes are usually PVC or TPO
(Thermoplastic Olefin) rolled goods with the ability to be fused together by
heat welding. These membranes have first been used in the 1960s in
Europe and are currently the fastest growing and largest roofing segment
TPO and PVC membranes are root proof, no inhibitors needed. Root
barriers may be specified but are not required.
Hot air welded seams will prohibit root penetration.
Can be applied as ballasted systems i.e. loose laid with little fastening.
Are the more economical choice for green roofs.
60 mils minimum thickness recommended or more for “intensive” roofs.
Flashing techniques and details require little to no maintenance and are
less prone to root penetration.
They are light weight and safe to install.
General Roof Installation
Safety & Fall Protection
Cal OSHA requires fall protection equipment for any
construction work performed over 15 feet.
Federal OSHA guidelines are more stringent but only
apply for work on Federal Government property
Fall protection measures can be:
1. Guard Rails
2. Personal Fall Arrest Equipment (Harness, Line and
3. Warning Line or Safety Monitor.
All ladders have to be securely tied off at the top and
have to extend 36” over the landing.
Fall protection and safety orders should also be followed
during maintenance operations.
General Roof Installation
Positive drainage is a “must”. Plants don’t tolerate
standing water. Small ponding can be allowed if the
drainage layer is thick enough.
Flashing heights for penetrations and walls should be
increased to allow for thickness of planting substrate and
Standard galvanized metal flashings for pipe
penetrations are not recommended for bituminous
roofing in green roof application.
Water tests are recommended because repairs to
defects are more costly after green roof layers were
If loose laid membrane is used and the ballast is applied
later fastening of membrane should be sufficient to not
allow roof to be damaged by wind uplift. Perimeter
fastening is a “must”.
Important! Install gravel or pavers around penetrations
that require maintenance. E.G. drains, pipes, walls and
roof edges. Gravel separation at up–going walls is also a
Mechanical equipment of the roof requires the same
separation. Equipment that needs frequent service such
as HVAC should have a walkway provision for each it
without harming vegetation.
The safest way to specify and install a green roof is to
follow the manufacturer’s specifications. Most
manufacturers have published green roof specs
Currently the specifications in the US are very material
intensive. E.g. fully adhered insulation and membrane
plus root barrier on TPO roofs. Manufacturer’s will allow
less costly alternatives while still guaranteeing their
system if asked.
Manufacturer’s Labor and Material warranties of up to 20
years are available.
Manufacturers offer their own filter and drainage
products but those may not be desirable for supplier of
growth media and plants.
Fire and wind uplift standards for green roofs are still in development.
The roof system in itself should comply with local fire resistance
It is recommended to comply with wind uplift requirements for non-ballasted
roof systems, in case the vegetation and growth media will be removed at a
Drainage should be designed and implemented for a non-vegetated system
for the same reason.
Since codes are still in development the insulation “R-value” should
currently be the same as for a non-vegetated system. R-values for the
vegetation are a benefit but can no be relied on for thermal efficiency due to
variability caused by moisture content, plant coverage, etc.
Fire Ratings are classified as U.L. classes A through C. The City of San
Diego requires Class A on all buildings.
Wind uplift ratings are usually defined by Factory Mutual (FM) San Diego is
an area that requires FM I-60 (60 lbs per sq. ft.) wind uplift for FM insured
Pavers and green roof
Brucker Offices Bremen Germany
Filter and Drainage layers
Manufacturers specify different systems
Filter layer is usual spunbond polyester or polypropylene
fleece and keeps silt from building up on roof membrane.
Drainage layer could be aggregate (blown clay, rock, etc.)
or a manufactured good. It allows excess water to run to
There are products that combine drainage and filter layer.
San Diego City
Installation of filter and drainage layers
Mori Residence San Diego
San Diego City College
Drainage medium installed at drain boxes only
Plants and growth Media
Use a Specialist
Growth media is the “soil” the plants grow in and needs
to be specifically formulated for use on roofs, especially
in Extensive systems. Here are different installation
Conventional application of drainage layers, growth media
in bulk and bags and planting plugs is currently the most
widely used in the US.
Hydro seeding extensive green roof system is the most
economical but needs a lot of initial irrigation and does not
allow for immediate wind uplift resistance.
Pre-grown mats, rolls or grid could be installed by Roofing
Contractor and allow for immediate wind uplift resistance.
Intensive Green Roof Systems are planted like a regular
Separation of Trades
Roof Installation and possibly
Filter and drainage layers
should be performed by a
qualified roofing contractor
In many cases the roofing
contractor roof loads and
install the growth media.
A landscape professional will
plant or seed and establish
growth. In Germany the “Roof
Gardener” was established as
a separate specialty trade.
Irrigation if needed should also
be installed and monitored by
Vegetation on Steep Roofs
Steep roofs for vegetated
covering are waterproofed in
the same manner as low slope
roofs. Traditional steep roof
materials like shingles are not
Provisions need to be taken to
keep the growth media form
sliding. There are many
prefabricated grids, blocks, etc.
Irrigation is more complicated
because water will move down
the slope quickly.
Wind uplift potential is
The amount of sunlight may
differ greatly on the roof.
Steep Roof with blocking to keep
vegetation and media from sliding
All roofs require periodic (yearly) maintenance.
Visual inspection of roof details, drainage, sealants, etc. should
be followed by correction of all unsatisfactory conditions.
Single-ply and liquid applied
roofs do not require
any maintenance at seams.
The replacement of sealants at
tops of penetrations and at walls
can be done without disturbing
Maintenance of vegetation should be performed by a landscape
It is desirable to have inspections performed by landscaper and
roofer together to address any overlapping issues such as plant
growth into roof details.
Failure of the Waterproofing
Today’s roof systems are very reliable. Total failures are
rare if installed and designed correctly. Root penetration
can be avoided by specifying the right materials.
Do not install vegetation over a roof system that is in any
way compromised or not suitable for vegetation. Most
existing roofs are not and replacement costs for a
vegetated roof are much higher.
Membranes under green roofs will last longer than
95% of roof leaks occur at detail areas. Repair involves
removing the gravel around the detail or penetrations
and then repairing with conventional methods.
Solar Photovoltaic on Green Roof
Can be installed on the same roof.
The cooling effects of the green improve solar performance.
Possible less dust accumulation on solar panels.
Photo Courtesy of