Green Roof Webinar
This presentation focuses on common design and construction errors found in green roof project delivery and offers solutions to prevent such errors from occurring in the future.
- Green Roof Definitions & Design Options
- Common Construction Errors and Lessons Learned
- Common Design Errors and Solutions
- Recycling Initiatives
Watch the Recording
Sika Roofing, a Division of Sika Corporation, is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) cannot be earned for the above webinar as the live event has concluded. However, we are happy to schedule a Lunch and Learn for your team!
“A waterproofing membrane is a layer of material that is able to resist hydrostatic pressure for periods of time. The membrane, in conjunction with other elements of the waterproofing system, prevents water from entering the building and facilitates run off during storm events.”
Source: Green Roofs for Healthy Cities, Green Roofs Design 101 Manual, 2nd Edition, sec. 5.3.2, p. 58. www.greenroofs.org
Waterproofing vs. Roofing
In this project, the roof is made up of two types of roofs. In the front part of the building is a large exposed roof area, where in the back part of the building there is a vegetated roof area. The difference between these two roofs is in the waterproofing system the membrane is buried. Therefore, access to the membrane is very costly and difficult to remove after the overburden is placed on top of the membrane. To reduce membrane removal, there needs to be a quality system including a good design, installation and quality insurance during the installation process.
Two Design Types for Green Roofs
Conventional Design- Metal Deck
Here is a conventional metal deck design where you have a metal deck with a insulation grounding screen in this case separation cover board for impact resistance, followed by a waterproofing membrane then drainage composite filter fabrics and then your overburden on top. This is a conventional design or extensive design that can handle large areas economically but cannot handle a lot of weight.
Protected Membrane Assembly (PMA) - Concrete Deck
Here is a more traditional plaza deck design or a protective membrane typically seen on larger projects. It might be a grade level, or an upper level that has a heavy construction concrete deck waterproofing membrane on the deck. The advantage of this system is it supports projects that have more weight involved such as a higher plant diversity or pedestrian access. This type of roof can handle higher loads, but is more expensive.
Construction Errors & Lessons Learned
Example #1: Millennium Park- Chicago, IL
- The medium was specified to be loaded evenly across the structure but instead the contractor came back and basically spot loaded the material.
- Spot loading across the deck caused damage to the structural column components underneath the deck and they had to be repaired at a cost of almost $100,000.
- Loading of materials may exceed structural capacity of the deck
- A plan for loading the deck should be reviewed and approved by the project team
Example #2: Chicago Lakefront Project
- Insulation was not stored properly and due to windy conditions insulation ended up in the marina.
- Temporary ballast of loose-laid materials should be reviewed by the project team
- Have a plan for temporary ballast- sand bags, water bags, tires, heavy lumber
- Need heavy ballast (e.g. sand bags) in higher wind areas
Example #3: Office Building Project- Maryland
- Topsoil from the site was substituted for the lightweight engineered growing medium.
- Plants did not survive on the roof.
- Additional cost required to remove topsoil and failed plants, install specified media & plants.
- Make sure the project that is designed is the one that is built!
- Review growing media design prior to product delivery
- Include a quality control plan for delivered growing medium
- Consider a 3rdparty to QC growing media
Example #4: Membrane Protection
- The PVC membrane was not protected with the correct material.
- XPS insulation, or asphalt which is a popular insulation flow cell material is not compatible with PVC membranes.
- Request written direction from membrane manufacturer’s Technical Dept. for membrane protection requirements.
- Include specific instructions in the specification and construction documents regarding protection.
- Written direction from contractor or non-technical staff is not acceptable.
- Identify responsible parties for membrane protection (i.e. chain of custody.
Example #5: Protect XPS Insulation From Heat Build Up
- Sunlight reflecting off the windows damaged the extruded polystyrene insulation that was installed under the membrane.
- Dark colored membrane absorbed heat causing the extruded polystyrene to curl up.
- The membrane had to be removed and then the excreted polystyrene had to be replaced.
- If reflective heat is a concern, then modify system design.
- Consider adding ½″ cover board over insulation to act as a heat sink.
- Cover board provides additional membrane protection for impact & load transfer over membrane.
- Temporarily protect the insulation with a white fabric.
Example #6 Insufficient Water During Vegetative Cover Insulation
- Did not have enough pressurized water during vegetated cover installation.
- Contractor wasted time and effort trying to find source of water for plants.
- Secure ample water supply and pressure on the roof prior to placing vegetation
- Plan for a backup/2nd source of water if the primary source is not adequate.
12 Keys to a Successful Green Roof Design & Delivery
|1. Specify only the highest quality waterproofing membrane with a documented performance record|
|2. Specify minimum 1/4" slope to drain with drainage at the membrane level|
|3. Clarify 'chain of custody' responsibility for membrane protection during construction in project documents.|
|4. Include hose bibb access on the roof- Hose bibb must be independent of irrigation system.|
|5. Use compatibility with electronic leak detection (ELD) as the design driver for the Green Roof assembly.|
|6. Pre-qualify bidders- Qualifications of the field superintendent is key –do not accept the ‘B” team.|
|7. Include a QC plan to ensure growing medium confirms to specifications.|
|8. Use an edge restraint with perforations covered with filter fabric to allow water to move outward and not displace growing medium.|
|9. Prepare a maintenance plan & inspection budget post construction.|
|10. Use details that are specific to green roofs.|
|11. Educate your Client on Warranties.|
|12. Consider ‘end of life’ recycling options for waterproofing membrane.|