|J. Peter Jordan|
Post Number: 421
|Posted on Saturday, June 05, 2010 - 11:30 am: |
This has been on my plate for several months now. I think I have it under control, but am seeking feedback.
The City of Houston recently incorporated energy performance requirements into the energy code which required "Cool Roof" performance on low-slope roofing membranes. This has complicated working on LEED projects since we really need documentation on both SRI (required for LEED) and solar reflectance and thermal emittance as measured by the Cool Roof Rating Council's criteria in CRRC-1. While I have assumed there is a correlation of some kind, no one has been able to explain it to me. By examining product literature, I have found that the SRI on products meeting Cool Roof requirements is about 0.88 (10 points higher than LEED requirements). Energy Star seems to have been left behind in this discussion.
This would be a slam dunk if everyone was using single-ply membranes; however, most of the roofs that I specify in this area are modified bit, and there are a number of local government and institutional clients which have "design standards" requiring modified bit.
My research indicates that there are several strategies for getting a "reflective" roof membrane with a modified bit system:
(1) Field-apply a special acrylic emulsion to the installed cap sheet material. The installed cost in this area is approximately $1.00 per square foot. The product has been around for at least 10 years. Acrylic resins will oxidize at a predictable rate under exposure to UV radiation so the life of this coating in our area is about 7 years when it is applied in the thickness recommeded by the manufacturer. If owners would recoat with a good grade of acrylic house paint every 5 to 6 years, the useful life of the roofing system may be extended significantly.
(2) Factory-applied acrylic coatings applied to cap sheet product (offered by Johns Manville and GAF). Not sure what the cost premium over a basic cap sheet product is for these products. The manufacturers are saying that these require maintenance, but are not very specific about the requirements.
(3) Factory application of a film to the cap sheet product (offered by Derbigum and Soprema). The manufacturers are very cagey about the composition of this film, but it seems to have a significant acrylic component. Again, the manufacturers will tell you that it will require maintenance, but are not very specific. Soprema has some very good data about the extended reflectance.
(4) Cap sheet with highly reflective mineral granules (look more like flakes) which has been offered by Siplast for about 5 years and has just become available from Firestone. The white color is inherent in the mineral granules so that degredation of reflective characteristic will be minimized.
This 4th strategy seems to me to be the best approach.
Another stategy undertaken by roof consultants in this area is to install two plies of modified bit sheets and cover with a TPO (or in one case, a KEE) sheet.
I am seeking input and feedback from anyone who has done some research or has some experience in this area. Shared experience through posting to 4specs is appreciated or if you would rather be somewhat discrete, please e-mail me at email@example.com.
Post Number: 439
|Posted on Tuesday, June 08, 2010 - 10:33 pm: |
Our manufacturer client Tremco Roofing won a CSI Tech Innovation award a couple of years ago for their BUR system that meets LEED and Energy Star SRI requirements. Combination of highly reflective marble aggregate and white adhesive: http://www.tremcoroofing.com/product_detail.asp?id=262&pselect=1&cselect=1
|J. Peter Jordan|
Post Number: 423
|Posted on Wednesday, June 09, 2010 - 10:04 am: |
The link led me to an adhesive product for roof aggregate. City of Houston does not permit aggregate/ballasted surface roofs, especially in close proximity with high density development. They will allow paver systesm. Will have to check wth my Tremco rep to see if this has been acceptable. Even then, one has to choose the aggregate/ballast material carefully.
I have had some discussion with a roofing manufacturer who takes the position that aggregate/ballast surfacing is inherently cooler because of the voids in the materials, but don't know how this plays with Cool Roof or LEED requirements. My hunch is that it does not, and one is left relying on the reflectivity of the aggregate/ballast.
Post Number: 337
|Posted on Wednesday, June 09, 2010 - 10:29 am: |
Soprema also has multi-ply SBS systems. Membrane Cap Ply is Soprastar Flam 180, 120 mils, with top surface of reflective white reinforced film (SRI = 96 initial, 85.9 weathered). Apply this membrane by torching only. Roof walkway membrane upper face is covered with white colored granules. Walkway coating is Soprema "R" Nova roof coating (SRI = 111.5).
|J. Peter Jordan|
Post Number: 424
|Posted on Thursday, June 10, 2010 - 10:13 am: |
As I noted above, both Derbigum and Soprema offer a film laminated to a capsheet. Soprema has more performance data for reflectivity both immediate and long term, and that performance data is very impressive. Both companies are very cagey about disclosing the composition of this film, but both indicate it may have an acrylic base. Both say that the product needs maintaining, but are very ambiguous about the nature of this maintenance. I am also wondering about hail resistance.
I do have to disclose that it took several weeks and numerous phone calls to get a Soprema representative to talk to me so I was a bit testy with them from the get go. Derbigum insisted that since their product's technology had been in service in Europe for 30 years, it should have comparable service in South Texas. My experience is that European service for exterior systems does not necessarily indicate comparable service south of I-10.
|Di Ann Hassloch, CSI, CCS, CCCA, LEED AP|
Post Number: 23
|Posted on Thursday, July 01, 2010 - 12:41 pm: |
An owner in New York, is interested in turning his existing ballasted roof white using an acrylic coating. Does anyone have any experience with any of the products currently available?
|Anne Whitacre, FCSI CCS|
Post Number: 971
|Posted on Thursday, July 01, 2010 - 02:46 pm: |
remind owner in New York that in order for the roof to be white, it will require some regular maintenance by their staff. (I didn't have much luck with my owner in New York who wanted a white roof, but at least we got it documented). Especially in large cities, white roofs don't stay white very long, or without regular cleaning.
In addition, if the owner does agree to keep the roof clean, you will need to coordinate with roof membrane for equipment pads, rated loading on roof membrane and a whole bunch of other stuff that is more trouble than its worth.