Galvalume : Light Reflectance Values

Project: Cabin on Mt. Lemon, In Arizona, North of Tucson. Temperatures range from 90 in the summer, to below freezing in winter. Issue: LRV of Corrugated Galvalume (3.5:12 slope, over SIPs by Premier Panel Industries) We recently learned that our zoning requirements prohibit roofing with LRV over .60 (60%). We're told by the manufacturer that galvalume has an LRV of .65, but after three years of weathering, the LRV is reduced to .5. Do you know of any type of galvalume that has an LRV of .6 or less as a new roof? Also, any suggestion for installation of roofing over SIPs? We haven't done it before, and don't want to damage the SIP panels. Bottom side of SIPS will remain exposed, and will receive two coats of polyurethane to act as a vapor barrier.
Guest User
5/24/2004
There are numerous painted products which should have less reflectance, including various light gray colors. There are also now dark colors produced from special paints which reflect radiant heat for energy efficiency. The International Building Code requires a minimum 1" airspace under any roof deck. This can be accomplished with metal panels but you will need to get details from your roofing manufacturer which pertain to the product you've chosen. Feel free to write back later once you have a product manufacturer and model chosen.
Guest User
5/25/2004
thanks for your reply. the metal roof panels chosed for this project are galvanized corrugated metal panels by Mueller Inc. these panels have already been ordered by the contractor, and thus we're in a bit of a bind as far as the LRV is concerned. yesterday, the Mueller manufacturer took a reading with a light spectrometer (is that correct?) and got a reading of .41 from our particular panel type. if this is truely the LRV, then we should be fine with regards to our zoning regulations. we discussed applying a painted finish to the panels, but this finish would not last as long as the bare galvalume, and would add additional cost to the project. i also contacted the SIPs manufacturer's rep for my area, and he explained that we can attach the metal panels to the SIPs just as if we were attaching to plywood substrate over roof joists. we provide underlayment under the metal panels ofcourse. i was concerned that the fasteners might damage the insulation, but he did not share the same concern. the code in our area is the 2000 international residential code, and it does not appear that the 1" air space is required. we are accustomed to designing for a very hot + dry climate. this project, which is at a higher elevation, is not only subject to hot temperatures in the summer time, but is also subject to ice and snow. we are hopeful that the SIPs panels are the appropriate choice, and that we will avoid ice dams. any additional advice/suggestions for this appliacation + climate are very much appreciated.
Todd Miller
Isaiah Industries, Inc.
5/27/2004
I am glad to hear things will work out in regards to the reflectivity. Roofing products are directly attached to SIPs regularly so I do not anticipate any problems there. Follow the SIPs installation instructions, especially in regards to sealing the seams between the panels and getting a vapor barrier on the bottom side. The risk here that I see would be the possibility of condensation gathering in the outer skin of the SIPs when you have cool temps outside but warm moist air inside. You might want to consider a dehumdifier inside the home to be used during situations when weather conditions could cause this situation -- this is normally during the spring and fall when it is getting cool at night but there is a lot of moisture in the ambient daytime air.
Guest User
5/27/2004
The county government where I will be building requires LRVs (Light Reflective Values) of less than 60%. The metal roof manufacturers don't seem to supply this information. How can I know I can meet county requirements?
Todd Miller
Isaiah Industries, Inc.
5/28/2004
If pressed, all quality metal roofing manufacturers can supply this. Generally, most painted or stonecoated metal roofs will meet this requirement, unless it is a very high gloss painted product.
Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.