Decking vs lath, techshield, icynene, fiberglass b

Guest User
9/8/2002
My husband and I are in the final design stages for our retirement home in central Texas. Temps can range from 8F to 100F or more. Standing seam roofing is a given. We're having a tough time deciding on the best type of decking/insulation and radiant barrier system to use in our situation. Energy conservation is our primary goal in building this house. Our architect wants to use lath with fiberglass batts in the attic floor and no radiant barrier. We really think we should be considering Techshield radiant barrier as the decking material, with a felt overlay and then the metal panels. We also think icynene would be a great alternative to the fiberglass. If we use lath, we still think we should be using Techshield between the roof joists and then spray the underside with icynene. Recommended R factor for our area in the roof is R49. We'll also be using a ridge vent to ensure good attic ventilation. Any help or advice that you can give will be greatly appreciated. Thanks, Leslie
Allan Reid
Dura-Loc Roofing Systems, Inc.
9/9/2002
Most of your questions are regarding heat infiltration. There are a number of things one can do to reduce this effect. Heat from the sun has three basic effects on the roof. First you can reflect it away. A white roof is excellant at this. Next,some rays are turned to heat and will be emitted back into the atmoshere and the balance will radiate into the attic. There are also a number of metal products that have good emmittance however they are usually caoted with the better paints or granulars. This then leaves you with the radiat heat which a barrier will help reflect back out however if the first two items will substantially reduce the effectiveness. I am a firm believer in having the metal roof up on strapping so that there is a separate air chamber that vents vertically that will exhaust the radiant heat before it can transfer into the attic. Then ensure that you have proper balanced ventilation on your attic. The reflective barriers that you are referring to are an excellant item for retrofitting over exixting cathedral type ceilings where they can reflect the heat out and keep the cool in. Remember even in an attic it will reflect any heat back in which is not the best. Again, assuming you have a vented attic space, I have to side with the acrchitect as the fiberglass batts are very cost effective insulation and you will get more for your dollar. Ensure that they put a very good air barrier on the ceiling side to stop any air movement and especially to seal around all joints and penetrations. Hope this helps.
Guest User
9/10/2002
Al, Let me make sure I understand what you are saying. 1. If we are using a metal roof, use strapping to ensure good vertical ventilation. 2. By doing this, the ridge vent, along with soffitt and gable vents would ensure adequate vertical ventilation that would reduce or prevent the impact of radiant heat. 3. We won't be using a white roof, but will probably use a uncolored metal. We can also buy the metal coated with a material to help reduce heat transfer??? 4. By doing these things we don't need to add an additional radiant barrier (e.g. Techshield). Thanks for helping us make sense out of all of the information out there. It's pretty overwhelming for non-experts and we're trying to make smart decisions! Leslie
Allan Reid
Dura-Loc Roofing Systems, Inc.
10/28/2002
Uncoloured metal will loose its high reflective value after a few years and without paint unfortunately it does not emit the infared rays very well however the vented air space and a well vented attic will make up for a majority of this transfer. There are a number of rflective pigments now being used in the Kynar 500 paints that can boost dark colours up considerably and the paint then becomes highly emittive as well so there is additional value there. Just imagine the heat trasfer on an asphalt roof. Other than that I think you have a good understanding of a good metal roof and hope you enjoy it for years to come.
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.