- Installing the radiant barrier on the floor of the attic: The idea is that this method is effective in two ways. First, it reflects the heat from the roof deck upwards. Second, it reflects the interior energy downwards. Personally, I do not like this method because it creates hazards and in a study done by Oak Ridge National Laboratory the barrier looses its effectiveness as dust accumulates on the barrier. In addition, a study done by Texas A&M noted that reflective barriers work best when they directly face the radiant energy. The attic floor is not directly facing the roof deck so efficiency is lost. It creates hazards by covering the ceiling joists, potentially creating a hazard if one were to need to access the attic. If you cannot see the joist, you may just fall through the ceiling! Also, many homes have their utilities (electric, water, etc.) running through the attic. Reflective barriers contain metal…a conductor! Need I say more?
- Installing the radiant barrier or insulation to the bottom of the roof deck: In my opinion, this is the most effective method that should yield the greatest efficiencies. The insulation directly faces the radiant source. Second, if attached to the bottom of the rafters there is an adequate space for the radiant heat to be reflected back towards the roof deck. In addition, this space will allow for the least accumulation of dust allowing the barrier/insulation to work at its greatest efficiency for the longest period. Finally, the placement should eliminate most, if not all contact with electrical lines reducing risk.
Thursday, September 16, 2010
Radiant barriers and radiant insulation: Real energy science or real scam?
Over the years, the subject of radiant barriers and radiant insulation has crossed my radar from time to time. Until now, I have not done any proper research or given it serious consideration. This past week however, I saw an ad in the local newspaper touting 75% savings and radiant insulation being more effective than twelve inches of insulation. So, I looked into the hype and science and I have come to the following conclusion:
Are radiant barriers and insulation real or just a fraud? Yes and No. I guess I should explain my position…
Radiant barriers and insulation work by reducing thermal transfer of heat from the roof itself and the attic floor. During the day, the shingles heat up and conductively heat up the supporting structure of the roof. These temperatures become very high and the heat from the roof deck and supporting structure radiates into the attic heating up the insulation on the ceiling of the home. Through this conductance and radiant heat, a greater load is placed on the air conditioning unit(s) to keep the home (structure) cool. Basically, the radiant barrier reflects the heat back to the roof and reduces heat gain in the attic…more importantly, the heat gain to the insulation.
The science seems sound, but is it effective?
This is where the whole subject gets foggy. By definition, radiant barriers reflect RADIANT heat. With that information, I can immediately eliminate some installation procedures and barrier types. For example, some installers claim placing the radiant barrier directly below the shingles is acceptable and effective…Impossible! In order for a radiant barrier to work there ABSOLUTLY must be an AIRSPACE otherwise conduction takes over and immediately discounts any benefit of the radiant barrier. Studies done for the Department of Energy show the effectiveness of radiant barriers and insulation and two major installation procedures appear to be the most effective:
Without making this article a 400-page novel, I will summarize some of my points.
Yes, radiant barriers and insulation are effective. However, through the independent and government studies I have seen that I deem to be accurate any number over a 10% reduction in heating/cooling bills is difficult for me to swallow. The Department of Energy states “…radiant barriers can lower cooling costs between 5%–10% when used in a warm, sunny climate.”
Radiant barriers and insulation are one of the most cost effective ways to add efficiency. Generally, the materials and installation are less expensive than adding other insulation types.
Radiant insulation is better than a radiant barrier. This is due to the added insulation between two layers of barrier. The additional cost is minimal.
Studies also show that the major effects of radiant barriers and insulation are for reducing summer cooling bills in warm, sunny areas. The effect on winter heating bills is immeasurable in most cases and may even cause the heating bill to increase as the radiant heat from the roof deck is not warming the attic.
With all of this, my biggest gripe is with the manufacturers and installers that make huge energy savings claims. I have no idea why an installer would want to hurt his or her reputation or possibly even be sued from making these incredulous claims of energy savings.
Back to the newspaper ad…
“…cut your heating and cooling bills by 75% guaranteed.”
Really? Who is going to guarantee that? The installer? The manufacturer? I do not even know what to write about this. It is such an outlandish claim that I cannot imagine what is included with the installation to generate a 75% reduction in heating and cooling bills. Has such a reduction ever been documented?
“…delivers more energy savings than twelve inches of additional fiberglass insulation.”
I really have a hard time with this one. Again, from what I have read, this amount of additional fiberglass insulation should yield a much greater savings. I am not a scientist or a lawyer, but maybe there is something in the way this entire statement is worded that does not make it completely untrue.
So why do the manufacturers and installers feel the need to beef up their claims of such a great effect? My guess…this is needed to justify increasing the price of the product and the installation. I have no idea what companies that install this product charge their customers, but I have a feeling it may be more than it should be.
My bottom line…radiant insulation installed should run about one dollar per square foot installed. Depending on the particular structure and the potential difficulties, I can see no reason why it should ever be over $1.50 per square foot installed. Anything over this price almost completely nullifies your return on investment based on the research I have seen.
The studies and literature I based this article on: