Attic Facts, Myths & Misconceptions

Article Summary

This article attempts to address some of the myths and most common misconceptions surrounding attic insulation, attic energy efficient strategies and insulation products. We routinely meet with potential customers on estimates who are genuinely confused and not sure who to believe in the marketplace. This article attempts to sort through the noise. When possible we cite independent third party resources to better establish the facts. Our goal is to provide our customers with credible resources so they can make more informed decisions.


1. There are no silver bullets

Many companies want you to believe if you invest in their one product or service, be it a attic insulation, radiant barrier, foam insulation, attic ventilation, powered attic fan, etc. that you will dramatically reduce your utility bills. The truth is no one product makes a home energy efficient. If you want to save energy you need a comprehensive solution that is tailored to your home’s unique problems.


2. When more attic insulation is not the solution?

We routinely perform Manual J thermal analysis when we size air conditioning equipment. A well-insulated and air sealed attic in Phoenix will only comprise 10% – 15% of the sensible cooling load. In other words, when you get the basics right, your attic insulation and air barrier, you then need to focus on other energy conservation strategies like duct sealing, shade screens or more efficient HVAC equipment.


3. Powered attic ventilators are a bad idea!

Most consumers who have an electrician install a powered attic fan never consider the unintended consequences. Arizona utilities are offering rebates for air barrier work because the ceiling between the house and attic is a significant source of air leakage. Once the attic fan turns on it will draw outside air through attic vents, but also cool conditioned air directly from the house through air leaks and recessed electrical lights. Simply turning these fans off can be an effective energy conservation strategy.

Powered attic fan
Attic fan thermostat

An article titled Powered Attic Ventilators, Unplanned Impacts on Houses published in 1996 by John Tooley and Bruce Davis drew the conclusion that “powered ventilators should not be used.” In tests on eight homes these researchers found that “on average, powered attic ventilators draw 231 cfm of conditioned air out of the house and by themselves cause 0.72 air changes per hour.” Look at the photos of how leaky these old recessed cans are. The fans draw conditioned air out of every leak in your ceiling – thus we don’t recommend them.

Attic view of recessed can with light leaky out
Recessed can in dark attic

According to an article in the October 2002 ASHRAE Journal by William Rose and Anton TenWolde titled Venting of Attics & Cathedral Ceilings, “with the cost of operating the fan included, mechanical ventilation was a net energy loser.” Not only are the fans net energy losers, but if the fans are large enough and the ceiling is leaky enough the fans can create enough negative pressure on a structure that they can actually back draft combustion appliances.

http://www.advancedenergy.org/buildings/knowledge_library/ventilation/Attic%20Ventilation%20Case%20Studies.pdf

https://www.dom.com/about/conservation/pdf/attic_ventilation.pdf


4. Passive attic ventilation

Passive attic vents are the vents installed in attic during the construction to let moisture escape from an attic in the event moisture gets into the attic. Many homeowners falsely assume that since their attics are extremely hot in the summer the best way to reduce their cooling load is to get the heat out of the attic. The problem is that most naturally ventilated attics don’t have enough air exchange to make a difference.

Research done by Professor Bill Rose, Research Architect, Building Research Council-School of Architecture University of Illinois, found that “in roof cavity assemblies which are poorly insulated (less than R-10), ventilation can reduce cooling loads by 25 percent. However when these assemblies have thermal resistance greater than R-25 ventilation has a negligible effect.” If an attic is under-insulated the solution is insulation, not attic ventilation.

Older home with asphalt shingle and turbine vent

Heat gain through a well-insulated ceiling represents a small amount of the total sensible gain. In The Moisture Control Handbook written by Joseph Listiburek and John Carmody it states that “where roof assemblies are tight and well insulated, ventilation of roof assemblies has a negligible impact on cooling loads.” p. 71


5. Attic Baffles

An extension of the passive attic ventilation myth is that attic baffles are essential to maintain attic ventilation. They maintain an air space between the vent at the frieze block and the roof sheathing. Attic baffles in cold climates can help reduce wind blowing through insulation and undermining its R-value. They can also help reduce ice damning. We believe attic baffles are not essential, although desirable.

Eve vents exterior of house
Eve vents at seen from attic
Card board baffle at eve
Foam baffle at eve

6. Radiant Barriers

Radiant barriers are highly reflective materials designed to block radiant heat transfer. Research conducted at Oak Ridge National Laboratory has shown that the effectiveness of radiant barriers is minimal, if you have proper insulation

Many radiant barrier manufacturers aren’t telling the truth. The following ad is completely fallacious: “Regardless of how much insulation you have in your attic, adding radiant barrier will save on your heating and cooling expense, and keep you more comfortable. Energy savings vary from 17% to 25% …” When radiant barriers are sold for more than $1 or $2 a square foot to consumers they fall into the category of a scam.

Radiant barriers can’t compete with proven energy conservation strategies like duct sealing, shade screens and adding more insulation. Advantage Home Performance will not sell or install radiant barriers in homes because we believe they are a poor value for customers.

Dirty radiant barrier over a 2” of rock wool with an R-value 5 – 7

Furthermore, dust will be driven into attics through attic vents and over time this dust will accumulate on radiant barriers installed on an attic floors and thus reduce their effectiveness. Radiant barriers reflect radiant energy and dust undermines their reflectivity. Examine the dust on the radiant barrier in the photograph above. If a radiant barrier is multi-layered it will compensate for dust, but if this multi-layered product cost more than a blown in insulation it is a bad value. Conventional insulation still works fine when it gets dusty. For more information on radiant barriers see our dedicated article on this topic.

Dust covered radiant barrier – eve vents in background

Ask yourself, why are the Arizona’s four largest utility companies giving rebates for air barrier work, duct sealing, insulation, shade screens and mechanical equipment upgrades, but not radiant barriers? They are not giving rebates for radiant barriers for the same reasons we refuse to install them, which is because they are not a good investment.


7. Removing misaligned fiberglass batts – really?

Some home performance contracting companies advocate removing fiberglass batts and replacing the removed batts with blow-in-insulation. It is rare that we’ll tell a customer that they need to remove misaligned attic batts. A misaligned fiberglass batt has been installed in such a way that it is not in direct contact with the sheetrock. In other words, it is sitting on top of wires, framing, sprinkler system pipes and plumbing vents. We believe that is too expensive to remove batts, dispose of them and then replace the batts with blown insulation.

There is no doubt that poorly installed fiberglass batt insulation is a huge problem. In the infrared photograph below, the white areas show heat gain around fiberglass the batt insulation. The whole ceiling should be black, but since the batts are misaligned heat gets around the batts and warms up the sheetrock (as seen as white in the infrared image). It is impossible to say exactly how degraded the R-value is, but we know it is substantial.

Infrared image of misaligned fiberglass batts being thermally bypassed

Our approach is simpler and much less expensive. We have our crews realign the batts that are not in contact with the drywall. Although this cannot be done perfectly in all areas we can do a pretty good job. We then blow a cap of insulation over the batts, which typically fill all the gaps, cracks and voids around and between the batts.

If a customer really wants a high performing attic insulation job, and there is an air distribution system in the attic, we recommend spray foam insulation sprayed at the underside of the roof deck. We have an article on this topic.


8. More insulation is better?

If a home has an R-30 or R-38 insulation in an attic that is free of the common insulation defects, there is very little to be gained in terms of energy efficiency by adding more insulation. The utility companies in Arizona are providing rebates to customers who have an effective R-value of less than R-19, and the incentive is to get them to an R-30. They do not incentivize higher R-values because the savings are not there.

http://www.aps.com/_files/services/ResFAQ/wallceilinginsulation.pdf

If a customer wants to increase their attic insulation for philosophical or environmental reasons we respect that and are glad insulate an attic to an R-50 or R-60. We simply will tell them the added insulation will save them very little energy compared to other possible strategies like duct sealing, solar control or air barrier work.


9. Replacing one type of insulation with another is a waste of money

At Advantage Home Performance we know that in the marketplace there are a lot of people with strong opinions about insulation. We believe that many of the manufacturers and sales people who are sowing confusion in the marketplace are more interested in market share than they are an honest discussion about the pros and cons of different materials. Although we have preferences, replacing one type of insulation with another is a waste of money in most cases.


10. False energy saving claims abound

Too many energy conservation companies and manufacturers mislead consumers to believe that they can reduce their utility bills by 25% to 50%. This might be the case in homes with extremely bad insulation or duct leaks, but typical homes will not see this level of energy savings.

We tell customers if they want to save 30% to 50% on their utility bills they are going to have to invest in a deep energy retrofit. These types of retrofits encompass the whole house and not simply the easy parts of it. They also are expensive. These jobs range on the low end of $10,000 and go as high as $50,000.


Solution – Get the basics right and you win

Get the basics in your attic right and you will not need to invest in radiant barriers, attic fans or more insulation. In most cases it is not difficult to air seal and insulate an attic. Instead of spending money on radiant barriers, attic fans, or levels of insulation above an R-40, investing duct sealing and shade screens would make more sense.

Please refer to our “A Quality Attic Insulation Quote” in order to know how to get a quality attic insulation quote. We also have a very informative article on “Duct Leakage & Repair.” Thanks


What's going on in your attic?

We have the solution!