#AskEnergySaver: Insulation

on February 24, 2014 at 5:00 PM


To help you save money by saving energy, we launched #AskEnergySaver — an online series that gives you access to some of the Energy Department’s home energy efficiency experts. During 2014, experts from the Department and our National Labs will be answering your energy-saving questions and sharing their advice on ways to improve your home’s comfort.

This month, we asked you to share your insulation questions. To answer them, we reached out to Iain Walker, a scientist at Lawrence Berkeley National Lab’s Residential Building Systems Group. With more than 20 of years experience in residential efficiency, Walker focuses on how things like ventilation and air leakage impact a home’s energy use and its indoor air quality.

What is better overall, blown-in insulation or sheet rolls?
— from @coynebrendan on Twitter

Iain Walker: For insulation, the installation is usually more important than the material that is used. Both types of insulation can be installed well or badly. The key is to have insulation that completely fills any cavity you are insulating. Any voids that are left (whether from compressed batts in the sheet rolls or incomplete fill from blown-in insulation) are performance killers.

Also, the particular application may change your preference. For example, kraft faced batts are easier to install under a sloped roof or a floor over a crawlspace. But in a remodel it is much easier to blow insulation into a wall cavity than it is to open the cavity to install batts.

What is the recommended safety clothing for working in an attic that has blown fiberglass insulation? I want to add a blanket.
— from @ladykayaker on Twitter

IW: My preference is to use disposable paper overalls. Also protect your eyes with goggles (not safety glasses — you want to keep the dust out of your eyes), use gloves (glass fiber is a skin irritant) and wear a dust mask (disposable ones are fine). While the level of protection might make you hot and uncomfortable — especially when installing insulation in an attic on a hot day — it is better to take these precautions than suffer from itchy, irritated skin and eyes.

We live in a house with concrete walls and concrete air ducts in the floor. The roof is flat and only about 8 inches to the ceiling. Is there anything we can do to insulate anything? Our energy bills are extremely high.
— from Sloan Marlowe via email

IW: To preface, my suggestions are based on your home being in a predominantly cold climate. Your best approach might be to insulate on the outside of your walls. A contractor can apply an exterior insulation system called EIFS (Exterior Insulated Finish System). You could also put some insulation on your ceiling (six inches is better than none), and depending on this ceiling space, you could install a radiant barrier that will reduce summer time overheating.

Another way to reduce your heating bills would be to consider air sealing and window improvements. In your case, the concrete air ducts in the floor are a curiosity. We recommend that air ducts be sealed and insulated well — it seems like your ducts would present a challenge. I would suggest you have them tested for leakages, and if they have leaks, you could use a technology called Aeroseal to seal them. Installing window shades can reduce your home’s heat gains in the summer, helping you to save on energy costs.

Can I increase the insulation effectiveness by just piling up more batts in my attic, or do I HAVE to use vapor barrier (it reaches -40 here)?
— from jsanderc via email

IW: More batts will equal more insulation effectiveness. However, you want to air seal your ceiling and attic floor before you start piling up the batts. Once the space is filled with batts, it is hard to go back and air seal.

In your cold climate, a vapor barrier is a good idea, but you need to put it on the warm side of the insulation — for an attic, that would be the floor under the batts. This will also form an air barrier and reduce ceiling leakage. Another reason to add the vapor barrier before insulating is that it will keep the warm, moist indoor air out of your cold attic — preventing condensation(which can lead to mold) in your attic.

I own a condo townhouse built in 1936. It is brick on the outside with a crawl space below the living level. Our house is very cold and you actually feel the cold air seeping through the wood flooring. Our crawl space is owned by the condo association and just two years ago they replaced the 30 year old insulation with R-19 fiberglass batting along the floor joists. What kind of insulation should be between the floor joists? And what else would you recommend we do to the crawl space or our interior to make the house energy efficient?
— from Jean via email

IW: Not owning the crawlspace limits your options, but below are things to address for homes with a crawl space instead of a basement.

  • Whether your crawlspace has moisture problems or not, it is a good idea to cover any exposed dirt with a membrane (6-mil polyethylene sheeting will do) before you do anything else. This will make it easier and nicer to work in a crawlspace.
  • If your crawlspace is very wet, you’ll need to fix the site drainage by adding drains and making sure the downspouts direct rain away from the foundation.
  • You should also air seal your floor before you insulate with polyethylene sheeting or spray foam.
  • Then homeowners have to decide whether to insulate the crawlspace floor and walls or their house’s floor. (Jean, in your case, since you don’t own the crawlspace, you probably can’t seal and insulate it, and instead you’ll have to insulate the floor.)
  • Once you have air sealed the floor, it should cure those cold drafts. After which, R-19 batt (or blown-in) insulation is fine (I assume this fills the space between the joists).
  • In very cold climates there might be something gained from putting sheathing insulation on the bottom of the joists (plus this could even count as your air sealing if you tape the joints) but in all other climates, this would be overkill.

For more ways to save energy at home, check out Energy Saver.