07-11-2011 03:25 PM
We just bought a house, and it has blown in insulation in the attic, but it doesn't seem like a lot, just bascially filling in the spaces between the framing, and it is likely original to the house, so from the 70's. I wanted to put down some fibreglass insulation on top of that to increase the R value, but I have questions about the vapor barrier. Since I already have insulation in there, I don't want to have a vapor barrier on the fibreglass insulation, right? It would either be between the 2 types of insulation, or it would be on the cold side, both seem bad. I'm sure there isn't a vapor barrier below the blown in insulation though.
Also, the blown in doesn't seem even. Do I have to have the blown in insulation completely filling the framing cavity before I place fibreglass insulation on top (running 90 deg to the framing)? If there is a air gap between them, does that eliminate any benefit of adding new insulation?
07-11-2011 06:26 PM - edited 12-29-2011 07:18 PM
Hi Travismikjaniec, this is Mike The omeHome Home Depot Answer Man. Welcome to the community.
You are correct, always use unfaced bat insulation for the additional layers. Lay the new insulation across the ceiling joists perpendicular to the existing insulation. This assures the ceiling joists are covered.
The existing blown in insulation can be fluffed up with a small rake to bring it up to the top of the rafters. It is vital that the blown insulation be fluffed up and not compressed.
The Department of Energy recommends at least 15.5 inches of insulation in your attic. Be sure to leave at least 3 inches of space between the insulation and any device that produces heat, such as an attic mounted furnace.
Since it will take several layers of roll insulation to achieve the recommended 15.5 inches of insulation depth, blown in insulation may be a more viable option in terms of cost and the labor required.
This will also solve your problem with the existing insulation not covering the rafters. You can buy the blown in or cellular insulation and rent the machine to install it at your local Home Depot.
Another good idea is to install Durovent attic ventilation panels. These panels install between the rafters and butt up against the attic vents to prevent the insulation from blocking them.
They assure proper attic ventilation and will improve attic air flow for greater energy efficiency. You can buy Durovent panels at your local Home Depot. I have included links below.
I hope this answers your question
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07-12-2011 01:16 AM
Mike is absolutely correct. If you went any more than 15.5 inches you won't get enough energy savings for the cost of extra material. And may I suggest using a throw away tyvec suit and respirator when you do the job. It does get dusty. And while your up there check for any other building defects. Any water spots on the rafters or joists? Are duct seams sealed and connected properly? Any cracks around the chimney? Noticing these things and fixing them first will save a lot of aggrevation later.
From a guy in the business
07-12-2011 05:09 PM
Hey ddepo25. Welcome to the Home Depot community!
Absolutely you can insulate your attic as a DIY project. Few tools are required and with a little guidance it’s a pretty easy job!
One thing to keep in mind concerns vapor barriers. If you live anywhere near cold climates, you will need vapor barriers on the interior side of insulated areas. Without one, moisture will degrade the ability of the insulation to function. Here is a map link to the U.S. Department of Energy. LINK.
How you install the barrier depends on where you live.
There are a number of threads on this community that address attic insulation. Here are a few:
When you say “little or no” insulation I am not sure what that means. For areas with no insulation, using faced bats makes the most sense. This is the easiest way to quickly provide both insulation and a vapor barrier. Where there is “little” insulation, you will want to determine if a vapor barrier is present. If it is, then blown in insulation may make the most sense. If not then consider removing what is there so that you can install one.
Homedepot.com has a great buying guide to get you started. You can find it here: Buying Guide
Also, Owens Corning has some excellent installation videos at their website: Installation Video
A few minutes reading through these links should give you a really good start.
I hope this helps,
I'm a Home Depot Store Associate, trained and authorized to help people on the Internet.