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How To Install Blanket (Batts) Insulation 
Over Existing Attic Insulation




Valerie M. wrote:

Hey Itchy,

I have an old home with an attic and I am planning to add insulation to the attic floor. There is a very small layer of fiberglass insulation already there and I purchased R19 to lay over it. They sold me kraft paper faced fiberglass batts. Can I lay this over the old stuff? Do I have the really wrong thing? I live on an island with only ferry boat access. Please don't make me send it back! What should I do?

Valerie, there are a couple of methods you could use to add new insulation over existing insulation in your attic - blown in insulation or batts. Since you have purchased fiberglass batts, I'll cover that option.


Before you can insulate the attic you need to make sure it's prepped. Put on your protective clothing, grab a light and head on up into the attic. You need to inspect it to make sure everything is right before you start insulating. All of the lower vents need to be uncovered. If you have existing loose fill insulation it's possible that it may be covering the vents if baffles (vent chutes) were not installed. If this is the case it's easier to unclog the vents from the outside of the house using a leaf blower on the vents to blow the insulation away from them. Once the vents are clear you need to install baffles.

Next, take a look at the existing insulation. Make sure it is away from any heat sources by at least 3". Sources of heat include recessed lighting and metal chimneys. If you have a bathroom fan make sure it is not covered with insulation and that it is vented out. This is done by using aluminum flex tubing that extends from the opening of the fan to one of the upper or lower vents.

Is your home very old? If you have frayed or degraded wiring or the old knob and tube wiring DO NOT PLACE INSULATION OVER IT. This is a extreme fire hazard and you will need to call a electrician to update your electrical wiring system. 


You will also need to determine how much insulation is required for your neck of the woods. You can ask your local building code department or look at the comparison chart.

You don't want to use kraft faced batts to cover existing insulation. The kraft paper acts as a vapor barrier and can trap moisture that will cause damage to the attic structural members. When using fiberglass batts to reinsulate the attic make sure they're unfaced. If the existing insulation is level with the top of the ceiling joists it's best to install the batts perpendicular to the existing ones. The reason for this is that it will completely cover the joists and will provide a better thermal coverage. I like to stock the attic first. Start laying the fiberglass blankets at the far end of the attic and work your way back. Make sure they are placed snug against each other with no gaps and try not to compress them as it will reduce the r-value. Use a utility knife to make cuts in the batts in areas where they don't fit. Scrap pieces can be used to fill any gaps or voids. Once the attic has been insulated, don't forget to insulate the attic hatch cover.

Finally, remember safety first. Make sure you are walking only on the joists. Don't try walking on the sheetrock or you will soon find yourself on the floor below you. Make sure the attic area is well lit and always wear protective clothing and a dust mask. 

Related Tips and Advice:

How To Install Blown In Insulation In A Attic
How To Insulate Access Covers

How To Insulate Attic Drop-Down Stairs

How To Install A Radiant Barrier In A Attic


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