Green Remodel Forum

I have fiberglass insulation in the attic. When the roofers removed the old roof they left a lot of the old roof materials on top of the insulation two years ago. I did not know until I went up there recently. Can I add new insulation on top of the old insulation?

Yes, you can add new insulation on top of old insulation. But if it is wet or appears that the insulation has previously been wet, you should look for the cause and repair the problem. Wet insulation can lead to mold, mildew, or even the rotting of your ceiling. Be sure to use "un-faced' insulation on top of existing insulation. Any new batt insulation added on top of existing insulation needs to be without a vapor retarder (face). The paper vapor retarder on top of between layers of insulation can trap moisture leading to mold or even rotting. Any existing batt in the attic should have the facing against the attic drywall. Or you can hire a contractor to blow in cellulose on top of the insulation.

Before you insulate, I would suggest you to air seal the evelope of your house first. Sealing your home's ceiling, walls, floors,windows, & doors is the most cost effective to achieve comfort and energy efficiency. A Do-It-Yourself Guide to Sealing and Insulating see http://www.energystar.gov/index.cfm?c=diy.diy_index

How much insulation is enough for the attic?

The recommended level for most attics is to insulate to R-38 (or about 12 -15 inches, depending on the insulation type), but you can install more than that. It's just like when you are cold you put on more layers to keep cold air from getting into your body. But I would not recommend to install more than R-50.

Don't forget to insulate attic stairs access. You can construct a lightweight, moveable box from rigid foam to fit over the stairs from the attic side. Insulating kits are also available from weatherization suppliers stores.

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It depends where you live. If you live in California (zone 3) R30 - 60 is enough. In more severe cold weather like Minnesota (zone 7) you need R49 - 60. The higher R-values mean greater insulating power. Heat always goes to cold. In the winter, good insulation prevents heat to escape from the living spaces. It also prevents heat to come into the house in the summer.

To find out what zone you live in and R-value, click the tab "Materials & Products", click "insulation".

Cellulose is a good choice to fill up the cracks and gaps. If you choose to use fiberglass, make sure there is no gap, void or compression. Otherwise you still loose quite a bit of the heat in the winter. Pay attention to details. Quality installation does matter.

The recommended level for most attics is to insulate to R-38 (or about 12 -15 inches, depending on the insulation type), but you can install more than that. It's just like when you are cold you put on more layers to keep cold air from getting into your body. But I would not recommend to install more than R-50.

Leave the old insulation in place. As far as the mouse droppings - you are going to have more in the new insulation so why remove the existing. You don't spend too much time in the attic so don't worry about the droppings.

It can happen that new mouse droppings on new insulation. However, if you do air sealing on all the gaps and cracks in the attic you not only prevent critters coming into the attic. The heat in the summer and cold air in the winter can not enter your attic either which can transfer into the living spaces. After air sealing and than add more insulation, it will make your home more comfortable and have more even temperature through out the home.