Short answer: if the insulation in your attic is dry, clean and free of rodent droppings, you can usually add new insulation right on top of it. Take it out first if it is contaminated by rodents, wet or moldy, damaged by smoke or a roof leak, or flattened into a thin, patchy layer. And if it is vermiculite (a pebble-like, gray-brown or silver-gold fill), don’t touch it at all. More on that below.
Add on top when the old insulation is:
- Dry. No water stains on the roof boards above it and no damp or matted spots.
- Clean. No droppings, nests, tunnels or urine smell.
- Fairly even. Thin in places is fine, as long as it isn’t crushed or missing in large areas.
- Not vermiculite. Fiberglass (pink, yellow or white) and cellulose (gray, shredded paper) can be topped up.
Adding on top costs less than a full removal and keeps the job short. The one step you shouldn’t skip is sealing the air leaks first (more on that below).
Remove it first when:
- Rodents have been living in it. Droppings and urine soak into the insulation, and the smell stays. It is a common problem in older homes around San Ramon, Danville and Dublin.
- It got wet. A roof leak, a bathroom fan venting into the attic or a broken duct can leave insulation compressed and moldy. It won’t insulate well again.
- There was smoke or fire damage anywhere in the house.
- It’s old batts that have slumped, shifted or been trampled during past repairs, leaving gaps you can see the drywall through.
- You need to work on the attic floor anyway. Major air sealing, new ducts or wiring work is far easier with the old material out of the way.
How much insulation does a Tri-Valley attic need?
The Tri-Valley is in climate zone 3 on the U.S. Department of Energy map. For zone 3, ENERGY STAR recommends:
- R49 for an attic with no insulation;
- R38 when adding to an attic that already has 3 to 4 inches.
Many older homes around San Ramon, Danville and Pleasanton have far less than that. ENERGY STAR’s quick check: if your insulation is level with or below the tops of the attic floor joists, you probably need more.
Seal the leaks before you insulate
ENERGY STAR’s advice is simple: seal attic air leaks before adding insulation. Once new insulation is in, those gaps are buried and hard to reach. Common spots are the tops of interior walls, recessed lights, plumbing and wiring holes, the attic hatch and the gap around flues (which needs metal and fire-rated sealant, not foam). If a contractor wants to blow in insulation without sealing first, ask why.
Rodent contamination: why it usually comes out
Rodent droppings and urine can carry disease. The CDC warns not to sweep or vacuum droppings before they are disinfected, because that can put virus particles into the air. Its guidance is to wear gloves, spray droppings with a bleach solution (1 part bleach to 9 parts water) or an EPA-registered disinfectant until very wet, and let it soak for about 5 minutes before wiping up. That works for a few droppings in a garage. A whole attic of contaminated insulation is a different job: the material comes out, the attic floor is cleaned, the entry points are closed, and only then does new insulation go in. Otherwise the smell and the rodents come back.
Vermiculite: stop and call a specialist
The EPA says to assume vermiculite insulation contains asbestos and not to disturb it. Don’t store boxes in that attic, don’t let kids play up there, and don’t try to remove it yourself. If you plan any attic work, hire a professional asbestos contractor first.
What we check during a free attic inspection
- Insulation type and depth, compared with the R38–R49 target
- Signs of rodents: droppings, nests, chewed wiring, entry points
- Moisture and roof-leak stains
- Ducts: disconnected, crushed or uninsulated runs
- Air leaks and attic ventilation
You get photos of what we find and a written quote. Then you decide whether to add on top, remove first, or leave it alone.
Not sure what’s in your attic? Call (510) 725-4073 or request a free estimate. We serve San Ramon, Danville, Pleasanton, Walnut Creek and the rest of the East Bay. More about our attic insulation service.
Sources: ENERGY STAR, recommended home insulation R-values · ENERGY STAR, attic air sealing · EPA, vermiculite insulation · CDC, how to clean up after rodents