Do You Have to Remove Old Insulation Before Adding More During Renovation?

If your home improvement project includes insulation, you’ve likely been looking into hiring insulation contractors to reinsulate your attic, crawlspace, rim joists, or open walls (in the case of a renovation project). Ineffective insulation leads to higher energy bills, poorly functioning HVAC units, multiple moisture-related problems, and more. 

As you consider the costs of reinsulating your home, you may wonder what to do with all of that pre-existing insulation. Should you chuck it, or can you just insulate right over it? The answer? It depends. In other words, there are times when you should remove old insulation, and there are situations where it’s fine (and even preferred) to take a combination approach.

When Should You Remove Old Insulation?

Whether you’re renovating your home office or sprucing up the kitchen, you might find you need to first remove the old insulation. Here are a few scenarios in which you should absolutely remove and dispose of old insulation before adding in any new insulating materials. 

You’re Replacing Current Insulation With Spray Foam

If you’re hiring a local spray foam insulation contractor, you should remove any pre-existing insulation before going ahead with the project. Why? Spray foam insulation creates an ultra-tight air seal, which is one of the primary reasons homeowners end up choosing this insulation type. 

A tight air barrier translates to lower energy bills, reduced noise throughout the home, and an increase in the effectiveness of your heating and air conditioning units. But spray foam cannot expand to create that sought-after air seal if there’s a bunch of old insulation in the way. 

A competent pro will bring a powerful vacuum to suck up old fiberglass or cellulose so the spray foam can squeeze its way into every nook and cranny. If needed, the same pros will carry away old fiberglass batts.

You’re Replacing Current Insulation With Faced Insulation

Faced insulation features a vapor barrier, otherwise known as a vapor retarder, that prevents moisture from moving from one space to another. This facing, as it’s called, also protects the surface of the insulation and helps fasten it to various building components. Faced insulation is incredibly useful when it comes to reducing moisture and preventing mold, but only if it’s placed correctly.

A general rule of thumb? Don’t install faced insulation on top of existing insulation unless it’s the final insulating layer and the barrier is placed toward the interior of the home. Any other setup creates a moisture pocket, which is a breeding ground for mold and rot.

You’ve Had Rodents or Related Pests

Rodents and other pests love to make their home inside of loose-fill insulation and fiberglass batts. Both are pretty cozy, after all. If your insulation has become a critter condo, remove it before adding any new insulating materials. Why? Rats and related pests leave behind urine and droppings, which permeate the insulation itself. 

There is no real way to separate these nasty substances from the insulation, so your best bet is total removal. Before installing any new insulation, sanitize and disinfect the area for added peace of mind.

You’ve Experienced Water Damage

Water may make for a refreshing drink, but it should not go anywhere near your insulation materials. If you’ve experienced a roof leak, flood, or even just spilled condensation from an air conditioner, you should check on your insulation. 

Insulation holds moisture for a long time and becomes a breeding ground for mold spores and mildew. Yuck. Even worse? Water damage causes the insulation to lose its effectiveness, as it will slow down the transfer of heat throughout your home. 

Remove that old waterlogged insulation before adding anything new. You can, however, be surgical about it. Remove only the affected patches of insulation.

When Should You Keep Old Insulation?

You don’t always have to remove old insulation. Sometimes it’s totally acceptable, and even preferable, to add new insulation to old insulation to make one big happy insulating family. 

You’re Adding Loose-Fill Insulation

Loose-fill insulation is great for adding to pre-existing insulation. You can squeeze some in anywhere and there are no potentially harmful chemical interactions between mixing loose-fill and other types of insulation. 

Even cooler? Adding new loose-fill insulation to old insulation should add to your home’s R-value, saving you money on that monthly energy bill and increasing the overall effectiveness of your building’s insulation. 

Of course, you should only add loose-fill insulation to old insulation if the old stuff is in good shape. If there is water damage, mold, rodents, or evidence of fire damage, toss that old insulation as a precautionary measure.

You’re Adding Batt or Rolled Insulation

The same goes for batt or rolled insulation, whether it’s made from fiberglass or cellulose. These insulation types retain their R-values and continue to operate effectively, so long as they avoid moisture, mold, rodents, and the like. So mix and match to your heart's content, with one major caveat. 

If you have conducted an energy audit and the report indicated a multitude of misaligned insulation rolls or batts, removal could be the easiest option. Misaligned insulation still has its insulative properties, but the misalignment has rendered it useless. 

Depending on the design of your house, a qualified pro could recommend removal and reinstallation or something called the “lift and fill” method. In this scenario, technicians lift up each roll or batt and blow loose-fill underneath, creating a cushion to fix the alignment issue.