Insulation decision guides

The three decisions that matter are: top up or remove and replace; DIY or hire; and budget material or premium material. Contractors have a financial interest in the more expensive answer to all three, so it is worth having your own position before the sales visit.

Top up or replace. Ask for the specific defect. "It's old" is not a defect. Wet, compacted under stored boxes, contaminated with droppings, or covering a wiring problem are defects. If the answer is vague, get a second opinion before agreeing to a removal line item.

DIY or hire. The dividing line is not difficulty, it is consequence. Air sealing and batt work in an accessible attic are recoverable if you get them slightly wrong. Spray foam, dense-pack wall injection, and anything involving knob-and-tube wiring or a moisture problem are not. Spend money where a mistake is expensive to undo.

Budget or premium. Premium is worth paying for in three situations: limited cavity depth, fire or moisture exposure, and assemblies where an air and vapor barrier is part of the design. Everywhere else, extra depth of cheap material beats a thinner layer of expensive material at the same R-value, and costs less. Whole-home conventional insulation averages about $4,700 for 2,000 sq ft; whole-project spray foam averages about $20,000. That difference should buy you something specific.

How to choose

Make the contractor name the defect

Any recommendation to remove existing insulation should come with a photograph and a specific reason. Get it in writing.

Spend where mistakes are permanent

Hire out foam, dense-pack and anything moisture-related. DIY the reversible work.

Buy depth before you buy product

In an open attic, more inches of a cheap material is almost always the better dollar-per-R purchase.

Sequence around other work

If a roof, rewire, or HVAC change is coming in the next couple of years, do the insulation after. Otherwise you pay for it twice.

Do the diagnostic when the house is complicated

Cathedral ceilings, knee walls, ducts in the attic, or a finished attic room are all cases where an audit before purchase pays for itself.