Insulation cost on Long Island in 2026: attic, walls and spray foam, after PSEG rebates

Insulation cost at a glance

Most insulation is priced by the square foot of area covered, so the first number to know is the size of the attic floor, wall area or basement you are insulating. The table below gives the installed cost, material plus labor, from the most recent national price guides, and the Long Island project median from NYSERDA for comparison.

The national guides do not adjust for Long Island labor rates. Treat the middle of each range as a starting point, and compare it with the NYSERDA numbers for Long Island in the next section.

What 6,938 Long Island insulation projects cost

NYSERDA publishes a record of every project done through its Residential Existing Homes program on data.ny.gov: county, completion date, total project cost, heating fuel, the size of the home and the type of measure. We pulled every Nassau and Suffolk project on October 4, 2026. Of 7,011, there were 6,939 recorded as building shell projects, meaning air sealing, insulation and other work on the house's outer shell, and 6,938 had a usable cost and date. Almost all list the Long Island Power Authority as the electric utility. NYSERDA describes the program as using contractors accredited by the Building Performance Institute (BPI), and most of these projects were completed between 2012 and 2016.

These are whole-house projects, not a single attic. That is why the median, $9,600 in the dollars of the day, is higher than a national attic price. To make the older jobs comparable with a 2026 quote, we adjusted each project's cost from the average Consumer Price Index of its completion year to the August 2026 index (334.980, Bureau of Labor Statistics). That puts the median at about $13,600, with the middle 60% of projects between about $8,370 and $21,200.

• Bigger houses cost more, but not in proportion: the median rises from about $12,270 under 1,500 square feet to about $14,520 at 3,000 to 4,000 square feet (August 2026 dollars). One likely reason is that much of the work is in the attic and the basement or crawl space, which grow more slowly than total floor area.
• Oil-heated houses had bigger projects than gas-heated ones: a median of $14,500 against $10,880 in 2026 dollars. Seven in ten of the projects were in oil-heated homes.
• Nassau projects ran a little higher than Suffolk: $14,570 against $13,160 at the median, in line with Nassau's older housing.
• The CPI adjustment is general inflation, not insulation prices, so read the 2026 figures as an estimate. The dollars-of-the-day column is exactly what NYSERDA recorded.

Cost by material: blown-in, batts and spray foam

The material decides both the price per square foot and how many inches you need. Loose-fill cellulose and fiberglass are blown onto an open attic floor or packed into closed wall cavities. Batts are pre-cut blankets for open framing. Spray foam is sprayed onto the underside of a roof, a rim joist or a basement wall and seals air as it insulates, which is part of why it costs more.

R-value per inch is what turns a target into a depth. Fixr gives 3.2 to 3.7 per inch for cellulose and 2.5 to 3.5 for blown fiberglass. The Department of Energy's spray foam guide gives about R-3.6 per inch for open-cell foam and about R-6 for closed-cell.

• For an open attic floor, blown cellulose or fiberglass gives the most R-value per dollar. It does not stop moving air, so the ceiling below has to be air sealed first.
• Closed-cell foam is a common choice at the rim joist, where it seals and insulates in one pass.
• Spray foam under a roof deck brings the attic inside the insulated shell. That changes the ventilation plan, so it is a design decision, not just a material upgrade.

Cost by part of the house

On a Long Island house the work usually splits into four areas, and a useful quote prices each one separately. The attic floor usually comes first: it is the cheapest per square foot and where warm air leaves the house. The basement rim joist is often next. Walls and finished attics cost more because the insulation has to go into closed spaces.

Capes deserve their own note. Many older Long Island capes have a finished upper floor with knee walls, sloped ceilings and small attic spaces behind and above the rooms. Those need dense-pack or spray foam in the slopes and insulation on or behind the knee walls, which is slower work than blowing an open attic, and the price reflects it.

How much insulation a Long Island house needs

Nassau and Suffolk are in climate zone 4 on New York's climate zone table, along with the five boroughs and Westchester. For zone 4A, ENERGY STAR recommends R-60 for an attic that has no insulation, or adding R-49 where 3 to 4 inches are already there. Its guidance is based on the 2021 International Energy Conservation Code.

Most houses on the island were built long before those levels were common. In the Census Bureau's 2024 survey, 84% of homes in Nassau and 68% in Suffolk were built before 1980, and the median Nassau home dates to 1956.

• The depths are our arithmetic from the R-value per inch above; the installer works from the manufacturer's coverage chart for the exact product.
• Measure what is there now. A ruler in the attic tells you which row you are in, and an assessment with a blower door shows how leaky the ceiling is before more insulation goes on top.

Net cost after PSEG Long Island rebates

On a PSEG Long Island bill, the insulation rebate comes from PSEG Long Island's Home Performance program, not from NYSERDA's Comfort Home program that many New York insulation pages quote; Comfort Home is limited to homeowners who pay the System Benefits Charge, and Long Island Power Authority customers do not. PSEG's 2026 measures list, effective January 1, 2026, pays by tier for single-family homes heated by oil, natural gas, propane or electricity.

The condition that matters most for a quote: insulation is only rebated together with comprehensive air sealing, done with a blower door to BPI standards. The rebate is paid through a PSEG Long Island participating contractor, and the process starts with PSEG's free Whole House Energy Assessment. Ask any contractor, including us, to show that status in writing before you count the rebate. The full rebate list, with an estimator, is in our PSEG Long Island rebates guide.

• The deductions are PSEG's insulation and air sealing amounts added together: $2,500 + $1,000 at market rate, $3,125 + $1,250 for moderate income or a Disadvantaged Community, $5,200 + $2,000 for low income.
• PSEG requires every duct in unconditioned space, such as an attic or crawl space, to be sealed. Duct sealing pays a separate $500, $625 or $800.
• Program financing for every eligible measure is available through NYSERDA, according to PSEG's measures list.
• There is no federal tax credit for insulation installed in 2026. The Energy Efficient Home Improvement Credit (25C) covered improvements made through December 31, 2025.

Vermiculite, asbestos and New York's survey rule

Older Long Island attics sometimes hold vermiculite: a pebble-like, pour-in insulation, usually light brown or gold. The EPA explains that vermiculite insulation came from a mine near Libby, Montana, that also had a natural deposit of asbestos, and EPA and ATSDR strongly recommend leaving it undisturbed and hiring professionals if it has to be removed. New York's Department of Labor lists vermiculite attic insulation among the materials assumed to contain asbestos until sampling shows otherwise.

New York's asbestos rule, Industrial Code Rule 56, adds a step for older houses. Before renovation, remodeling, repair or demolition work, an asbestos survey by a licensed asbestos contractor using certified inspectors is required for buildings whose construction began before January 1, 1974. On a one- or two-family home where you hire a contractor and do not direct the work, the rule puts that duty on the contractor side rather than on you. Only licensed asbestos contractors may remove asbestos material, apart from an owner who lives in a single-family house and does the work personally.

• About 77% of Nassau homes and half of Suffolk's were built before 1970 (Census, 2024), so the survey question comes up on most Long Island jobs.
• If the assessment finds vermiculite, the insulation scope waits for testing, and removal or containment is priced separately by a licensed abatement contractor.
• Ask on the first visit: does the price include the asbestos survey where the rule requires one, and what happens if the attic has vermiculite?

What insulation saves on a Long Island heating bill

ENERGY STAR estimates that air sealing and adding insulation in attics, floors over crawl spaces and basement rim joists saves an average of 15% on heating and cooling costs, or 11% of total energy costs. Its model assumes a 25% cut in air leakage and insulation brought up to the 2012 energy code.

NYSERDA's Long Island records give a second reading. The median oil-heated project was modeled to save 34 MMBtu of fuel a year. NYSERDA's disclaimer says an independent evaluation, based on a sample of 2007 and 2008 projects, found actual fuel savings averaged 65% of the modeled figure, so the realistic number is about 22 MMBtu, or roughly 160 gallons of heating oil at 138,500 Btu a gallon (EIA). The table prices both readings at last winter's average Long Island oil price and at the latest weekly price.

• The 400 gallons is EIA's estimate for households heating with oil in the 2025–26 winter. A leaky house that burns 700 or 800 gallons has more to gain.
• Simple payback on the median Long Island project after the market-rate rebate ($10,100) is about 10 years at $6.37 oil and about 15 years at $4.30.
• Gas-heated houses were modeled to save a little less fuel (a median 31 MMBtu), and their dollar savings depend on the gas rate.
• The other return is the heating system that comes next. A sealed, insulated house has a smaller heating load, and a heat pump sized by Manual J on that house can be smaller.

What an insulation quote should list

Two quotes for the same house can be thousands of dollars apart because one includes the air sealing, baffles and testing and the other leaves them out. Ask for each line below, by area, so the quotes compare line against line.

Questions to ask before you sign

• Are you a PSEG Long Island Home Performance participating contractor, and can you show it in writing?
• Will you test with a blower door before and after, and give me both numbers?
• What R-value or depth will each area reach, and with which product?
• Does the price include air sealing, baffles, the attic hatch, fan venting and the combustion safety test?
• Was the house built before 1974, and how do you handle the asbestos survey rule?
• Which rebate tier have you assumed, and who files the application?
• If I am planning a heat pump, will you share the assessment so the Manual J is run on the insulated house?