911 of the hamlet of Islip’s 6,373 homes, 14.3%, were built before 1940. Islip here means the hamlet on the Great South Bay, not the much larger Town of Islip that contains it along with Bay Shore, Central Islip, West Islip, East Islip and part of Holbrook; every figure on housing below is for the hamlet alone. It covers 4.9 square miles on the north side of the bay, across from Fire Island, with its shopping district along Main Street and the Seatuck National Wildlife Refuge at its southeastern corner.
The older houses sit beside a much larger post-war stock. The median home dates from 1965, 29.5% of homes went up in the 1960s and 16.0% in the 1970s, and 13.1% came in the 1980s. 74.3% are detached houses, 7.2% are townhouses and other attached homes, 5.1% are in buildings of fifty or more units, and 1.7% are mobile homes. 84.5% of occupied homes are owner-occupied.
Utility gas heats 50.0% of occupied homes, fuel oil 37.5% and electricity 10.1%. PSEG Long Island supplies the electricity, and National Grid gas is available on many of the hamlet’s streets but not all. In the oil-heated houses the savings from sealing come back as fewer deliveries; in the 10.1% on electric heat they come straight off the PSEG Long Island bill.
The houses we insulate in Islip
Islip began as a farming community on land William Nicoll assembled in the 1680s and named after his family’s ancestral home in East Northamptonshire, England. Over the 19th and early 20th centuries it became an enclave for wealthy families, lined with Colonial Revival, Greek Revival, Romanesque Revival, Federal, Moorish and Victorian mansions. Many of those have been razed, some remain beside newer large homes, and the hamlet still has a wealth of Queen Anne Revival houses.
Those 911 pre-1940 houses are where we look hardest before planning anything. We expect balloon framing, where the wall studs run from sill to roof and every wall cavity is an open flue between the basement and the attic, until we see fire blocking. We expect knob-and-tube wiring until the basement and attic show otherwise, and live knob-and-tube is replaced before insulation touches it. Plaster walls stay: dense-packed cellulose goes in through small holes, and the holes are patched.
The 961 homes of the 1950s and 1,882 of the 1960s are capes, ranches and splits. The cape leaks at its knee walls and the open floor bays behind them. The ranch leaks across its whole attic floor, at the top plates, the chimney and the bath fans, with batts gone thin at the eaves. The 1,017 homes of the 1970s and 838 of the 1980s add high ranches and colonials, with a lower-level rim joist, a garage ceiling under a bedroom, and in the later houses central air ducts in the attic.
The 323 homes in buildings of fifty or more units and 138 in buildings of twenty to forty-nine are envelope decisions for boards and owners, not individual residents. The 109 mobile homes are a different kind of job; call and we will say whether yours is one we can take on.
Queen Anne houses and the Bayberry Point estates: porches, towers and many small attics
A Queen Anne house was built to look complicated, and its roof is. Cross gables, a turret or tower, bay windows with their own small roofs, dormers, and a porch wrapping one or two sides all mean that the house has not one attic but several: a main attic under the ridge, closed pockets behind the gables, the cavity above each bay, and the hollow inside the tower roof. Some can be reached from a hatch. Others can be reached only by opening a ceiling or a wall, and it is rare for all of them to have been insulated.
The porch is the part most people overlook. On many houses of that era the porch roof framing ties into the house wall, and the porch ceiling cavity connects to the wall cavities or the floor joists of the house. In a balloon-framed wall that creates a direct path from the outdoor air under the porch roof into the house’s framing. It is one of the reasons the room behind a porch is often the coldest in the house.
Bayberry Point, the hamlet’s three streets separated by canals on the Great South Bay, was begun at the end of the 19th century as a cooperative living experiment financed by Horace Havemeyer and completed in 1916, with Moorish mansions along the canals. Many of those houses still exist, and most have been extensively renovated. In a house renovated more than once, we find walls opened and closed at different times, some cavities insulated and some not, and newer roofs framed over older ones, so we map what each section holds before we price it. Near the bay, wind finds every open eave and gable vent, and the basement or crawl space is often damp.
We seal before we insulate
Insulation slows heat passing through a surface. Air moving through an opening takes heat with it anyway, and an old house full of connected cavities moves a lot of air.
In an Islip Queen Anne or older house the sequence begins at the top and bottom of the framing: block the tops of balloon-framed wall cavities from the attic and seal the bottoms from the basement, then close the path from the porch ceiling into the house framing. Next come the attics, each one sealed at its floor and around its chimney with metal and fire-rated sealant, then insulated. The walls get dense-packed last. In a 1960s ranch the order is simpler: seal the attic floor at the top plates, chimney, fans and hatch; baffle the eaves; blow insulation to full depth; then the rim joist.
If a quote specifies a depth of insulation and never mentions air sealing, it is half a job.
What insulation costs in Islip
Most of our projects run between $3,500 and $12,500. A 1960s Islip ranch with one attic and an open basement is usually at the low end, and a 1950s cape with knee walls sits a little higher. A pre-war house moves up with every separate attic, every run of balloon-framed wall to block and dense-pack, and the porch connection, and a large Queen Anne house can reach the top of the range or be phased over time.
Open cell foam runs R-3.9 to R-4.2 per inch. Closed cell runs R-6.9 to R-7.1 per inch and also acts as a vapor retarder, which is why it costs more and why it is right in some assemblies and unnecessary in others. All products are manufactured in the United States and meet applicable building code and safety standards. ENERGY STAR says sealing air leaks and adding insulation can save up to 10% on annual energy bills.
Insulation rebates in Islip
Islip gets its electricity from PSEG Long Island and, where lines run, its gas from National Grid. The electric company determines the program a home can use, and PSEG Long Island homes are not eligible for NYSERDA’s Comfort Home program.
PSEG Long Island’s path begins with a free Whole House Energy Assessment, including a check of insulation and drafts, a thermal scan and a blower door test, arranged through one of its participating contractors. For market-rate single-family homes it lists a $2,500 rebate for insulation and a $1,000 rebate for air sealing, with higher amounts for income-qualified homes and homes in state-designated disadvantaged communities. Insulation in an attic, wall, floor, band joist, basement or crawl space counts, in homes heated by oil, natural gas, propane or electricity, provided it goes in with comprehensive, blower-door-assisted air sealing. The rebates are paid through PSEG Long Island’s participating contractors, so ask an installer about that before you sign and confirm it with PSEG Long Island.
National Grid’s Long Island insulation rebate program is not taking new applications. Income-eligible Suffolk households, owners or renters, can turn to EmPower+: NYSERDA’s EmPower+ program can pay for air sealing and insulation at no cost up to $14,000 at the lower-income tier (at or below $98,925 for a household of four), or half the cost up to $7,000 at the moderate-income tier (below $131,900 for four), with up to $1,600 more in federal HEAR funds for air sealing, insulation and ventilation. The work is done by an EmPower+ contractor, and Long Island households should check eligibility on the MyEnergy portal.
NYSERDA’s Green Jobs–Green New York program lends $1,500 to $25,000, unsecured, over 5, 10 or 15 years, after a no-cost energy assessment; PSEG Long Island customers apply for the on-bill loan through PSEG Long Island, and every loan must be repaid. The federal Section 25C credit ended for work placed in service after 31 December 2025, so a 2026 insulation job has no federal credit, and New York has no state tax credit for insulation. Our New York and New Jersey rebate guide goes through each program.
Code and climate in Islip
79.4% of the hamlet’s homes were built before 1980, including the 14.3% that predate 1940. New York’s first statewide energy code took effect on 1 January 1979. Suffolk County is Climate Zone 4.
New houses today follow the 2025 Energy Conservation Construction Code of New York State, in force since 31 December 2025, which asks for R-49 in the ceiling, allowing R-38 over the entire ceiling where it holds full uncompressed height over the wall top plate at the eaves. Floors are held to R-30. Basement and crawl space walls take R-15 continuous, R-19, or R-13 plus R-5 continuous. Windows must meet U-0.27, and the finished house may not leak more than 3.0 air changes per hour at 50 pascals.
An old house is not required to meet that table. Unaltered parts need not comply, and New York’s code does not require a blower door test when you insulate an existing home. The rule that reaches a Queen Anne restoration is the one on exposed cavities: when an alteration opens a wall or roof, those cavities must be insulated to full depth before they close, so a plaster wall taken down during a kitchen or bath renovation is the time to fill it. ENERGY STAR recommends R-60 in an uninsulated attic in this zone and R-49 in an attic that already holds 3 to 4 inches.
Common questions about insulation in Islip
Do you install insulation in Islip, NY?
Yes, across the hamlet of Islip down to Bayberry Point and the bay, and in the neighboring hamlets of the Town of Islip. Most of our Islip work is the 1950s and 60s cape, ranch and split, and the hamlet’s 14.3% of pre-war houses, including Queen Anne houses with several attics and balloon-framed walls. We also work on 1970s and 80s high ranches and colonials. Larger apartment buildings are for their boards and owners to decide. Call and we will tell you where your house fits.
How much does insulation cost in Islip?
Most projects run $3,500 to $12,500. A 1960s ranch with one attic sits near the low end and a 1950s cape with knee walls a little above it. A pre-war house costs more for each separate attic, each run of balloon-framed wall to block and dense-pack, and the porch connection, and a large Queen Anne house can reach the top of the range or be done in phases. A renovated house is priced after we map what its walls already hold. Written prices follow a free walk-through.
Are there insulation rebates in Islip?
Islip is PSEG Long Island territory. PSEG Long Island lists a $2,500 insulation rebate and a $1,000 air-sealing rebate for market-rate single-family homes, more for income-qualified homes, paid through its participating contractors after a free Whole House Energy Assessment. Comfort Home is not available to PSEG Long Island homes. EmPower+ serves income-eligible owners and renters, and Green Jobs–Green New York loans can cover the rest of a larger job. The federal 25C credit has ended, and New York has no state credit for insulation.
Our Islip Victorian has a wraparound porch. Does the porch change how the house is insulated?
It can. On many older houses the porch roof is framed into the house wall, and the porch ceiling cavity opens into the wall cavities or the floor joists, so outdoor air under the porch roof moves straight into the house’s framing. We find where the porch meets the house and block and seal those bays from inside, from the basement or through the porch ceiling. The porch itself stays outdoors and is not insulated. An enclosed porch used as a room is different, and it gets its own plan.
Free energy audit in Islip
In an older Islip house we start by finding every attic, including the ones without a hatch, then check the wiring, the tops and bottoms of the wall cavities, the porch connection and the basement sill. In a post-war house we walk the attic floor, the eaves, the knee walls or the rim joist, and the burner in an oil-heated home. If the biggest loss is a porch connection and an open wall cavity, we say so. The written scope and price are free, with no obligation.
Call 914-825-6824 or use our contact form. We are open 8am–8pm, seven days, and work out of New Rochelle, NY with a 100-plus in-house crew that never subcontracts.
Learn more
- Insulation contractors across Suffolk County
- Insulation in Bay Shore
- Insulation in East Islip
- Insulation in Central Islip
- Insulation for older homes
- Basement insulation
- Open cell and closed cell spray foam compared