These are the questions homeowners in New Jersey, Connecticut, the Hudson Valley and Long Island actually ask us, answered short, and pointed at the fuller guide wherever one exists. Almost none has a single universal answer, because insulation is chosen by location: the right material for an attic floor is the wrong one for a crawl space wall.
Two rules run underneath most of the answers. The Department of Energy’s Energy Saver guidance on adding insulation to an existing home puts the first ahead of everything else: before you insulate, make sure the house is air sealed. The second comes from its separate Energy Saver page on insulation — the R-value on the bag is the material under test conditions, and it also depends on temperature, aging and moisture; compressed insulation never delivers its rated value; and a wall performs differently from the insulation in it because heat moves through the framing.
Choosing a material
What is the best insulation for a house?
There is no single answer, and a contractor who gives you one is selling a product rather than solving a problem. Attic floors get blown-in cellulose or fiberglass, because depth is cheap there. Open wall cavities get batts or blown fiber; closed walls get injection foam or dense-pack. Foundation walls, crawl space walls and rim joists get closed cell foam or rigid board, because those spots need air and moisture control as well as R-value. We install all of them, and mineral wool for sound, so the recommendation is not driven by what is on the truck. Start with types of insulation.
What R-value does each material give per inch?
- Closed cell spray foam — R-6.9 to R-7.1, plus an air barrier and vapor retarder in the same pass.
- Open cell spray foam — R-3.9 to R-4.2. An air barrier, but vapor-open.
- Fiberglass batts — about R-3.1 to R-4.3, depending on density.
- Mineral wool — about R-4. The Department of Energy’s Building America guide calls it non-combustible with excellent sound insulation.
- Cellulose — about R-3.2 to R-3.8.
- Rigid foam board — depends which board. The same Building America guide puts extruded polystyrene at R-5.0 per inch, expanded polystyrene at R-3 to R-4, and polyisocyanurate highest per inch of the three. Any of them is also an air barrier and vapor retarder when the seams are properly sealed, and blocks thermal bridging. See rigid foam board.
The Federal Trade Commission’s R-value Rule is blunt about the arithmetic: do not multiply the one-inch R-value by the number of inches installed. Blown products are rated by coverage chart, not per-inch math.
What is the difference between open cell and closed cell spray foam?
Density, and what the foam does besides insulate. Closed cell carries roughly 70 percent more R-value per inch and stiffens the assembly, and at about an inch and a half closed cell foam typically tests under 1 perm, which makes it a vapor retarder. Open cell is lighter, cheaper per inch and vapor-open, so the assembly can dry inward; it is also the one of the two with a published sound number, since the Department of Energy’s Building America comparison of the two foams lists open cell at STC 37 in a 2x4 wood stud wall and no sound data for closed cell. The same guidance states the moisture side plainly: closed cell spray foam is also a vapor retarder, and open cell foam is not. Full comparison: open cell vs closed cell.
Can you insulate a wall that is already closed?
Yes: a line of small holes, a filled cavity, a patch. The Department of Energy’s Building America guide calls drill-and-fill popular and time-proven, notes that dense-pack gives a higher R-value and reduces both settling and air leakage inside the wall, and says it should be done only by a trained professional who fills every cavity at the correct density. Injection foam is the other option. One hard stop: the same guide says active knob-and-tube wiring must be replaced before the insulation project begins, and that drill-and-fill should not be used in a wall that has it, because added insulation can push the wiring against the studs and create a fire hazard. Replacing that wiring is an electrician’s work, not ours, and we will not fill a wall until it is done. See wall insulation.
What is a radiant barrier used for?
Reflecting radiant heat rather than resisting conduction. The Department of Energy is direct about the limit: its Energy Saver page on insulation says a radiant barrier has no inherent R-value, and its page on types of insulation says reflective systems are most effective at preventing downward heat flow — which is why they belong under a hot roof deck, not in a wall. In our climate it is an add-on, never a substitute for depth. See radiant barriers.
How much, and how thick
What R-value do I need in New Jersey, Connecticut and New York?
Three code editions apply across our territory, so the honest answer names the state.
- New Jersey adopted the 2024 IECC on 17 August 2026. Under its Table R402.1.3: ceilings R-49 statewide; floors over unheated space R-19 in the zone 4A counties and R-30 in the zone 5A counties — Bergen, Hunterdon, Morris, Passaic, Somerset, Sussex and Warren; walls R-30, or R-20 cavity plus R-5 continuous; basement and crawl space walls R-10 continuous or R-13 cavity in zone 4, R-15 continuous or R-19 cavity in zone 5. One live wrinkle: complete applications filed under the 2021 edition are still being accepted into February 2027, and that edition called for R-60 ceilings. If your permit is already in flight, ask the building department which edition it sits under before you set a target.
- Connecticut runs on the 2021 IECC through the 2022 State Building Code, and every county is zone 5A: ceilings R-60, floors R-30, walls R-30, basement and crawl space walls R-15 continuous or R-19 cavity. Section R402.2.1 of that code gives a second path on the ceiling — R-49 installed over 100 percent of the attic area satisfies the R-60 requirement wherever the full height of uncompressed R-49 extends over the wall top plate at the eaves. That turns on baffles and eave detailing rather than on more material, and it is worth asking about.
- New York’s 2025 energy code applies to permit applications filed from 31 December 2025: ceilings R-49, floors R-30 or R-19 plus R-7.5 continuous, walls R-30, basement and crawl space walls R-15 continuous or R-19 cavity, in every zone the state covers.
ENERGY STAR’s retrofit guidance, which it says is based on the 2021 IECC table, cross-checks an existing house: an uninsulated attic in zones 4 through 6 gets R-60, an attic already holding three or four inches gets R-49, and floors get R-19 in zone 4A and R-30 in zones 5 and 6. State-by-state detail: recommended R-values.
How thick should blown-in attic insulation be?
Thickness is an output, not a target. Section R402.1.4 of all three energy codes — the 2024 IECC in New Jersey, the 2021 IECC in Connecticut, New York’s 2025 code — requires the manufacturer’s settled R-value to be used for blown-in insulation, and Section R303.1.1 makes the installer post the initial installed thickness, the settled thickness, the settled R-value, the density, the coverage area and the bag count, signed and dated. Depth then follows the product and the target. For R-49, the New Jersey and New York ceiling number, one common cellulose reaches it at 15 inches installed, settling to 13.5, and a common blown fiberglass reaches it at about 16 3/4 inches. For R-60, Connecticut’s number, the same cellulose needs 18.3 inches installed, settling to 16.5, and the same fiberglass needs 20 inches. Ask for the bag count, not just the depth — the Department of Energy’s Energy Saver guidance warns that thickness must not be used as the sole factor in determining the R-value of loose-fill insulation. See attic insulation.
Air sealing or R-value: which matters more?
They do different jobs, and neither substitutes for the other. Insulation slows conduction; it does not stop air moving through gaps at top plates, chases, recessed lights and the attic hatch. That is why the Department of Energy’s sequence is air seal first, insulate second, and why EPA’s savings estimate assumes both. If a quote specifies a depth of insulation and never mentions air sealing, it is half a job. See air sealing.
Attics
How do I know if I have enough attic insulation?
ENERGY STAR gives a check anyone can do from the hatch: if the insulation is level with or below the attic floor joists, you probably need more; if you cannot see any joists because the insulation sits well above them, you probably have enough, and adding more may not be cost-effective. Depth is only half of it — look also for insulation pushed aside at the chimney, dark patches where air filters through it, and bare framing at the eaves.
Should I remove old attic insulation before adding new?
Usually not. Adding loose fill or unfaced batts over sound, dry existing insulation is standard, and the Department of Energy’s Building America guide sets the rules for it: no facing between the layers, and no dense material laid over a lighter one that compresses easily, because compression cuts R-value. It comes out when it is wet, moldy, rodent-soiled or badly compacted, or when the plan is a sealed roof assembly — the same guidance has you strip the attic floor insulation and its vapor retarder before foaming the deck. Removal and replacement is our own crew and our own vacuum, and so is cleaning up a rodent-soiled attic.
Does attic insulation settle?
Loose-fill cellulose settles by design, which is why its coverage chart carries both an installed depth and a settled depth. Blown fiberglass charts usually show the same number twice. Density decides whether it settles past the chart: the Department of Energy’s Building America guide warns that insulation blown at too low a density — fluffing, in the trade — settles excessively and gives a lower R-value, and its Energy Saver materials page notes that cellulose installed at proper densities cannot settle in a building cavity. Batts sag and compress instead. See roof insulation.
Walls
What is the best insulation for existing walls?
Dense-pack cellulose or fiberglass, or injection foam, blown through the siding or from inside — but three things decide the method before the material does, and two of them decide it outright. Knob-and-tube wiring stops drill-and-fill entirely until an electrician has replaced it. Lath and plaster pushes the work outward: the Department of Energy’s Building America guide says drilling from the outside can break the plaster keys off the inside of the wall, and that drilling from inside damages plaster, disturbs lead paint and produces a great deal of dust, so on a plaster house its own advice is rigid insulation on the exterior if you want to keep the plaster, and otherwise air sealing alone. The third is timing. If the siding is coming off anyway, ENERGY STAR’s retrofit guidance is to blow the empty cavity from the sheathing side and add R-5 to R-10 insulating sheathing in zones 4 through 8 — the one moment when continuous exterior insulation is affordable. See wall insulation and insulation for older homes.
What is the best insulation for exterior walls in new construction?
Whatever reaches the code number, which in all three states is R-30 in the cavity or a cavity-plus-continuous equivalent: R-20 cavity plus R-5 continuous, R-13 plus R-10 continuous, or R-20 continuous alone. A 2x6 wall usually gets dense-pack or high-density batts plus exterior board; a 2x4 wall needs closed cell foam or exterior board to get there. Vapor control follows the zone: Section R702.7 and Table R702.7(2) of the residential code — the 2021 IRC in Connecticut, the 2024 IRC in New Jersey and in New York’s 2025 code — permit Class I and Class II interior vapor retarders in zones 5 and 6, while in zone 4 outside marine areas a Class I retarder is not permitted on the interior of a frame wall. We do new construction and commercial work on the same terms as retrofits. See wall insulation.
Basements and crawl spaces
Should I insulate an unfinished basement?
Yes, and the question is where. The Department of Energy’s Building America guidance insulates the basement ceiling only when all of these hold: dry climate, no moisture problem, not living space. It insulates the walls instead when any one holds: you want living space down there, you are in a humid climate zone, or the basement shows evidence of moisture. Every county we work in sits in a moist “A” zone, and the furnace and ducts are usually down there too, so most of our basements get insulated walls, with closed cell foam or rigid board rather than fiber. The same guidance is emphatic that fiberglass batts and cellulose do not belong against a foundation wall, because they hold water. See basement insulation and basement ceiling insulation.
What is the best insulation for a crawl space?
It follows a decision made before material. A vented crawl space gets the floor above insulated; a sealed one gets its walls and rim insulated with closed cell foam or rigid board while the ground is covered with a sealed liner. The energy code requires one or the other, never neither — Section R402.2.11 of the 2024 IECC in New Jersey and in New York’s 2025 code, R402.2.10 of the 2021 IECC in Connecticut. Sealing one up is not finished at the liner, though: Section R408.3 of the residential code also requires one of four ways of drying or conditioning the space, which is covered in the next answer. Fiber against a crawl space wall is the classic mistake. See crawl space insulation.
What is a vapor barrier in a crawl space?
The sealed ground cover, and in a sealed crawl space it is only half of what the code asks for. Section R408.3 of the residential code — the 2021 IRC in Connecticut, the 2024 IRC in New Jersey and in New York’s 2025 code — requires a continuous Class I vapor retarder over the exposed earth, joints lapped 6 inches and sealed or taped, edges run at least 6 inches up the stem wall and sealed to the wall or the insulation. It then requires one of four things as well: continuously operated mechanical exhaust at 1 cfm per 50 square feet of crawl space floor, conditioned supply air at the same rate, a plenum in an existing structure, or dehumidification sized to the manufacturer’s specification. A liner and wall foam on their own are not a compliant sealed crawl space. In a vented crawl space the liner is not required, but a Class I ground cover cuts the vent area the code otherwise demands from 1 square foot per 150 down to 1 per 1,500 (Section R408.2), and the Department of Energy’s Building America guidance calls for 6-mil polyethylene on the ground either way. We install liners and do full encapsulation; the dehumidifier or the exhaust fan, where that is the route chosen, is set by the mechanical scope.
Spray foam questions
Does spray foam need a vapor barrier?
Closed cell foam at normal thickness is the vapor retarder, so a poly sheet over it is not only unnecessary — it can trap moisture between two barriers. Open cell foam is not a vapor retarder. Where that matters most is an unvented roof: Section R806.5 of the residential code, the same number in the 2021 IRC and the 2024 IRC, requires that in climate zones 5 and colder, air-impermeable insulation at the roof deck be a Class II vapor retarder or carry a Class II vapor retarder coating or covering in direct contact with its underside — which in practice means closed cell foam, or open cell with a vapor-retarding paint. Never put poly on the inside of a foam-insulated foundation wall; that wall has to dry inward.
Can spray foam be left exposed?
Not where it faces living space. The residential code requires foam plastic to be separated from the interior by a thermal barrier — Section R316.4 in Connecticut’s 2021 IRC, renumbered R303.4 in the 2024 IRC that New Jersey and New York’s 2025 code adopt — typically 1/2-inch gypsum wallboard or 23/32-inch wood structural panel, or an assembly tested to NFPA 275. Crawl spaces entered only for repairs and maintenance get an ignition-barrier exception (R316.5.4 in the 2021 IRC, R303.5.4 in the 2024), and rim joist foam within the code’s thickness, density and flame-spread limits may stay exposed (R316.5.11, renumbered R303.5.11).
Is spray foam safe?
The hazard is during and just after application, and it is real. EPA’s guidance addresses exactly that window: other trades and occupants should vacate during installation, re-entry should stay restricted until the product has finished curing and the building has been adequately ventilated and thoroughly cleaned, and homeowners should ask their contractor for the specific re-entry time in advance. EPA’s page speaks to timing, not to cured foam, so the rest is ours to say: once the foam has fully cured and the space has been ventilated and cleaned, we treat it as ordinary finished construction, and the questions worth putting to any foam contractor are about mix ratio, pass thickness, ventilation and the re-entry time in writing. See is spray foam safe and spray foam insulation.
Cost and rebates
How much does insulation cost?
Most of our projects run between $3,500 and $12,500. What moves a job inside that range is area, the R-value target, the material, access, the air sealing, and whether anything has to come out first. Anyone quoting a firm price without seeing the space is guessing.
How much does spray foam cost per square foot?
A per-square-foot number means little without a thickness, because foam is sold by board foot — a square foot at one inch. Two inches of closed cell costs roughly twice what one inch costs, and closed cell costs considerably more per inch than open cell. So ask the estimator for what is actually being priced: which foam, how many inches, over how many square feet, and the total for that scope in writing. Foam jobs sit inside the same overall range as the rest of our work, $3,500 to $12,500, with the thickness and the square footage deciding where. Breakdown: spray foam insulation cost.
Are there rebates for insulation?
State and utility programs exist in all three states, each with its own qualifying R-values, pre-approval steps and approved-contractor requirements. Start at New York and New Jersey rebates or Connecticut rebates. There is no federal credit on current work: the IRS limits the 25C energy efficient home improvement credit to property placed in service before 31 December 2025.
Do I need a permit to add insulation?
In New Jersey, the Uniform Construction Code treats blown-in or batt insulation installed against the interior finish as ordinary maintenance needing no permit, while spray foam and other foam plastic insulation do need one — which we pull as part of the job. In Connecticut and New York, ask the town building department; foam and anything that changes an assembly are the usual triggers. Insulating one attic does not oblige you to bring the rest of an existing house up to current code: New Jersey handles existing buildings through its Rehabilitation Subcode, and Section R501.1.1 of New York’s 2025 energy code says unaltered portions of an existing building are not required to comply.
Common questions about home insulation
How long does insulation last?
None of the common materials has an expiration date, and most attics we open still hold whatever went in decades ago. What ends an insulation’s useful life is an event, not age: water, rodents, compression, or a renovation that disturbs it. The Department of Energy’s Energy Saver page on insulation notes that R-value depends on moisture accumulation as well as temperature and aging, and its Building America guide adds that wetting cellulose reduces its thermal resistance and drains its fire retardant, that batts are nesting material for rodents, and that polyisocyanurate board loses some R-value over time as gas escapes the cells. Keep the water and the pests out and insulation outlives most of the rest of the house.
Will more insulation stop ice dams?
Not on its own, and not if the real problem is air. The Department of Energy’s Building America guide describes an ice dam as what happens when the outside air is below freezing but the roof surface is above freezing — warmed by the sun, by leaky heating ducts in the attic, or by warm air leaking into the attic from the living space below — and its prevention list starts with an airtight ceiling plane: limit the number of holes through the ceiling, air seal every one, insulate well and especially over the top plates, and vent the underside of the roof deck. ENERGY STAR treats a history of ice dams as an indication of serious air leaks. So the fix is air sealing plus depth carried out over the eaves, not depth alone over a leaky ceiling. Taking the ice off the roof is a roofer’s or an ice dam service’s job; we do the ceiling below it. See air sealing.
Does insulation help with noise?
Some of it does, and it is worth asking for by name rather than hoping for it as a side effect. The Department of Energy’s Building America guide calls mineral wool non-combustible with excellent sound insulation, which is why it is the usual pick for a shared wall, a media room, or a bedroom over a garage. Between the two spray foams, the same source’s comparison lists open cell at STC 37 in a 2x4 wood stud wall assembly and no sound data for closed cell. Air sealing contributes as well: EPA lists reduced noise from outside among the benefits of sealing and insulating a house. We install soundproofing insulation as its own scope, not only as a byproduct of an energy job. See garage insulation.
Can I install insulation myself?
Some of it. ENERGY STAR’s do-it-yourself guide says attic air sealing and adding insulation are do-it-yourself projects if the attic is accessible and not too difficult to move around in, and it is specific about the gear: an OSHA-approved particulate respirator or double-strap dust mask, and walking on joists or truss chords rather than on exposed ceiling drywall or insulation. Two jobs are not do-it-yourself. The Department of Energy’s Building America guide says drill-and-fill in a closed wall should be done only by a trained professional who fills every cavity at the correct density, and spray foam carries a vacate-and-re-entry protocol along with a mix ratio and a pass thickness that need equipment and training. And nobody should disturb vermiculite: ENERGY STAR says not to unless an approved lab has tested it, and abatement is a licensed trade we do not take on.
How long does an insulation job take?
Most residential jobs finish inside a day or two. Setup, protection and air sealing take a real share of that, removal adds a stage, and a multi-area job runs in sequence. You get the schedule with the quote, because it depends on what the audit found, not on square footage.
Do I have to leave the house while insulation is installed?
For blown-in, batts and rigid board, no. For spray foam, yes: EPA’s guidance is that occupants and other trades vacate during installation and that re-entry stay restricted until the foam has cured and the building has been ventilated and cleaned, with pets included in the plan. Ask any foam contractor for the vacate and re-entry time before the day, and be wary of one who will not give a straight answer.
What happens to my heating bills afterwards?
EPA’s estimate, published through ENERGY STAR, is that homeowners save an average of 15 percent on heating and cooling costs, or an average of 11 percent on total energy costs, by air sealing their homes and adding insulation in attics, floors over crawl spaces and basements. Your own result depends on what the house started from, how it is heated and how it is used. The comfort change — cold floors, the room over the garage, a drafty second floor — usually shows up before the bill does.
What does an insulation contractor actually do?
We install spray foam, blown-in cellulose and fiberglass, fiberglass and mineral wool batts, rigid foam board, radiant barriers, soundproofing insulation, and injection foam and dense-pack in closed walls; we air seal; we remove and replace failed insulation and clean up rodent-soiled attics; we install crawl space vapor barriers and full encapsulation; and we do commercial and new construction work. What we do not do, and will say so rather than quote it, is asbestos or vermiculite abatement, mold remediation, waterproofing, HVAC or duct replacement, roofing and electrical. Each of those is a licensed trade of its own, and we will tell you which one you need.
Ask us the one that isn’t here
The free energy audit is the real answer to most of these: attic depth and condition, the leakage paths, what is in the walls, the basement or crawl space, where the ducts and water heater sit, and what the house was built as. Then you get a plan with an R-value target and a scope, not a per-square-foot slogan. See what is an energy audit.
Call 914-554-2289 or use the contact form, 8am–8pm, seven days. The Home Insulators is family-owned, based in New Rochelle, NY since 2015, with a 100-plus-person in-house crew that never subcontracts. We work across all of New Jersey, all of Connecticut, New York’s Hudson Valley including Westchester, and Long Island; see our service area.