Can fallen crawl space insulation just be put back up?

Sometimes. If the batt is dry, clean, free of rodent droppings, and was a reasonable thickness to begin with, re-hanging it with proper supports is a legitimate repair. If it has been wet, is contaminated, or shows mold, replacement is the better scope. If you hope to use a rebate, check its rules before anything comes out: PSE pays where existing insulation averages 4 inches or less and says existing insulation may not be removed to qualify, and Snohomish County PUD pays where it is R-11 or less. Ask the utility's contractor how failed insulation is handled under those rules.

What R-value do I need in my crawl space?

Washington's energy code sets R-30 for floors in new construction and additions, one figure for the whole state, and no city can set a different one for houses. For an existing house, the code asks that a floor cavity opened during the work be filled with insulation, and asks nothing where it is not exposed. Both utility rebates aim at R-30: PSE to R-30 or a full joist cavity, whichever comes first, and Snohomish County PUD from R-11 or less to R-30. If you intend to claim one, specify that figure in writing, and confirm the joist depth can hold it: batt compressed into a shallow bay counts at its compressed R-value.

Should I use batt insulation or spray foam?

Batt held against the subfloor is the standard for vented crawl spaces, which are the default in Washington: lower material cost, faster install, and the method the energy code describes when installed with proper support. Mineral wool batt is a middle option that resists moisture better than fiberglass. Closed-cell spray foam on the foundation walls is the approach some sealed crawl spaces use elsewhere, but in Washington it runs into two problems: the residential energy code read for this site gives no insulation path for crawl space walls, so confirm with the building department before treating it as compliant, and PSE's rebate does not allow the thermal boundary to be moved off the floor. Spray foam at the rim joists is a different matter and is common in either case.

Does crawl space insulation qualify for a rebate in the Seattle area?

It can, depending on what heats the house. Puget Sound Energy pays $2.50 per square foot, up to $5,000 for floor insulation where PSE electricity or natural gas is the primary heat, in a site-built home built 1989 or before with 4 inches or less of existing insulation, and only as an instant discount through a PSE Recommended Energy Professional or other PSE Trade Ally; self-installed work does not qualify. Snohomish County PUD pays $1.00 per square foot in electrically heated homes it serves, from R-11 or less to R-30, through a PUD registered contractor. Seattle City Light lists no standard insulation rebate for single-family homes; its insulation help runs through HomeWise, the City of Seattle’s free weatherization program for income-qualified households. The federal tax credit ended for work after December 31, 2025. The 2026 rebate guide has the full conditions.

Why does my insulation keep falling down?

Older fiberglass batt was typically installed without permanent support, just friction-fit between the joists. Gravity, moisture cycles, and any disturbance from pest activity or HVAC service pulls it down over time. Proper replacement uses insulation support wires or rigid wire mesh along the joist bay to hold the batt against the subfloor; Washington's energy code sets those supports at no more than 24 inches apart on new work. Skipping the supports is the most common reason replacement insulation also falls down within a few years.

Do I need to address rodents before replacing insulation?

Yes. If there is active rodent activity, replacing the insulation without exclusion work means rats or mice nest in the new material within months. A complete scope includes rodent exclusion (sealing entry points around foundation vents, plumbing penetrations, and rim joists), trapping if needed, and removal of any contaminated material before new insulation goes in. In King County, Public Health puts preventing rodent harborage on the property owner and points to CDC's guidance for cleaning up after rodents; contaminated insulation should be bagged and handled with protective equipment, not swept into the open air. Crawl space cleaning covers the clean-out.

How long does crawl space insulation replacement take?

One to three days for a batt replacement; spray foam runs two to three.

Will new insulation reduce my heating bills?

Usually yes, but the size of the change depends on where you are starting from. A home with no floor insulation at all has more to gain than one whose batt is merely sagging. How well the rim joists get air-sealed matters as much as the R-value of the batt itself, because air leakage at the rim is a separate heat-loss path that new insulation alone does not close. Be skeptical of any specific percentage quoted before an inspection. The improvement homeowners consistently comment on is warmer floors, which is more noticeable day to day than the line on the bill. The utility rebates for this measure, and who can install it, are set out in the 2026 rebate guide .

Crawl Space Insulation Repair and Replacement in Seattle

Replace wet, sagging, or rodent-damaged crawl space insulation with R-30 batt held tight to the subfloor. Floor insulation can qualify for a Puget Sound Energy or Snohomish County PUD rebate when the utility's own contractor installs it.

Free Inspection

Pink fiberglass batt sagging out of the floor joists across a crawl space, with water standing on the soil below it and a work light on the dirt

Crawl space encapsulation, repair, and waterproofing across the Seattle metro, starting with a free in-home inspection and a no-obligation quote.

19 service areas covered

free inspections

Verify any contractor's registration: Washington L&I

Overview

What Is Crawl Space Insulation Replacement?

Last updated November 11, 2026

Fiberglass batt was never built to survive a damp crawl space, and after a couple of decades it shows. It wicks up moisture and loses most of its R-value, it sags off the joists and ends up hanging in the dirt, or rodents shred it for nesting. Replacement means pulling all of that out and putting back insulation that does the job: new batt held tight to the subfloor in a vented crawl space, which is the default in Washington. The point is not just warmer floors. It is insulation that will still be doing its job in fifteen years instead of rotting on the ground.

A complete insulation replacement scope involves removing the old material (bagged and disposed of as construction debris, with extra handling where rodent droppings are present), inspecting the underside of the sub-flooring for moisture damage or wood rot, treating any visible mold, and installing new insulation. For a vented crawl space, that usually means R-30 unfaced batt fit snug between the joists and held against the subfloor with insulation supports or wire. Insulating the foundation walls instead of the floor, the approach used with some sealed crawl spaces elsewhere, is a harder question in Washington: the state energy code read for this site gives no insulation path for crawl space walls, and Puget Sound Energy's rebate does not allow the thermal boundary to be moved.

Insulation replacement is one of the most common crawl space scopes because so many homes still carry their original batt. It was rarely installed with permanent support, gravity and time have pulled it down, and decades of pest activity have damaged much of it. Replacement is usually bundled with vapor barrier installation, crawl space cleaning, encapsulation, or rodent exclusion work.

Insulation repair or full replacement?

Not every sagging crawl space needs new insulation. Batt that has simply dropped off the joists but is still dry, clean, and free of rodent droppings can be pushed back up against the subfloor and held with proper supports, which is a repair measured in hours rather than days. That is the right call when the existing batt is a reasonable thickness and the only failure is that nothing was holding it up.

Replacement is the answer when the batt has been wet (it does not recover its R-value after drying), when rodents have nested in it or left droppings, when there is mold on the paper facing or the subfloor above it, or when it was never thick enough in the first place. Check the rebate rules before anything comes out: PSE pays only where the existing insulation averages 4 inches or less and does not allow existing insulation to be removed to qualify, and Snohomish County PUD pays only where it is R-11 or less. Have the existing depth and condition documented first.

Friction alone was never going to hold batt insulation up for thirty years. Skip the support wires on the replacement and you are just buying the same failure again. Why replacement insulation falls down too

Before / After

What Crawl Space Insulation Replacement Looks Like

Failed friction-fit batt out, new insulation held tight to the subfloor in. Air-sealing the rim joist is the piece many older homes are missing entirely.

Before insulation replacement: soaked fiberglass batt hanging out of the joist bays over a torn black vapor barrier in a crawl space

After replacement: spray foam insulation filling the joist bays tight to the subfloor, with white liner sheeting across the walls and floor below

Signs to Watch For

Signs You May Need Crawl Space Insulation Replacement

Visible sagging insulation hanging down between the floor joists
Wet, matted, or discolored insulation, especially near foundation walls
Insulation chunks on the soil (fallen out completely)
Rodent droppings, nest material, or shredded insulation evidence
Floors above the crawl space feel cold even with the heat running
Insulation that appears compressed against the joists with no loft
No insulation at all visible in the joist bays
Higher heating bills than similar nearby homes

Seattle Context

Why Crawl Space Insulation Replacement Matters in Seattle

Washington's energy code sets floor insulation at R-30 for new construction and additions, in a single column for the whole state, and the code is both the maximum and the minimum for houses, so no city in this area can set a different figure. It has been in force since March 15, 2024. On new work it also says how the insulation goes in: held in permanent contact with the underside of the subfloor, on supports no more than 24 inches apart, with foundation vents below the insulation. Batt squeezed into a joist bay shallower than its label thickness counts at its compressed R-value, not the number printed on it.

An existing house is treated differently. Where a floor cavity is opened up during the work, the energy code asks only that it be filled with insulation; where it is not exposed, there is no requirement at all. So R-30 is the target to hold a new floor job against, and it is also what both utility rebates ask for, but a retrofit is not made non-compliant by joists too shallow to hold it. In the City of Seattle, insulating an existing building is on the list of work that needs no building permit, provided the building envelope is not changed. The pending 2024 energy code proposal keeps R-30 and would add alternatives using continuous insulation under the joists; nothing may be built to it until it is adopted.

Three insulation situations are common:

Original batt in 1960s to 1980s houses. 52.8% of Seattle's housing units were built before 1980. Batt from that era is often thin, sagging between joists, wet near the perimeter, and sometimes rodent-damaged. Standard scope: remove the failed batt, treat any mold, install new R-30 batt with permanent supports.
Older houses with little or no floor insulation. Houses built before insulation was routine often have none, or a first layer added decades later that has since degraded. Low clearance complicates replacement.
Newer homes with wet rim joists. Better starting condition, but rim joist insulation that has trapped condensation. Targeted rim joist air sealing or spray foam is the typical fix.

The rebates, and who can claim them

Which program applies turns on what heats the house and who supplies that fuel, not on the address alone.

Puget Sound Energy, where PSE electricity or PSE natural gas is the home's primary heat: floor insulation at $2.50 per square foot, up to $5,000, in a site-built home built 1989 or before with 4 inches or less of existing insulation, finished to R-30 or a full joist cavity, whichever comes first. Floor air sealing pays $0.20 per square foot, up to $400. The work must be done by a PSE Recommended Energy Professional or other PSE Trade Ally, who takes the rebate off the invoice; PSE does not pay the customer, and self-installed work does not qualify. Existing insulation may not be removed to qualify, and the thermal boundary may not be moved, so a conversion that insulates the crawl space walls instead of the floor is outside it.
Snohomish County PUD, in electrically heated homes it serves: $1.00 per square foot for insulation, where floor insulation goes from R-11 or less to R-30, done by a PUD registered contractor who includes the rebate in the bill.
Seattle City Light. Seattle City Light lists no standard insulation rebate for single-family homes; its insulation help runs through HomeWise, the City of Seattle’s free weatherization program for income-qualified households.

Washington’s HEAR program pays toward electric equipment such as heat pumps, not insulation or air sealing. The federal Energy Efficient Home Improvement Credit covered improvements made through December 31, 2025, so insulation installed in 2026 does not qualify for it. The 2026 Seattle-area rebate guide sets out every condition and the ways homeowners lose the rebate.

What the rebate is worth against the job

The rebate is quoted per square foot and the job is quoted as a total, which is why the two are rarely set against each other. Over the reference crawl space this site prices — 1,200 to 1,500 square feet of floor — a floor insulation replacement works out at roughly $1.67 to $4.85 per square foot installed. PSE's $2.50 per square foot sits inside that band: on a qualifying 1,200 square foot floor it comes to $3,000, and the PUD's rate to $1,200, against $2,500 to $5,825 for the whole job.

Two qualifications matter before you budget on that. The rebate pays on the insulated floor area, so removal, disposal and rim joist work sit outside the floor insulation rate, and PSE says its rebate cannot be more than the price of the work. And both utilities pay through their own approved contractors, so the installer has to be one of them for the rebate to apply at all.

Process

How Crawl Space Insulation Replacement Works, Step by Step

Inspection and material spec

Existing insulation is inspected and its depth documented, crawl space dimensions are measured, any wet or contaminated material is identified, and the R-value, material type and rim joist treatment are specified.
Quote and scope

Written scope: square footage, R-value, material type, removal and disposal method, rodent exclusion (if needed), and whether the installer can apply a PSE or Snohomish PUD rebate on the invoice.
Removal and prep

Old insulation is removed, bagged, and disposed of. Contaminated material is handled with the protective equipment it calls for. Sub-flooring is inspected for damage. Mold treatment is done if needed.
Install and documentation

New insulation is installed in contact with the subfloor with permanent supports, rim joists are sealed, and the finished depth and R-value are photographed for the record and any rebate paperwork.

Pricing Factors

What Affects the Cost of Crawl Space Insulation Replacement?

Modeled 2026 Seattle-area range, before sales tax: Floor insulation replacement (batt removal, new R-30 batt, rim joist air sealing) is modeled at $2,500 to $5,825 for the reference crawl space of 1,200 to 1,500 square feet. Spray foam on the foundation walls (closed-crawl approach) is $4,025 to $8,075, but see the code and rebate notes on this page before choosing it in Washington. Rodent exclusion, mold remediation and vapor barrier replacement are separate scopes: this site models mold remediation at $1,600 to $4,025 and a vapor barrier at $3,400 to $4,675, and publishes no range for rodent exclusion, which is priced by the number of entry points to seal.

Square footage : The floor area insulated sets most of the material and labor, and it is also the figure a per-square-foot rebate is paid on.
Insulation type : Fiberglass batt is cheapest; mineral wool batt costs more but resists moisture better; closed-cell spray foam is most expensive.
R-value : Washington's energy code sets R-30 for new floors, and both utility rebates ask for R-30 (PSE also accepts a full joist cavity). Higher values add material cost.
Old insulation removal : Clean batt is straightforward to remove; rodent-contaminated material adds disposal and protective-equipment labor.
Rim joist treatment : Closed-cell spray foam at the rim joists, beyond the air sealing a standard replacement includes, is priced separately at $1,075 to $2,150.
Support system : Support wires or rigid mesh hold batt against the subfloor; the energy code sets supports no more than 24 inches apart on new work.
Mold remediation : Pre-existing mold on framing or sub-flooring is a separate remediation scope, modeled at $1,600 to $4,025.
Crawl space clearance : Clearances under 18 inches significantly slow batt handling and installation.

Estimate your crawl space insulation replacement cost with the calculator · See the full Seattle-area cost guide

Common Issues

See all crawl space problems and what causes them

Service Area

Crawl Space Insulation Replacement by City

Each city page describes the local ground and housing stock, which shape what a crawl space insulation replacement scope involves there. These are 4 of the 19 service areas this site covers.

More Crawl Space Repair

Related Crawl Space Repair Services

Areas We Cover

King County

Snohomish County

All 19 service areas

Sources

The floor R-value, installation rule, existing-building rule and statewide reach of the 2021 Washington State Energy Code, with the pending 2024 proposal; the City of Seattle's permit exemption for insulating an existing building; the Puget Sound Energy, Snohomish County PUD, Seattle City Light, HomeWise, state HEAR and IRS pages behind every rebate statement; the housing age from this site's dataset; and King County Public Health on rodents. Installed ranges are this site's modeled estimates; see the cost methodology.

Washington State Building Code Council (via Washington State Legislature), WAC 51-11R-10100 — Section R101, Scope and general requirements (2021 Washington State Energy Code, Residential) Checked November 10, 2026

The energy code edition in force and its reach. R101.1 adopts the 2021 edition of the Washington State Energy Code, effective in all counties and cities on March 15, 2024. R101.2 makes it both the maximum and the minimum energy code for residential construction in each town, city and county, so a city cannot set a different floor insulation value for houses.

Note: An emergency rule filed November 4, 2026 (WSR 26-23-002) touches R101.2 for owners rebuilding after the 2026 wildfires. It is not about crawl space work.
Washington State Building Code Council (via Washington State Legislature), WAC 51-11R-40213 — Table R402.1.3, Insulation minimum R-values and fenestration requirements by component (2021 Washington State Energy Code, Residential) Checked November 10, 2026

The floor insulation value for new construction: R-30, in a table with a single column for Climate Zone 5 and Marine 4, which covers the whole state. The table’s columns are fenestration, skylight, ceiling, wood frame wall, floor, below-grade wall and slab; there is no crawl space wall column. Footnote a: insulation installed in a cavity shallower than its label thickness counts at its compressed R-value.
Washington State Building Code Council (via Washington State Legislature), WAC 51-11R-40220 — Section R402.2, Specific insulation requirements (2021 Washington State Energy Code, Residential) Checked November 10, 2026

How floor insulation over a crawl space has to be installed, and what the section leaves out. R402.2.7 gives three ways to comply; the first is cavity insulation kept in permanent contact with the underside of the subfloor decking, with supports no more than 24 inches on center and foundation vents placed so the top of the vent is below the lower surface of the insulation. R402.2.4 requires access hatches and doors from conditioned space to unconditioned space, crawl spaces included, to be insulated to the level of the surrounding surface and weatherstripped. The section has no subsection for crawl space walls: the word “crawl” appears in it only for access hatches.
Washington State Building Code Council (via Washington State Legislature), WAC 51-11R-50300 — Section R503, Alterations (2021 Washington State Energy Code, Residential) Checked November 10, 2026

What the energy code asks of an existing house. R503.1.1: altered parts of the building envelope meet the new-construction requirements, with exceptions that apply where the building’s energy use is not increased. Exception 2: existing ceiling, wall or floor cavities exposed during construction need only be filled with insulation. Exception 3: no requirement where the existing roof, wall or floor cavity is not exposed.
Washington State Building Code Council, WSR 26-14-101, proposed rules adopting the 2024 Washington State Energy Code, Residential (chapter 51-11R WAC) (Filed June 30, 2026; intended adoption September 25, 2026) Checked November 10, 2026

What the pending residential energy code would do to floors over a crawl space. The proposed Table R402.1.3 keeps the floor value at R-30 and adds two alternatives that use continuous insulation, printed as “30 or 19+7.5ci or 20ci”. The proposed R402.2.7 replaces “comply with one of the following” with a list that all applies (insulation to the table value, air-sealed floor framing, supports no more than 24 inches on center, vents below the insulation) followed by a choice of three installation methods. The proposal would move the effective date to May 3, 2027.

Note: A proposed rule, still being revised: the council held work sessions on its R402 provisions in November 2026. Additions are marked by underline in the filing, which is lost when its text is extracted, so this entry reports only what could be read without the marks.
Seattle Department of Construction and Inspections, 2021 Seattle Residential Code, Chapter 1, Administration (Sections R105.1 and R105.2) Checked November 10, 2026

When a building permit is needed in the City of Seattle. R105.1: a permit is required to construct, alter or repair a building, and all work must meet the code whether or not a permit is required. R105.2 item 1: no permit for minor repairs or alterations valued at $6,000 or less in any six-month period, provided no loadbearing support is removed, reduced, altered or relocated and ventilation is not reduced. R105.2 item 2: no permit, provided the building envelope is not changed, for listed work that includes insulating existing buildings and in-kind or similar replacement or repair of deteriorated members.

Note: City of Seattle only, and it is the building permit only: electrical, plumbing and side sewer permits are separate. The chapter does not say how the department classifies a ground cover, a sealed crawl space or a sump basin.
Puget Sound Energy, Weatherization rebates Checked November 10, 2026

The PSE amounts and conditions this site quotes: floor insulation at $2.50 per square foot up to $5,000, in a site-built home built 1989 or before with 0 to 4 inches of existing insulation, finished to R-30 or a full joist cavity, where existing insulation may not be removed to qualify and the thermal boundary may not be moved; floor air sealing at $0.20 per square foot up to $400; duct sealing and insulation up to $1,000 per home, duct sealing only up to $550; that the customer must use PSE electricity or PSE natural gas as the primary source of space heating and live in a single-family home of four units or fewer or a manufactured home; that the work must be done by a PSE Recommended Energy Professional or Trade Ally, who takes the rebate off the invoice; that self-installed work does not qualify; and that the rebate cannot exceed the price of the work.

Note: PSE states that this is a tariffed service that can change or end without notice, and the page gives no program year. The page lists no rebate for a ground cover, vapor barrier, dehumidifier or drainage. It still says a federal tax credit may be available; the IRS says that credit ended for work after December 31, 2025.
Snohomish County Public Utility District No. 1, Weatherization Rebates Checked November 10, 2026

The Snohomish PUD amounts and conditions this site quotes: insulation at $1 per square foot for customers with electrically heated homes, where floor insulation must go from R-11 or less to R-30; duct sealing in a single-family home at $5 per linear foot up to $450; that the customer must own a single-family or manufactured home, or a townhouse or condominium in a building of up to four attached dwellings; and that the work must be done by a PUD registered contractor, who includes the rebate in the bill.

Note: The page states no cap on the insulation rebate and no end date. It lists no rebate for a ground cover, vapor barrier or air sealing.
Seattle City Light, Home Energy Solutions Checked November 10, 2026

That Seattle City Light’s residential page lists no standard rebate for insulation, air sealing or duct sealing: it advises sealing and insulating floors over crawl spaces, and sends insulation help to the income-qualified HomeWise program.

Note: An absence read from one page on one day. City Light’s offers change; check the page before relying on this.
City of Seattle, Office of Housing, Weatherization (HomeWise) Checked November 10, 2026

That HomeWise provides free weatherization, including insulation and duct and air sealing, to income-qualified households: homeowners or renters inside Seattle city limits, and Seattle City Light customers outside the city whose homes are electrically heated; that eligibility depends on income, heat source and whether the home is rented or owned; and that the program selects and manages the contractor.
Washington State Department of Commerce, State Home Electrification and Appliance Rebates (HEAR) Program Checked November 10, 2026

That the state HEAR program’s eligible items are electric equipment (heat pumps, heat pump water heaters, induction cooking, heat pump dryers, and the panel and wiring upgrades they need), and that insulation, air sealing and vapor barriers are not on the list.
Internal Revenue Service, Energy Efficient Home Improvement Credit Checked October 20, 2026

That the credit can be claimed for improvements made through December 31, 2025, so crawl space work done in 2026 does not qualify for it; that it equalled 30% of qualified expenses, with insulation and air sealing materials or systems meeting IECC standards among the qualifying building envelope components; and that it applied to improvements to an existing main home, not to a landlord who does not live in the home.

Note: The IRS summary page, not the statute or the form instructions. It is cited only for the credit’s end date and scope; it says nothing about deductions, rental property or a home sale, which this site does not cover.
United States Census Bureau, American Community Survey 5-Year Estimates — Year Structure Built (B25034) and Median Year Structure Built (B25035) (ACS 2020–2024 5-year estimates, tables ACSDT5Y2024.B25034 and ACSDT5Y2024.B25035) Open dataset Checked November 10, 2026

The housing-age columns for the 19 Washington cities in the Seattle-metro climate and housing dataset: total housing units, median year built with its published margin of error, and the shares of units built before 1980, before 1960 and before 1950, each summed from the B25034 decade buckets per Census place GEOID. Pulled through the data.census.gov table endpoint on 2026-11-10; for every place the ten buckets were summed and checked against the table total.

Note: Survey estimates carrying sampling error, not a census of buildings. They cover ALL housing units in a place, apartments included, rather than single-family homes — and the ACS does not ask about foundation type, so nothing here identifies which units have a crawl space.
Public Health — Seattle & King County, Preventing rodents and keeping them away Checked November 11, 2026

That in King County it is the property owner’s responsibility to prevent conditions on the property that attract rodents; the advice to check inside and outside the house for gaps and holes; and that the department points to CDC’s guidance for cleaning up after rodents rather than publishing its own. Also, read 2026-11-11: that the best trap indoors is the wooden snap trap baited and set near droppings, and poisons are not recommended for rat control inside buildings because poisoned rats die in hard-to-reach places and smell; that firewood should be stacked 18 inches off the ground and bushes, vines and branches kept 3 feet from the house, since roof rats get in from branches over the roof; that heavy infestations may be too extensive to control alone and Public Health then recommends a professional pest control company, asking about integrated pest management; that some crawl space and attic companies also offer pest control; and that pest control companies should be licensed with the Washington State Department of Agriculture.

Note: King County only. Snohomish County’s health department does not run a pest program.

Sources last checked between October 20, 2026 and November 11, 2026; the date beside each one is when it was last opened. Where a figure comes from a document that is revised on a schedule, the edition or version is named above so you can confirm it against the current one yourself.

Questions, Answered

Crawl Space Insulation Replacement FAQs

: Sometimes. If the batt is dry, clean, free of rodent droppings, and was a reasonable thickness to begin with, re-hanging it with proper supports is a legitimate repair. If it has been wet, is contaminated, or shows mold, replacement is the better scope. If you hope to use a rebate, check its rules before anything comes out: PSE pays where existing insulation averages 4 inches or less and says existing insulation may not be removed to qualify, and Snohomish County PUD pays where it is R-11 or less. Ask the utility's contractor how failed insulation is handled under those rules.
: Washington's energy code sets R-30 for floors in new construction and additions, one figure for the whole state, and no city can set a different one for houses. For an existing house, the code asks that a floor cavity opened during the work be filled with insulation, and asks nothing where it is not exposed. Both utility rebates aim at R-30: PSE to R-30 or a full joist cavity, whichever comes first, and Snohomish County PUD from R-11 or less to R-30. If you intend to claim one, specify that figure in writing, and confirm the joist depth can hold it: batt compressed into a shallow bay counts at its compressed R-value.
: This site models floor insulation replacement with batt removal, new R-30 batt, and rim joist air sealing at $2,500 to $5,825 in 2026 Seattle-metro pricing for the reference crawl space, before sales tax. Closed-cell spray foam on foundation walls (closed-crawl approach) runs $4,025 to $8,075. Rodent exclusion, mold remediation and vapor barrier replacement are separate scopes: this site models mold remediation at $1,600 to $4,025 and a vapor barrier at $3,400 to $4,675, and publishes no range for rodent exclusion, which is priced by the number of entry points to seal. Where PSE supplies the home's heating fuel, its floor insulation rebate of $2.50 per square foot, up to $5,000 can come off the invoice through a PSE contractor; the rebate guide has the conditions.
: Batt held against the subfloor is the standard for vented crawl spaces, which are the default in Washington: lower material cost, faster install, and the method the energy code describes when installed with proper support. Mineral wool batt is a middle option that resists moisture better than fiberglass. Closed-cell spray foam on the foundation walls is the approach some sealed crawl spaces use elsewhere, but in Washington it runs into two problems: the residential energy code read for this site gives no insulation path for crawl space walls, so confirm with the building department before treating it as compliant, and PSE's rebate does not allow the thermal boundary to be moved off the floor. Spray foam at the rim joists is a different matter and is common in either case.
: It can, depending on what heats the house. Puget Sound Energy pays $2.50 per square foot, up to $5,000 for floor insulation where PSE electricity or natural gas is the primary heat, in a site-built home built 1989 or before with 4 inches or less of existing insulation, and only as an instant discount through a PSE Recommended Energy Professional or other PSE Trade Ally; self-installed work does not qualify. Snohomish County PUD pays $1.00 per square foot in electrically heated homes it serves, from R-11 or less to R-30, through a PUD registered contractor. Seattle City Light lists no standard insulation rebate for single-family homes; its insulation help runs through HomeWise, the City of Seattle’s free weatherization program for income-qualified households. The federal tax credit ended for work after December 31, 2025. The 2026 rebate guide has the full conditions.
: Older fiberglass batt was typically installed without permanent support, just friction-fit between the joists. Gravity, moisture cycles, and any disturbance from pest activity or HVAC service pulls it down over time. Proper replacement uses insulation support wires or rigid wire mesh along the joist bay to hold the batt against the subfloor; Washington's energy code sets those supports at no more than 24 inches apart on new work. Skipping the supports is the most common reason replacement insulation also falls down within a few years.
: Yes. If there is active rodent activity, replacing the insulation without exclusion work means rats or mice nest in the new material within months. A complete scope includes rodent exclusion (sealing entry points around foundation vents, plumbing penetrations, and rim joists), trapping if needed, and removal of any contaminated material before new insulation goes in. In King County, Public Health puts preventing rodent harborage on the property owner and points to CDC's guidance for cleaning up after rodents; contaminated insulation should be bagged and handled with protective equipment, not swept into the open air. Crawl space cleaning covers the clean-out.
: One to three days for a batt replacement; spray foam runs two to three.
: Usually yes, but the size of the change depends on where you are starting from. A home with no floor insulation at all has more to gain than one whose batt is merely sagging. How well the rim joists get air-sealed matters as much as the R-value of the batt itself, because air leakage at the rim is a separate heat-loss path that new insulation alone does not close. Be skeptical of any specific percentage quoted before an inspection. The improvement homeowners consistently comment on is warmer floors, which is more noticeable day to day than the line on the bill. The utility rebates for this measure, and who can install it, are set out in the 2026 rebate guide.

Ready to Fix Your Crawlspace?

Request a free in-home crawl space inspection and a no-obligation quote for homes in the Seattle metro.