Buying a House With Aluminum or Knob-and-Tube Wiring in Snohomish or King County (2026)

Short answer: You can buy a house with aluminum branch wiring or old knob-and-tube wiring in Washington, but treat it as something to evaluate before your inspection deadline, not after closing. A home inspector will describe the wiring type and flag conductors known to be potentially hazardous. The next step is a licensed electrical contractor, who can tell you what’s there and what a repair involves. For aluminum, the federal CPSC’s repair guide (Publication 516) recognizes only three permanent repair methods. For knob-and-tube, Washington has a specific rule before anyone blows insulation around it.

This is general information, not electrical, legal or insurance advice. Only a licensed electrician can tell you the condition of the wiring in a particular house.

Why these two wiring types come up

An older house may have been rewired in pieces over the decades, so one house can have more than one kind of wiring. Two older types get extra attention.

• Aluminum branch wiring. CPSC Publication 516 (June 2011) says homes built before 1965 are unlikely to have aluminum branch circuit wiring, but cables installed between 1965 and the mid-1970s, in new homes, additions and rewired circuits, may contain it. A national survey by Franklin Research Institute for the CPSC found homes built before 1972 and wired with aluminum were 55 times more likely to have one or more outlet connections reach "Fire Hazard Conditions" than homes wired with copper.
• Knob-and-tube wiring. This is an early system found in some of the oldest houses. Washington doesn’t ban existing knob-and-tube, but WAC 296-46B-394 limits when insulation can be installed around it (see below).

The CPSC also warns that failing aluminum connections "seldom provide easily detected warning signs" and can overheat without any earlier problems. Signs it does list include cover plates or switches that are warm to the touch, flickering lights, circuits that stop working, and the smell of burning plastic at outlets or switches.

What the inspection covers, and what it doesn’t

Washington’s standards of practice for home inspectors (chapter 308-408C WAC) set the floor for what you get. For the electrical system, WAC 308-408C-110 says the inspector will:

• Describe the service, overcurrent devices (fuses or breakers) and "the type(s) of branch wiring used."
• Report "the presence of electrical conductors known to be potentially hazardous" and that a licensed electrical contractor should further evaluate the wiring.
• Test a representative number of accessible switches, receptacles and light fixtures in every room, and the grounding and polarity of a representative number of receptacles.
• Report missing GFCI or AFCI protection where it’s recommended or required, and panels or fuse boxes known to have inherent risks based on design or age.

The same rule says the inspector doesn’t have to remove switch and receptacle cover plates, operate breakers, or move furniture to reach components. WAC 308-408C-030 adds that inspectors don’t judge code compliance, remaining service life or repair costs. So an inspection is a screening step. For more on its limits, see what a standard home inspection covers.

Based on: WAC 308-408C-110 and WAC 308-408C-030 (as amended by WSR 26-15-037, effective Aug. 7, 2026).

Aluminum wiring: what a permanent repair looks like

Aluminum branch circuits are typically No. 10 and No. 12 AWG, compared with No. 12 and No. 14 for copper, according to the CPSC. You can sometimes spot it in an unfinished basement or attic, where the cable jacket is printed "Al" or "Aluminum" every few feet. Read the marking fully: "CU-clad" or "Copper-clad" means copper-coated aluminum, which the CPSC repair guidance doesn’t cover.

The CPSC says it approves only three methods for a permanent repair:

• Complete replacement of the aluminum branch circuits with copper cable.
• The COPALUM method, which crimps a short copper pigtail onto each aluminum wire. The CPSC says every connection has to be done, not just the ones that seem to have trouble.
• The AlumiConn connector, an alternative way to attach a copper pigtail.

The CPSC’s guidance doesn’t apply to the larger aluminum conductors used for service entrance cables, electric dryers and ranges. It also says plainly: "DO NOT TRY TO DO IT YOURSELF." Hire a qualified electrician.

Knob-and-tube: the insulation rule

Old homes with knob-and-tube wiring often also have thin or missing insulation, and buyers usually want to add it. WAC 296-46B-394 allows loose or rolled insulation in spaces with existing knob-and-tube only if all of these are met:

• A licensed electrical contractor surveys the wiring and certifies in writing to L&I that it’s in good condition, with no improper overcurrent protection, no insulation failure or deterioration, and no improper connections or splices.
• The electrical inspector inspects any repairs, alterations or extensions.
• The insulation is Class I with a flame spread of 25 or less. Foam insulation may not be used.
• The circuits have overcurrent protection matched to NEC Table 310.16’s 60-degree column, using circuit breakers or Type S fuses.

If the seller or a prior owner already insulated around knob-and-tube, ask whether that certification exists. If it doesn’t, an electrician’s evaluation is the place to start.

Permits, the seller disclosure and timing

Data from: RCW 64.06.020 (Form 17), RCW 19.28.261, WAC 296-46B-901 and L&I’s electrical permit pages and form F500-094-000. L&I’s list of cities with their own electrical inspection also includes cities outside Snohomish and King County.

RCW 64.06.020 currently has two versions on the Legislature’s site: one marked effective until January 1, 2027, and one effective January 1, 2027. The questions quoted here appear in both. If your sale runs across the new year, check which form is being used.

Schedule the electrician inside your inspection contingency period so you can ask for a repair, a credit, or walk away under the terms of your purchase agreement. If you find wiring done without a permit, our guide to unpermitted work explains the options. Opening walls in an older house can also mean dealing with asbestos in older homes, so ask about that before demolition. For the rest of the timeline, see the closing process.

FAQ

Will a home inspector tell me if a house has aluminum or knob-and-tube wiring?

Usually, if it can be seen. Washington’s home inspector standards (WAC 308-408C-110) require the inspector to describe the type of branch wiring and to report electrical conductors known to be potentially hazardous, with a recommendation that a licensed electrical contractor evaluate them. Inspectors don’t have to remove switch or outlet cover plates or open walls, so wiring hidden behind finishes can be missed.

How do I know if a house has aluminum branch wiring?

CPSC Publication 516 says homes built before 1965 are unlikely to have aluminum branch circuit wiring, while cables installed between 1965 and the mid-1970s may contain it. Visible cable jackets are marked "Al" or "Aluminum" every few feet. A "CU-clad" or "Copper-clad" marking means copper-coated aluminum, which the CPSC repair guidance doesn’t cover. If you can’t tell, the CPSC says to have a qualified electrician check.

Is aluminum wiring a deal-breaker?

Not by itself. The CPSC names three permanent repair methods for aluminum branch circuits: complete replacement with copper cable, the COPALUM crimp method, and AlumiConn connectors. What it costs and whether you want to take it on depends on the house, so get an electrician’s evaluation during your inspection period and decide with real numbers.

Can I insulate an attic or wall that has knob-and-tube wiring?

In Washington, only under the conditions in WAC 296-46B-394. A licensed electrical contractor has to survey the wiring and certify in writing to L&I that it’s in good condition, the insulation has to be Class I with a flame spread of 25 or less, foam insulation can’t be used, and the circuits need breakers or Type S fuses sized to the NEC 60-degree column. Plan for that before you schedule an insulation job.

Can I do the electrical work myself after I buy?

Washington lets owners do electrical work on their own property (RCW 19.28.261), with exceptions such as property offered for sale within 12 months after the owner got it. L&I says to buy a permit only if you’re doing the work yourself, and it strongly encourages hiring an electrical contractor. The CPSC says not to attempt aluminum wiring repairs yourself.

Talk it through with a local agent

Peter Kim and Odigo Real Estate Club can help you time an electrician’s evaluation inside your inspection period and negotiate based on what they find, with 25+ years combined experience, 593+ closings, and 122 five-star Zillow reviews. See our home buying services.

Odigo Real Estate Club · REAL Brokerage, WA #112064 · 16108 Ash Way, Suite 201, Lynnwood, WA 98087 · (425) 409-3823 · Mon–Sat 9 AM–6 PM, closed Sunday

Sources

• U.S. CPSC, Repairing Aluminum Wiring, Publication 516 (June 2011; 1965 to mid-1970s; 55 times; three permanent repair methods), https://www.cpsc.gov/s3fs-public/516.pdf , accessed Nov 4, 2026.
• Washington State Legislature, WAC 308-408C-110 (home inspector standards of practice: electrical), https://app.leg.wa.gov/wac/default.aspx?cite=308-408C-110 , accessed Nov 4, 2026.
• Washington State Legislature, WAC 308-408C-030 (home inspector standards: exclusions and limitations), https://app.leg.wa.gov/wac/default.aspx?cite=308-408C-030 , accessed Nov 4, 2026.
• Washington State Legislature, WAC 296-46B-394 (concealed knob-and-tube wiring; insulation conditions), https://app.leg.wa.gov/wac/default.aspx?cite=296-46B-394 , accessed Nov 4, 2026.
• Washington State Legislature, WAC 296-46B-901 (electrical work permits and fees), https://app.leg.wa.gov/wac/default.aspx?cite=296-46B-901 , accessed Nov 4, 2026.
• Washington State Legislature, RCW 19.28.261 (exemptions from electrical licensing, including owners working on their own property), https://app.leg.wa.gov/RCW/default.aspx?cite=19.28.261 , accessed Nov 4, 2026.
• Washington State Department of Labor & Industries, Electrical permits, fees & inspections (permits and the adopted NEC edition), https://lni.wa.gov/licensing-permits/electrical/electrical-permits-fees-and-inspections/ , accessed Nov 4, 2026.
• Washington State Department of Labor & Industries, Purchase permits & request inspections (owner permits; 1-year permits; inspection timing), https://lni.wa.gov/licensing-permits/electrical/electrical-permits-fees-and-inspections/purchase-permits-request-inspections , accessed Nov 4, 2026.
• Washington State Department of Labor & Industries, City electrical permits & inspections (cities that do their own electrical inspections), https://lni.wa.gov/licensing-permits/electrical/electrical-permits-fees-and-inspections/city-electrical-permits-inspections , accessed Nov 4, 2026.
• Washington State Department of Labor & Industries, Property Owner Electrical Work Permit Application, F500-094-000 (owner affidavit), https://lni.wa.gov/forms-publications/F500-094-000.pdf , accessed Nov 4, 2026.
• Washington State Legislature, RCW 64.06.020 (seller disclosure statement form; version effective until Jan 1, 2027 and version effective Jan 1, 2027), https://app.leg.wa.gov/RCW/default.aspx?cite=64.06.020 , accessed Nov 4, 2026.