Knob-and-tube isn't unsafe because it's old.

The history

Knob-and-tube (K&T) wiring was the standard residential wiring method in the United States from roughly 1880 to 1940. Two separate conductors — a hot and a neutral — run in air through ceramic insulators, with the conductors held off framing by porcelain knobs and passed through joists in porcelain tubes. The system has no equipment grounding conductor; the metallic enclosure of every fixture is bonded to nothing.

K&T was a competently engineered system for the loads it was designed to serve: incandescent lighting, a radio, perhaps an iron. Modern loads (refrigeration, HVAC, induction cookers, EV chargers) it cannot serve safely. The exact failure modes are visible in any house that has had its K&T re-fed by handy owners over a century:

1. Splice into NM-B with no junction box. A K&T conductor and a modern Romex meeting in mid-air, taped, behind plaster. Common.
2. Re-fed circuit overloaded. What was a 5A radio circuit in 1925 is now a 15A bedroom branch with a window AC. The original conductors and insulation aren't sized for it.
3. Insulation deterioration on un-loaded conductors. Cloth-and-rubber insulation degrades by oxidation, not by use. After 90 years it is brittle whether or not anyone ran current through it.
4. Insulation contact. K&T is rated to operate above ambient because heat dissipates by convection in air. Owners who blow cellulose insulation into the attic remove the convection path; the conductors run hotter, the insulation degrades faster, and the re-fed splices become tinder.

What this job is

A J-04 is a partial or complete rewire of a 1820–1940 Vermont farmhouse. We work it as an inventory: every K&T circuit gets traced, decided on, and either restored to the new panel via NM-B or marked dead. We do not leave a working house with a mix of K&T and modern in the same circuit; that is the failure mode that started the work. We also test every retained K&T circuit (sometimes there is a ceiling-light run that's safe to keep) with a 500V or 1000V megger and document the result.

Plaster-preserving fishing methods

Most of what makes a heritage rewire expensive is preserving plaster. The owner doesn't want to replace it; we don't want to tear it. The methods we use, in roughly the order we reach for them:

• Attic-floor and basement-ceiling fish. Most circuits in a Vermont farmhouse run through one of those two cavities; if we can get to the joist bay from above and below, we can fish a NM-B with steel fish-tape and a magnet without opening a single wall.
• Closet-back access. A bedroom closet is plaster-on-lath we will accept opening, because re-plaster on a closet back is straightforward and invisible.
• Outlet relocation. Sometimes the cheapest way to wire a 21st-century outlet on an exterior wall is to put it on the inside of the closet back instead, where the rough-in is a 6-inch hole.
• Surface-mount EMT or wireway in less-historic spaces (mudroom, shop, basement). Honest, reversible, and fast.
• Wall opening as last resort. When we open plaster, we mark the cut for a clean re-plaster, and we coordinate with a Preservation Trades Network-trained plasterer if the customer wants original-method repair.

We will tell you, in writing, before we start, which walls we expect to open and why. The number rarely exceeds three on a typical 5-bedroom farmhouse; on the Cabot Hill 1851 cape we opened only the closet back, and re-plaster cost the customer $0.

What's included

• Walkthrough of every K&T circuit, marked on a plan drawing.
• Megger test of every K&T circuit before the work starts.
• Replacement of every active K&T branch with NM-B 14/2 or 12/2.
• New AFCI/GFCI combination breakers on every replaced branch, per NEC 210.12.
• Panel changeout (typically Square D QO Plug-on Neutral, 30–40-space).
• Two-way switch restoration where the customer wants it (we use Lutron Diva for matching mid-century plate styles where the original was push-button).
• Junction-box accountability: every splice in the new system is in an accessible box.
• Permit at VT DFS; inspection coordination.

What's not included

• Plaster repair beyond rough patch. Coordinated to a separate plasterer; recommended is This Old House-style or PTN-trained.
• Insulation. If the customer is also re-insulating an attic, we coordinate the order: rewire first, insulation second.
• Retention of period push-button switches as functional. We keep them as collectible, not as in-circuit. Modern code requires a different mechanism.

Price band

Scope	Typical low	Typical median	Typical high
Targeted partial (1–3 circuits)	$1,200	$2,400	$4,800
Single floor (~5–10 circuits)	$3,800	$6,500	$11,000
Whole-house rewire (5BR farmhouse)	$14,500	$24,000	$38,000
Whole-house rewire + panel + service	$22,000	$34,500	$52,000

Related

For a worked example, see Cabot Hill knob-and-tube remediation. The companion almanac entry on what April mud-season service-call looks like is April: Mud-Season Service Calls.