# Does knob and tube wiring have asbestos?

> Does knob and tube wiring have asbestos? What only testing settles, how Massachusetts lead-safe rules apply to rewiring and why vermiculite changes the plan.

URL: https://deckerbostonknobandtube.com/guide/asbestos-and-lead-paint-during-rewiring/

Knob and tube conductors are insulated with rubber and woven cloth, and nothing in a visual inspection can prove whether a particular old material in a house contains asbestos. Only laboratory testing of a sample settles that. [Decker Boston Knob and Tube](https://deckerbostonknobandtube.com/) arranges knob and tube replacement across Boston and nearby cities, carried out by licensed and insured electricians, and in an older house the plan has to account for three materials that sit where the work goes.

Two of them have clear Massachusetts rules. Lead paint is governed by the state’s lead-safe renovation regulations, and vermiculite attic fill is named by Mass Save as a barrier to insulation. Asbestos is the one that has to be tested before anyone can say anything certain.

Key takeaways

- Knob and tube wire is covered in rubber and cloth. Whether any material near the work contains asbestos is a lab question, not a looks question.
- Pre-1978 house, more than six square feet of painted plaster opened in one room, no lead test: under 454 CMR 22.00 that’s renovation work for a licensed lead-safe renovation contractor.
- Fishing cable through small openings can stay under that line; opening long runs of plaster usually won’t.
- Mass Save treats vermiculite attic fill, like live knob and tube, as a barrier to insulation.
- Mass Save’s barrier incentive and HEAT Loan, and a Boston Home Center loan, can help with vermiculite as well as wiring.

## What the wire itself is made of

Original knob and tube conductors are solid copper with a layer of rubber, then a woven cloth covering. Where they enter a box or fixture, they run through loom, a flexible woven sleeve. That’s the standard construction.

### Why the asbestos question comes up anyway

Houses of this age were built and altered with materials whose makeup can’t be read from the outside, and wiring, fixtures and insulation were often added at different times by different hands. Looking at a wire or sleeve can’t tell you its contents, and neither can its age.

### What to do with the question

- **Don’t disturb it to find out.** Cutting, stripping or crumbling old insulation releases whatever is in it, and a run that seems dead may be live.
- **Raise it before the scope is set.** If something near the work looks suspect, say so at the first visit so testing, if needed, can happen before routes are planned.
- **Let the result decide.** If a material tests positive, it is dealt with by people qualified for that work before the electrical job disturbs it. If it tests negative, the rewire proceeds as planned.

## Lead paint and the openings a rewire needs

Lead paint is the material most likely to shape the plan, because a rewire has to reach behind painted plaster. Massachusetts sets a clear threshold.

### The rule

Under 454 CMR 22.00, from the state’s Department of Labor Standards, target housing is any housing built before 1978, with exceptions for elderly or disabled housing where no child under six lives and for zero-bedroom dwellings. Renovation includes removing portions of a structure, such as walls and ceilings.

| Work in a pre-1978 home | How the rule treats it |
| --- | --- |
| Six or fewer square feet of painted surface disturbed per room, inside | Minor repair and maintenance |
| Twenty or fewer square feet disturbed outside, in total | Minor repair and maintenance |
| More than six square feet per room inside, or partial demolition of painted surfaces, without lead testing | Renovation work, carried out by a licensed lead-safe renovation contractor under 454 CMR 22.11 |

### What it means for a rewire

A rewire fished through the house’s own cavities, with small openings at boxes, top plates and blocked framing, can often stay at or under six square feet in each room. A rewire that opens long runs of wall or ceiling, or one combined with a renovation, usually can’t. Once a room crosses the line, the work needs a licensed lead-safe renovation contractor and containment, which changes the setup, the cleanup and the cost.

### Exterior work

The exterior threshold is 20 square feet in total. A service upgrade that disturbs painted trim or siding around a new mast or meter can count toward it, which is worth knowing in a historic house where exterior work may already need review. The [historic district guide](https://deckerbostonknobandtube.com/guide/rewiring-a-house-in-a-boston-historic-district/) covers that.

> Plan opening size from the start
>
> The cheapest way to handle lead-safe rules is often a route plan that keeps each room’s openings small. Ask for the planned openings per room in writing, and see the [plaster wall rewiring](https://deckerbostonknobandtube.com/plaster-wall-rewiring/) page for how they’re cut.

## Vermiculite in the attic

Loose, granular fill between attic joists, often gray-brown with a shiny, pebbly look, may be vermiculite. It matters to a rewire for two reasons.

### Why it’s treated with care

The asbestos question owners ask about wiring applies to attic fill too, and so does the answer: only testing tells you what the fill in your attic contains. Until then, don’t dig through it, sweep it or store things on it, and tell the electrician before anyone works across the attic floor.

### Why Mass Save cares

Mass Save treats vermiculite as a barrier to recommended insulation, alongside live knob and tube. When both turn up in the same attic, they are planned together: deciding how the fill is handled comes before routing new cable across the joists or [removing old runs](https://deckerbostonknobandtube.com/knob-and-tube-removal/) there. The [insulation barrier service](https://deckerbostonknobandtube.com/knob-and-tube-insulation-barrier/) covers the knob and tube side of that certification.

## How the three change the sequence

Each material adds a decision near the start of the job, not a surprise in the middle. The usual order looks like this.

1. **First visit:** [trace the circuits](https://deckerbostonknobandtube.com/knob-and-tube-inspection/) and note any suspect materials, painted surfaces that routes will cross and attic fill.
2. **Testing, where needed:** before routes are fixed, so the plan reflects the results.
3. **Route plan:** openings per room sized with the lead-safe threshold in mind.
4. **Fill and hazard work, where needed:** done by the right specialist before electrical work disturbs the area.
5. **Rewire, inspection, disconnect, test:** the normal sequence in the [replacement process guide](https://deckerbostonknobandtube.com/guide/how-knob-and-tube-replacement-works/).
6. **Closing and cleanup:** to lead-safe standards where the rule applies.

For a household staying at home, the [living at home guide](https://deckerbostonknobandtube.com/guide/living-at-home-during-rewiring/) covers keeping children and pets out of work areas.

## Programs that help with these costs

Several programs that cover knob and tube also cover vermiculite or asbestos. Eligibility depends on income and, for Mass Save, on a Home Energy Assessment first.

| Program | What it covers here | Who qualifies |
| --- | --- | --- |
| Mass Save enhanced barrier incentive | Up to $7,000 of eligible removal costs for knob and tube or vermiculite | Moderate-income households in one- to four-unit homes whose assessment recommended insulation the barrier blocks |
| Mass Save HEAT Loan | 0% financing for pre-weatherization barriers, including knob and tube and vermiculite | Homeowners with a Mass Save sponsor account, after a Home Energy Assessment |
| Boston Home Center Home Repair and Improvement Loan | Its covered list names removal of asbestos, vermiculite or knob and tube wiring | Income-eligible Boston owner-occupants of one- to four-family homes |

Work done before approval isn’t reimbursed under the Boston Home Center program, and HEAT Loan financing doesn’t cover work finished before authorization, so apply before you sign. The [grants guide](https://deckerbostonknobandtube.com/guide/knob-and-tube-removal-grants-massachusetts/) explains each program, and the [cost guide](https://deckerbostonknobandtube.com/guide/knob-and-tube-replacement-cost-boston/) shows where hazard testing sits in a budget.

If you suspect lead, asbestos or vermiculite near wiring that needs replacing, mention it when you call Decker Boston Knob and Tube at [(617) 405-3599](tel:+16174053599) or [ask for an estimate](https://deckerbostonknobandtube.com/contact/), so the plan accounts for it from the first visit.

## Questions about this guide

### Can I send a sample of my old wiring insulation for asbestos testing myself?

Don't cut or strip wiring to get one. Even wiring that looks dead may be live, and taking a sample disturbs the material you're worried about. If testing is needed, the sample should be taken by someone qualified to do it safely, with the circuit confirmed dead by a licensed electrician first. Tell the electrician what you suspect before the work is scoped.

### Does Massachusetts lead-safe renovation apply if I own and live in the house?

The rules apply to work done for a fee in target housing, which Massachusetts defines as housing built before 1978, with exceptions such as housing for the elderly or disabled where no child under six lives, and zero-bedroom dwellings. A contractor rewiring your house is working for a fee, so the six-square-foot-per-room threshold applies to the openings the job needs.

### Will Mass Save help pay to deal with vermiculite before a rewire?

Possibly. Mass Save treats vermiculite, like live knob and tube, as a barrier to recommended insulation, and its enhanced barrier incentive of up to $7,000 for moderate-income households covers eligible removal costs for either. The HEAT Loan's 0% financing also covers pre-weatherization barriers. Both start with a Home Energy Assessment, so book that before signing a contract.

Want this answered for your house?

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## Related service

### Plaster Wall Rewiring →

New circuits fished through plaster-and-lath houses with routes planned to keep openings few and small, and patching scoped in writing.

## More guides

Learn

How is knob and tube wiring replaced?

A rewire runs in an order the code partly sets. Each stage depends on the one before it, and knowing the order explains most of the schedule and the price.

Learn

Can you live in a house while rewiring?

Most households stay put through a knob and tube rewire. What makes that comfortable is planning the shutdowns, the dust and the heat before the first circuit goes dark.

Learn

What changes when you rewire a historic home in Boston?

District commissions care about what the street can see, so most of a rewire never reaches them. The parts that do are the meter, the mast and the conduit, and inside, the plaster and trim are yours to protect.

Decision Guide

Are there grants for knob and tube removal in Massachusetts?

True grants are rare. The real help runs through Mass Save's insulation programs and a few city and state loans, and the order you apply in matters as much as which one you pick.

Learn

How do you identify knob and tube wiring?

A field guide for owners and buyers: where to look in a Boston-area house, what each part of the system looks like, what gets mistaken for it, and where looking stops being enough.