Retrofit and Existing Home Insulation

Most of Duluth was built before anybody thought about air sealing, and a good share of it was built before 1940. That means the work here is rarely a clean install. It is figuring out what somebody else did in 1912, 1954, and 1978, deciding what has to come out, and spending your money where it actually returns something.

Call (218) 514-6594 and we will walk the house with you.

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The order of operations, if you only read one section

If you have a cold, expensive old house and a real budget rather than an unlimited one, do it in this order.

1. Attic air sealing. $1,500 to $3,000. The highest return dollar in the building. This is foam and sealant at every penetration in the attic floor, blocking at open wall cavities, and dealing with the attic hatch. It is also the ice dam fix.

2. Attic insulation to depth. $1,500 to $3,000 on top of the sealing. R-49 minimum, R-60 if the budget allows. Usually blown cellulose over the sealed floor rather than foam, because that is far cheaper per R-value.

3. Rim joists. $1,200 to $2,500. Three inches of closed cell around the perimeter of the basement. See the rim joist page.

4. Crawl space, if you have one. $4,000 to $9,000. Jumps to the front of the line if it is wet or if pipes have frozen. See the crawl space page.

5. Basement walls. $3,000 to $5,000 if you are finishing the basement anyway.

6. Walls. Last. Most expensive per unit of benefit, most disruptive, and only really practical when you are already residing or gutting.

That order holds for the great majority of houses in this town, and it holds because of physics rather than preference. Warm air rises, so the leaks at the top of the house drive the leaks at the bottom, and the attic is the cheapest surface to reach.

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What is actually going on in an old Duluth house

Balloon framing

Houses built before roughly 1930, and there are a lot of them on the hillside and in the older neighborhoods, were framed with studs running continuously from the foundation sill to the attic. There is no plate between floors blocking the cavity.

What that means practically: your wall cavities are vertical ducts. Basement air, which is where the mustiness and the moisture live, has a straight uninterrupted path to the attic. The stack effect drives it up all winter.

You can fill those cavities with insulation and it will not stop the air movement, because insulation is not an air barrier. What stops it is blocking and sealing the cavities at the top, in the attic, where the stud bays open into the attic floor. That is foam work and it is one of the highest value things we do in this housing stock.

Knob and tube wiring

Still energized in more Duluth houses than you would guess. It is easy to spot: individual cloth-wrapped conductors run separately, supported on white ceramic knobs, passing through framing in ceramic tubes.

It was designed to run in open air and shed its heat that way. Burying it is a fire hazard, and it is also generally an insurance problem. If it is live in your attic, an electrician replaces it before insulation goes in. There is no version of this where we work around it.

We will tell you if we find it. Some contractors bury it and say nothing.

Vermiculite

Loose, pebbly, gray-brown granules in the attic. A large share of the vermiculite sold in North America came from a mine in Libby, Montana, that was contaminated with asbestos. It gets tested before it gets disturbed, and if it tests positive it is an abatement job for a licensed abatement contractor, not an insulation job.

We do not disturb it and we will tell you exactly what we are looking at.

Old fiberglass in the rim joists and crawl space

Comes out, every time. That is where it has been trapping moisture against cold wood for decades. Frequently there is staining or rot behind it that nobody has seen since it went in.

Bath fans venting into the attic

Very common in Duluth houses from the 1960s through the 1990s. A bathroom fan discharging into a cold attic is a frost machine and a direct heat source under the roof deck. It gets ducted through the roof or the gable with an insulated duct and a proper exterior termination.

Chimney chases

Old masonry chimneys usually have a gap around them at every floor and at the attic, and those gaps are big and warm. They need fire rated sealing with proper clearance to the flue. Spray foam does not go directly against a flue.

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Walls in an existing house, honestly

This is the question we get most and the answer people like least.

Spray foam needs an open cavity. If your walls are closed, spray foam is not the product unless something is coming off. So the real question is when the wall is open anyway.

Good moments to foam an existing wall:

• You are residing the house and the sheathing is coming off
• You are gutting a room to the studs
• You are doing an addition or bumping out a wall
• A section of wall is open for other work

When the wall is staying closed, the options are dense pack cellulose or injection foam through drilled holes. Both are real products installed by real contractors. Both have limitations worth knowing:

• They fill the cavity but they do not seal it as completely as spray foam applied to an open bay
• Neither can do anything about a balloon framed cavity’s vertical air path
• Plaster over lath is vulnerable. Expanding material behind old plaster can crack the keys and pop it off the lath. Anybody proposing this should tell you who owns that repair.

Our honest position: walls are the last dollar, not the first. On an old Duluth house, a well done attic and rim joist package will change how the house feels. Wall insulation rarely will on its own, and it costs multiples more.

If we are not the right contractor for what your wall needs, we will say so and point you elsewhere.

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Air sealing an old house without causing a moisture problem

This is a real consideration and we would rather raise it up front.

An old leaky house ventilates itself continuously by accident. It is a lousy, uncontrolled, expensive way to move air, but it does move air, and it carries indoor moisture out with it. Seal the house and that stops.

Signs the house needs a deliberate ventilation plan after tightening:

• Condensation on the inside of windows in cold weather
• A damp feeling in the house in winter
• Frost on the inside of window frames

The fixes, roughly in order of cost:

• Bath fans that actually vent to the outside and get used
• A kitchen range hood that vents outside rather than recirculating
• Running the bath fan on a timer or a humidity sensor
• A balanced ventilation system, an HRV or ERV, on a house that has been sealed well

We are not the mechanical contractor. What we can do is tell you honestly where the house is heading and whether the job we are quoting will get you there.

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Rebates and incentives

Here is the honest version, current as of July 2026.

The federal tax credit for insulation is gone. For years a homeowner could claim 30 percent of insulation and air sealing costs, up to $1,200 a year, under what the IRS called the Energy Efficient Home Improvement Credit. Congress ended it in the 2025 tax law. It does not apply to anything placed in service after December 31, 2025. If you are insulating in 2026 there is no federal credit waiting for you, and anyone who tells you otherwise is working off an old page. Nothing has replaced it.

One detail that catches people: the test is when the work was placed in service, not when you paid for it. A deposit written in 2025 on a job finished in 2026 does not qualify. If your project straddles the two years, that is a question for your own tax preparer.

Locally there is less than you might hope, and none of it is money off the insulation itself. Minnesota Power and the City of Duluth’s ComfortSystems both help pay for a real energy audit, the kind with a blower door test and an infrared scan. Minnesota Power puts $100 to $200 back depending on how your house is heated, and ComfortSystems rebates $150. Both want the audit done by a participating provider, so ask before you book one. Neither currently pays a rebate on insulation or air sealing. The audit is still worth doing before you spend money, because it tells you which part of your house is actually leaking.

If you are across the bridge in Wisconsin, you are in better shape. Focus on Energy is a Wisconsin program, it requires an account with a participating Wisconsin utility, and it is the one program in this region that pays real money toward the insulation work itself rather than just the audit. It is not available on the Minnesota side, so a Duluth address cannot use it. Three things to sort out before the work rather than after: the amounts and the eligibility window are set per program year and change, so confirm the current terms with Focus on Energy directly instead of trusting a number on anybody’s website. The air sealing rebate requires an energy assessment first. And the standard rebates require a contractor registered with the program, with the application postmarked within 60 days of installation.

One local program does pay for insulation outright, and it is income qualified. The Weatherization Assistance Program is run in St. Louis County by AEOA. If your household qualifies on income, the work is done at no cost to you, and it covers insulation and air sealing. It is their crews and their materials, not ours, so we do not make a dime telling you about it. Worth a call before you take a quote from anybody, including us.

Programs change. Verify anything here with the utility or the program before you count on it, and ask a tax professional about your own situation rather than trusting a contractor’s website, including this one.

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Walk the house with someone who will tell you the truth

The most useful thing we do on an old house is stand in the attic and the basement with you and say what we see, including the parts that are not our work. Sometimes the answer is a $1,500 air sealing job and a downspout extension.

Call (218) 514-6594 or send the form with the address, roughly when the house was built, and what it is doing that bothers you.

See also: attic insulation, rim joist insulation, crawl space insulation.