Attic, Wall & Crawl Space Insulation

The Department of Energy recommends approximately R-49 to R-60 for attics in Minnesota's cold climate zone. A great many Twin Cities homes built before the 1990s came in at R-19 to R-30 and have settled since, which means they are now well below even the standard of their own era.

Depth is a rough proxy you can check yourself. If your attic insulation is level with or below the ceiling joists, you are short. Blown fiberglass and cellulose can usually be topped up over existing material without removing what is there, provided the existing insulation is dry and not contaminated.

It is most of the answer, yes. Ice dams form when heat leaks from the living space into the attic, warms the roof deck, and melts snow that then runs down and refreezes over the cold eave where there is no heat beneath it. The ridge of ice that builds up backs meltwater under the shingles and into the house.

The fix is to stop heating the roof deck: air seal the ceiling penetrations, insulate to the correct R-value, and make sure soffit-to-ridge ventilation is actually moving cold air under the deck. Steaming the ice off treats the symptom and is sometimes urgently necessary — but a house that dams every single winter has an insulation and ventilation problem, and we would rather fix that once.

Blown fiberglass and cellulose are the workhorses for open attic floors — fast to install, good coverage over irregular framing, and easy to top up later. Cellulose packs slightly denser and resists air movement a little better; fiberglass does not absorb moisture.

Spray foam earns its higher cost in rim joists, crawl spaces, cathedral ceilings, and anywhere the insulation also has to be the air barrier. Rim joists in particular are a large, commonly-missed source of winter heat loss in Minnesota basements and are cheap to address.

Look at the joists. If you can see the tops of the ceiling joists when you look across the attic floor, or the insulation is level with them, you are well short of what Minnesota needs. Joists are typically 8 to 10 inches deep, and R-49 to R-60 in loose-fill means considerably more depth than that.

The other tells are practical ones: rooms that never hold heat evenly, a furnace that runs constantly through January, ice dams every winter, and snow melting off your roof faster than it does off your neighbours'. That last one is worth paying attention to — a roof that clears its snow early is a roof being heated from below.

Insulation slows heat conduction. It does very little to stop air moving. If warm, moist household air is streaming into the attic through gaps around light fittings, bath fans, plumbing stacks and the attic hatch, laying more insulation on top does not stop it — the air simply moves through.

That is why we air seal the ceiling plane before adding depth. Sealing those penetrations is usually the cheaper half of the job and it does more for both your heating bill and your ice dams than the insulation on its own. Insulation added over unsealed penetrations is the single most common mistake we find in Twin Cities attics.

It is the most commonly missed source of heat loss in a Minnesota house. The rim joist is the band of framing around the perimeter of the floor structure, sitting directly on the foundation, and in most older homes it is either bare or stuffed with a scrap of fiberglass that does nothing to stop air movement.

Spray foam here is genuinely worth the money. The area is small, so the cost is modest, and it addresses both insulation and air sealing in one pass at a spot that leaks continuously all winter.