The short answer: Williams County is in IECC Climate Zone 7, and the 2021 code minimums for a house here are R-60 in the ceiling, R-20 in the walls plus R-5 of continuous insulation, R-15 on basement walls, and R-10 at crawl spaces and slab edges. Most houses in Williston built before 1980 are well under those numbers, especially in the attic and at the rim joist, and boom-era houses from 2010 to 2015 met a lower code of the day with uneven execution. The attic is usually the first place to spend money, and air sealing should come before any of it.

What is R-value, in plain terms

R-value measures how much a material resists heat flowing through it. Higher is better. The number adds up through a layer: 2 inches of a material rated R-3.5 per inch is about R-7, and 4 inches is about R-14.

Different materials get there at different rates. Blown fiberglass and cellulose are in the neighborhood of R-3 to R-4 per inch. Fiberglass batts and mineral wool are similar. Open-cell spray foam is about R-3.5 to R-3.8 per inch. Closed-cell spray foam is around R-6 to R-7 per inch, and rigid foam board falls in between depending on the type. So R-60 in an attic means a deep blanket of blown material, somewhere in the range of 16 to 20 inches depending on the product, or a much thinner layer of foam.

What R-value does my house need?

Here is what the 2021 IECC says for Climate Zone 7, which covers Williams County and the rest of the northwest corner of the state.

Ceiling (attic floor): R-60. This is the biggest number and the most common place a house falls short.
Above-grade walls: R-20 cavity plus R-5 continuous. The continuous part means a layer of rigid foam board or similar on the outside of the studs, unbroken by framing.
Basement walls: R-15. That is the whole wall, top to bottom, not a couple of feet at the top.
Crawl space walls and slab edges: R-10.

These are minimums for new construction. Nobody is going to make you bring a 1975 house up to them. They are still the right target, and everything short of them is a compromise you pay for every month from November through March.

Zone 7 is the coldest zone in the lower 48. A lot of insulation advice online is written for Zone 4 or 5, where an R-38 attic is fine. Here it is not. If a national article tells you R-38 or R-49 is plenty, it was not written for Williston.

What Williston houses probably have

We cannot tell you what is in your walls without looking, but the housing stock here falls into a few groups, and each one has a pattern.

Pre-1980 houses

The older neighborhoods in Williston, the ranch houses and story-and-a-half houses from the 1950s through the 1970s, were built when insulation was an afterthought. Walls are often 2x4 with thin batts or nothing. Attics usually got a few inches of loose fiberglass or rock wool, and fifty winters of settling, wind-washing at the eaves, and people crawling through to fix a light have pushed that blanket down to 3 to 6 inches in a lot of places. That is R-10 to R-20 at best, with bare spots where it is nearly nothing.

The rim joist, the band of lumber sitting on top of the basement wall where the floor joists land, is almost always uninsulated in these houses. You can see daylight at the sill in some of them. The basement walls are usually bare concrete block or poured concrete.

The 2010 to 2015 boom builds

Williston grew fast during the boom, and a large share of its newer houses, along with the apartment and townhome complexes, went up between 2010 and 2015. Those houses were built to the code in force at the time, which asked for less than the 2021 version (attic R-49 was typical). Most of them have a reasonable attic by the numbers.

The problem with boom-era houses is execution. Crews were coming from everywhere, working through the winter, under pressure to close. We see attics with the right depth on the insulation bag tag and thin spots near the hatch and along the eaves, batts pushed aside for the HVAC crew and never put back, no baffles at the soffit so the wind blows the blanket off the edge, and air sealing at the ceiling plane that was never done at all. The house meets the number on paper and loses heat through every can light.

How to check your own attic

This takes ten minutes and a flashlight.

Find the attic hatch, usually in a closet or hallway ceiling. Pop it and look before you climb. You are looking for three things.

Depth. Lay a tape measure or a yardstick into the insulation straight down to the drywall. If you see the tops of the ceiling joists (usually 2x6 or 2x8, so 6 to 8 inches), you are at R-20 or less. Roughly, every 3 inches of blown fiberglass or cellulose is about R-10, so 10 inches is near R-35 and you need about 18 inches to be near R-60.

Evenness. Look toward the eaves and toward the far corners. Wind-washing pushes loose insulation away from the edges, so the depth near the hatch can be twice the depth at the eave. Look for dark patches, which are spots where air has been moving through the insulation and filtering dust out of it. Those are your air leaks, and they tell you where heat is escaping.

What it is. Gray, fluffy, paper-like material is cellulose. Pink, yellow, or white fibers are fiberglass. Coarse gray-brown material that looks like dryer lint with grit in it is old rock wool. Any of these can be topped up. If it is wet, compressed, moldy, or full of rodent activity, it may need to come out before anything goes on top.

While you are up there, look at the hatch itself. A bare plywood hatch with no weatherstrip and no insulation on its back is a hole in the ceiling the size of a window.

Why air sealing changes the effective number

Insulation slows heat moving through a material. It does nothing about warm air leaving the house through a gap. A Williston house on a January night with a northwest wind is under pressure: the wind pushes on one side, warm air rises and escapes at the top, and cold air is pulled in at the bottom to replace it. Every hole in the ceiling plane, every plumbing stack, wire penetration, recessed light, the chase around the chimney, the top of every interior wall, is a chimney.

Loose-fill insulation does not stop that air. It filters it. A foot and a half of blown fiberglass with air moving up through it performs nowhere near its rated R-60 because the air carries the heat right past the material.

The fix is to seal the ceiling plane first, then insulate. Foam the penetrations, seal the top plates, box the can lights or swap them for sealed fixtures, weatherstrip and insulate the hatch. Our air sealing work is almost always the first step before we add a blanket of blown material. Done in that order, the rated R-value of the new insulation is close to the real one.

The same logic applies at the bottom of the house. The rim joist leaks more air than any single spot in most older Williston basements, and it is too irregular for batts to seal. Two inches of closed-cell foam there closes the bottom of the chimney. We cover this on our crawl space and rim joist page.

How to prioritize

Most people cannot do everything at once. This is the order we would spend in for a typical older house in Williston, and the reasoning.

1. Seal and insulate the attic. Heat rises, so the ceiling is where the house loses the most, and it is the cheapest place to add a lot of R-value. Air seal the ceiling plane, fix the hatch, add baffles at the eaves, then blow in enough material to reach R-60.

2. Rim joist. Small area, big leak, sits at the cold bottom of the stack effect. Closed-cell foam here is a half-day job with an outsized effect on drafts across the floor.

3. Basement walls. Bare concrete below grade loses heat to frozen soil all winter. Rigid foam board against the wall, with or without a framed wall in front of it, gets you to R-15 and makes the basement usable. The rigid foam board approach here avoids the moisture problems fiberglass against concrete can cause.

4. Walls. Above-grade walls are last because they are the hardest to change in an existing house. If you are residing anyway, adding R-5 continuous foam board under the new siding is the time to do it.

Before you start, ask MDU, the gas and electric utility in Williston, about current utility rebate programs for insulation and air sealing. We cannot tell you what they are offering this season, and the programs change, but it takes one call.

Common questions

Is R-60 in the attic really necessary, or is R-49 enough?

R-60 is the 2021 code minimum for Climate Zone 7 and it is the right target here. R-49 was the previous requirement and a lot of boom-era houses have it. The difference is a few more inches of blown material on top of an attic that is already open, so if you are in there anyway, go to R-60.

Can I just add more insulation on top of what is already there?

Usually, yes, as long as the existing material is dry, clean, and the ceiling has been air sealed first. Adding a blanket on top of a leaky ceiling wastes much of the new R-value. If the old insulation is wet, moldy, or full of rodent mess, it should come out first.

Does my 2012 house already meet code?

Probably on paper, for the code in force when it was built, which asked for less than the 2021 version. Execution on boom-era houses varies a lot. Look for thin spots at the eaves, missing baffles, and dark patches in the insulation, which are signs of air movement. Many of these houses gain more from air sealing than from more insulation.

What R-value do I get from spray foam in a wall?

Closed-cell foam runs roughly R-6 to R-7 per inch, so 3 inches in a 2x4 wall is around R-20. Open-cell runs about R-3.5 to R-3.8 per inch and fills the cavity deeper. Closed-cell also acts as a vapor retarder at around 2 inches, which matters in an exterior wall in this climate.

Where should I start if I can only afford one thing this year?

The attic. Air seal the ceiling plane, fix the hatch, and bring the blown insulation up to R-60. It is the biggest heat loss in the house and the least expensive place to add a lot of R-value. The rim joist is the best second job if there is budget left.

If you would like us to look at your attic and rim joist and tell you where the house is actually losing heat, send a quote request through our contact page and we will set up a visit.

What R-Value Does a House in Williams County Actually Need?