R-value guide
How much attic insulation do you actually need?
In Metro Detroit the answer is R-49 to R-60. Most homes here have about a third of that. You can check yours in five minutes.
Recommended
R-49 to R-60
DOE Climate Zone 5 — all of Metro Detroit
Typical here
R-11 to R-19
Most pre-1980 homes — 3 to 6 inches
Cellulose adds
R-3.1
Per inch, settled
Measure it yourself in five minutes
- Open the hatch and look. A flashlight and a tape measure is all you need.
- Push the tape straight down to the drywall. Not to the top of a joist — all the way to the ceiling below. That is your depth.
- Check three or four spots. Middle of the attic and near the edges. The perimeter is almost always thinner, and the perimeter is where you feel it.
- Note the material. Pink or yellow fluff is fiberglass. Grey shredded paper is cellulose. Rectangular blankets between joists are batts.
Safety: step only on the joists or on decking. The drywall between them will not hold you, and going through a ceiling is a much more expensive problem than thin insulation. If the attic is tight, hot, or you are not steady up there, skip it — we do this for free.
Depth to R-value
Find your measured depth on the left, then read across to your material. Ranges are approximate — condition, compression and settling all shift the real number.
| Depth | Cellulose | Loose fiberglass | Batts | What it means |
|---|---|---|---|---|
| 3–4" | R-9 to R-12 | R-8 to R-10 | R-11 to R-13 | Well short. Top-up is worth it. |
| 5–6" | R-16 to R-19 | R-13 to R-15 | R-19 | Common in pre-1980 homes. Top-up is worth it. |
| 7–9" | R-22 to R-28 | R-18 to R-23 | R-25 to R-30 | Still below target. Worth topping up. |
| 10–12" | R-31 to R-37 | R-25 to R-30 | R-30 to R-38 | Getting close. Depends on air sealing. |
| 16" | R-49 | R-40 | — | At target. This is what we install to. |
R-value is not the whole story
This is the part most guides leave out, and it matters more than the number you just looked up.
R-value measures how well a material resists heat conducting through it. It measures nothing about air moving around it. If warm indoor air is pouring into your attic through unsealed top plates, an open furnace chase, recessed light housings and a leaky hatch, then the insulation is not being asked to do the job it is rated for — the heat is bypassing it entirely.
A carefully air-sealed R-38 attic will outperform a leaky R-49 one. This is why we seal before we blow, and why a quote that does not itemize air sealing should make you suspicious.
Reading the stains
While you are up there, look for grey or blackened patches in otherwise pink fiberglass. That is filtration staining — years of air moving through that exact spot, the insulation catching dust like a furnace filter.
It is essentially a map of your air leaks, drawn over time by the house itself. When we find heavy staining around a chase or a run of can lights, we know where to work before we have opened anything.
So should you top up?
Rough guide, for a Metro Detroit home:
- Under R-30: Almost certainly yes. The payback is real and reasonably quick.
- R-30 to R-38: Probably, especially if the attic has never been air sealed.
- R-38 to R-49: Depends. Air sealing may be the better spend.
- Above R-49: Leave it. Put the money into the rim joist, the walls, or nothing at all.
And if the material up there is wet, matted, or full of droppings, depth is not the question — see removal and replacement.
R-value questions
What R-value should my attic be in Michigan?
Metro Detroit sits in DOE Climate Zone 5, where the recommendation for attics is R-49 to R-60. Northern Michigan is Zone 6 and the recommendation is at the higher end. If you are below R-38, adding depth is almost always worth it here.
How do I measure what I already have?
Open the attic hatch, shine a light, and push a ruler or tape measure straight down through the insulation until it hits the ceiling drywall. Do this in three or four spots — the middle of the attic and near the edges — because the depth is rarely even. Note the material type while you are up there. Do not walk on the insulation; step only on the joists.
Does adding more insulation always help?
No, and the returns diminish steeply. Going from R-11 to R-49 cuts heat loss through that surface dramatically. Going from R-49 to R-60 is a marginal improvement you may never notice on a bill. Past a certain depth, your money does more good on air sealing, the rim joist, or somewhere else entirely.
Is R-value the whole story?
Not close. R-value measures resistance to heat conducting through a material. It says nothing about air leaking around it. An R-49 attic with unsealed top plates, an open chase and a leaky hatch will underperform an honestly sealed R-38 attic. This is the single most common misunderstanding in the trade, and it is why we seal before we blow.
My insulation looks dirty and grey in spots. What does that mean?
Grey or blackened patches in fiberglass are usually filtration staining — air has been moving through that spot for years, carrying dust that the insulation caught like a filter. It is a map of your air leaks. When we see it, we know exactly where to seal.
Not sure what you are looking at?
Send us a photo, or let us measure it. The assessment is free and we will tell you if you already have enough.