What is batt insulation?
Batt insulation comes in pre-cut blankets — usually fiberglass or mineral wool — that are sized to fit between the studs in standard walls and floors. If you have ever seen pink or yellow rolls of insulation at a hardware store, that is fiberglass batt. It has been the most common home insulation in the country for decades because it is affordable, easy to find, and works well when someone takes the time to install it right.
How much heat it blocks depends on how thick it is. Fiberglass batts give you about R-3.2 per inch. A 3.5-inch batt (the kind that fits a 2x4 wall) is rated R-13. A 5.5-inch batt (for a 2x6 wall) is R-19 or R-21, depending on how tightly the fibers are packed. Mineral wool batts are denser and come in at about R-4.2 per inch, plus they block more sound and hold up better in a fire.
Why does the installation matter so much?
Here is something most people do not know: a well-installed R-13 batt will keep your house more comfortable than a badly installed R-19 batt. With batts, how they are put in matters more than what they are made of.
These are the mistakes that ruin batt performance:
- Cramming them in — If you stuff a thick batt into a space that is too shallow, you crush the air pockets inside it. Those air pockets are what actually slow down heat. Crush them and the R-value drops.
- Leaving gaps — A batt that is cut too narrow or not pushed all the way into the wall leaves air channels along the studs and at the top and bottom. Heat and cold bypass the insulation through those channels like they are not even there.
- Wrong facing direction — In a humid climate like ours, the paper side of the batt needs to face the inside of the house. Put it backwards and moisture moves through the wall the wrong way.
- Sloppy work around wires and pipes — Electrical boxes, plumbing, and wiring all run through walls. If the batt just gets shoved behind a wire or bunched up around a junction box, that area is barely insulated.
We measure and cut every section individually. It takes longer than stuffing batts in and moving on, but the difference in how well the wall holds temperature is night and day.
Where do batts work best?
Batts are a solid choice for:
- New construction walls — When the studs are open and there is nothing in the way, batts can be cut to fit perfectly and they perform really well.
- Floors — Batts supported from below keep heat in the living space and work well above ventilated areas.
- Garage walls and walls between rooms — When cutting down noise matters as much as blocking heat, mineral wool batts are hard to beat.
- Combined with spray foam — On a lot of jobs, we spray closed-cell foam on the outer sheathing to seal the air and control moisture, then fill the rest of the wall with batt insulation. You get the air seal of spray foam with the lower cost of fiberglass filling out the rest of the cavity.
Fiberglass or mineral wool — which one?
- Fiberglass — Costs less, weighs less, and comes in every standard size. It is the all-around default for walls and floors. The main downside is that it loses performance if it gets wet, so keeping moisture out of the wall matters.
- Mineral wool (you might hear it called rock wool or see the Rockwool brand name) — Heavier, denser, naturally fire-resistant, and much better at blocking sound. It holds its shape in vertical walls better than fiberglass and does not soak up water the same way. It costs more per piece, but you get more R-value per inch.
We stock and install both. Which one we recommend depends on the job — what the wall or floor looks like, how moisture moves through it, and whether sound or fire rating is part of the picture.