Field note

Insulation in the drywall number: batt, SAFB, mineral wool, spray foam

On a commercial wall-and-ceiling bid the cavity is often your cavity. Thermal batt, sound-attenuation blanket, and mineral wool get hung with the metal stud and closed up with the board. Spray foam usually does not. Residential production is the opposite habit: an insulation contractor fills the wood walls, then the drywall crew hangs.

This page is scope language for estimators and PMs. It restates public class language from ASTM C665 (mineral-fiber blanket), related mineral-wool product standards, GA-600 / UL designs that name cavity fill, ASTM C840 / GA-216 for not burying a required gap, and manufacturer partition notes (Owens Corning, Johns Manville, and peers). It is not an R-value chart, not an STC calculator, and not a SKU list. Pull those numbers from the current data sheet and the listed design.

Four products, four bid conversations

Thermal fiberglass batt. Faced or unfaced blanket in a stud or joist bay, sold for R-value. ASTM C665 is the common blanket standard. On commercial interiors this shows up in exterior-adjacent furred walls, mechanical rooms, and wherever Division 07 did not take the partition. Unfaced is the usual interior-partition fill; kraft or foil facing is a vapor-retarder decision the wall type has to support — do not put a facing in a place the dew-point note did not ask for.

Sound-attenuation fire blankets (SAFB) / sound batts. Unfaced fiberglass cut for metal-stud partitions, sold for acoustics more than for thermal. Same ASTM blanket family, different product line on the ticket. This is the batt commercial drywall estimators actually miss when the wall type says “insulate for STC” and the thermal insulation spec is silent. Directory: Insulation.

Mineral wool (stone wool / slag wool). Denser, noncombustible fill used in fire-rated partitions, shafts, area-separation, and head-of-wall safing. Cavity batts and joint safing are not the same cut. Fiberglass leftover from an office wall is not a silent substitute for a mineral-wool listing. Density and thickness are whatever the UL / GA-600 design named — do not invent them.

Spray polyurethane foam (SPF). Open- or closed-cell foam applied in place. Thermal, air seal, sometimes a vapor note. This is usually a separate trade (Division 07) with its own ignition barrier / thermal barrier rules against occupied space. The drywall sub may still hang the board that is that barrier — coordinate, do not spray.

Do not copy an NRC from an ACT tile onto a batt, or an STC from a GA-600 row onto a wall that omitted the batt.

What often sits in the commercial drywall number

On interior metal-stud work the wall-and-ceiling shop already owns the stud and the both-sides hang. Filling the bay before the second face is the production moment. That is why GCs put partition insulation in the drywall package even when a Division 07 insulation section exists for the building envelope.

Commonly in the W&C / drywall number when the wall types or the invitation say so:

• SAFB / sound batts in acoustic and tenant-demising partitions
• Thermal batt in interior furring and in stud walls the envelope contractor did not take
• Mineral wool in rated partitions and shaftwall cavities when the listed design requires it
• Resilient channel and the batt that belongs with that acoustic stack, if RC is in the drywall scope

Commonly out, unless the scope is explicit:

• Building-envelope blanket in exterior CFS / backup walls — often the insulation contractor, next to exterior sheathing
• SPF in stud bays, rim joists, and underslab
• Blown attic or loose-fill
• Rigid continuous insulation outboard of sheathing
• Safing at the head-of-wall joint when Division 07 firestop took mineral wool and sealant
• Fireproofing (SFRM) on structural steel — not batt, not drywall

Read the wall-type schedule and Division 07 and Division 09. The same bay cannot be in two contracts and also in neither.

Residential production is a different split

Residential production. House and garden-style multi-family: the insulation contractor (or the GC’s labor) typically fills wood cavities; the drywall crew hangs after. Sound batts in an interior bedroom wall are still often not in the drywall number. Do not assume a commercial SAFB habit on a production house.

Exceptions that land on a residential shop: garage separation cavities the hang crew can still see, mixed-use podiums with metal stud, and light-commercial TI that arrived through a home-builder relationship. Those walls follow the commercial rule: if you close the face, you owned the chance to insulate.

Faced kraft does not make paper-faced gypsum a wet-area backer — MR vs tile backer.

Fire designs vs acoustic designs vs thermal notes

Three reasons a batt is on the sheet. They are not interchangeable.

Fire. If the listed design requires insulation of a named type and thickness, it is part of the hour. Omit it and you did not build the design. Some designs use insulation for the rating; some list it as optional; some are silent. Reading UL designs is the takeoff order. Mineral wool in a shaft or a 2-hour demising wall is this bucket.

Sound. GA-600 sound columns and the acoustic spec (STC, CAC at the head, isolation) often want unfaced SAFB or mineral wool full height, both sides closed, perimeter sealed. A thermal batt of “about the same thickness” is not the tested fill. Constrained-layer sound panels are a different SKU again.

Thermal / energy. Envelope R-value, continuous insulation, and SPF live in energy notes and Division 07. Interior partitions do not get a kraft-faced thermal batt “for the energy code” unless someone actually designed that wall that way.

Head-of-wall safing is a joint fill, not cavity batt. Packing leftover SAFB into a UL 2079 gap is how you fail the joint listing.

Field sequence the hang crew actually runs

Insulation in a metal-stud partition is a one-face operation:

1. Frame. Steel stud, including the deflection head that firestop will later claim.
2. Hang the first face. Do not insulate a closed wall from a cutout.
3. Fill the bay: friction-fit, full height, no voids at the web, no compressed wad that the listing did not ask for. Cut around boxes; do not stuff a batt in front of a damper the mechanical spec wants open.
4. MEP punch through the fill before the second face, or you own a second mobilization.
5. Hang the second face. Fasteners still hit steel, not a wool cushion — how to hang drywall.

Spray foam in a bay you still have to hang: the foam trade goes first, trims flush, and leaves a substrate the gypsum manufacturer will accept. Over-filled foam that bows the stud is a framing problem before it is a hang problem. ClarkDietrich limiting-height tables still govern the stud; foam is not a stiffener you get to count.

Bid notes

Qualify, in writing:

• Partition batt / SAFB in or out of the drywall number
• Mineral wool in rated walls and shafts in or out
• Head-of-wall safing vs cavity fill (two lines)
• SPF, blown, and exterior blanket excluded unless shown
• Thickness and product class (sound attenuation vs thermal vs mineral wool) from the wall type — not an R-value you guessed
• Full-height vs “above ceiling only” (a plenum left empty is a different STC)
• Re-stuff after MEP

Related: Insulation, Owens Corning, Johns Manville, Steel stud / framing, Products, Guides.

FAQ

Is partition insulation always in the drywall bid?

On commercial interiors, often — not always. Read Division 07 and the wall types. If both are silent, qualify it out rather than donate it.

Can I use thermal kraft-faced batt as SAFB?

Not as a silent substitute. Facing, density, and the listed / specified product class matter. Unfaced sound attenuation blanket is what most interior acoustic walls actually named.

Does mineral wool at the head come with the cavity batt?

No. Cavity fill and joint safing are different products and often different trades. See head-of-wall firestop.

Who owns spray foam in metal-stud walls?

Usually a foam / insulation contractor. The drywall sub still owns the gypsum that may be the thermal or ignition barrier. Write the sequence.

Do residential drywall crews carry batt?

Some shops do on small work. Production housing usually does not. Do not price commercial SAFB labor with a house hang rate, and do not assume a production house includes sound batts.

All field notes