Under Washington's HB 1110 middle housing mandate, residential lots across Lacey are converting from single-family homes into duplexes, triplexes, and fourplexes. Building multi-family homes requires specialized drywall construction: certified 1-hour fire-resistance rated party walls (UL Design U305 / GA-600) and acoustic isolation rated to STC 50+ between units. Solis Interiors provides commercial-grade metal and wood stud framing, fire-stopping, and fast-track multi-unit drywall finishing across Lacey and Thurston County.
Middle Housing Expansion in Lacey's Urban Core
From the Woodland District and Lacey Boulevard to the Sleater-Kinney and Pacific Avenue corridors, Lacey is growing rapidly under HB 1110.
For general contractors and real estate investors building fourplexes or cottage developments, project profitability comes down to schedule.
Drywall is the critical bridge between rough-ins and finishes. If party wall fire-stopping fails inspection or drywall crews drag out taping across four units, carrying costs eat your margin.
What fire-rated wall assemblies are required between middle-housing units under HB 1110?
Common demising party walls between adjoining dwelling units in Lacey require a certified 1-Hour Fire-Resistance Rated Assembly (UL Design U305 or GA-600 File WP 3620) constructed with double-layer 5/8-inch ASTM C1396 Type X gypsum board fastened with 1-7/8" Type W screws over staggered wood studs or cold-formed steel framing.
On an active fourplex jobsite, framing and MEP trades often crowd top plates and stud cavities. Here is how Solis Interiors protects your project:
- Continuous Draftstopping: We verify that fire-blocking and draftstopping are installed at all ceiling and floor transitions before boarding, preventing vertical flame paths inside party walls.
- Deflection Track Integration: In multi-story units where second-story floor joists settle under live loads, we install slotted deflection tracks along party walls so floor deflection never crushes or buckles the drywall.
- Certified Intumescent Penetration Seals: All plumbing vents, electrical conduit, and duct drops passing through the party wall are sealed with tested intumescent sealants compliant with IBC Chapter 7.
How do you achieve STC 50+ acoustic privacy between adjoining fourplex units?
Under IBC Section 1206, walls separating dwelling units must achieve a minimum Sound Transmission Class (STC) of 50, which stops normal conversations and television audio from carrying between units.
Here is how we eliminate the most common acoustic failures on middle-housing jobsites:
- Subfloor Flanking Decoupling: If the plywood subfloor runs continuously beneath the party wall, footstep impact vibrations travel straight under the drywall. We cut and seal the subfloor seam beneath the demising wall with viscoelastic damping compound to isolate vibrations.
- Resilient Sound Isolation Channels (RC-1): We mount RC-1 channels horizontally across studs at 24 inches on center, ensuring screws do not penetrate through into framing studs (which creates an acoustic short-circuit).
- Friction-Fit Mineral Wool Sound Batts: We install high-density mineral wool sound batts in every cavity with zero voids or compression gaps.
Middle Housing Drywall Assemblies: Specifications & Performance
| Assembly Component | Code Specification | Acoustic & Life-Safety Rating |
|---|---|---|
| Demising Party Wall (Unit-to-Unit) | Double 5/8" Type X on Staggered Studs | 1-Hour Fire Rating (UL U305) / STC 52 |
| Floor-Ceiling Assembly (Upper to Lower Unit) | Double 5/8" Type X on RC-1 + Sound Batts | 1-Hour Fire Rating (UL L521) / STC 55 |
| Corridor & Stairwell Enclosures | 5/8" Type X Gypsum with Fire-Taping | 1-Hour Fire Barrier (IBC Section 1020) |
| Unit Bathrooms & Kitchen Wet Walls | ASTM C1396 Moisture-Resistant Board | High humidity and mold resistance |
2026 Multi-Family Drywall Pricing in Lacey & Thurston County
We provide clear, itemized unit-by-unit proposals tailored for general contractors and private developers:
| Project Scope | 2026 South Sound Cost per Sq. Ft. | What Is Included in the Scope |
|---|---|---|
| Duplex / Fourplex Complete Drywall Package | $3.20 - $4.90 per sq. ft. | Staggered 5/8" Type X party walls, 1/2" interior board, 3-pass mechanical taping, primer |
| STC 55+ Acoustic Soundproofing Upgrade | +$0.90 - $1.65 / sq. ft. additive | RC-1 resilient channels, dense mineral wool batts, perimeter acoustic caulking |
| Turnkey Multi-Unit Painting Package | +$1.20 - $2.20 / sq. ft. additive | Airless spray application of high-build primer and 2 coats commercial scrubbable paint |
Why General Contractors Rely on Solis Interiors
- Production Speed & Crew Depth: We run mechanical taping tools (bazookas, flat boxes) for uniform, high-speed joint fill that keeps multi-unit projects on schedule.
- Code Submittals for Lacey Inspectors: We provide manufacturer cut sheets and UL design numbers for all Type X gypsum, acoustic sealants, and fire caulking.
- Single-Source Accountability: We manage framing inspection, drywall hanging, fire-taping, texture, and painting under one clear agreement.
Authoritative Multi-Family Codes & References
- Washington State Legislature: HB 1110: Middle Housing Mandates
- International Building Code (IBC): IBC Chapter 7 (Fire Protection) & Chapter 12 (Sound Transmission)
- Gypsum Association: GA-600 Fire Resistance and Sound Control Design Manual
- Underwriters Laboratories: UL Fire Resistance Directory (Wall Design U305)
Submit Middle Housing Floorplans for Commercial Bidding in Lacey
Planning a duplex, triplex, or fourplex build in Lacey, Olympia, or Thurston County? Contact master finisher Jesus Solis for competitive commercial estimating and code-certified drywall craftsmanship.