Garage Construction Project

Critical Pre-Insulation Requirements

9 min read

Garage Construction – Critical Pre-Insulation Requirements

A concise, contractor-ready checklist of all items that must be installed before the builders finish framing, roofing, windows, and siding. These items are essential to ensure proper insulation, air sealing, moisture control, and future utility installation for the 24’ × 40’ garage with habitable loft.

Confirmed with Marcus (Hershberger's) — 2025-12-01

Called Marcus today and confirmed the following pre-insulation work will be completed by the framing crew:

  • ✅ Exterior seam taping — All exterior sheathing seams will be taped
  • ✅ Tyvek house wrap — Will install Tyvek WRB with proper overlap
  • ✅ Window flashing — All windows will be flashed and taped after install
  • ✅ Exterior penetrations — Will seal all exterior penetrations
  • ✅ Vented roof assembly — Vented soffits + continuous ridge vent (vented assembly confirmed)

This confirmation covers the critical air/moisture control and roof venting items below.

✅ ALREADY COMPLETED (Foundation Phase)

Slab Insulation

  • ✅ R-10 perimeter slab edge insulation — Installed Oct 29, 2025 (bright orange foam panels around entire foundation perimeter)
  • ✅ Under-slab Creatherm insulation — 2” foam, R-10, installed Oct 22, 2025
  • ✅ Radiant PEX loops — Installed and pressure tested Oct 22-23, 2025

See drone photos: DJI_0886.md through DJI_0891.md

🔴 CRITICAL — Must Be Done DURING Framing

These items must be completed while walls/roof are being framed. Cannot be done after sheathing/siding installed.

Air & Moisture Control

  • ✅ Tape all exterior sheathing seams (Zip tape or 3M 8067) — CONFIRMED 2025-12-01
  • ✅ Properly install WRB (housewrap) with shingle-style overlap — CONFIRMED: Tyvek 2025-12-01
  • ✅ Flash all windows correctly (sill pan, corner flashing, fully taped flanges) — CONFIRMED 2025-12-01
  • ✅ Seal exterior penetrations (vents, pipes, electrical through-sheathing) — CONFIRMED 2025-12-01

Roof / Ceiling Structure

  • ✅ Finalize roof insulation strategy now — CONFIRMED 2025-12-01: VENTED ASSEMBLY
    • Vented: ✅ Vented soffits + continuous ridge vent — CONFIRMED
  • ✅ Rafter/truss depth — Pre-engineered attic trusses (Letherer Truss Job #123907):
    • A1 24’ Attic trusses: 10:12 pitch, top chord 2x8, designed for 40 PSF live load in attic floor area
    • Max truss height: 11’-03-08”, attic room width: 5’-0” to 19’-0”
    • Spacing: 24” OC (standard) / 48” OC (girders)
    • See Truss Engineering Drawings for full specifications
  • ✅ Soffit depth for airflow — Truss overhangs are 1’-0” (12”) on both sides per loading ticket; adequate depth for vented soffit panels
  • ✅ Dormer transitions — Covered by pre-engineered truss package (SP1 modified trusses + T1/TX/AM dormer trusses); additional blocking can be added after framing if needed

Structure & Fire Safety

  • ✅ Garage-to-loft fire separation — Requires three components:
    1. Garage ceiling: 5/8” Type X drywall (owner DIY)
    2. Stairwell enclosure: 2x4 framed walls by Hershberger’s under stairs/mechanical room; owner to drywall
    3. Fire-rated door: Required at top of stairs — 20-minute fire-rated self-closing door (owner to purchase/install)
  • ✅ Type X drywall framing — Owner to install 5/8” Type X drywall on garage ceiling (not in Hershberger contract; DIY with lift)
  • ✅ Pressure-treated bottom plates — Standard construction practice for slab-contacting walls

Fire-Rated Door Required

A 20-minute fire-rated, self-closing door is required at the top of the stairwell to maintain fire separation between garage and habitable loft. Standard interior doors are NOT fire-rated. Look for doors labeled “20-minute” or with a fire rating stamp. Self-closing hinges or door closer also required.

Future Apartment Conversion Strategy

The loft will initially be finished as office/hobby/theater space (no bedroom). However, fire-rated ceiling drywall and fire-rated stair door are being done now because they would require tearing out work later. Additional apartment requirements (kitchen plumbing, bathroom, separate entrance, bedroom egress windows, etc.) can be added later without demolishing existing work.

Roof Penetrations

  • ✅ Sewer vent stack — Roof penetration for plumbing vent included in roofing phase; will be capped for later connection

Exterior Wall Penetrations - Can Be Added Later

Mini-split line sets, boiler vent, dryer vent, bathroom exhaust, and other wall penetrations can be cut through finished sheathing/siding when needed. Slightly more work than during framing, but common practice and doesn’t require pre-planning exact locations now.

Paint booth exhaust option: West and north walls have windows that could accommodate temporary window-mounted exhaust fans for paint/ventilation projects without requiring a dedicated permanent penetration.

🟡 CAN BE DONE AFTER FRAMING (Before Insulation/Drywall)

These items can be completed after framing is done but BEFORE insulation and drywall installation. Easier access while walls are still open.

Blocking & Backer Boards

  • Install blocking needed for insulation baffles (eaves and mid-span)
  • Add extra studs or blocking where cabinets, shelves, or minisplit heads will mount
  • Install ¾” plywood backer board on interior mechanical wall

Mechanical Runs & Drilling

  • Drill or frame large-diameter holes for future mechanical runs (HVAC, plumbing, electrical)
  • Pre-frame any necessary vent penetrations (bath fan, dryer, kitchen vent)
  • Air-seal rim joists at sheathing connection

Utility System Pre-Stubs (Air, Fumes, Vacuum)

  • Compressed air riser to loft: Install capped 3/4” Rapidair Maxline vertical riser from main floor to loft through utility chase; terminate with capped NPT fitting behind blank wall plate; include drip leg + ball valve at base (see Compressed Air System Shopping List)
  • Fume extraction riser: Install capped 6” spiral steel duct vertical riser from main floor to loft; route through utility chase; cap both ends with metal caps; label “FUME EXTRACTION - DO NOT CONNECT TO DUST COLLECTION” (see Fume Extraction Strategy)
  • Central vacuum riser: Install 2” thin-wall PVC riser to loft with low-voltage control wire alongside; stub floor sweep inlet rough-in near garage doors; install backing/blocking at planned retractable hose station locations (see Central Vac Planning)
  • Label all stubs clearly at both ends before drywall

Utility Runs to Loft (Vertical Chases)

  • Route utilities from mechanical room to loft through wall cavities before drywall
  • Standard stud bays (3.5”) accommodate: electrical, mini-split line sets (~3”), 3/4” Maxline compressed air
  • 6” fume extraction duct: run in corner or use 2x6 wall section if needed
  • No special framing required during initial construction — just need access before drywall

Conduit & Low-Voltage

  • Add conduit runs for fiber, ethernet, cameras, AV, and future circuits
  • Pre-run conduit routes for minisplit line sets if possible

⭐ HIGHLY RECOMMENDED (Strongly Advisable for Best Performance)

Experienced Contractor Note

Hershberger’s builds 100+ pole barns/garages per year. Items like synthetic underlayment, vapor-open sheathing, and proper window rough openings are standard practice for experienced contractors. The items below are either standard (verify with photos) or owner-responsibility (add after framing).

Roof & Wall Performance (Likely Standard - Verify with Photos)

  • ✅ Use synthetic roof underlayment rated for metal roofing — standard for metal roofing
  • ✅ Ensure roof sheathing is vapor-open (OSB or plywood; avoid foil-faced) — standard practice

Owner Responsibility - After Framing

  • Add blocking throughout sloped ceiling and knee wall areas — for insulation baffles, owner to add
  • Install ¾” plywood backer board on interior mechanical wall — custom to owner’s layout
  • Add conduit runs for fiber, ethernet, cameras, AV, and future circuits — owner scope
  • Pre-run conduit routes for minisplit line sets if possible — owner scope
  • Add extra studs or blocking where cabinets, shelves, or minisplit heads will mount — owner to specify locations
  • Ensure rim joist areas are easily accessible for later insulation and air sealing — verify during framing

Garage Door & Window Prep (Likely Standard - Verify with Photos)

  • ✅ Ensure air-sealing gaps around windows/doors are correct (for later foam sealing) — part of confirmed window flashing
  • Install jamb extensions if future drywall alignment requires them — depends on owner’s finish plans

📸 Photo Documentation

See Framing - Photo Documentation Checklist for a comprehensive phase-by-phase checklist of what to photograph during construction.

💡 OPTIONAL / NICE-TO-HAVE (Improves Efficiency or Future Flexibility)

Energy Efficiency & Durability Upgrades

  • Upgrade WRB to high-performance membrane (Tyvek Commercial, Zip System)
  • Add exterior rigid foam (polyiso) under siding for increased R-value — EVALUATED & DECLINED (see below)
  • Use advanced sheathing tapes for long-term durability (Siga, Pro Clima)

Exterior Rigid Foam — Considered But Not Needed (2025-12-02)

After analysis, exterior rigid foam was determined unnecessary for this project:

  • Split thermal envelope: The loft is primarily insulated by attic floor (R-49+), knee walls, and sloped ceiling — not the exterior garage walls
  • Garage doesn’t need tight temperature control: Exterior foam would mainly benefit the semi-conditioned garage level
  • Small gable-end walls: The only loft walls exposed to exterior are small triangular gable ends, adequately served by R-21 cavity insulation
  • Better ROI elsewhere: Max attic insulation (R-60), quality knee wall air sealing, upgraded windows (already ordered), and garage ceiling insulation provide more benefit per dollar
  • Not standard practice: Exterior rigid foam is uncommon for detached garages/workshops; typical in Passive House or high-performance residential builds
  • Cost avoided: $3,000-6,000 redirected to higher-impact improvements

See 2025-12-02 — Exterior rigid foam insulation (not needed) for full decision rationale.

Interior-Facing Preparation

  • Add nailers/backing for future TV mounts, cabinets, railings
  • Pre-frame for potential skylights or roof windows

Future-Proofing

  • Install extra conduits from garage → house for data or power
  • Oversize soffits for future lighting, cameras, or wiring
  • Add additional attic or knee wall access doors for maintenance

📌 SUPER CONCISE SUMMARY FOR BUILDER

✅ ALREADY DONE (Foundation Phase - Oct 2025)

  • ✅ R-10 perimeter slab edge insulation (Oct 29)
  • ✅ Under-slab Creatherm R-10 foam (Oct 22)
  • ✅ Radiant PEX loops installed & tested (Oct 22-23)

🔴 CRITICAL — During Framing (Confirmed with Marcus 2025-12-01)

  • ✅ Tape all sheathing — CONFIRMED
  • ✅ Proper window flashing — CONFIRMED
  • ✅ Proper WRB install (Tyvek) — CONFIRMED
  • ✅ Roof venting: VENTED ASSEMBLY — CONFIRMED
  • ✅ Install soffit/ridge vent — CONFIRMED
  • ✅ Truss depth: Pre-engineered A1 24’ attic trusses (10:12, 2x8 top chord) — See Truss Specs
  • ✅ PT bottom plates on slab — standard practice
  • ✅ Fire separation: Type X ceiling (owner DIY) + enclosed stairwell + fire-rated door at top
  • ✅ Sewer vent stack — roof penetration in roofing phase, capped for later

🟡 AFTER FRAMING (Before Insulation/Drywall)

  • Drill holes for mechanical runs
  • Install insulation baffle blocking
  • Add cabinet/minisplit mounting blocking
  • Plywood backer on mechanical wall
  • Route utilities to loft through wall cavities (no special chase framing needed)
  • Compressed air riser to loft (3/4” Maxline, capped)
  • Fume extraction riser to loft (6” spiral steel, capped)
  • Central vacuum riser to loft (2” thin-wall PVC + low-voltage wire)
  • Floor sweep inlet stub near garage doors
  • Retractable hose station backing at planned locations
  • Mini-split line sets to loft
  • Conduit for wiring & low-voltage
  • Label all stubs before drywall

⭐ HIGHLY RECOMMENDED

  • Synthetic underlayment
  • Vapor-open roof sheathing
  • Blocking for knee walls / dormers

💡 OPTIONAL

  • Higher-grade WRB
  • Exterior rigid foam — DECLINED (not needed for split thermal envelope)
  • Extra nailers and conduits
  • Oversize soffits

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