Insulation

Even though I completely answered this question a few years ago (not), I need to revisit the requirements for thermal insulation.

We're in zone 4 Marine, according to the 2018 Seattle Energy Code, Chapter 3.

• The 2018 Seattle Energy Code for zone Marine 4 dictates:
• Windows U-Factor 0.30
• Skylight U-Factor 0.50
• Ceiling R-Value R-49 (R402.2.1 says R-38 is enuf?)
• Wall R-Value R-21 intermediate framing - this is why 2x6 studs
• Floor R-Value R-30
• Slab: R-10, 2 feet depth

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The International Energy Conservation Code is strict. Luckily, it doesn't apply.

Ceiling: R-49 (R-60 per Intl Energy Conservation Code)

Wall: R-13 (R-20 or 13+5ci per IECC)

Slab: R-10, 2 feet depth (10ci, 4 feet depth per IECC)

ci = Continuous Insulation

13+ci or 13+5 means R-13 cavity insulation plus R-5 continuous insulation or insulated siding

Table N1102.1.3 in the 2021 IRC

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City of Seattle Department of Construction & Inspections (SDCI)

Energy Code 2018 Seattle Energy Code (Energy code advisor Duane Jonlin duane.jonlin@seattle.gov)

• 3 General Requirements
• Looks like King County is designated Zone 4 Marine.
• 4 Residential Energy Efficiency
• 
  
• 5 Existing Buildings
• Table R402.1.1
• R502.1: "Additions to an existing building...shall conform [to rules for new]...without requiring the unaltered portion of the...building...to comply."

Includes Building Envelope as well as Lighting

Residential Code SRC, which adopts the 2018 Intl Residential Code with amendments

• 3 Building Planning
• R302.11 Fireblocking in walls
• 4 Foundations
• 5 Floors
• Table R502.3.1 gives floor joist spans 30 or 4psf live, 10 or 20 dead
• Table R502.3.3 is allowable cantilever for joists supporting ext bearing wall and roof
• R502.7 - blocking and bridging
• R503 is floor sheathing
• 6 Wall Construction
• R602.3 framing diagram - balloon framing still ok
• Table R602.7 for headers - depends on snow load (30-50-70 psf) and building width (12'-24'-36')
• 602.10.2 "Braced wall panels" - they mean shear
• 7 Wall Covering
• 5/8 Type X for "garage clg beneath habitable rooms"--I think we're good in the main part of the garage. 6" oc fasteners.
• Vapor retarder is required (on the int side, behind the drywall) because we're in Zone 4 Marine
• Seattle has replaced the 15# felt paragraph with a "Water-resistive barrier" paragraph which allows 15# felt
• 8 Roof-Ceiling
• Table R802.4 has rafter spans
• Table R802.5 has ceiling joist spans
• 9 Roof Assemblies
• Allowed underlayment is in terms of ASTM standards. Under asphalt shingles, D226 Type I, D4869 Types I-IV, or D6757 are allowed
• 10 Chimneys and Fireplaces (also 18 Chimneys and Vents)
• 11 Energy Efficiency - Nope, fooled you. Seattle has not adopted Ch. 11. They have the Seattle Energy Conservation Code instead.
• 20 Water Heaters