How to Insulate a Metal Building in Spokane: Energy Code, Condensation and What Works (2026)

Bare steel and a Spokane winter make water. Warm, moist air inside a shop hits the cold underside of the roof panels, condenses, and drips on your truck, your tools and your slab. Insulation done right stops that. Here's what Washington's energy code requires, which insulation works on a pre-engineered metal building (PEMB), and how to keep a steel shop dry in the Inland Northwest.

Should you insulate a metal shop in Spokane?

Almost always, yes, even if you won't heat it every day:

• Condensation: the Metal Building Manufacturers Association (MBMA) explains that condensation forms when warm, moist air reaches a surface below its dew point. In winter, that's the inside of your roof and wall panels
• Cold: Deer Park's building code lists a -5°F winter design temperature for the north Spokane area, so an uninsulated steel shell loses heat fast
• Noise and light: faced insulation quiets rain and hail on the roof and gives a bright, reflective interior

An unheated storage building can sometimes skip insulation, but if you plan to heat it later, it's far cheaper to insulate while the building goes up than to retrofit around wiring and doors.

What Washington's energy code requires

Washington's commercial energy code (2021 WSEC, Table C402.1.4) sets maximum U-factors for metal buildings. Lower is better:

• Metal building roofs: U-0.031
• Metal building above-grade walls: U-0.050
• Unheated slab-on-grade floors: F-0.54
• Overhead garage doors with less than 14% glass: U-0.31

Those values apply statewide, because Washington's commercial code puts all of the state in its climate zone 5 and marine 4 column. Two details matter for shops:

• Semi-heated spaces: a space with no cooling and heating output of no more than 8 Btu/h per sq ft is exempt from the wall insulation requirement, though windows in those walls must still meet code
• Metal roof assemblies: the code's Appendix A rates metal roofs by how insulation is installed, from a single layer draped over the purlins to filled-cavity and liner systems, and requires a thermal spacer block of at least R-3 between purlins and roof panels unless the overall assembly U-factor shows compliance

Your permit drawings will show which assemblies meet the code for your building's use. We size the insulation package with the engineered building so it passes plan review.

The main ways to insulate a steel building

• Faced fiberglass blanket (the standard): laminated vinyl or foil-faced blankets installed over the purlins and girts as the panels go on. The Insulation Institute (NAIMA) says metal building insulation should carry the NAIMA 202-96 label, printed with the maker and R-value
• Liner systems: a continuous membrane under the purlins with unfaced insulation on top. This avoids compressing the insulation at every purlin, which is how high-performance roofs reach lower U-factors
• Rigid board or continuous insulation: boards installed without gaps at the framing, with sealed seams
• Insulated metal panels: foam-core panels that serve as both skin and insulation

Spray foam is another option on existing buildings. Whatever you choose, get it on the drawings so the engineer and the energy code reviewer see the same thing.

How to stop condensation in a metal building

The Insulation Institute lists four steps, and they match what we see on Inland Northwest shops:

• Put the vapor retarder on the warm side: for a heated shop in our climate that's the inside face
• Use enough thickness: the insulation has to keep the facing warmer than the inside air's dew point. That thickness can be more than the energy code alone requires
• Seal every seam and tear: tape laps, joints and punctures, and seal around penetrations
• Ventilate the cold side: venting to the outdoors helps carry off moisture that gets past the facing

Facing matters too. NAIMA recommends a vapor retarder rated at no more than 0.10 perms, and 0.02 perms where the inside is humid, like a wash bay. The MBMA notes that plain white vinyl rated at 1.0 perm is not an effective vapor retarder, especially in humid buildings.

Moisture also comes up from below. A vapor barrier under the shop slab keeps ground moisture out of the building. Our shop slab thickness guide and PEMB foundation guide cover what goes under the slab.

Plan it before you order the building

Insulation thickness affects trim, door framing and how the panels fasten, so it belongs in the original building order. Raven isn't tied to one manufacturer: we price your building with whichever PEMB supplier can deliver soonest, with the insulation package already specified. See our metal building lead time guide and our Spokane-area permit guide.

Raven's going installed rate for a metal building in the Spokane area is about $60 to $75 per sq ft, and electrical, plumbing and utility hookups are extra. We'll spell out the insulation package in your written quote.

Get a metal building quote

Tell us your size, how you'll use and heat the building, and your address. Call 509-350-2016 or request a free quote. See our steel building services.

Sources

• Installed pricing: Raven Buildings' current going rate for the Spokane area
• Washington State Energy Code WAC 51-11C-402141, Table C402.1.4
• 2021 WSEC Commercial, Appendix A (metal building roof assemblies)
• Washington State Energy Code commercial envelope webinar (semi-heated spaces)
• MBMA, Condensation Fact Sheet
• Insulation Institute, Metal Building Insulation (MB306)
• Insulation Institute, Recommendations for Installing Fiber Glass Insulation in Metal Buildings (MB316)
• City of Deer Park Municipal Code 15.04 (winter design temperature)