What to know before you buy: systems, R-values, vapor barriers, condensation physics, detailing, and retrofit options — explained without the fluff. First, confirm your site’s Loads & Codes or run CodeSmart™ to pull local criteria.
Insulation reduces summer heat gain, limits winter heat loss, and keeps warm, moist air from condensing on cold steel skins. Even “unconditioned” shops benefit from thermal breaks and vapor control for tool protection, occupant comfort, and reduced corrosion risk.
Related: closures & fasteners that protect your insulation layer: Sheeting & Trim Standards.
Spending a bit more on the right facing, thickness, and sealing usually saves far more in rework, callbacks, and energy costs. Optimize for lifecycle: durability of facings, perm class, and ease of maintenance matter as much as nominal R-value.
The most common PEMB approach: rolls install over purlins/girts with banding. It’s cost-effective, fast, and predictable when laps are sealed and compression is controlled at supports to preserve real R-value.
Pick a facing with the right perm rating and tensile strength. Use proper tension/banding to avoid sags and oil-canning looks.
Closed-cell adds air & vapor control plus stiffness; open-cell is lighter/forgiving but typically needs additional vapor control in cold or humid zones.
Hybrid win: thin closed-cell foam for control + fiberglass for affordable R. This combo often provides the best balance of cost, condensation resistance, and noise damping.
Pick R-values by climate and occupancy. Storage needs less; conditioned or high-occupancy spaces need more. Roof R typically exceeds wall R because hot air and solar load stack at the roof plane.
Concept ranges: Warm/Dry roof ~R-13–19; Mixed/Humid ~R-19–25; Cold ~R-25–38. Always verify with local energy code and the engineer of record. For site criteria, see Loads & Codes.
Steel purlins/girts bridge heat. Where targets are tight, add thermal spacers or liner systems, or increase thickness strategically. Pay attention to edge zones where wind pressure and detailing can reduce effective R.
In heating-dominant climates, locate the vapor barrier on the warm-in-winter side. In mixed/humid regions, consider Class II facings and robust ventilation strategies to handle seasonal reversals.
Vapor barriers fail at edges first: eave, ridge, base, corners, and around openings. Seal laps and penetrations; protect facings from UV and jobsite damage. Small tears become big condensation problems.
Warm, moist air hits a cold metal surface → water condenses. Control the three levers: reduce humidity (ventilate/dehumidify), raise surface temperature (insulate), and block moist air from the skins (air/vapor control).
Don’t over-compress insulation at panel laps/fasteners. Use closures at ridge/eave, seal around framed openings and penetrations, and protect the insulation layer during install to prevent hidden moisture paths.
Slab moisture: new concrete releases moisture for months—manage interior RH early. See Concrete Foundations 101.
Base trims, jambs/heads, corners, ridge/eave, transitions to liner panels or interior walls—each needs a continuous, sealed path for air/vapor. Mock up one bay and photo-log the details for repeatability.
Keep insulation dry/clean. Stage rolls close to work areas. Sequence installs to avoid exposure to rain/high winds. Coordinate penetrations and curbs before closing the roof to reduce rework.
Fix leaks before insulating. Inspect for rust, fastener back-out, failed sealants, and clogged gutters. Confirm ridge/eave vent condition and air pathways so new insulation doesn’t trap moisture.
Hybrid retrofit: apply a thin layer of closed-cell foam for air/vapor control, then add faced fiberglass for economical R. This often solves condensation while minimizing panel removal and cost.
Verify electrical clearances & ignition barriers with foam, and coordinate with local fire/energy code officials.
Unsealed/torn facings, over-compression at laps, no vapor plan in humid/mixed climates, ignoring slab moisture for the first months, and skipping closures at ridge/eave leading to seasonal drips.
Weak documentation complicates warranties. Keep SKUs, batch numbers, and photos of critical details and sequences. File the installer’s spacing/fastener pattern with as-builts.
If interior humidity can rise (wet slabs, equipment, occupancy), yes—moisture can still condense on cold metal. Use appropriate facings and ventilation sized for your use patterns.
Closed-cell foam adds air/vapor control and stiffness at higher cost. Fiberglass is affordable and fast. Hybrids often win on retrofit value and control—foam for the control layer, fiberglass for the bulk R.
Your insulation spec depends on site loads, code adoption, and use. Lock those with Loads & Codes to avoid rework and permit delays. Edge zone pressures can change fastener counts and spacer choices.
Pull local criteria and see pre-qualified suppliers/installers for your project type. Compare options apples-to-apples against the same criteria sheet to see true value.
Disclaimer: Educational guidance only. Always verify local energy code, loads, and manufacturer details with the engineer of record.
