Passive House x CLT: Mastering Thermal Performance and Airtightness
Today we explore Passive House strategies with cross‑laminated timber, zeroing in on thermal performance and airtightness that hold up from drawings to site realities. Expect practical detailing, measurable targets, and cautionary tales that help you avoid costly rework while achieving relaxed, even temperatures everywhere. We will connect science and craft so comfort becomes predictable, not accidental. Share your own challenges and wins so we can compare notes, refine details, and raise the bar on resilient, low‑energy buildings together.
CLT as the High‑Performance Structure
Cross‑laminated timber delivers structural stiffness, rapid assembly, and a welcoming interior surface, yet it needs smart layering to reach Passive House comfort and energy targets. Wood’s thermal conductivity is relatively low but not enough alone, so continuous exterior insulation becomes the hero. Understanding panel layups, moisture behavior, and dimensional stability at joints ensures your envelope remains steady, silent, and tight under seasonal swings while keeping craftsmanship efficient and predictable for builders and designers working to rigorous standards.
Heat Flow Without Surprises
Predictable comfort begins with honest heat‑flow math and detailing discipline. CLT’s warmth invites complacency, yet edges, fasteners, and frames still leak energy if not explicitly managed. By resolving U‑values, psi‑values, and repeating thermal bridges early, you cut risk while making construction simpler. This section translates calculations into drawings your site team can actually build, so the building behaves as modeled, rooms feel even, and occupants enjoy quiet, steady warmth without fiddling with controls or wearing sweaters indoors.
Airtightness From Design to Tape
Windows, Doors, and Penetrations That Respect the Layer
Openings decide how honestly your envelope performs. In CLT buildings, rough openings are clean and stiff, yet thermal and airtight continuity depends on careful buck design, placement of the primary seal, and drainage paths that forgive mistakes. Equip teams with mockups, numbered steps, and cross‑sections showing interior and exterior planes. When windows land in the insulation layer, frames feel warm, condensation disappears, and occupants forget winter exists, even as storms hammer glass without whispering through joints.
Moisture, Diffusion, and Drying Resilience
Comfort dies when moisture wins. CLT wants to stay dry, yet also breathe enough to release construction moisture. Favor diffusion‑open strategies outward, protect against bulk water, and let interiors regulate humidity smoothly. Variable vapor membranes, ventilated cladding, and disciplined flashing create a forgiving buffer against errors. Use hygrothermal modeling to confirm drying reserves and to size insulation correctly. When assemblies dry from both sides intelligently, you avoid musty smells, warped finishes, and hidden rot that steals performance and trust.
Verification, Commissioning, and Long‑Term Feedback
Performance becomes real when measurements agree with intentions. Plan blower‑door tests, infrared scans, and commissioning checklists like you plan concrete pours—carefully and with time to correct issues. Compare PHPP results to monitored energy and interior conditions during the first year. Celebrate airtightness scores and share details that worked, including what failed. Invite readers to submit data, photos, and lessons so the next CLT Passive House goes smoother, faster, and even calmer for occupants, builders, and neighbors.
