Passive House Comfort, Timber Precision

Today we dive into achieving Passive House performance with CLT wall and roof assemblies, exploring how cross‑laminated timber pairs with continuous insulation, airtight detailing, and balanced ventilation to deliver ultra‑low energy use, exquisite comfort, and long‑term durability. Expect practical build‑ups, field‑tested tips, and honest lessons that help you design, model, and construct with clarity and confidence.

From Solid Panels to Solid Results

Cross‑laminated timber brings speed, precision, and a warm interior finish, yet it does not achieve ultra‑low energy performance by itself. Success comes from pairing the structure with continuous exterior insulation, meticulous air sealing, smart vapor control, and details that avoid thermal bridges, so every joint, window edge, and roof transition contributes to comfort and reliability.

Why Mass Timber Needs Continuous Insulation

CLT is strong and beautiful, but its R‑value per inch is modest, so exterior insulation becomes the quiet hero. Wrapping the structure with wood fiber, mineral wool, or high‑performance foam keeps heat where you want it, simplifies dew point control, and reduces temperature swings at panel joints, protecting both comfort and the timber.

Airtightness as a Craft, Not a Product

No single membrane guarantees airtightness; it is the choreography of tapes, gaskets, liquid flashings, and disciplined sequencing. Plan every seam, fastener, and service penetration. Train teams to clean substrates, roll tapes, and document tests. With rehearsed details, CLT panels become a continuous air layer, delivering consistently low leakage without drama on test day.

Carbon, Beauty, and Occupant Delight

Mass timber locks carbon while offering natural warmth, tactile ceilings, and a calming acoustic character. When paired with Passive House metrics, occupants experience even temperatures, quiet rooms, and fresh air that feels invisible yet restorative. The design conversation expands from efficiency alone to include biophilia, material honesty, and the emotional quality of lived spaces.

Wall Build‑ups That Hit the Target

A great wall starts with a clear order of layers: structural CLT for strength and airtightness, a robust weather layer, thick continuous insulation, a ventilated rainscreen, and an interior service cavity to protect the seal. This approach tames thermal bridges, keeps fasteners dry, and gives trades space to work without risking performance or finish quality.

Roofs That Balance Heat, Vapor, and Durability

Roofs see the harshest weather, so assemblies must marry continuous insulation with smart vapor control and forgiving drainage. Whether you choose a warm roof or a vented overbuild, control layers should stay legible, dew point locations predictable, and penetrations minimized, ensuring decades of resilience without sacrificing the elegant simplicity of timber ceilings below.

Warm Roof Over CLT with Continuous Insulation

Place the air and vapor control on the CLT roof deck, then stack rigid insulation above for unbroken thermal performance. With taped seams and careful parapet transitions, you gain simple detailing and excellent comfort. Choose insulation types and thicknesses guided by climate, drying potential, and fire requirements, verifying with hygrothermal checks for peace of mind.

Cold Roof Strategy with Vented Overbuild

When exterior insulation depth is limited, an over‑roof with vent channels can manage moisture and heat. Create a uniform ventilation path from eave to ridge, ensure intake and exhaust are protected, and maintain continuous air sealing at the CLT plane. This approach respects timber aesthetics inside while supporting robust, predictable drying behavior outside.

Fresh Air, Quiet Rooms, and Steady Temperatures

High performance is more than heat loss; comfort depends on ventilation quality, acoustic control, and summer strategies. Proper HRV or ERV sizing, thoughtful duct routing within service cavities, and selective acoustic layers under timber ceilings turn crisp energy numbers into everyday wellbeing, protecting sleep, focus, and delightful indoor air through every season.

Design Proof: PHPP, Hygrothermal Checks, and Testing

Numbers guide confidence. Use PHPP to iterate assemblies, glazing, shading, and ventilation until heating demand, cooling demand, and airtightness targets align. For moisture safety, run hygrothermal simulations of key details. On site, rehearse blower‑door protocols and document results, transforming assumptions into verified performance that owners and builders can trust for decades.

01

Iterating Assemblies in PHPP Without Guesswork

Start with measured material values, conservative infiltration targets, and climate‑specific shading. Adjust insulation thickness, window placement, and ventilation efficiency while tracking comfort criteria like temperature asymmetry. Keep versioned notes of each change. This honest record helps teams explain choices, reduce contingency, and reach performance confidently without chasing unrealistic, brittle, or costly solutions.

02

Moisture Safety Checks with Hygrothermal Modeling

Model wall and roof sections through multiple years using real climate data and rain exposure. Confirm that wood moisture content stays safely below risk thresholds and that drying pathways remain open. Test variations, including unexpected leaks, so you know assemblies recover gracefully. These simulations turn complex physics into practical, field‑ready confidence.

03

Blower‑Door Day: A Playbook for Teams

Success begins before test day. Sequence membranes early, pre‑tape service holes, and maintain a running punch list of seams, corners, and window transitions. Assign roles for smoke‑pencil scouting, fan adjustments, and documentation. Celebrate the result, share lessons, then seal the remaining suspects, locking in airtight performance long before finishes hide your work.

Lessons from the Field and Your Voice

Real projects teach best. Builders report that pre‑cut CLT, labeled membranes, and mock‑ups turn complexity into rhythm, while rainy weeks reward temporary roof protection and disciplined sequencing. Share your details, costs, and test numbers so the community learns faster together, improving resilience, comfort, and beauty with every build, sketch, and conversation.

Case Note: A Timber Home Finished During Storm Season

A crew assembled panels under threatening skies, relying on rapid temporary drying‑in and staged tape work. Because penetrations were pre‑planned, the air barrier stayed intact despite schedule pressure. The final test impressed everyone, validating methodical preparation, clear drawings, and daily checklists that caught tiny leaks before they became frustrating, expensive surprises.

What We Would Change Next Time

We would prefabricate more window bucks, increase sill slopes, and photograph every membrane handoff during installation. A dedicated airtightness lead would track penetrations, while a pre‑blow test before insulation would reduce rework. These small process shifts protect budgets, preserve finish quality, and keep performance predictable, even when weather or timelines misbehave unexpectedly.

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