Window Install in CLT with SIGA®

Illustrated installation sequence of a non-flanged window into a Kalesnikoff CLT wall panel using SIGA® membranes, tapes, and primers for airtightness, moisture protection, and vapour control while preserving the exposed timber interior.

Preparation

Remove Wetguard® 200 SA factory protection from the CLT panel before starting membrane work.

Prime sill, jambs, head, and cut edges with Dockskin® 100. Allow to dry until tacky, approximately 30 minutes; apply membranes the same day.

Corner + Perimeter Flashing

Install triangular dog’s-ear corner patches with Wigluv® 100, bridging sill → jamb → exterior face.

Apply folded gusset reinforcement with Wigluv® 100 over the sill and jambs corners for redundant sealing.

Install continuous vertical jamb membranes with Fentrim® 230 grey (100/150 mm), starting 175 mm below the sill and extending past the head.

Apply a sill infill strip with Wigluv® 100, sloped outward for drainage, and overlapping jamb membranes.

Window Placement

Place the window on composite shims set over SIGA® Primer Tape, adjust plumb/level, and fasten with window clips (150 mm from corners, 400 mm spacing).

WRB + Exterior Sealing

Seal exterior frame-to-CLT joints with Fentrim® 230 grey at jambs and head; tape clips with Rissan® 60

Dry-fit the Majvest® 500 SA sheet flush over the rough opening, cut an inverted “T,” and peel back the flaps. Lap the Majvest® shingle-style onto the jamb and head membranes—tape all Majvest® seams with Wigluv® 100 and seal penetrations with Fentrim® grommet black.

Interior Finish

Apply interior vapour control membrane using Majrex® 200 and seal the perimeter around the window frame with Fentrim® 20.

Step 11

Finish the interior joint with a closed-cell PE backer rod and SikaHyflex® 150, tooled for two-sided flexible adhesion.

This installation sequence demonstrates how SIGA® membranes integrate with CLT window openings to ensure airtightness, drainage, and vapour control. By hiding these performance layers, the architecture provides what matters most: durable protection with the natural beauty of exposed timber interiors.
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References
SIGA Cover Inc. Majvest® 500 SA System Guideline (North America). Section 5.2 Fenestrations
RDH Building Science Inc. Mass Timber Building Enclosure Best Practice Guide: Moisture Management Strategies. 2023.
BCIT Zero Energy Buildings Learning Centre. Building Enclosures for Mass Timber (TMBR 1040: Module 6 – Mass Timber Enclosure Details).
SIGA Cover Inc. Application Guide: Fentrim® 230 Grey / Fentrim® IS 20. Product data sheets and installation manuals.
Sika Canada Inc. SikaHyflex® 150 Construction Joint Sealant – Technical Data Sheet.
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