In Practice

Warm Window Installation: Moving the Frame Into the Insulation Layer

Warm window installation treats the window as part of the thermal envelope, not as a cold insert fixed to the edge of the structural wall.

Thermal bridge detail showing a window installed in the exterior insulation layer of a passive house wall
Layer:
04 - Openings
Function:
Installed performance
Updated:
May 24, 2026

Overview

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The strongest window detail moves the frame outward into the continuous exterior insulation layer.

Frame linePlaced with the insulation, not behind it
Load pathSupported by profiles, brackets or consoles
3 layersAirtightness · insulation · weather protection

When a high-performance window is installed directly on the face of a concrete or masonry bearing wall, the frame often sits outside the best thermal line. The insulation then has to wrap back around the reveal, and the window perimeter becomes the place where heat flow concentrates.

Passive House Block logic

The structural concrete remains inside the warm mass of the building, and the insulation stays outside. Window installation should respect that same physics so the opening does not become the weak point in an otherwise strong wall.

Installation target

The frame should align with the insulation plane whenever the wall system and structural calculation allow it. Foam alone is not a load path; the support detail must be engineered.

VST80x90 Detail

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The VSThermo VST80x90 reference shows the type of pre-wall frame logic needed for warm installation.

Reference use: this diagram is used to explain the installation principle: support the window in the insulation zone while keeping the thermal line continuous.
VSThermo VST80x90 pre-wall frame system for window installation in the insulation layer
Reference image from VSThermo. Marker positions follow the source VST80x90 diagram coordinates.
  1. 01Thermal insulation profiles VST 80x90 form the upper and side pre-wall frame around the window opening.
  2. 02Vapour-permeable tape or sealant closes the exterior joint while allowing outward drying.
  3. 03Hybrid polymer bonds the upper profile zone and coordinates the support with the sealing line.
  4. 04Thermal insulation profiles VST 50x30 / 56x30 / 63x30 / 69x30 complete the lower warm support stack.
  5. 05Thermal insulation profiles VST 80x90 provide the deeper lower support layer in this reference arrangement.
  6. 06Hybrid polymer bonds the lower support profile without adding a hard thermal bridge.

Source: VSThermo VST80x90 system

Layer Sequence

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Warm installation works only when support, airtightness, insulation and weather protection are designed as one node.

Interior side
Connect the window frame to the interior air barrier without gaps or weak tape transitions.
Middle layer
Control movement and insulation around the joint so the frame perimeter does not become a cold bridge.
Exterior side
Protect against wind-driven rain while allowing the assembly to dry in the correct direction.

Before construction

Draw the frame position, support bracket, insulation return, sill slope, tapes or membranes, plaster or facade termination and drainage path before ordering or installing the window package.

Site control

Photograph hidden layers before closure and verify that the opening does not become an air-leakage path during blower-door preparation.

PHB Fit

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For Passive House Block, opening details belong to the same system logic as exterior insulation, thermal mass and airtight envelope design.

The wall can deliver its full value only if openings are handled with the same discipline as the wall field. A thick insulation layer and a reinforced concrete core do not automatically create a passive-house-grade envelope if windows are left as unmanaged bridges.

Product connection

Coordinate warm window sections with the Passive House Block product system so frame position, insulation return and structural support are resolved together.

Technical library

The practical next step is a library of section drawings for typical window positions, sill details and balcony-door thresholds.

Design rule: protect the continuous insulation line first, then solve the structural support and sealing layers without creating a new thermal bridge.