Double-shell metal window with narrow muntins and thermal break

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Solution Overview

Problem

Historic cast iron windows in converted spaces face challenges in meeting modern thermal insulation and structural support requirements while preserving their historical integrity.

Innovation Solution

A double-leaf metal window and door system with narrow profile widths using flat steel and a solid insulating core, connected with screws or rivets, provides thermal insulation and structural stability, allowing for modern glazing options like insulating, bulletproof, or fire-resistant glass.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If historic cast iron windows are reused as mounting sides, then the original structure's integrity is preserved and protected from moisture damage, but the thermal insulation performance is insufficient for modern requirements

Engineering Contradiction:
Improvestructural integrityVSAvoidheat loss
Core Design Contradiction:
ReliabilityVSLoss of energy

Solution Approach 1:

The window system is divided into separate components: the historic cast iron window frame serves as the outer shell, while a new inner shell with improved insulation properties is added. This segmentation allows the historic structure to be preserved while adding modern insulation layers between the two shells, reducing heat loss without compromising the original integrity.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent employs composite construction by combining the historic cast iron frame with modern insulating materials in the cavity between the two shells. This composite approach integrates the structural value of the historic material with the thermal insulation properties of modern materials, simultaneously addressing both structural integrity and energy loss concerns.

Inventive Principle:
Principle #40Composite materials

2Loss of energy

If a double-leaf metal window system with narrow profile widths is used, then modern thermal insulation regulations are met and structural support is provided, but the device complexity increases

Engineering Contradiction:
Improvethermal insulationVSAvoidsystem complexity
Core Design Contradiction:
Loss of energyVSDevice complexity

Solution Approach 1:

The double-leaf metal window system is designed to perform multiple functions simultaneously: the outer shell provides structural support and historic preservation, the inner shell provides thermal insulation, and together they offer burglar protection, sound insulation, and fire resistance. This multi-functionality reduces the need for separate systems, managing complexity through integrated design.

Inventive Principle:
Principle #6Universality (Multi-functionality)

Solution Approach 2:

The inner shell is nested within the outer shell, creating a cavity for insulation materials. This nested configuration allows the insulation layer to be contained within the structural framework, providing thermal insulation while maintaining a compact overall structure that manages system complexity through hierarchical organization.

Inventive Principle:
Principle #7Nested doll (Nesting)

3Loss of energy

If insulating glass panes are installed between the shells, then thermal insulation and burglar protection are improved, but the manufacturing precision requirements increase

Engineering Contradiction:
Improvethermal insulationVSAvoidglass installation precision
Core Design Contradiction:
Loss of energyVSManufacturing precision

Solution Approach 1:

The cavity between the two shells serves as an intermediary space that accommodates insulating glass panes and other insulation materials. This intermediate layer provides a buffer that tolerates minor dimensional variations, reducing the stringency of manufacturing precision requirements while still achieving the desired thermal insulation and security performance.

Inventive Principle:
Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system meets current thermal insulation regulations, supports historic buildings, and enables installation of modern glazing while maintaining the original structure's integrity and reducing heat loss and moisture damage.

Implementation Method 1

The two flat window sides are connected to a solid insulating material, preferably wood, as a thermal barrier

Methodology Applied
Scientific EffectThermal insulation: Thermal Insulation

Implementation Method 2

This system relieves the load on historic buildings or new buildings by acting as a self-supporting element

Methodology Applied
Scientific EffectStructural support:

Implementation Method 3

appropriate glass for burglary protection, sound insulation, bulletproof glass or fire protection glazing can also be installed

Methodology Applied
Scientific EffectSound insulation: Acoustic Absorption

Data Source

PatentEP4400686B1Double-shell metal window and door system with narrow web widths for historical cast iron windows / industrial, office and residential windows, doors with protective glazing
Publication Date: 2025.06.25 WITTIG WOLF-DIETER
  • EP4400686B1 patent drawingFigure 1/3
  • EP4400686B1 patent drawingFigure 2/3
  • EP4400686B1 patent drawingFigure 3/3

AI summary

All currently available technical solutions cannot achieve the very narrow window muntins required with minimal glazing depth. Sufficient thermal break within the window is not achieved by most manufacturers using conventional profile designs. This patented system enables narrow muntins and thermal break, provides additional structural rigidity, is easy to handle, and even allows for relatively simple repairs in case of damage to the window glass. It is virtually maintenance-free and, using wood for insulation and linseed oil paint as a coating, is also highly sustainable. Since this design allows historic cast-iron windows to remain in place and essentially "only be doubled up," it represents a true breakthrough for historic preservation and should soon become standard practice in this field.