Windows (Leaving Cert Construction Studies): Revision Notes
Installing windows
Windows are fitted into openings created within building walls during construction. The installation process requires careful attention to moisture prevention, thermal efficiency, and structural support. Proper installation ensures the window performs effectively while maintaining the building's weatherproofing and insulation properties.
Window installation is a critical building process that affects both the structural integrity and energy performance of a building. Poor installation can lead to moisture problems, heat loss, and reduced building lifespan.
Window cills
Purpose and construction
A window cill sits at the bottom of the window opening and serves several important functions. This component is typically a precast, reinforced concrete element that is bedded into mortar during installation. The cill provides a solid base for the window frame whilst directing water away from the building.
Moisture protection requirements
Every cill installation must include a Damp Proof Course (DPC) to prevent moisture from penetrating through the wall from outside. The DPC wraps around the cill, creating an effective barrier against water ingress. This is essential for maintaining the building's weatherproofing and preventing dampness problems.
Thermal considerations
Thermal insulation is installed around the cill area to prevent cold bridging and reduce heat loss from inside the building. Cold bridging occurs when heat travels through materials that conduct thermal energy, leading to energy waste and potential condensation issues.
Cold bridging is one of the main causes of heat loss in buildings. Proper insulation around window installations can significantly improve a building's energy efficiency and reduce heating costs.
Construction variations
Block construction cills
In block-built walls, the cill integrates with the masonry construction. The reinforced concrete cill (typically 275 x 100mm) sits within the wall thickness, with insulation (usually 100mm thick) filling the cavity space. The external render and internal plaster finish provide the final weatherproofing layers.
Timber frame cills
Timber frame construction requires different detailing, with the cill working alongside the frame's structural elements. A proprietary cavity barrier helps manage airflow, whilst breather membranes and vapour checks control moisture movement through the wall assembly.
Securing windows in position
Steel strap method
Windows are held securely in place using galvanised steel straps. These metal fixings are nailed directly to the wall structure during installation. The straps remain hidden once the internal plaster finish is applied, creating a clean appearance whilst maintaining structural security.
The external render creates a weatherproof seal around the window frame perimeter when the installation is complete. This sealing prevents water and air penetration around the window edges.
Lintels above windows
Function and importance
A lintel is the structural element installed above each window opening. Its primary job is to distribute the weight of the building structure above across to both sides of the opening, preventing the wall from collapsing into the window space.
Types of lintels used
Reinforced concrete lintels
These are most commonly used in block-built houses where the outer wall leaf consists of concrete blocks. The lintel integrates well with masonry construction and provides excellent load-bearing capacity.
Galvanised steel lintels
Steel lintels are typically chosen when the outer wall leaf is built from bricks, whether in block-built or timber frame dwellings. These lintels include integrated DPC profiles and factory-fitted insulation to maintain thermal performance.
Timber lintels
Timber frame construction uses wooden lintels that work with the structural timber framework. These lintels require support from trimmer studs and integrate with the overall timber structural system.
Installation requirements
All lintel types must be installed to prevent moisture penetration and heat loss. DPC protection and adequate insulation are essential regardless of the lintel material chosen.
Window head details
Block construction heads
The window head in block construction involves careful detailing where the lintel meets the window frame. Key components include:
- Reinforced concrete lintel (typically 100 x 65mm)
- Window head section (100 x 70mm)
- Top rail (65 x 65mm)
- Vertical DPC to prevent moisture penetration
- Insulation within the cavity (100mm thickness)
- External render (18mm) and internal plasterboard (12mm)
Timber construction heads
Timber frame window heads require different detailing to accommodate the frame structure:
- Timber lintel supported by vertical studs with insulation (150 x 50mm)
- Headplate (150 x 50mm)
- Top rail integration with the window frame
- Breather membrane and sheathing material (12mm)
- Proprietary cavity barrier for airtightness
- Vapour check on the internal side
- Plasterboard internal finish (12mm)
The different dimensions and components between block and timber construction reflect the different structural requirements and thermal performance standards of each building method.
Storm-proof window systems
Advanced glazing systems
Storm-proof timber casement windows represent high-performance window installation. These systems typically feature triple glazing for enhanced thermal performance and weather resistance.
Construction details
The storm-proof system includes:
- Weather board for external weather protection
- Triple glazing units for thermal efficiency
- Transom sections for structural division
- Enhanced sealing systems
- Integration with both cill and head details for complete weather protection
The complete system provides superior protection against severe weather conditions whilst maintaining excellent thermal performance.
Complete Storm-Proof Installation
A typical storm-proof window installation combines:
- Reinforced concrete cill with integrated DPC
- Galvanised steel straps for secure fixing
- Steel lintel with thermal break
- Triple-glazed window unit with weather sealing
- Complete perimeter insulation and weatherproofing
This creates a high-performance system suitable for exposed locations.
Key Points to Remember:
- Window cills must include DPC protection - this prevents moisture penetration and protects against dampness problems
- Three main lintel types are used - reinforced concrete (for block walls), galvanised steel (for brick outer leaves), and timber (for timber frame construction)
- Steel straps secure windows permanently - they're nailed to the wall and hidden by internal plaster finishes
- Thermal insulation prevents cold bridging - proper insulation around windows reduces heat loss and energy waste
- Proper sealing is essential - external render and internal finishes create weatherproof barriers around the entire window perimeter