Windows and Doors

All windows and external doors placed on the market must carry a CE marking in accordance with DIN EN 14351-1 (EN 14351-1 for windows and external pedestrian doors). The CE marking must be accompanied by a Declaration of Performance (DoP) stating the essential characteristics: air permeability (EN 12207), watertightness (EN 12208), wind resistance (EN 12210), thermal transmittance (Uw value), acoustic performance (Rw) and, where applicable, burglar resistance (EN 1627). The declared performance values must meet or exceed the project specification and comply with the applicable GEG requirements for thermal transmittance. Internal doors intended for fire or smoke protection must comply with DIN EN 16034 and carry separate CE marking for fire resistance.

1. Verify that each window and external door unit carries a visible CE marking label with reference to EN 14351-1

2. Request and review the Declaration of Performance (DoP) — confirm all essential characteristics are declared

3. Compare declared Uw values against the GEG maximum requirements and the project specification

4. Check declared air permeability and watertightness classes against the project requirements

5. Verify acoustic performance (Rw value) meets the specification, particularly for units facing roads or noise sources

- CE marking label missing or illegible on delivered window and door units

- Declaration of Performance not available or incomplete, missing key characteristics

- Declared Uw value does not meet the GEG maximum thermal transmittance requirement

- Acoustic performance class insufficient for the noise exposure of the building location

- Fire-rated door sets delivered without the required EN 16034 CE marking and classification

Window and door installation must follow the RAL Leitfaden zur Montage (RAL Installation Guideline) which establishes the three-layer sealing principle for the wall-frame junction. The outer layer must be weather-tight and vapour-open (sd ≤ 0.3 m), the middle layer provides thermal and acoustic insulation (typically PU foam or mineral wool), and the inner layer must be airtight and vapour-tight (sd ≥ 10 m). The frame must be mechanically fixed to the structural opening using appropriate fixings at specified spacings — maximum 700 mm for PVC frames, 800 mm for timber frames and 600 mm for aluminium frames, with fixings within 150 mm of each corner and mullion junction. The installation must accommodate thermal expansion and building movement without compromising the seal integrity.

1. Verify the three-layer sealing principle — outer (weather-tight, vapour-open), middle (insulation), inner (airtight, vapour-tight) layers all present

2. Check mechanical fixings — correct type, spacing (maximum 700 mm for PVC, 800 mm for timber) and distance from corners (within 150 mm)

3. Inspect the inner airtight seal — continuous, unbroken connection between frame and wall using appropriate sealing tape or membrane

4. Verify the outer weather seal — rain-tight but vapour-open, allowing moisture to dry outward

5. Confirm that the insulation layer (middle) completely fills the gap between frame and wall with no voids

- Inner airtight seal missing or incomplete, allowing warm moist air to reach the cold zone and cause condensation

- PU foam used as the sole sealing layer without the required inner airtight and outer weather-tight layers

- Mechanical fixings too far from corners or at excessive spacing, causing frame deflection under wind load

- Outer seal not vapour-open, trapping moisture within the joint and causing mould or frame damage

- Insufficient gap between frame and wall for proper insulation and sealing (minimum 10 mm recommended)

Window thermal transmittance (Uw value) must comply with the German Building Energy Act (GEG). For new buildings, the maximum permitted Uw value is 1.3 W/m²K for windows. For renovations where individual windows are replaced, the GEG requires a maximum Uw of 1.3 W/m²K (or Ug of 1.1 W/m²K for glazing replacement only). KfW funding programmes for energy-efficient construction and renovation typically require Uw ≤ 0.95 W/m²K. The Uw value is calculated from the glazing U-value (Ug), the frame U-value (Uf) and the linear thermal transmittance of the glass edge spacer (Ψg) per DIN EN ISO 10077-1. Warm-edge spacers (Ψg ≤ 0.06 W/mK) are standard practice to reduce thermal bridging at the glass edge.

1. Review the window product data sheet — verify declared Uw value meets the GEG maximum of 1.3 W/m²K or the project specification

2. Check glazing specification — verify Ug value and gas fill (typically argon or krypton) on the insulating glass unit marking

3. Inspect the glass edge spacer — warm-edge spacer (stainless steel or composite) should be installed to minimise thermal bridging

4. Conduct thermal imaging survey of installed windows — check for thermal bridges at frame-wall junction, glass edge and sill

5. Verify that the installed frame depth and insulation position align with the wall insulation plane to minimise the installation thermal bridge

- Windows delivered with Uw values exceeding the GEG requirement or the project specification

- Aluminium spacers used instead of warm-edge spacers, creating a visible cold edge and condensation risk

- Frame positioned outside the insulation plane, creating a significant thermal bridge at the wall-frame junction

- Thermal imaging reveals cold spots at sill and lintel due to missing or insufficient insulation at the installation joint

- KfW funding requirements not met due to Uw values above the funding programme threshold

Air permeability of windows and doors must be classified per DIN EN 12207 (Classes 1-4, with Class 4 being the most airtight). Watertightness must be classified per DIN EN 12208 (Classes 1A-9A for fully exposed or E for partially sheltered conditions). German building practice requires minimum Class 3 air permeability and Class 7A watertightness for standard applications. The GEG and DIN 4108-7 require a continuous airtight building envelope, and window installations must contribute to this by achieving airtightness at the frame-wall junction. A blower door test per DIN EN ISO 9972 (formerly DIN EN 13829) at 50 Pa must demonstrate a maximum air change rate of n50 ≤ 1.5 h⁻¹ for buildings with mechanical ventilation or n50 ≤ 3.0 h⁻¹ for naturally ventilated buildings.

1. Verify air permeability classification — minimum Class 3 per EN 12207 on the product Declaration of Performance

2. Check watertightness classification — minimum Class 7A per EN 12208 for standard exposure conditions

3. Conduct a smoke pencil or anemometer test around the frame-wall junction to detect air leakage paths

4. Review blower door test results — n50 value must comply with GEG requirements (≤ 1.5 h⁻¹ with mechanical ventilation, ≤ 3.0 h⁻¹ without)

5. Inspect weatherstripping and gaskets — continuous, undamaged and properly compressed around the entire frame perimeter

- Air permeability below Class 3 resulting in excessive infiltration, energy loss and draught complaints

- Watertightness failure at sill corners due to poor drainage or missing end dams on sill profiles

- Weatherstripping not correctly seated in its groove, leaving gaps at corners and compression points

- Blower door test revealing leakage at the frame-wall junction due to incomplete inner airtight seal

- Drainage slots in the outer frame blocked or missing, allowing water to accumulate and overflow inward

Insulating glass units (IGUs) must comply with DIN EN 1279 series — EN 1279-2 (moisture penetration), EN 1279-3 (gas leakage rate) and EN 1279-5 (evaluation of conformity). Double or triple glazing with low-emissivity coating and gas fill (argon or krypton) is standard for achieving the required Ug values. The edge seal must be a dual-seal system (primary PIB seal and secondary polysulphide, polyurethane or silicone seal). Safety glazing per DIN 18008 is required at locations with increased risk — glass doors, floor-to-ceiling glazing, overhead glazing and glazing adjacent to door openings. Laminated safety glass (VSG) or toughened safety glass (ESG) must be specified per DIN 18008 Part 4 for the specific application.

1. Check the IGU spacer marking — verify glass thickness, gas fill, coating type and manufacturer identification per EN 1279-5

2. Verify safety glazing requirements per DIN 18008 — VSG or ESG at all required locations (doors, floor-to-ceiling, overhead)

3. Inspect edge seal integrity — no visible sealant defects, delamination or moisture between panes

4. Confirm glazing block placement — setting blocks and distance pieces correctly positioned per the system provider's guidelines

5. Verify that the correct glass type has been installed per the specification — check for low-E coating presence using a reflection test

- Standard float glass installed where safety glazing (VSG/ESG) is required per DIN 18008

- IGU edge seal failure causing fogging and condensation between panes, indicating moisture penetration

- Glazing blocks missing or incorrectly positioned, causing glass to rest on the frame and crack under thermal movement

- Low-E coating on the wrong surface, reducing thermal performance of the IGU

- Argon gas fill leaking prematurely due to poor edge seal quality, increasing the Ug value over time

Sealing of exterior wall joints at the window-to-wall interface must comply with DIN 18542 for impregnated sealing tapes (Kompribänder/BG1 tapes) and DIN 18540 for sealant-filled joints. Impregnated sealing tapes per DIN 18542 are classified into BG1 (driving rain-tight, vapour-open) and BG2 (air-tight, vapour-tight). BG1 tapes are used on the outer seal and must achieve driving rain tightness at 600 Pa while maintaining vapour permeability (sd ≤ 0.5 m). The tape must be compressed to minimum 20% and maximum 33% of its initial width when installed. Joint sealants per DIN 18540 must be of the correct movement class (F-12.5, F-20 or F-25) for the expected joint movement. Backing material (closed-cell PE foam) must be installed to achieve the correct joint depth-to-width ratio (minimum 1:2).

1. Verify outer seal tape classification — BG1 per DIN 18542 with declared driving rain tightness at minimum 600 Pa

2. Check tape compression — tape must be between 20% and 33% of its uncompressed width after installation

3. Inspect inner seal tape or membrane — BG2 classification or equivalent airtight membrane continuously applied

4. For sealant joints, verify joint geometry — minimum depth-to-width ratio of 1:2 with closed-cell PE backing rod installed

5. Confirm sealant movement class is appropriate for the expected thermal movement of the joint

- Compriband tape over-compressed (below 20% width), reducing driving rain tightness

- Compriband tape under-compressed (above 33% width), leaving gaps and reducing contact with joint surfaces

- Sealant applied without backing rod, resulting in three-sided adhesion and early cohesive failure

- Inner airtight seal missing, relying solely on PU foam which is neither airtight nor vapour-tight long-term

- Joint surfaces not primed before sealant application, causing adhesive failure at the sealant-substrate interface