Curtain wall

What is a curtain wall?

A curtain wall is a non-loadbearing outer wall that hangs from the building structure. A frame holds glass or opaque panels. The floors and columns carry the building, and the facade only closes it against the weather. The European product standard EN 13830 describes a curtain walling kit as a unit intended to be used as a building envelope. It covers weather resistance, safety in use, energy economy and heat retention. It applies to kits from vertical up to 15 degrees off vertical.

The frame is a grid of vertical profiles, called mullions, and horizontal profiles, called transoms. Schüco calls this a mullion-transom facade. Because the facade does not carry the building, it can run full height and wide. That is why the system appears on offices, shops and public buildings.

What do the standards say about curtain walls?

EN 13830 is the product standard for curtain walling. The edition read for this page is dated November 2020 in the Austrian Standards catalogue. The standard excludes patent glazing kits, roof glazing and precast concrete panel facades, which fall under EN 14992. A testing laboratory notes that EN 13830 is a harmonised standard under the Construction Products Regulation (EU) 305/2011. For a product under a harmonised standard, the manufacturer draws up a declaration of performance before it places the product on the market.

Two test standards give the classes for the joints. EN 12152 covers air permeability of the fixed and openable parts. Its 2023 edition replaced the 2002 edition and added a classification at negative pressure. EN 12154 covers watertightness of the fixed and openable parts under positive static air pressure. Each manufacturer reports the class its system reached in a test. This page gives no class value, because the sheet of one manufacturer does not apply to another system.

What is the difference between stick and unitised curtain walls?

There are two erection methods. The table gives the description of each by Reynaers.

System	Where the assembly happens	Effect named by the maker
Stick	The profiles are assembled mainly on site	Most framing work happens at the building
Unitised	Large pre-assembled units arrive for installation	Assembly time on site drops greatly

Some systems mix both methods. The Reynaers ConceptWall 86 cassette variant fits glass into a frame in the workshop and then places that frame in a stick facade. Schüco states that a high level of prefabrication gives unitised facades considerable benefits for deadlines and quality requirements. Unit size is a limit. Schüco says units of 3 by 4 metres and weights up to 1000 kg are possible in its AF UDC 80 system.

How does a curtain wall differ from rainscreen cladding?

The two sit outside the structure, but they are different systems. Rainscreen cladding is an outer layer fixed over a ventilated cavity, with the insulation behind it, as the page on the ventilated facade describes. A curtain wall is a frame kit that closes the building envelope itself.

Feature	Curtain wall	Rainscreen cladding
What it is	A frame kit with glass or opaque infill, covered by EN 13830	An outer layer on a ventilated cavity, fixed to a facade substructure
Assembly	Stick on site, or unitised factory units	Rails or battens fixed to the wall, then boards or panels
Where the weather and thermal work happens	In the frame, the glazing units and the opaque panels together	Insulation sits behind the cavity and the outer layer sheds the rain

How does a curtain wall affect heat loss and fire spread?

The frame and the glazing both lose heat, so judge the system as a whole. The glass value alone says little about the installed wall. Reynaers lists a frame value of Uf = 1.9 W/(m²K) for its ConceptWall 86 stick facade, and describes the profiles as well-insulated aluminium profiles. That value belongs to that system. Ask each supplier for the declared values of the exact system. See thermal bridge and U-value.

Fire spread is a separate check. Schüco states that compartmentation comes from fire-resisting walls and floors. The envelope must not weaken it at the spandrel zone, the opaque band between floors. It also states that a curtain wall specified to European standards does not necessarily guarantee fire compartmentation. For its Deflame spandrel zone in the FWS 50 and FWS 60 systems, Schüco lists EN 13501-2 classes of EI 90 and EI 60. They apply to the facade and the perimeter seal. The designer states the fire requirement of the project, and the manufacturer shows test evidence for that exact build-up.

Does a curtain wall make sense for a family house?

A full curtain wall is rarely the right choice for a family house. A glazed skin loses more heat than an insulated opaque wall, and the energy performance rules below apply to the whole building. Large glass areas also need shading, and a glazed wall leaves less wall for furniture and privacy.

The curtain wall idea still works in a limited form. Examples are a glazed living room facing the garden, a double-height bay or a winter garden. See structural glazing for a variant with a glass-to-frame bond. The wall around these glazed parts stays opaque and insulated.

How do the Slovak energy rules affect a curtain wall?

The energy performance act, zákon 555/2005 Z. z. o energetickej hospodárnosti budov, requires a new building to meet minimum energy performance requirements (§ 4 ods. 1). An existing building must meet them after major renovation where that is technically, functionally and economically feasible. The act defines major renovation as works that affect the building envelope over more than 25% of its area (§ 2 ods. 7). Some renovations change the envelope in a way that significantly affects energy performance. Then the designer must propose a solution that meets the requirements for a new building with the same function (§ 4 ods. 5).

Buildings are placed in energy classes A to G (§ 3 ods. 7). An energy certificate is required for a building or part sold or let to a new tenant. It is also required when a new building or a major renovation is completed (§ 5 ods. 2). A certificate is valid for up to ten years. It loses validity earlier if building works affect energy performance (§ 7 ods. 7). The calculation for a glazed facade must use the curtain wall as it will be built.

What should you check on a curtain wall product?

The frame, glazing units and infill panels are construction products. Under the Slovak act on construction products, zákon 133/2013 Z. z. o stavebných výrobkoch, the manufacturer must arrange assessment of the product parameters before placing the product on the domestic market (§ 4 ods. 1). EU law also requires a declaration of performance for a product under a harmonised standard. Regulation (EU) 2024/3110 sets this in Article 13(1). Its repeal clause keeps parts of Regulation 305/2011 in force until 8 January 2040. Ask for these documents for each component, not only for the glass.

• Thermal data for the whole system, including frame and edge effects, not only the centre-of-glass value.
• Air permeability and watertightness classes under EN 12152 and EN 12154, with the test report of the system you will buy.
• Fire behaviour between floors and at the opaque panels, with test evidence for the exact build-up.
• Access for cleaning and seal replacement, since joints and seals need the most maintenance.
• Installation instructions from the manufacturer, and an installer with experience of this system.