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From frame and sash to Eref calculation — how a modern window is built and documented
Windows and doors are among the most demanding tasks in the building carpentry trade. They must look good be able to open and close without problems for decades keep out rain and drafts — and at the same time meet some of the most detailed requirements in the entire building code. Here classical craftsmanship meets modern documentation requirements in a way that is rare in the rest of the trade.
Frame and sash are traditionally assembled with mortise-and-tenon joints or mitre joints at the corners. The joint must provide a large gluing surface and mechanical locking so that the corner can absorb the forces, wind and temperature fluctuations that subject the window to year after year without opening up.
Most new windows are built today with two or three-pane glass. Energy-saving windows have a low-emission coating on one glass surface and are often filled with argon instead of ordinary air between the panes. This significantly reduces heat loss compared to a traditional insulating window without coating.
Siden 1. februar 2021 skal vinduer og glasfacader i nybyggeri som udgangspunkt overholde et komponentkrav til energibalancen Eref, der beregnes som Eref = 196,4 × gw – 90,36 × Uw. Kravet er, at Eref for referencevinduet ikke må være mindre end 0 kWh/m² pr. år, svarende til energiklasse A. For sommerhuse og uopvarmede rum gælder en lempeligere grænse.
| Building part | Requirement |
|---|---|
| Windows and glass facades (new construction heated rooms) | Eref ≥ 0 kWh/m² pr. år (Eref = 196,4 × gw – 90,36 × Uw) |
| Windows in summer houses/unheated rooms | Eref ≥ 1,8 kWh/m² pr. år |
| Glass doors and sliding doors | Uw ≤ 1,0 W/(m²K) |
| Doors without glass | Uw ≤ 0,8 W/(m²K) |
Since February 1, 2010, all windows and external doors marketed in the EU must be CE marked according to the Building Products Regulation (CPR) and product standard DS/EN 14351-1 ("Windows and doors — Product standard, performance — Part 1: Windows and external doors"). CE marking is based on a type test, a quality management system at the manufacturer and a performance declaration (DoP — Declaration of Performance), which as a minimum must specify the window's energy performance in accordance with building regulations.
For the building carpenter it means that windows and doors must not only be professionally correct — they must also be documentable. A well-executed element without correct DoP and energy data can create problems for the building owner when the building is handed over. Therefore it is part of the trade to know both the craft and the figures that must accompany it.