Girl At The Window

In the UK and mainland Europe, windows in new-build houses are usually fixed with long screws into expanding plastic plugs in the brickwork. A gap of up to 13mm is left around all four sides, and filled with expanding polyurethane foam. This makes the window fixing weatherproof but allows for expansion due to heat.
A beam over the top of a window is known as the lintel or transom, while a beam under the bottom of a window is known as the sill plate or window sill.
In the US, the NFRC Window Label lists the following terms:
• Thermal transmittance (U-factor). Best values are around U-0.15 (equal to 0.8 W/m2/K).