Door frame

A door frame (zárubňa) is a lining that is fixed in a wall opening and receives the door leaf. It carries the hinges and the lock strike plate, and it holds the seal that the closed leaf presses against. Manufacturers sell three families: steel frames, timber casing frames and concealed systems. This entry covers the first two and the general rules for ordering and fitting. The hidden Z-profile system has its own entry, concealed door frame.

What does a door frame do in a wall?

A door frame has three jobs. It carries the leaf on its hinges. It gives the opening a fixed, square edge so that the leaf closes evenly. It forms the joint between the leaf and the wall. The Sapeli installation manual for steel frames says the frame must be rigid enough to stop the door from sagging. It also says the frame must carry the weight of the leaf and of parts such as stops and door closers.

The installation manuals stress that the frame must match the order. Sapeli tells the installer not to fit a frame that deviates from the ordered dimensions. SOLODOOR asks the installer to measure the opening in at least three places and to check flatness with a spirit level before fitting.

What are the main door frame types?

The families differ in material, in how they fix to the wall and in when they go in. The table compares them using the manufacturer documents listed in the sources.

Type	Material and fixing	When it goes in
Built-in steel frame	One-piece steel profile with masonry anchors, braced and filled with mortar or concrete	During the masonry work, with a load-bearing lintel above, and plaster applied afterwards
Steel frame concreted into an opening	The same steel frame, set in a completed masonry opening and filled with concrete	After the masonry, in an opening that has no final plaster
Timber casing frame	Hinge-side, lock-side and top casing parts, assembled and fixed with spacers and foam	In a finished opening, after the wall and the dry trades are done
Concealed frame	Hidden system for frameless doors	See concealed door frame

What door and opening sizes do manufacturers give?

Manufacturers name a frame by the nominal door width in millimetres, for example 600, 700, 800 or 900. The wall opening is larger than the nominal width, and the difference depends on the frame type. The table repeats the SEPOS sheet "Doporučené rozměry stavebního otvoru pro zárubně" for a single-leaf door. SEPOS is a Czech frame manufacturer and its sheet carries no date.

Nominal door width	Opening, casing frame	Opening, fire-rated frame	Opening, concealed frame
600 mm	700 mm (±10)	720 mm (±5)	735 mm
700 mm	800 mm (±10)	820 mm (±5)	835 mm
800 mm	900 mm (±10)	920 mm (±5)	935 mm
900 mm	1000 mm (±10)	1020 mm (±5)	1035 mm

The same SEPOS sheet gives the opening height for a casing frame. It is 2020 mm for a 1970 mm door and 2150 mm for a 2097 mm door. The SOLODOOR assembly manual for timber casing frames gives the same widths. It lists 700, 800, 900 and 1000 mm openings for 600, 700, 800 and 900 mm doors, with a tolerance of 10 mm. SOLODOOR covers wall thicknesses from 60 to 360 mm with an undivided jamb and from 370 to 700 mm with a divided jamb.

Steel frames follow a different rule. The Sapeli manual covers a frame concreted into an opening. It gives the opening width as the order width plus 85 to 100 mm. It gives the opening height as the order height plus 45 to 50 mm. Its example is an 800 by 1970 mm frame in a 900 by 2020 mm opening. Sizes differ between manufacturers, so take the dimensions from the sheet of the product you order and not from a general rule.

When does the door frame go in during the build?

The timing depends on the frame type. A built-in steel frame is part of the masonry work. Sapeli says it becomes an integral part of the wall structure and needs a load-bearing lintel above. The installer sets the frame plumb and braces it horizontally with at least three braces. The installer bends the masonry anchors into a mortar joint and fills the gaps with mortar or concrete. Once the wall surface is plastered, the frame is painted and the seal is fitted.

A steel frame can also go into a completed masonry opening that has no final plaster. In that case the opening is sized as given above and the frame is filled with concrete. Sapeli supplies each steel frame type in two versions, for installation on a finished floor or for installation in the floor. The second version carries a height mark 1 m above the finished floor. The floor build-up therefore has to be known when the frame is ordered.

A timber casing frame goes in last. SOLODOOR says to install it in ventilated, dry rooms. The relative humidity must be 30 to 50 percent and the temperature 15 to 35 °C. The installer spaces the frame in three places, wedges it and foams it. For a leaf up to 25 kg, foam in the corners, at the middle of the top and at three places on each side. For a heavier leaf the whole hinge side must be foamed. The manual also gives a gap between the door leaf and the floor. It is 7 mm (±3) for a casing frame and 10 mm (+3, −5) for a metal frame.

How do fire-rated frames differ?

A fire-rated frame has stricter rules for the opening and the fixing. The SEPOS sheet asks for a minimum wall thickness of 100 mm and an opening 120 mm wider than the door. SOLODOOR says a fire-rated frame must be foamed around the whole perimeter and through the full wall thickness with special fire foam. The hinge side has a block with drilled holes for fire hinges. Sapeli says to use only non-combustible shims under the jambs of a frame for fire-resistant doors. SOLODOOR also says the fire door closer must be checked within 12 months of handover and then every year.

These documents describe the installation of the frame only.

How do timber frames cope with damp rooms?

Wood decays when conditions suit the fungi that feed on it. The USDA Forest Products Laboratory Wood Handbook states that the growth of fungi depends on suitably mild temperatures, moisture and air. It adds that wood needs protection when these conditions are present. A timber frame in a bathroom or a utility room therefore needs a protected foot. SOLODOOR recommends sealing the cut at the bottom of the casing frame with an elastic adhesive or sealant. This applies to a water-resistant floor covering.

Steel does not decay, but it can corrode. Sapeli says the installer must apply a new primer coat after installation to protect the frame against corrosion. The installer also cleans mortar off the frame after each work session to protect the primer.

Does the door frame matter for thermal bridges?

Only for doors in the building envelope. The Passive House Institute criteria for transparent building components and opening elements cover window frames, entrance doors and sliding doors. They do not cover interior doors. In these criteria the installation of a component is a thermal bridge of its own, and a two-dimensional heat flow simulation determines it. The installation gap is part of the installation-based thermal bridge. Because of this extra loss, the requirement rises by 0.05 W/(m²K) for the uninstalled components. It rises by 0.10 W/(m²K) for the glazing. Both are relative to the values of the installed components.

Which door frame suits a Slovak family house?

The manufacturer documents give the practical rule. If you choose a built-in steel frame, the decision comes before the masonry is built, because the frame is part of the wall. If you choose a timber casing frame, the frame comes after the wall, the floor and the dry trades. Concealed frames suit interiors designed around frameless doors. Pocket doors need their own housing in the wall, which is covered by sliding pocket door, not by a standard frame.

Replacing interior doors does not need a permit under Act 25/2025. Section 18 (5) a) 2. lists replacement of doors among maintenance work that needs neither a building-intent decision nor a notification. Section 18 (3) f) and g) set notification rules for work on a cultural monument or in a heritage area. Ask the building office when the house is in one of these.

What are common misconceptions about door frames?

• The frame is only decorative. It carries the hinges and the strike plate and holds the seal.
• Any frame fits any opening. Each manufacturer gives its own opening size for each frame type, and the sizes differ between steel, casing, fire-rated and concealed frames.
• A steel frame can be adjusted after plastering. Sapeli describes a built-in frame as part of the wall structure, and the frame position is fixed by the masonry work.
• Every interior door frame is a thermal bridge issue. The Passive House criteria cover doors in the envelope, such as entrance doors.