The Gap Under a Filomuro Door: Threshold and Floor

Kulttur Team · Published: 10 August 2026

The question comes up at every site survey, right after the frame, the hinges and the finish have been settled: how much space stays under the door? On a conventional door the answer is hidden by the threshold and by a frame that runs all the way down. On a filomuro door there is no threshold, and the bottom line is visible from anywhere in the room. A badly calculated gap is both seen and heard. Here are the real figures used on site, and why they are not chosen by eye.

How much space goes under a filomuro door

The reference value is 8-10 mm between the bottom edge of the leaf and the finished floor surface. Not the screed, not the plasterboard, but the surface you will actually walk on once the job is done. It is the only dimension that matters, because the door is installed once and cannot be lowered afterwards.

Below 8 mm two practical problems appear. The first is mechanical: wood flooring moves with the seasons, and a 15 mm oak board can rise 1-2 mm during humid months. With a 5-6 mm gap, the door starts to rub. The second is maintenance: you can no longer pass a vacuum or a mop without hitting the leaf.

Above 12 mm the gap reads as a strip of light from the adjacent room, which contradicts the exact reason you chose a door flush with the wall. Exceptions exist and are covered below, but they are technically justified exceptions, not preferences.

The reference level changes with the stage of the build

The difference between a correct gap and a botched one is not measured in millimetres but in timing. If the floor is already laid, measuring is direct and the error tends towards zero. If only the screed is down, the fitter works with the declared thickness of the flooring system, and any later change of material is paid for in the gap.

In descending order of safety, the cases look like this:

• Flooring laid before the door is fitted, with protection over it. This is the ideal situation and the reason why the timing of installation within the build sequence matters more than it seems.
• Flooring ordered and confirmed but not yet laid. Acceptable, provided the product data sheet exists and there is written agreement that the material will not change.
• Flooring undecided. Here you work from an assumption, and the assumption goes into the quotation. If the client moves from 5 mm vinyl to 15 mm engineered oak, the door is left with a 20 mm gap or has to come off the hinges.

Why the bottom gap is not just an aesthetic question

In a flat without transfer grilles in the walls, the space under the door is the only route by which air moves between rooms. The bathroom extractor or the kitchen hood pulls air out, and that air has to come from somewhere. If it has no path, the system runs on nothing, draws current and evacuates very little.

The arithmetic is simple. On an 800 mm wide door, a 10 mm gap gives 80 cm² of free cross section. At 15 mm you reach 120 cm². For a windowless bathroom with a ceiling extractor, figures in the 100-150 cm² range are what separate a mirror that clears in five minutes from one that stays fogged for an hour. That is why on doors for bathrooms and wet rooms we deliberately go to 12-15 mm, even though the gap shows slightly more.

The alternative, when a perfectly tight line is wanted in the bathroom too, is a transfer grille in the wall or an air channel above the frame. It costs more and has to be decided at design stage, not at installation.

The correct sequence on site

The rule we apply is: the frame goes in before finishes, the leaf goes on after the flooring. The extruded aluminium frame is built into the wall along with the structure, plastered or skimmed over, and then the site is left to work. The leaf arrives last, once the floor is laid, clean and protected.

There are two reasons. First, a finished leaf has no business in a space where filler is being sanded and adhesive poured. Second, this is the only way to measure the gap against the real level. Fitters who hang the leaf before the flooring end up taking it off and trimming it on site, which means a hand-retouched edge and, on factory-painted models, a visible difference in tone along that edge.

This reversal of stages appears constantly in the list of common installation mistakes and is the most expensive of them all, because the only real repair is replacement.

Transitions between two different floor finishes

The classic case: engineered oak in the bedroom, porcelain tile in the bathroom, and the door in between. The two materials rarely end up at the same level, even when the designer specified it. A 3-4 mm difference between them is normal in execution.

The gap is always calculated against the higher material. If the tile sits 4 mm above the oak and you leave 9 mm over the oak, the door will have 5 mm over the tile and will rub at the first change in humidity. Measured correctly, you end up with 9 mm over the tile and 13 mm over the oak, which is perfectly acceptable visually.

The joint line between the two materials is positioned on the axis of the leaf, directly under the closed door. That way it is invisible from either room, whether the door is open or shut. It is a 30-second detail at setting out that completely changes how the finished work reads.

When you do need a threshold

The threshold comes back into the conversation in three concrete situations, and only these:

• Serious acoustic separation. An open 10 mm gap cancels a good part of the leaf's acoustic performance. If the door separates a home office from a living area, an automatic drop-down seal is fitted into the bottom edge: it lowers on closing and lifts on opening. The rest of the time air transfer is preserved.
• Large level difference. Above 15 mm between the two floors, a flat aluminium threshold resolves things more elegantly than an uneven gap.
• Water thresholds. With a walk-in shower and no enclosure, where water can reach the door, a stop profile is mandatory regardless of aesthetics.

Otherwise, the absence of a threshold is exactly what makes a filomuro door seem not to be there at all. Combined with a constant perimeter reveal on the three remaining sides, it produces that clean 2-3 mm outline that reads as a drawn line rather than a door.

How big is the standard gap under a filomuro door?

Between 8 and 10 mm, measured against the finished floor and not the screed. This is the dimension that lets wood flooring move seasonally without the door rubbing, while leaving enough free area for air transfer between rooms.

Can a filomuro door be installed before the flooring?

The frame yes, the leaf no. The aluminium frame goes in at structural stage, before finishes. The leaf is hung once the flooring is laid, otherwise the gap is calculated from a theoretical level and the deviation frequently reaches 3-5 mm.

What do I do if the door starts rubbing after a year?

The first check is at the hinges, not the leaf. Concealed hinges adjust on three axes, and a 1-2 mm vertical correction solves most cases. Only when the adjustment is at its limit does trimming the bottom edge come into question, an operation that requires removal and retouching of the finish.

Does the bottom gap affect sound insulation?

Yes, significantly. An open gap reduces the real acoustic performance of the assembly no matter how well the leaf is built. The solution is an automatic drop-down seal in the bottom edge, which closes the gap only while the door is shut and lets air circulate the rest of the time.

The gap under the door is one of three dimensions settled at the site survey, alongside wall thickness and the direction of opening. We go through all of them in the showroom at Bulevardul Dacia 153-155 in Bucharest, with doors fitted in real walls, where the difference between 8 and 14 mm is visible to the naked eye. If you want to start from dimensions, the configurator on the site gives you a live price.