Why a Seaside Apartment Feels Stuffy, Damp and Noisy

Let us start with the conclusion so the rest of the text has a shape.

An apartment needs air exchange. People exhale carbon dioxide; cooking, showering and drying laundry release water vapour. All of it has to go out, and fresh air has to come in. There are exactly two routes: through leaks in the building envelope, or through a machine.

A modern building is built airtight — for heating costs and for quiet. The tighter the envelope, the less air moves on its own. That removes the first route in practice.

The window remains. And here the coast enters: in summer it is hot and humid outside, in autumn it rains and blows, and there is always a road, a building site or a promenade nearby. So the window is opened rarely and briefly.

And now the knot. A soundproof window only insulates while it is genuinely closed. Anyone who sleeps with the sash on tilt because there is otherwise nothing to breathe has, at that moment, switched off the sound insulation they paid for.

So: no air exchange → stuffiness and moisture → condensation on cold surfaces → mould. And the attempt to solve it with an open window → noise. Three complaints, one cause.

The solution is also one: controlled mechanical air exchange with the window closed. Everything that follows is the argument for that sentence — with numbers, standards and sources.

Let us begin with the sensation, because that is what sends people searching.

«Stuffy» is almost never about temperature, and it is not about oxygen either. Oxygen lasts a long time in a room: a person consumes it slowly. The sense of stale air comes from three things together — accumulated carbon dioxide, raised humidity and the absence of air movement.

Carbon dioxide. People exhale it continuously. In a closed bedroom the concentration rises through the night, and the morning heaviness in the head comes from that more often than from «I did not sleep enough». We wrote about this separately in the column on what everyday life in Montenegro is made of, but here the mechanism is what matters: carbon dioxide can only be removed by replacing the air. Neither a purifier, nor an air conditioner, nor a humidifier does that.

Humidity. Warm humid air feels stuffier than dry air at the same temperature. The body cools itself by evaporation, and evaporating into humid air is harder. Hence the coastal paradox: 26 °C in Podgorica is easier to bear than 26 °C by the sea.

Stillness. Even air of the right composition feels stale if it stands. Half an air change per hour is not only chemistry — it is also the requirement that air in a room should move.

The practical conclusion to accept before any technical decision: «stuffy» is a diagnosis of air exchange, not of climate. An open window cures it because it replaces the air. An air conditioner does not cure it because it circulates the same air.

Now the cause that is usually underestimated.

The number to start from: a four-person household releases around ten litres of water vapour per day. That figure comes from Verbraucherzentrale Energieberatung, the German state consumer advice service on energy. It adds up from perfectly ordinary things: breathing and perspiration, cooking, showering, drying laundry, houseplants, washing floors.

Ten litres is a bucket of water evaporating inside the apartment every single day. With no air exchange, that water goes nowhere. It either hangs in the air, raising relative humidity, or it condenses out on the coldest surfaces.

This is why the advice «shower less and do not dry laundry indoors» is correct but secondary. Ten litres is not excess, it is ordinary life. A building has to be built so that it copes with those ten litres without the occupants changing how they live.

The everyday norm. The same service puts it briefly: relative humidity should exceed 60 percent only briefly. Briefly — after a shower, while cooking. Permanently above that is already a state in which moisture accumulates in the structure.

The same source gives recommended temperatures: living rooms and kitchen 19–21 °C, bathroom 21–23 °C, bedroom 18 °C. And a number worth knowing before economising on heating: every degree of lower room temperature cuts heating costs by about six percent. But the relationship also runs the other way — an over-cooled apartment is precisely the road to cold surfaces where condensation forms.

This is the most important misconception about damp, and it costs people real money.

Mould does not appear where «the room is damp». It appears where there is a cold surface. The same room air gives 55 percent humidity in the middle of the room and 85 percent in the corner behind the wardrobe — because the air there is colder, and the same amount of water in colder air means a higher relative share.

That is exactly how the standard puts it. EN ISO 13788 — adopted in Montenegro as MEST EN ISO 13788 — requires the monthly mean relative humidity at the surface to stay below 80 percent. Not in the room: at the surface.

It is calculated through the temperature factor: fRsi = (θsi − θe) / (θi − θe), where θi is the internal temperature, θe the external one and θsi the lowest internal surface temperature. For opaque surfaces an internal surface resistance of Rsi = 0.25 m²·K/W is used.

Translated into everyday language, the formula says: the more a spot on the internal surface cools relative to the rest of the wall, the sooner mould will appear there — at completely normal room humidity.

Where do such cold spots come from? Thermal bridges: balcony slabs, window reveals, corners of two external walls, places where insulation is interrupted. And from furniture-packed corners where air does not circulate.

The practical conclusion is unwelcome for a buyer: mould is usually not a problem of occupant behaviour but a problem of construction. And you cannot see it during a viewing. That is why there is a section below on what to ask instead.

We wrote about mould as a subject in its own right separately and at length — that text is more about diagnosis and removal, this one about prevention at the building stage.

A short section, but it clears up a great deal of confusion.

60 percent is the relative humidity of the room air, measured roughly in the middle of the room, the way any household hygrometer does it. The consumer advice recommendation refers to that: 60 percent should be exceeded only briefly.

80 percent is the relative humidity at the surface, from EN ISO 13788, averaged over a month. Nobody measures it with a household device; it is calculated.

Mixing the two produces two opposite errors. First: «mine reads 55 percent, so mould is impossible» — it is not, if the corner is cold. Second: «humidity is 65 percent, I am buying a dehumidifier right now» — the dehumidifier removes the symptom, but if the cause is a corner that keeps cooling, it will run forever.

And one more caveat we owe you. Both numbers come from building physics and from everyday guidance, not from medicine. We quote them as engineering reference points and do not present them as medical limits.

What the World Health Organization does state is something else, and more important than the numbers: according to WHO, in many EU countries 20–30 % of households have problems with damp; people living in damp and mouldy buildings carry a higher risk of respiratory symptoms, respiratory infections and worsening asthma. The main recommendation is stated without numbers: persistent dampness and microbial growth on interior surfaces and in building structures should be avoided or minimised.

Now to the legal anchor, because Montenegro has a regulation on this.

The «Pravilnik o minimalnim zahtjevima energetske efikasnosti zgrada» — the rulebook on minimum energy-efficiency requirements for buildings, published in «Službeni list Crne Gore» No. 47/2024 and applied since 1 July 2024 — contains four things that concern us here.

Air exchange. The minimum number of air changes per hour in buildings where people are present — residential and working rooms explicitly included — is n = 0.5 h⁻¹. When nobody is present, n = 0.3 h⁻¹. Half an air change per hour means the entire volume of air in a room should be fully replaced every two hours.

Airtightness. The number of air changes at a pressure difference of 50 Pa must not exceed n50 = 3.0 h⁻¹ for buildings without mechanical ventilation and n50 = 1.5 h⁻¹ for buildings with it. The test method is named in the regulation itself — MEST EN ISO 9972, the familiar blower-door test.

Condensation. Building elements bordering the outside air must be designed and built so that condensation on internal surfaces is prevented; the calculation follows MEST EN ISO 13788.

Heat recovery. Where several conditions are met, heat recovery from the exhaust air is required, and its efficiency must exceed 50 percent.

And now the conclusion that appears nowhere in the regulation as a sentence but follows inevitably from two of its numbers. A building must be airtight — no more than one and a half volumes of leakage per hour. And it must simultaneously deliver half an air change per hour while people are inside. Through gaps, that volume physically does not add up in such a building. So an airtight building must have mechanical ventilation — not because it is written down, but because otherwise two requirements cannot be met at the same time.

That formulation is ours, not the legislator's, and we present it explicitly as our own conclusion.

And here the climate intervenes.

In summer you do not want to open the window. The muggy period on the coast lasts about four months — roughly from early June to early October, with August the muggiest month. That comes from Weatherspark, and it should be read with a caveat: it is derived from the MERRA-2 reanalysis rather than measurements at a specific station. The direction is right, and anyone who has spent an August on the coast will confirm it. An open window during the day lets in hot humid air — that is not ventilation.

In autumn and winter the window is awkward for a different reason. Bar, according to the municipality, is among the sunniest places in Southern Europe with an average of 270 sunny days a year, but in rain and wind off the sea the window is opened rarely and briefly. The annual pattern is set out in our month-by-month weather guide to Bar.

And there is always noise nearby. The main road, neighbours, a building site, the summer promenade. How districts differ in this respect is covered in where it is better to live in Montenegro and in the piece on why microclimate matters more than distance to the sea.

Add salt in the air. It is the reason metal corrodes faster on the coast — we wrote about that separately. For ventilation it means the incoming air should be filtered, and the filter class is discussed below.

Taken together this is an uncomfortable picture. The apartment needs air exchange every day of the year. The window can supply it only on some of those days, and always at the cost of noise, heat or humidity from outside. If nothing else is provided in the building, a person lives permanently inside a compromise and takes it for the norm.

The section everything above was gathered for.

Start with the window numbers. The Umweltbundesamt, the German federal environment agency, gives this reference: the sound insulation of windows, depending on construction and quality, covers a wide range from roughly Rw = 20 to 60 dB; old windows are around 25 dB, a single window with insulating glazing «a good 30 dB», and such windows in better versions reach 50 dB. The classes under VDI 2719 go in steps: class 1 — 25–29 dB, class 2 — 30–34, class 3 — 35–39, class 4 — 40–44, class 5 — 45–49, class 6 — 50 dB and above.

For a sense of what is a lot and what is a little: the World Health Organization, in its 2018 environmental noise guidelines, strongly recommends staying below Lden 53 dB and Lnight 45 dB for road traffic noise; below 54 and 44 dB for railways; below 45 and 40 dB for aircraft. All six values are classed there as strong recommendations.

And now the thing that turns the subject over. In the same Umweltbundesamt document two statements stand one after the other.

The first: soundproof windows reduce noise exposure only if they actually stay closed. A window on tilt insulates nothing.

The second: the suppressed air exchange between outside and inside leads to a sharp rise in relative humidity, and condensation forms on internal surfaces. And the way out is named right there — either regular burst ventilation every few hours, or sound-insulating ventilation units, especially for bedrooms, with a reference figure of at least 50 m³ per hour at around 70 cm² of cross-section.

So a German federal agency states precisely what we began with: sound insulation without ventilation is incomplete. You can buy an apartment with excellent class-6 windows and still sleep with the sash open because there is otherwise nothing to breathe — and at that moment the entire window class is doing nothing.

The practical conclusion for a buyer: when you ask about sound insulation, ask about ventilation in the same sentence. One without the other is half a solution paid for in full. Why silence became scarce at all we described in a separate column: why quiet became the main shortage.

Before the technology, the honest part about the free option.

Manual ventilation works. The consumer advice service recommends ventilating at least two to four times a day and names the most effective method: short cross-ventilation with opposite windows and internal doors wide open.

The difference between burst or cross ventilation and leaving a window on tilt is fundamental and constantly underestimated. With the window wide open the air is replaced in a few minutes and the walls stay warm. With the window on tilt for hours, little air passes through, but the reveals around the window cool down — and that is exactly where the black edges appear. A tilted window is the worst of all options: it barely ventilates, it chills the structure, and it lets in all the noise at the same time.

What manual ventilation cannot do. It does not work at night while everyone is asleep — and night is precisely when carbon dioxide builds up in the bedroom. It does not work when nobody is home. It works poorly in August, when it is more humid outside than in. It works poorly on a busy road. And it works only for as long as somebody remembers to do it.

So the right formulation is not «ventilating or a system» but: manual ventilation is a working supplement and an unreliable foundation.

Now the technology, without the marketing vocabulary.

A supply-and-extract system with heat recovery is arranged like this: one fan draws fresh air from outside, a second expels used air from inside, and a heat exchanger sits between them. The two streams pass alongside each other without mixing, and the warm outgoing air gives its heat to the cold incoming air — or the other way round in summer, where the hot incoming air gives its heat to the cooler outgoing stream.

Hence the main property: the air is replaced without losing heat. The Montenegrin regulation requires efficiency above 50 percent — but only where heat recovery is required at all, and it is required under four conditions at once, one of which is a total airflow above 2500 m³/h. A single apartment never reaches that airflow, so for housing heat recovery is a developer's decision and not a state requirement. Modern domestic exchangers deliver noticeably more than half, but we will not quote a specific figure — it depends on the model and the operating point, and we have no reliable data on real performance in the Montenegrin climate.

What the system gives you day to day.

The windows can stay closed — so the sound insulation works around the clock, including at night in the bedroom.

Air exchange is steady and does not depend on somebody remembering, on somebody being home, or on the weather outside.

Moisture is removed continuously instead of accumulating between two airings. For those ten litres a day, that is the decisive part.

The incoming air is filtered — on the coast this is not a detail but the subject of the next section.

What has to be said honestly alongside. The system costs money to build in, uses electricity, needs space for ducts and requires maintenance — changing filters is an obligation, not a suggestion. A dirty filter is worse than none. If you use the apartment only part of the year, work out in advance who changes the filter; our text on what happens to an apartment while you are away belongs next to this.

A small but useful section, because the word «filter» in apartment descriptions means almost nothing.

Ventilation filters are classified by ISO 16890, which replaced EN 779:2012 and has applied since 2018, after an eighteen-month transition period, as the binding international standard. It has four groups, and a filter falls into a group if it retains at least 50 percent of the particles in its fraction:

ISO Coarse — coarse dust, sand, lint, hair. Essentially protection for the equipment rather than for the air.

ISO ePM10 — particles up to 10 micrometres: pollen, mineral and agricultural dust.

ISO ePM2.5 — particles up to 2.5 micrometres: bacteria, mould and fungal spores, pollen.

ISO ePM1 — particles up to 1 micrometre: the finest fraction, which includes soot and combustion products.

And now about sea salt, because this is easy to get wrong and we nearly got it wrong ourselves. It is tempting to say «by the sea you need ePM1, otherwise the salt goes straight through». The measurements say otherwise. The mass of marine aerosol sits in particles larger than a micrometre — the main modes are at 1–2 µm and around 5 µm, and the supermicron fraction accounts for roughly nine tenths of the mass. So salt is already captured at ePM10 and ePM2.5 level, and ePM1 adds not salt but combustion fines: exhaust, soot, smoke.

The conclusion is not weakened by this, only made more precise: on the coast the filter class matters, not the word «filter» in the description. ePM1 as a reference for the second filter stage is recommended by VDI 6022 Part 1 and the January 2023 revision of VDI 3803 Part 4 — but that is a recommendation for ventilation systems in general, not a standard for housing.

What we did not find and therefore will not claim: there is no mandatory filter class for residential buildings in the Montenegrin regulation — at least, we saw no such requirement in the text available to us. The filter class is a question for the developer, not for the state.

Briefly, because this misconception is very common.

An ordinary split air conditioner does not take air from outside. It draws air from the room, cools it on the exchanger and returns it to the same room. Oxygen is not replenished, carbon dioxide is not removed, used air is not replaced.

What it actually does: it lowers the temperature and removes some moisture along the way, because water condenses on the cold exchanger and runs off through the drain. That is why air under an air conditioner feels drier, and that is where the impression that it «ventilates» comes from.

Why this is dangerous. Somebody with an air conditioner considers the problem solved and stops ventilating. The temperature is pleasant, humidity feels lower — but carbon dioxide and used air remain. And the cold surface of the air conditioner itself becomes one more place where, with poor maintenance, microbial growth develops.

Put correctly: an air conditioner and ventilation solve different problems and do not replace one another. One controls temperature, the other controls air exchange. A well-designed building has both, and they do not interfere.

Soberly, without the usual promises of «payback in three years».

On the cost side. A supply-and-extract system with heat recovery costs noticeably more to build in than its absence: the unit, ducts, penetrations, dropped ceilings to route them, commissioning. After that come electricity for two fans and filter replacement.

On the savings side. Heat recovery returns heat that would otherwise leave through the window. Only, electricity in Montenegro is cheap: according to Eurostat data for the second half of 2025 it cost around 10.8 euro cents per kilowatt-hour against roughly 28.8 on the European average (households, consumption 2500–5000 kWh a year, all taxes and levies included). In absolute money, therefore, the heating saving here is smaller than the same system would deliver in Germany. This deserves a sober view: in the Montenegrin climate supply-and-extract ventilation pays for itself mainly through dry walls and quiet, not through a line in the electricity bill. What running costs are actually made of is set out in our text on electricity bills in Montenegro.

On the side of what does not happen. And this is where the substance is. Removing mould is not cleaning, it is remediation: move out the furniture, strip the plaster, dry, treat, re-plaster, repaint. If the cause is in the structure, the mould returns. Add the loss of value: every buyer sees damp marks in the corners and prices them in. We wrote about the most expensive mistakes you cannot see when buying separately.

Honestly: we cannot calculate a payback period, because we have no reliable figures on how such systems actually perform in the Montenegrin climate. Anyone who quotes you an exact number has invented it.

The practical part, which works without specialists.

Look into the corners behind furniture and curtains. Not the middle of the wall but the corners of two external walls, behind the wardrobe, behind the curtain, under the window sill. Dark spots, wavy wallpaper, lifting paint are traces of condensation. A freshly painted corner against otherwise older paint is a signal in itself.

Touch the window reveals. They should not feel noticeably colder than the wall. A clear difference means a thermal bridge, and that is where mould appears first.

Use your nose. The smell of damp and staleness holds in textiles and wardrobes and is hard to mask. If the place has been aired hard before your arrival and every window stands open, that is not necessarily courtesy.

Look at the bathroom. Is there an extract opening, and does it work? A sheet of paper held to the grille should stay put. A bathroom without working extraction is a moisture source for the whole apartment.

Ask what it is like in August. If you are viewing in winter, the muggy season is invisible. Neighbours in the building answer this more honestly than the seller.

Ask whether an airtightness test was done. The regulation names MEST EN ISO 9972 — the standard blower-door test. In a new building it is worth asking whether it was carried out and what n50 came out.

Look at the ceilings. Dropped sections in the hallway or kitchen often mean ventilation ducts run there. Their absence usually means there is no system. More viewing points are in our guide to checking a property and in the collection of fifteen most common mistakes when buying.

A short list you can take with you.

Is there mechanical supply-and-extract ventilation — and in which rooms? Extraction only in the bathroom and kitchen is not ventilation of the apartment. What matters is whether there is supply air into the living rooms and bedrooms.

Is there heat recovery and what efficiency is stated? The figure should be in the design documents.

Which ISO 16890 filter class is specified, and who changes the filters? If the answer is «there are filters», that is not an answer.

Was an airtightness test carried out and what n50 resulted? This is the question that immediately separates a developer who understands the subject from one who does not.

What sound insulation class do the windows have? VDI 2719 classes run from 1 to 6; if there is no class, there should at least be an Rw value in decibels.

How is the anti-mould build-up solved and where are the thermal bridges? An open answer to that question — naming specific locations — says more than any brochure.

Without the marketing tone, because this text is not for that.

Our project in Bar includes: 10 cm of insulation, double-chamber insulating glazing, underfloor heating with an air-to-water heat pump, supply-and-extract ventilation with anti-allergen filters, full sound insulation and an anti-mould build-up. The energy class target is A+. More about the project is on the project page.

The logic behind it is exactly the one described above. An airtight envelope means forced air exchange is needed. Supply-and-extract ventilation means the windows can stay closed, and then the sound insulation works. Warm surfaces from insulation and underfloor heating mean fewer places where moisture can condense. Filters mean pollen and marine particulate stay outside instead of settling indoors.

What we do not promise. We do not promise a specific figure for heat recovery efficiency in operation — it depends on the operating point, and we have no measurements from the Montenegrin climate. We do not promise that mould is impossible under all circumstances: switch the ventilation off in a finished apartment, dry laundry in the bedroom every day and keep the heating at 14 degrees, and any building will get wet sooner or later.

And we make no medical claims. WHO writes about the link between damp and respiratory problems but sets no quantitative thresholds — and neither will we.

If this subject has become your subject, the following texts connect to it.

On mould as a problem in its own right — diagnosis, causes, removal: why mould appears in Montenegrin apartments.

On running costs and what the bills consist of: how much it really costs to keep an apartment in Montenegro.

On microclimate and why it matters more than distance to the water: microclimate instead of metres.

On the weather in Bar through the year: weather and climate in Bar by month.

On build quality and why it matters particularly here: earthquakes and construction in Montenegro.

On the purchase itself — from checking the property to the tax: how to check a property, what tax applies on purchase, how the purchase works and how a mortgage looks for a foreigner.

On life afterwards: honestly about living in Montenegro, a residence permit through property, who manages the building, renting out as a business and renting long term.

And for the city overview: the full guide to Bar and how much an apartment costs by city.