The living room faces north, and the curtains are always open, but it is still dark. The bathroom has no windows. The bedroom feels clammy in the morning. Light and fresh air are the two things that make the greatest difference to how a home feels — and the two things most often lacking in Danish homes.
Here is what you can do.
Why it matters
Daylight and health
Daylight regulates the circadian rhythm, affects mood and strengthens the immune system. According to The Danish Health Authority, lack of daylight has a documented association with winter depression (SAD), sleep problems and reduced concentration.
In Denmark we have 7 hours of daylight in December and 17 hours in June. The design of the home determines how much of that light reaches indoors.
Air quality and health
Indoor air is 2–5 times more polluted than outdoor air, according to BUILD/SBi. The sources are many: cooking, moisture, dust, furniture (off-gassing), candles, cleaning products and CO₂ from the occupants themselves.
Poor air quality worsens asthma and allergies, causes headaches and fatigue, and increases the risk of respiratory infections — especially in children.
What is typically wrong
Windows that are too small. Houses from 1940–60 often have small, deep windows with wide reveals. BR18 requires a minimum glazed area of 10% relative to floor area, but many older homes do not even reach that.
Windows facing the wrong direction. North-facing rooms get no direct sun. South-facing rooms overheat in summer, and people close up with curtains.
No mechanical ventilation. Houses built before 2000 rarely have mechanical ventilation. Extract in bathroom and kitchen (often insufficient) is typically the only provision.
Airtight windows without trickle vents. New, airtight windows reduce natural ventilation. Without trickle vents or a mechanical system, CO₂ and moisture build up.
Closed floor plans. Many small rooms with closed doors block the flow of light. Light from one window does not spread to an adjacent room.
What you can do — step by step
-
Paint walls and ceilings light colours. White or light surfaces reflect daylight and distribute it better in the room. The cheapest and easiest measure. Cost: 2,000–8,000 DKK per room.
-
Switch to slimmer window frames. Modern windows in timber/aluminium have slimmer profiles than older windows — this gives 10–15% more glass in the same wall opening. Cost: 5,000–12,000 DKK per window.
-
Install skylights. In rooms with a sloping ceiling or flat roof, a skylight provides up to twice as much daylight as a facade window. Cost: 8,000–20,000 DKK including fitting.
-
Remove walls or install glass doors. Opening between rooms allows light to travel. A glass door costs 5,000–15,000 DKK and maintains sound insulation. Removing a lightweight partition: 5,000–15,000 DKK.
-
Install ventilation. Decentralised ventilation units with heat recovery (8,000–15,000 DKK each) provide fresh air without heat loss. Fitted in an exterior wall, requiring a 160 mm core hole. Central ventilation system for the whole house: 40,000–80,000 DKK.
-
Add humidity-controlled ventilation in wet rooms. A humidity-controlled extractor hood or extract fan that responds to moisture keeps the bathroom dry and reduces the risk of mould. Cost: 2,000–5,000 DKK.
-
Consider larger windows or new openings. New window openings in the exterior wall require a building permit and structural engineer’s calculations (lintel over the window). Cost: 15,000–40,000 DKK per new opening. The effect is dramatic.
Which homes are most at risk?
Single-aspect flats. Flats that only face one direction — especially north — have permanent lack of daylight.
Basement dwellings. Light shafts and basement windows provide minimal daylight. Not permitted as primary accommodation without sufficient ceiling height and daylight.
Detached houses with many partitions. 1960s–70s houses with separate kitchen, living room and dining room. Walls block the flow of light.
New builds with insufficient glazing. Surprisingly common — especially facing north, where the architect has minimised glazing to reduce heat loss. The result is dark rooms.
When planning renovation
Every renovation is an opportunity to improve daylight and ventilation. Replacing windows? Consider larger openings. Removing a wall? Think light through the entire sequence of rooms. Replacing the roof? A couple of skylights cost almost nothing extra when the roof is already open.
Insulation retrofitting and sealing the building envelope must be followed up with better ventilation — otherwise you exchange heat loss for poor air quality.
Ventilation — what does the law require?
BR18 sets requirements for ventilation in new homes and during major renovations:
- Residential rooms: Minimum 0.3 l/s per m² of floor area
- Kitchen: Minimum 20 l/s extract (extractor hood with ducting)
- Bathroom: Minimum 15 l/s extract
- WC: Minimum 10 l/s extract
Most older homes do not meet these requirements. When renovating the building envelope (new windows, insulation), ventilation becomes even more important — a tighter house requires more active air exchange.
The cost of doing nothing
Poor air and lack of daylight cost more than most people think:
- Health costs. Asthma, allergies and winter depression are treated with medication and therapy costing thousands per year.
- Energy. Artificial lighting all day costs 2,000–5,000 DKK/year — daylight is free.
- Property value. Light, well-ventilated homes sell faster and at higher prices. A buyer’s first impression often depends on light.
How to move forward
Daylight and air quality can be measured. A CO₂ meter for 500 DKK reveals whether the air is too poor. A lux meter (or a free app) shows how dark it actually is. Start by understanding the problem — then the solutions are easier to prioritise.
For deeper dives into each topic separately, we have guides to daylight in the home and poor air quality. If you generally lack space, a revised floor plan can both bring in more light and improve air circulation.
Sources: BUILD/SBi — indoor climate, Danish Health Authority, BR18