Glass Verandas and Conservatories: Heat and Condensation

Choosing glazing, frames, ventilation and shading so a glass veranda does not overheat in summer, chill in winter or stream with condensation.

A glass veranda gives a house an extra room full of light that opens onto the garden. Yet this room is often only comfortable for a few months a year: in summer it becomes a greenhouse, in winter a cold space with streaming windows. The cause is usually not the glass itself, but the fact that heat, sun and ventilation were not considered together.

The more glass, the more delicate the balance

Compared with walls and roofs, glass lets heat through more easily and admits solar radiation. As the glazed area grows, the room temperature follows the outdoor weather more closely. A glass roof in particular is the main source both of summer overheating and winter heat loss, because the sun strikes it directly and warm air rises to the ceiling.

So the first design question is: does the roof really need to be fully glazed? Often a partly solid, insulated roof with glazing only in certain strips gives a better-balanced result. In a hot climate, a fully glazed roof facing south or west makes summer use difficult without serious shading.

Glazing units and frames

If the conservatory is to be used as a living space, single glazing will not do. When choosing, look at:

• double or triple glazed units — more cavities mean less heat loss;
• low-emissivity (low-e) coating — helps keep heat in the room;
• solar control glass — reduces solar heat entering in summer, though it may also cut some light;
• warm-edge spacer — reduces the cold strip along the glass edges;
• thermally broken aluminium or multi-chamber frames — stop the frame itself becoming a cold spot.

Safety is a separate issue for roof glazing: glass breaking overhead is dangerous, so laminated or toughened glass is used there. It also gives protection against hail and falling branches.

Where condensation comes from

Water droplets on the inside of the glass mean warm, moist indoor air is meeting a cold surface. The usual causes are:

• the inner surface of glass or frame is too cold (poor units, thermal bridges);
• too much moisture inside — plants, watering, drying laundry, steam from the kitchen;
• stagnant air, especially in corners and under roof glazing;
• heating placed far from the glass.

A conservatory full of plants naturally has high humidity. The solution there is not just better glass but regular ventilation and warm air moving along the glazing: floor trench convectors, heaters in front of the glass or underfloor heating.

Ventilation and shading

In summer you need openings at the highest point to let hot air out and low-level openings to let cooler air in. This creates natural stack ventilation and eases the load on air conditioning. Automatic roof vents that close with a rain sensor are a convenient option.

Shading works best on the outside, stopping the sun before it reaches the glass. External awnings, louvres and plants on a pergola are examples. Internal blinds and curtains soften the light, but most of the heat is already inside.

Floor, heating and the junction with the house

A conservatory floor often sits directly on the ground or a cold base. Without insulation under the floor, much of the heating goes into the ground and the lower part of the room stays cold. Underfloor heating suits glazed rooms because it spreads warmth evenly and sets up air movement along the glass; it works best with conductive finishes such as stone and ceramics.

The line where the veranda meets the house is one of the most sensitive spots. The junction between roof and facade, rainwater run-off and the different settlement of the two structures all need attention. A veranda added to an existing house usually needs its own foundation, and how it relates to the main building's foundation should be resolved by a specialist. If the room opens freely into the rest of the house, its heat loss will affect the heating balance of the whole home.

Before you start

• will the veranda be a year-round living room or a seasonal space?
• will it connect to the main heating system of the house?
• which way does it face, and does it get afternoon sun?
• which parts of the roof and walls will be glazed?
• if there will be plants, how will humidity be managed?
• how will waterproofing be handled where it joins the existing house?

In building private houses and in its architectural designs, Zaferoğlu İnşaat develops additional volumes together with the main structure and facade of the house. If you are planning a veranda or conservatory, we are happy to discuss its form and proportion of glazing on a computer model.