Wall Talk · Glossary
Building science, defined.
The words we use, explained in plain language. If a term on this site is unclear, it should be here.
- Airtightness
- How well a building stops air leaking through gaps, joints and cracks. Uncontrolled leaks waste heat and carry moisture into walls. Airtight buildings then need planned ventilation.
- Building envelope
- Everything that separates inside from outside: walls, roof, ground floor, windows and doors. Its job is to keep heat in, water out and let vapour escape.
- Bukhari
- The traditional Kashmiri wood or kerosene stove. It heats the space around it strongly and the rest of the room much less.
- Chillai Kalan
- The forty days of hardest winter in Kashmir, from 21 December, followed by Chillai Khurd (twenty days) and Chillai Bachha (ten days).
- COP (coefficient of performance)
- How much heat a heat pump delivers for each unit of electricity it uses. A COP of 3 means three units of heat for one of electricity. It changes with the outdoor temperature.
- Condensation
- Water that forms when warm, moist air touches a surface colder than its dew point. On walls and windows in winter, it is the usual cause of black mould.
- Design temperature
- The outdoor temperature a heating system is sized for: a cold winter night, not an average day.
- Dew point
- The temperature at which moisture in the air starts to condense. For a room at 21 °C and 60% humidity it is about 13 °C.
- ERV (energy recovery ventilation)
- Like HRV, but it also transfers some moisture between the outgoing and incoming air.
- Hamam
- The traditional Kashmiri room heated from beneath its stone floor. Underfloor heating works on the same principle.
- Heat loss
- How much heat a room or building loses to the outside, measured in watts. A heat-loss calculation adds it up room by room.
- Heat pump
- A machine that moves heat from the outside air (or ground) into a building, delivering more heat than the electricity it uses.
- HRV (heat recovery ventilation)
- A system that replaces stale indoor air with fresh, filtered outdoor air and passes most of the outgoing heat to the incoming air.
- Hydronic heating
- Heating that carries heat around the building in water, through pipes in the floor or radiators.
- Kangri
- The traditional Kashmiri earthenware pot of embers, carried under the pheran for personal warmth.
- Manifold
- The distribution unit that sends heated water from the heat source to each underfloor heating circuit.
- Passive house principles
- A way of designing buildings that need very little heating: continuous insulation, airtightness, high-performance windows and heat-recovery ventilation. Certification is a separate, formal process.
- Screed
- The layer of sand-cement or similar material laid over the floor slab, in which underfloor heating pipes or cables are often set.
- Thermal bridge
- A spot where heat escapes faster than through the rest of the envelope, such as a slab edge, lintel or balcony. Thermal bridges are cold inside and often where mould starts.
- U-value
- How much heat passes through one square metre of a wall, roof or window for each degree of temperature difference. Measured in W/m²K. Lower is better.
- Vapour control
- A layer that limits how much moisture from inside the building moves into walls and roofs, where it could condense.
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