Opening Adjacency Lab…
OTTV / RTTV Calculator
How much heat flows through each square metre of a building's walls and roof, and whether that stays within the Department of Energy limit. The wall figure is the overall thermal transfer value (OTTV); the roof figure is the roof thermal transfer value (RTTV).
- Heat gain through each facade, from wall and window construction and the window-to-wall ratio.
- Heat gain through the roof.
- A pass or fail against the Department of Energy maximum.
- Follows: Department of Energy Department Circular 2020-12-0026, energy-conserving design of buildings.
- The Green Building Code sets its envelope rules differently, by glass performance and roof insulation, not by this value. Confirm which limit your locality applies.