Building attached (rooftop) solar photovoltaic heat dissipation factors, based on the widely used Faiman module temperature model, were experimentally determined from long term tests, and are presented in this paper. Tests were conducted at three gap clearances (50, 100 and 150 mm) and four tilt angles (0°, 5°, 15° and 23°). Open-racked scenarios were tested using the same apparatus and the results shown to be within reported ranges in literature. Constant and wind-dependent heat dissipation factor ranges of 23.32 ≤ U₀' ≤ 26.11 W/m²K and 3.2 ≤ U₁' ≤ 5.52 Ws/m³K respectively are reported for the building attached scenario. These values are lower than for open-racked photovoltaic modules. Building attached photovoltaic heat dissipation factors are shown to increase with higher gap clearances and tilt angles due to enhanced flow in the channel behind the modules. Consideration of these parameters for the optimal design of such installations is recommended. A sensitivity analysis involving the simulation of a rooftop photovoltaic array, using default heat dissipation factors versus the results of this work, illustrates that using specific heat dissipation factors can have a noticeable effect on the predicted output of a building attached photovoltaic system.