Saturday 28 June 2014


With current daytime temperatures in excess of the mid-thirties centigrade and overnight only dropping to the mid twenties we are struggling in the upper floor of our rented apartment. Downstairs, shaded from the fierce June dawn to dusk sunshine and with a short wall below ground level and ventilation provided from an adjoining shady courtyard things are far more pleasant.

This experience, if I felt proof was needed, is completely bearing out my decision to design a house that will be earth sheltered, high thermal mass, solar passive, with no windows on the western or eastern aspects, (thus avoiding the intense afternoon sun that causes such a problem in our rented apartment by heating up a long stone wall that then gives up its stored heat overnight directly into the bedroom!), and a deep overhang/canopy (2.5metres) shading the three metre high south facing windows from the intense summer sun whilst allowing the low winter sun to warm the thermal mass. The high thermal mass of the design allows the summer heat to be absorbed on hot days, helping to lower the internal temperature and prevent any overheating problems. Any stored heat is then removed by night-time ventilation.

Thus a passive cooling system has been incorporated into the design to take advantage of the cool air that falls down the mountainside in the evening.

Shuttering in place for living room vent.
The optimum ventilation rate for night cooling is generally recognised as around 10 air changes per hour. Higher rates than this may improve the cooling rate only marginally since it is also affected by the length of time the air is in contact with the internal surfaces; high air change rates resulting in less contact time.

Concrete poured for all three vents.
The effective control of natural ventilation requires well designed and user friendly windows to take full advantage of the prevailing conditions. For earth sheltered designs the normal approach is to incorporate ventilation tubes low down in the walls, well clear of the earth sheltering, and opening high window vents to provide a stack type system.

Shuttering removed and concrete vents proving in the glorious weather.
For my particular design, whilst I will have ventilation tubes to provide draft for the three wood burning stoves I am incorporating into the house to meet winter heating requirements, in the heat of the summer more overnight ventilation will be required. After long discussions with the engineer considering the possibility of incorporating cooling towers, we settled on a series of three large vents to be incorporated into the roof. When the earth sheltering is in place these vents will in effect be at ground level, albeit, some 4 metres above the floor of the house! These vents are north facing and have been designed to take advantage of the cool air that comes down the mountain in the evening to push the hot air that may have accumulated at ceiling level throughout the course of the day out through the run of high level vents above the wall of southerly facing windows. Given that the earth sheltering and high thermal mass has been designed to  keep the house at a very steady 16-18 centigrade this will be sufficient to remove any of the hot air that has accumulated over the day from the opening and closing of doors.

Looking towards the vents from the south west corner.
During the heating season windows will be kept shut at all times, with ventilation being provided by trickle vents incorporated into the window frames.