Owner Building a Strawbale House
in the Bega Valley,
“Building Performance Statistics”
We have started to collect a number of different statistics about the performance of the building.
We'll add them to this section of the website. Eventually we hope to get this section to automatically update.
Until then here is a start...
Temperature is given in degrees Celsius. It is collected at 20 minute intervals. In the above graph for October
you can see that the house got much cooler over night after very hot days, that is because we made an effort to coolit down by leaving windows open over night. Otherwise there was no heating or cooling during October. It was a strangely hot spring month with just 5mm of rain at our place.
In order to interpret the above temperature statistics you need to know a bit about our house. Some of this information is available in other parts of the website, but here is a summary.
- The raft concrete slab is able to directly absorb any heat from the sun entering the building (no carpet or other insulating fittings). The slab also has external edge insulation.
- At the summer solstice the eaves block all sun entering the building. At the end of October the sun reaches about 0.4 m inside. At the winter solstice the sun reaches about 4 metres inside the building (and you almost need to wear sunglasses inside).
- The ratio of north glass to thermal mass (concrete & render) that we tried to aim for was 1:6. What we have ended up with is about 82 sq m concrete floor in rooms with north windows and about 18 sq m north glazing, plus all the lime & sand rendered walls which is more than 30 sq m of around 50mm thick render in the northern rooms. In the whole house we have about 35 sq m of glazing (facing all directions) to 140 sq m of concrete slab and more than 55 sq m of internal rendered walls.
- All the windows are double glazed. Window frames are timber internally & aluminium externally. Except the bathroom where the frame is all aluminium and you can feel the heat transfer easily as the frame gets quite warm when the sun is falling directly on the window, even in winter.
- There is only one window (1.8 sq m) on the west that gets significant sunshine through it. A pergola will eventually be added to shade this. The eastern windows in the bedroom and bathroom will have external shade sails (70% shadecloth) during the summer months and full solar access for heat gain during winter.
- Ceiling insulation consists of an R1.5 blanket directly under the colourbond steel roof and R3 batts in the ceiling cavity.
- All the external walls are lime rendered strawbale, except for panels above the windows which are cement sheet clad stud walls rendered to match the strawbales. R3 insulation batts were inserted into the external clad stud walls.
- All references to insulation ratings are using the Australian R value units (quite different from the USA and other countries).
- Windows were placed to allow through breezes for summer cooling. Some of the cooling effects are not expected to work effectively until the external landscaping, including construction of pergolas, is completed and plantings have had time to grow.
- We have yet to install any interior window coverings, so all stats are without the benefit of curtins or blinds to help control temperature variations.
The house has been very comfortable to live in.
In winter we have observed internal temperatures of up to 15 deg C above the external temperatures during the day, solely due to solar heat gain. This is more than is required in our climate and we have had to open windows and doors on cold, sunny days in order to keep the inside temperature comfortable. We have also noticed heat gains on quite cloudy, overcast days, so even without direct sunshine the house has achieved comfortable temperature levels in winter.
We weren't setup to log all the data to the computer last winter so we'll have to wait for next winter in order to share winter performance graphs. In the middle of winter typically the house was around 22 to 23 deg C at 6pm and around 15 to 16 deg C at 6am and up to 30 deg C during the middle of the day (depending on whether we had doors open or not and whether the sun was out or not). Local daytime temperatures were typically around 15 - 16 deg C and nighttime temps around 0 deg C. We often lit our combustion stove at night time for the pleasure of sitting in front of the fire and because we are not very good at putting on extra layers of clothing.