Browse Forums Heating, Cooling & Insulation 1 Feb 19, 2009 9:15 am I'm designing a house for Castlemaine, central Victoria, usually 3-5 degrees hotter than Melbourne and winter minimums sometimes close to zero. The basic approach I'm following is to build an insulated box.
In regard to the question of insulating the concrete slab, I get different opinions. One point of view says don't insulate because the coupling of the slab with the ground will use the earth's property of being "cooler than the air in summer, warmer than the air in winter" to contribute to cooling and heating. The other point of view says put insulation under the slab to reduce the heat loss in winter, particularly if using in-slab heating, on which I've not yet decided. Presumably, the insulation hinders the loss of heat to the ground in summer. A variation on my issue is that I could insulate the slab under just the front, north half of the house which contains the living areas or just the back, south half containing the bedrooms. Does anyone know of solid research or well-documented experience that can help me decide one way or the other. Thanks David Re: Under-slab insulation - yes or no? 2Feb 19, 2009 11:38 am I had the same dilemma for my design. And yes, it will have hydronics. In the end I've done for slab edge insulation (polystyrene foam installed vertically alone the sides) extending down for 1metre.
Look at http://www.concrete.net.au/publications ... fing07.pdf. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Under-slab insulation - yes or no? 3Feb 19, 2009 1:25 pm LikelyLad Does anyone know of solid research or well-documented experience that can help me decide one way or the other. http://apps1.eere.energy.gov/consumer/y ... opic=11490 Re: Under-slab insulation - yes or no? 5Feb 23, 2009 4:53 pm That site relates to USA and is very general, doesn't take into account the climate differences. If I remember correctly, the under-surface ground temperature in Zone 5 (Perth, Melbourne, etc) is relatively stable at approx 14 C all yeard round. I'm not sure if 5-6 degs difference in winter justifies the cost of insulation. My common sense tells me that in summer it could be counter-productive, making the slab to radiate stored heat back into the house instead into the ground. I visited a very unusual house 10 days ago, a "Solar Hemi-cycle House", supposed to be 100% passive. It had numerous large diameter poly pipes, running underground through the garden, up through the slab into the living area, to supply the ground cooled air inside in summer.
Chris My father rode a camel, I drive a car, my son flies in a jetliner, his son will ride a camel.Saudi saying Re: Under-slab insulation - yes or no? 6Feb 23, 2009 6:36 pm You only want edge insulation (1 metre horizontally into the slab or vertically just outside it). This way you get the summer and winter benefit of a large thermal mass. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Under-slab insulation - yes or no? 7Feb 23, 2009 8:18 pm kristofw That site relates to USA and is very general, doesn't take into account the climate differences. Heating/Cooling degree days (HDD/CDD) is a generic measure to assist in predicting how extreme a climate is that is independent of location. It is important to use the same formula when comparing sites. This is the US definition: http://www.cpc.noaa.gov/products/analys ... yexp.shtml Here is a HDD/CDD calculator from a large database of international weather stations. It also gives the limitations and application of this metric. http://www.degreedays.net/# kristofw If I remember correctly, the under-surface ground temperature in Zone 5 (Perth, Melbourne, etc) is relatively stable at approx 14 C all yeard round. I'm not sure if 5-6 degs difference in winter justifies the cost of insulation. For an example assuming 65F (18C) base temperature: Hobart airport 3957 HDD Fahrenheit Melbourne airport 3288 HDD Fahrenheit Perth airport 1967 HDD Fahrenheit kristofw I visited a very unusual house 10 days ago, a "Solar Hemi-cycle House", supposed to be 100% passive. It had numerous large diameter poly pipes, running underground through the garden, up through the slab into the living area, to supply the ground cooled air inside in summer. Sounds like earth cooling tubes. The extension of this are ground source heat pumps which use the stability of the earth temperature at 10m deep to provide a heat-exchange mechanism with the dwelling. Re: Under-slab insulation - yes or no? 8Feb 23, 2009 8:28 pm recent studies have indicated that up to 75mm of the earth under the slab warms up with the slab in OZ - - therfore this section of earth = greater mass to your slab.
I'd agree that some slab edge insulation is of use. http://www.yourhome.gov.au/technical/fs512.html Re: Under-slab insulation - yes or no? 9Feb 23, 2009 8:46 pm Yak_Chat recent studies have indicated that up to 75mm of the earth under the slab warms up with the slab in OZ - - therfore this section of earth = greater mass to your slab. I'd agree that some slab edge insulation is of use. http://www.yourhome.gov.au/technical/fs512.html Depends on what the mass is being used for. If it is for releasing stored heat, previous research has shown that increasing mass thickness beyond 6 inches doesn't yield much discernible benefit. However, there may be value in high mass to buffer excess heat. The EERE site confirms that slab-edge insulation is the most cost-effective means to reduce significant heat loss if you intend to pursue this strategy. Thanks for the insights, that makes perfect sense, and yeah, I will be leaning on the experience of the excavator operator entirely. 6 16125 4 5105 To me, that's what it looks like: poor backfilling and/or compaction. The width is about 1000mm maybe. That conduit in the photo is for the NBN. The water is about… 4 8039 |