Here is some info on insulating under a foundation:

GBA: Foam Under Footing



Here is information on an affordable and super-insulated home: (R-60 Walls / R-80 Roof / Intus R-8 Triple Pane PVC Windows)

GBA: Striving for Passivhause Affordability

Here is a link to my CockamameeCalc.xls excel spreadsheet: https://www.dropbox.com/s/cq9gu7xwotxygna/CockamameeCalc.xls

((an improved version of the spreadsheet called Insulcalc can be found here: https://www.dropbox.com/s/ei29pl3ac1331hk/InsulCalc.xls?n=8915286 )

It will allow you to enter your house details and some insulation costs, then it will calculate a hypothetical heating cost.

Or, you can put in a monthly heating cost and it will tell you your hypothetical required R-Values. Note: insulations costs must be entered as: $ per square foot / R-value.

It is just sort of a guide - don't send me your heating bills!

Thank you for sharing your Excel spreadsheet to estimate heating energy requirements and the effect of insulation levels. Because I have measured my energy use over the last 2 ½ years, I was interested to see how my results compared with your spreadsheet predictions. My average total natural gas usage over the last two 12-month periods has been 22.6 MillionBtu. This was for two warmer than historical average winters, with heating degreeF days corrected to a house temperature of 65F of 4810 HDD(degF). If I assume only a small amount of gas is used from heating hot water and cooking, say 15% of the total, then that would leave 19.2 MillionBtu for space heating.

Using your spreadsheet, I compute 47.7 MillionBtu requirement for space heating. It is easy to see that the values for the heat loss through the slab and crawl space walls are way too high. Heat losses through those surfaces must travel through a lot of insulating dirt before reaching the outside air or ground water. If I multiply the actual R-value of the “slab” insulation (under the bottom of my crawl space) by a factor of 5 plus adding a fixed value of R-25 to get an effective value of R-50, and the actual R-value of the crawl space wall insulation by a factor of 2 plus a fixed value of R-19, then the total heat loss computed by your spreadsheet is reasonable, 20.6 MillionBTU, compared to measured value of 19.2.

For this quick calculation, we shall assume that the heat losses due to infiltration and forced ventilation are offset by passive solar heat gains, which is not a bad assumption for my house.

Your treatment of slab insulation is clearly inaccurate, as all other houses in this subdivision have zero insulation under their crawl spaces, but they do not use 139 BillionBtu annually as the model suggests for R=0.001. The ground is usually a pretty good insulator, and that must be taken into account.

Otherwise, the model seems like a good estimator for the conduction part of heat losses. I assume that your cost values do not include all the associated costs for labor and changes in construction required for additional insulation, which are much higher than the insulation costs for specialized walls.

Hi Lee:

I have tweaked and updated CockamameeCalc.

The spreadsheet, in its Cockamamee way, takes into account the R-Value of the soil and the depth of the slab below grade.

I hope that it more accurately reflects your actual data.

It can be found at: https://www.dropbox.com/s/cq9gu7xwotxygna/CockamameeCalc.xls

(an improved version of the spreadsheet called Insulcalc can be found here: https://www.dropbox.com/s/ei29pl3ac1331hk/InsulCalc.xls?n=8915286 )

Rob.

Rob-

Thanks. Now your spreadsheet is NOT so cockamamee! You put in a big effort, but the spreadsheet gives much more reasonable answers now, and should provide a better trade-off for insulation for the slab and basement walls. My soil is sandy with a lot of fist-sized and smaller rocks (this area is called the Rocky Mountains for a reason). Water content is variable, since they irrigate the land behind me, but it is dry most of the time. I used a value of 8 for the soil R-value, and the conductive portion of the annual heat loss is computed to be 23.9 MillionBtu, compared to my "measured" value of about 19.2 MillionBtu, so within the "experimental" error. Again, I have assumed the passive solar gain input approximately offsets the losses due to infiltration and forced (by the HRV) ventilation, which should be fairly accurate for my house.

I have also reduced the heating degree days (in deg F) by 24% from the measured degree days based on a 65 F base, which is intended for an indoor temperature of about 70 F, to account for the fact that my indoor temperature averages about 65 F rather than 70 F. (The difference between the standard degree days base temperature of 65 F and the indoor temperature of 70 F is used to account for appliance heat losses and heating by human beings, as I understand it.) Your degree days looked low for your area, as pointed out by Dana1, and I wonder if you were doing the same thing that I am doing?

Thank you also for introducing me to Dropbox. Looks like a good way to share information.

Posted By Dana1 on 13 Dec 2012 12:08 PM
6500 heating degree days Celsius is a lot more seasonal heating than 6500HDD-F, and is a realistic number only for places well north of Montreal, or locations at much higher elevations. Whitehorse Yukon runs about 6500-6800 HDD-C, and Edmonton Alberta only ~5700-5800 HDD-C.

But the heating degree days in Montreal are well over 6500HDDF. Montreal proper over the past 25 years had averaged about 4400-4500HDD-C (or about 8000HDD-F) but that's down from ~4600HDD-C from the middle of the last century. (Burlington VT which is a bit south of Montreal runs about 7800HDD-F, or 4300HDD-C.)

Subsoil temps in southern Quebec are cool (low 40s F, maybe 5-6C), but nowhere near permafrost. Unless it's very light porous insulating type of bedrock (not likely) it's of no use for heat storage.

Insulating the crawlspace walls AND the bottom side of the floor is probably going to be necessary for performance in a high-R house. Leveling up the top of the bedrock with sand and insulating the floor of the crawlspace with at least 4-6" (R15-R25) of cheap low density Type-I EPS (roofing insulation for flat commercial roofs) protected by a non-structural 1-2" concrete "rat-slab" is also a good approach. If you're at PassiveHouse type R for the walls & attic, even going to ~10"/R40 under the rat-slab may be in order. (Using reclaimed roofing foam rather than virgin-stock is cheaper than batts or blown fiber between the joists.)

Hi Dana:

HDD on Canadian charts is calculated at 18 degrees C which is approximately 65 degrees F.

This would mean that there is no conversion required, right?

Rob.

If the base temperatures are the same, then the deg F heating degree days are 1.8 times the deg C heating degree days.

Posted By Lee Dodge on 17 Dec 2012 12:20 PM
If the base temperatures are the same, then the deg F heating degree days are 1.8 times the deg C heating degree days.

I don't understand...

If the base temperature is the same, i.e. 65 degrees F, how could the HDD days be different?

Signed: Very confused!

There are two guys comparing heating degree days, one in Detroit, Michigan, USA and the other across the river in Windsor, Ontario, Canada. The guy in Detroit is measuring 32 F over a 24-hour period, so he computes 65 F - 32 F = 33 F heating degree days (for the 65 F base) for that one day. The guy in Windsor is measuring 0 C, and using the same base temperature, which in this case would be 18.3 C, he computes 18.3 C - 0 C = 18.3 heating degree days for that one day. They call each other and start to argue about how many degree days should be counted for the previous 24 hours, 33 or 18.3.  Finally the Canadian says, "You Americans need to catch up with the rest of the world and use the metric system. Then we would not have these problems. But, if you take your 33 heating degree F days and divide by 1.8, you will get 18.3 heating degree C days, and be in agreement with Canada and the rest of the world."

Thanks Lee.

I consulted this link http://atlas.nrcan.gc.ca/site/english/maps/archives/5thedition/environment/climate/mcr4033?maxwidth=1600&maxheight=1400&mode=navigator&upperleftx=1808&upperlefty=1456&lowerrightx=5008&lowerrighty=4656&mag=0.125 and determined that the HDD for my new house will be 5250. (computed as the difference between outside temperature in celsius degrees and 18 degrees celsius)

Now, I think that I need to know if I should use 5250 HDD or 9450 HDD in my spreadsheet?

Signed: Obviously, still confused!

Rob-

Since I don't know the equations that you are using, your questioin is tricky to answer. However, since you were using American (or English) units for everything else, I assumed that you would be working in American units (deg F) for heating degree days in your spreadsheet. R-values in the U.S. have units of hr ft^2 degF/Btu, and thermal conductivity u = 1/R, and has units of Btu/(hr ft^2 degF). So working in these units, the heating degree days should be in degrees F. I would check the units in all your equations, and make sure they cancel out properly to get the result in the units that you desire.

On a different matter, heating degree days for Montreal historically are about 4300 to 4400 (days deg.C), so your area must be significantly colder than Montreal if you are at 5250 HDD (deg C). Some people on the forum suggested an air source heat pump (ASHP) for your house, but that may not work well in your area since Montreal is already getting pretty cold for ASHPs, and your location is much colder.

I have 'unlocked' CockamameeCalc.xls for those of you who wish to 'fiddle' with it. :)

It is just a 'Micky Mouse estimator' and was patched together with info that I found on the WWW - remembering a recent TV commercial, "If its on the internet, then it's true!"

Thanks to Lee, it is much less inaccurate than it was initially, but, it is not 'the definitive guide to insulating your house'.

Here is a pretty good site on thermal mass and other energy builds. First time I heard of this site but it seems like a good site for info:

Homepower.com