JohnRia
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| 09/18/2009 10:13 PM |
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We are building a new home in southern Missouri. It has a 2200 sq ft main floor with a full daylight basement. We also have approx 700-800 feet in a bonus area. The exterior walls are all 2x6 and I wanted to do spray in foam. I am trying to determine if spray foam is the best solution. The quotes are coming in at 13,000-14,000+
My framer suggested using an inch or so of spray foam for the sealing properties and then fiberglass on top of that. I'm not sure I like that approach. Currently I live in a colder climate and that would not be a good solution. Maybe it would work in the area we are building.
HVAC is still under consideration. We would like to have GeoThermal but so far the quotes have been higher than anticipated. The original idea was to spend the $$ on foam and save on the HVAC and utilities but the numbers we currently have are not working. The GeoThermal does not seem to be as popular there as where I am from, maybe due to the milderclimate. We have firm bids on air-to-air and will end up there if we cannot find a justifiable Geo bid prior to time to do the HVAC.
We start digging next week so any input is appreciated.
Thanks!
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wes
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Posts:637
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| 09/20/2009 9:53 AM |
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When you say southern MO, are we talking south of St. Louis, or south of Cape Girardeau? Makes a big difference in the answers to your questions.
If you have not started construction, please consider SIPS, for your walls at least. In our market, they can be equal or less expensive than the spray foam by itself. Add in the cost of framing materials and savings can add up quickly. And truely, there is no comparison between SIPS and framed construction with fiberglass insulation.
Again in our area, the savings in operating costs between geo-thermal and conventional HVAC systems, in SIPS homes, is not enough to justify the additional costs of the geo system. |
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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JohnRia
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Posts:7
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| 09/20/2009 10:25 AM |
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| We will be 12 miles form the Arkansas line in SW MO and 50 or 60 miles from Oklahoma. On Table Rock Lake with a North South facing home with walk out basement. The Southern exposure has a lot of windows. We looked at SIPS but after crunching the numbers, for the house we are building, decided to go with stick build. |
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rykertest
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Posts:132
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| 09/26/2009 9:39 AM |
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| Hey john, have you considered Multi SPlits for your Hvac or ICF as your method of construction? ICF's are usually much less in cost compared to sips for the area. Geothermal is great but very expensive as you have noticed and the ICF allows a smaller hvac system saving money. I'll send you our info and if you would like to talk, you can contact us. Thanks! |
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JohnRia
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Posts:7
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| 10/01/2009 9:08 AM |
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| We are doing an ICF basement and will probably use a mini-split in the bonus area. I don't think we want mini-splits for the whole house. Footings went in yesterday. |
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rykertest
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Posts:132
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| 10/01/2009 12:05 PM |
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| Hi John, may I ask why you do not want to use the mini splits for the whole house? Also, what are you doing for your water heater? Thanks and good luck on the build. |
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JohnRia
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| 10/01/2009 1:11 PM |
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| Well the ones we have seen remind us of units in hotel rooms, not something we would want through out the house. Maybe we just have not seen the latest or more updated units. We have not made a decision on the water heater yet. We are thinking of using a tankless LP unit. |
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rykertest
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| 10/01/2009 1:35 PM |
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All of the major mini split companiesnow offer 3 or 4 different wall registers that look like a traditional American vent, and the wall mounted hotel regiter doesn't have to be used. You can get all the benefits of the mini splits without the euro look most American's don't care for. Regarding the tankless, they are a good product for certain areas, but Southwest Missouri is not one of them. Our water is so VERY hard here, they can really have issues with that. Also, if you lose power, you have no storage tank. If I may, I'd suggest looking at Marathon electric water heaters. They are amazingly efficient and have a 45 (yes you read that right) year warranty. They have no metal tank, no anode rod, and they have a round bottom with a drain at the very bottom so draining any hard water deposits is a snap. In my opinion it is the best water heater on the market and the last water heater you should ever have to buy; literally.
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rykertest
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| 10/01/2009 1:39 PM |
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| I sent you a PM with my contact info. |
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Dana1
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| 10/01/2009 1:51 PM |
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The flash & batt (or flash & spray-cellulose) works, and works well. An inch of 2lb foam will add a lot of structure as well a sealing, but with the thermal short-circuit of the studs the benefit of 5" of 2lb foam vs something else are largely diminished.
My preference would be spray-cellulose over batts though- there will be fewer gaps, and less convection internal to the insulation, so it's real-world performance ends up closer to theoretical. Sprayed at 3lbs/ft^3 density or higher it also adds surprisingly substantial thermal mass to the structure- about the same as if there were a 1.5-2" concrete slab embedded in the wall. The water-activated adhesives in the material keep it from sagging over time too (a longer issue with less dense application of dry-blown cavity fill.) The thermal mass inserts a time lag on the thermal gain through the wall, lowering the peak load on the AC measurably (if not as much as with ICF, with a 6" concrete EPS sandwich.)
If you want to really beef up the R value of the framed wall, go with thicker insulating sheathing on the exterior. An inch of XPS or ISO over the thermal short-circuits of the framing elements DOUBLES the R-value in those places, and the whole performance will meet or beat that of an all 2lb foam cavity fill without insulating sheathing (!). If you use foil-faced ISO and a 1/2"-3/4" rainscreen gap between the insulating sheathing and the siding you'll pull an extra effective R4-R7 in cooling season (with the greatest effect on the portions that get direct sun, since it has the highest radiated heat flux and will get a convection cooling effect as well.)
Play around with this tool a bit:
http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/Calc.htm
Add another R2 to the clear wall values it returns if you use 1" ISO, or R1 if you use 1" XPS instead of 1" EPS (the R4/inch in the model). If you're using a 1" flash of 2lb foam under fiberglass or cellulose, add another R2-3 to the the FG or cellulose results. Then look at it with all-polyurthane cavity, no insulating sheathing.
The for 2x6" 16" o.c. the clear-wall values will end up something like:
all foam, no sheathing:----------------------- R25 (staight up, as calculated by the tool)
1" foam-flash, 1" ISO, cellulose fill--------- R26 (above factors added except for rainscreen/radiant)
1" foam-flash, 1" ISO, FG batt fill-----------R24 (above factors added except for rainscreen/radiant)
Foam is a really great air sealant, and at 2"+ thicknesses 2lb foam becomes a Class-II vapor retarder as well, but it's a premium product at a premium price. There are usually cheaper ways to get the R-value out of it, and once you have a perfect air seal, it's almost ALL about R value (with some weighting for thermal mass, the value of which is very climate-dependent.)
Price it out, but flash-foam + spray cellulose + insulating sheathing will probably cost less, perform the same or better.
If you want to go super-insulated, skip the flash foam, put 3" ISO on the exterior with cellulose cavity fill (after air-sealing with caulk & spot foaming) and get about R38-R40 out of it. (That's what I'd probably do.) 4x8 sheets of 3" (R21) ISO were sub $60 last time I priced it out, or just under $2/square foot (delivered, not installed) 2lb foam in a 3" thickness has the same R-value, but that would come in ~$3.30-3.50/square-foot (installed), but in a cavity fill it's performance is severely undercut by the framing. Which is the better value? Depends on what it costs to install the ISO.
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JohnRia
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| 10/02/2009 6:40 PM |
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Thanks for the replies. As with most things the more data I collect the more I realize I don't know.
Dana, the web page was very helpful. I like the sound of the spray-cellulose after looking at the results using it vs foam or the other options. Is the foam the most cost effective way of sealing the home. Seems the flash of 1 inch isn't tremendously cheaper than foaming the whole thing which surprised me.
We have a lot of windows in the home and realize that going to the extreme on the insulation is only going to help so much due to the large expanse of glass. But we did buy the lot for the view so windows we will have. Does that come into play on which insulation makes the most sense? I mean having an r30 wall isn't going to help much if 80% of it is glass. The view is to the south so most of the glass faces that direction. The exterior will be all brick which surprised me on the calculator that the wall value is lower than wood. Out of curiosity how does brick compare to Hardi or vinyl?
One of my big questions is moisture barrier i nthat area. I've asked three different people and had three different answers. Do you have any suggestion on that?
Thanks for the great info so far! |
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Dana1
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| 10/05/2009 12:27 PM |
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With an over-glazed area the glazing & overhangs & shade factors are going to dominate the cooling load equations as well as the heating season heat-loss. It probably makes sense to have exterior shades to pull down on high-heat days, eg:
http://www.builditsolar.com/Projects/Cooling/RollupSunShades.htm
A half-inch to inch of iso or XPS sheathing is still worthwhile (taped/caulked seams, staggered with the OSB/plywood seams) is still worthwhile. But it'll be hard to rationalize the foam- going with sprayed cellulose will give you a bit more thermal mass to work with.
To get the tightest possible seal, install all the doors & windows (using flexible "windows & door" expanding foam, not stuffed fiberglass around them) prior to blowing the cellulose, then wither with a blower door or tight fitting window fan alternately pressurize/depressurize the shell and run around finding & sealing all the leaks with a can of expanding foam & a caulking gun to make it as absolutely tight as possible (pay attention to the foundation sill band joists as well.) Then spray the cellulose, give it a few days to dry before sheet-rocking, and don't paint it for at least a month to allow the moisture used to activate the adhesives to stabilize.
As for the vapor retarders, you're probably better off without them, but find the city with the closest climate to yours here:
http://www.climate-zone.com/climate/united-states/
Then we can fine-tune it a bit as to whether/where/where-NOT to place any vapor retarders in the stackup.
The R-value of masonry is effectively zero and it's vapor permeability (and water storage capacity) quite high. On the S side the vapor drive toward the interior in direct sun after a wetting event is quite high, so it's important that it both drains & breathes well on the interior side of the brick- there needs to be at least a 3/4" gap between the brick and sheathing. It may make sense to use vapor impermeable foil-faced ISO on that side to both block the vapor drive and reflect the radiated heat from the solar-baked brick.
A few documents to ponder while figuring out your wall stackup, and where you MIGHT place vapor retarders:
http://www.buildingscience.com/documents/reports/rr-0104-solar-driven-moisture-in-brick-veneer
http://www.buildingscience.com/documents/reports/rr-9302-humidity-control-in-the-humid-south
http://www.buildingscience.com/documents/reports/rr-0105-brick-stucco-housewrap-and-building-paper
http://www.buildingscience.com/documents/information-sheets/3-water-management-and-vapor-control/reservoir-claddings/
http://www.buildingscience.com/documents/information-sheets/3-water-management-and-vapor-control/drainage-plane-water-resistive-barrier/
http://greensburg.buildingscience.com/downloads/BSP-033_MH_Haymount.pdf
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JohnRia
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Posts:7
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| 10/08/2009 10:43 AM |
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Dana,
Thanks for all of the great links. A lot of good information. In looking up our location there is nothing real close however in doing research and using a 65 degree base it shows that we have approximately 4500 Heating Degree Days and 1200 Cooling Degree Days per year.
If I am interpreting correctly it would appear from some of the data at the above links that we would not want a vapor barrier. Probably just a good housewrap over the OSB sheathing. As far as adding a layer of foam with foil will that cause issues with the windows and doors? We have already ordered them due ot the long lead times and ordered them with 6 9/16" jambs. |
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