I need advice/opinions on different insulation options. DH and I (both in our fifties,kids raised and out on their own) are building the house we expect to live in the rest of our lives. Will not be mortgaging the place or worried about resale value so will build only to suit ourselves. High priority is to build so we can afford to heat it thru retirement years. House will be all electric since natural gas is not available here and propane has always been pretty much the same price per btu as electric around here. Want to keep wall thickness to 6 1/2″ so we can use standard sill extensions. Will definitely do fiber cement siding. We’ve ruled out SIPS and ICF. Options under consideration are :
2×6 framing,16″ oc,1/2″OSB sheathing, closed cell foam sprayed between studs
2×4 framing’ 16″ oc, 1/2″ OSB sheathing,Mooney wall type setup with horizontal 2×2 strapping and denspack cellulose, maybe with 1/2″ thick rigid foam insuation squares under the strapping where it fastens to the 2×4.
considered putting rigid foam on exterior but don’t see any good way to install FC siding over it. I’m thinking it may be more effective to do something to bring the R value over the studs up from 6 to 11 than to have the stud bays R30 but the 15% or so of wall that is studs only R6.Any thoughts, anyone?
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How large a home are you building? You can skin the outside with continuous layer of foam to virtually eliminate thermal bridging, just need to install a rain screen detail (vertical strapping at 16" OC) over the foam layer so you have something to fasten siding to.
Personally, if it were my last house and I was looking at 20+ yrs there, I'd be looking at SIPs or way fatter walls than 2x6. The cost to do wider extension jambs/sills on windows and doors will seem minor compared to the potential energy savings over the next 20 yrs.
Just curious why you have ruled out SIPs and ICFs. They may cost more upfront, but long term energy savings will be well worth it. Both are good choices for thermal performance, ICF's are even better in tornado country.
Should also optimize your siting to take advantage of insolation, and also design sufficient roof overhangs for shading in the summer months.
We're building 1098 sq' on main floor with 9' ceilings, a full basement, big attached garage on north side. Most of the windows will be in the south wall, 8' deep porch across west wall and 1/2 of east wall.Good shade trees to east and west,2' deep soffits. Nobody around here is familiar or comfortable with SIPS. All the builders I've talked to have said 24" OC studs make the walls too wavy. Can you tell me how you fasten fiber cement (5 1/4" lapped to show 3 1/2") to ICF ? Some reasons I'd prefer not to have thicker walls-We have to pay real estate tax, and sq', measured on the outside, is a big part of how its assessed. County assessor told me it would value at 105,000, taxes on that value would be $2,400 a year. I also don't realy like the effect of the deeper windowsill, kinda blocks the light. We are planning to have a storm shelter in the basement. ICF won't keep the windows from blowing in on you, or the roof from blowing off! Still,if I could find a good ICF or SIPS builder that would build the house I want (DH doesn't really care what kind of house it is as long as he gets his garage) I would consider either. Our house of 33 years, that we had finally almost finished remodeling, burned down in February. We're living in a perfectly adequate rental 2 blocks away and we hate to admit how much we really hate it since we were so lucky it was available the day after the fire. We want to take the time to do this right but we're both really anxious to have our own home again and most of the builders around here won't have time for months. I know we're going to have more money in the house than it will ever be worth but we love it here and I have mature fruit trees and shade trees and established asparagus patch and terrific neighbors. If we could find someone to do the foundation and get it closed in,I'd be comfortable doing the rest myself , except I'd sub out the drywall, I hate finishing drywall and hanging its really not a one woman job. So unless you know a competent SIPS or ICF builder in my area that will build it this summer, what's my next best option?
WW
You may enjoy this thread on superinsulated houses.
I agree with Redford. I would superinsulate the house and not worry about the extention jambs.
We don't live that far apart. I live in IA just up the road from Sioux City.
http://forums.taunton.com/tp-breaktime/messages?msg=102383.1
Rich
2x6 ... in Northwest we almost always go 24" oc ... reduces framing a lot. A friend of mine did diagonal braces let into studs for shear structure and then 1/2" polyiso sheathing for elimination of thermal bridging. Don't think he did the rain screen on the outside ... just siding over the polyiso ... and normal VB on inside w/ attention to details ... and a good ventilation system.
"... then 1/2" polyiso sheathing for elimination of thermal bridging."Why do so many speak of "eliminating" thermal bridging? All a layer of insulation does is to reduce it. The numbers can be calculated. A 2x6 will provide about R 6.6 (@1.2/inch). Adding a half inch of polyiso will improve that by another 3.5, for a total of 10.1. The heat loss through that stud will then be only 65% of what it was. OK, 35% of the heat loss through that stud has been "eliminated."I can't imagine, with all the attention fuel cost is getting and the expected long-term trend, why anyone designing and building a new house would go with old construction techniques. Superinsulation techniques are well known now, and the cost isn't that much more. Why not do a new house the right way?
Everyone seams to like the term thermal gridging, personally I would rather spend more time and energy on the windows and doors. They are the weak spot in every house. I go along with Clewless on the 2' center studs and the poly. on the outside.
As far as the wavieness in walls. if you are using poly on the outside, the actually is very little! I suspect thet the builders in your area are more familier with 16" center construction. It is hard to change the minds of people who have always done it this way!
I have a hard time with blown foam insulation, my house was done in the 70's and it is worthless. I suspect it has to do with site mixture being off, but if doing my own home I wouldn't take the chance. I would go with dense pack cellulose.
Again, I emphasise that I would find the most energy efficient windows possible. This would be more important to me than the heat loss in the studs.
We are planning on windows, either Anderson or Pella ,with very low U values. Having problem finding low U windows for south side with high SHGC. Uvalue seems to rise along with SHGC on everything I've looked at. We do plan to do very thorough air sealing. The idea is to make sure the things that would be very difficult to upgrade later are very high R, worry about looking for more efficient mechanicals, maybe solar or GSHP, if it seems worth it after everything else is done. We had 70's foam in our old house and were very happy with it, had a very good installer.
Very low U-values ... unless you are well under 0.25-0.30 it isn't 'very low' ... it is more like industry standard.
The lower the u-value, generally you tend to lower the SHGC ... basic science. Although I don't think argon or krypton gas affects SHGC ... someone may correct me here. Thicker double glazed units will/should not effectively affect SHGC, I think ... always go for thickest glass available ... 3/4" minimum ... propbably the downfall of both Pella and Anderson ... they may not allow thick glass units like in the vinyl frame options.
Where are you located? Have you considered high performance windows using Heat Mirror? They fine tune their low-E coatings for various conditions (e.g. passive solar vs. west facing high rise).
You are correct, lower the SHGC and you lower the U-factor of a window. In both cases you are simply limiting heat transfer thru the window.
SHGC defines how much direct solar gain thru the window is blocked - or radiant heat gain, and U-factor defines the insulating value of the window - primarily conductive. But, radiant energy on the window is going to result in conductive heat gain as well, and since U-factor defines how much heat loss (or gain) thru the window, and radiant is...etc. Point being that they are certainly interrelated.
Argon and krypton don't affect SHGC, they are there for improvement in the U-factor.
When dealing with IG units, wider isn't always better however.
The optimum airspace width for an IGU with a LowE coating is about 7/16". Add a couple of 1/8" lites and the overall IGU width is 11/16". Increasing the width of the airspace up to a 7/8" has no effect on performance, but as the airspace width goes above 7/8", performance actually begins to decline - not a lot, in fact it is very gradual - but it does lower performance because the wider airspace allows for convection currents within the airspace which do affect the insulating properties of the unit.
For a clear glass IGU, an airspace width of about 9/16" maxes the insulating performance.
Uh, not quite ... they are not directly correlated and I did NOT say lower the SHGC and it will lower the U-val. A lower U-value GENERALLY means the SHGC will go down, but the u-value aside you have MANY options to lower the SHGC (but not raise it). I've purchased 0.25 U-val glass before and had SHGC available to me from about 0.65 down below 0.20 ... and I've purchased both types for different applications (although the same house).
What brand of window were they? I met with the local Pella rep yesterday and was pretty unimpressed with his knowledge of anything technical.He had no idea why anyone would ever want a high SHGC. I wanted to know at what Uvalue you would have condensation on the glass at -10 if indoor temp was 70 at 40% RH. All he could say was the standard, if you have condensation you need to ventilate excess humidity.I want to maintain RH levels between 60% and 40% all year round.
I was buying glass only and stopping it into place. I've heard of a couple of window manufacturers that use Heat Mirror ... Hurd comes to mind. Someone else mentioned another. ...i.e. they some stock w/ Heat Mirror.
Most e.g. vinyl window suppliers could provide the Heat Mirror glass option ... although I caution you ... you think they looked at you like they didn't have a clue why you would need a low SHGC ... wait until you say "Heat Mirror" ... they will either look at you like they didn't have a clue or think you are talking about glass w/ a mirror finish (which I have ordered in addition to Heat Mirror). I'd say 95+% of most distributors will not know of Heat Mirror.
Heat Mirror has a problem ... it requires special manuf. equipment to make and there are only a handful of producers in the entire US, I think ... Out here in the west we had 4-5 in the 80s and now we may be down to two (Seattle and LA, last I heard). Scarcity drove the price up high ... I had to replace a broken pane and it cost me plenty! Maybe HURD does their own.
Southwall Corp is the ... maker of the mylar, I guess ... that is where the product originated. They have a website, u-values, SHGC, etc. Plus they list all of the product options.
Let me know if this still piques your interest and you are having difficulty finding information. Might be able to help out.
I called Pella and they had me talk to thier guy in Sioux Falls. He was much more helpful and knowledgable. According to him, if its zero outside, RH needs to be 25% or less to prevent condensation. Running ceiling fan on low speed would help too.He said adding an inch to jamb extensions would increase cost of the extensions less than 5%. I called FC manufacturer, they said you can install siding over up to 1" of foam, as long as nail goes at least 1 1/4" into stud so I'm thinking that may be a good option. How do I choose between a window with uvalue .37 SHGC .52 and a one with uvalue .31 SHGC .49, for the south windows. For all other windows will go with .25 uvalue.
For the south windows I would think you should be able to do much better (i.e. higher) than 0.49 SHGC I would think (I'm guessing easily around 0.70 or higher. Assuming they are summer protected, you would want a high SHGC. If they aren't protected from the summer sun ... consider options to do so or drop your SHGC.
I was agreeing with you that IN GENERAL...I just neglected to state it that way.
I am curious how you were able to get U-factor at .25 with a SHGC at .65 though.
Edited 6/28/2008 8:52 am ET by Oberon
no worries. I know you did, just the way you worded it
Heat Mirror (tm) glass ranges from 0.20-0.25 U-value and the SHGC ... or at least the SC I believe was up around 0.65 (if I recall correctly, but I've had my share of CRS).
Thanks
Heat mirror does have the low U-factors, but I have never seen them advertising the higher SHGC - that is interesting
My memory may be lacking ... go to Southwall and look it up to make sure. Always good to refresh the memory.
Anyone know how to do calcs to determine optimum ratio of uvalue to shgc for south facing windows, if I can't find a window that offers both. I can look up heating degree days and average sun during heating season. If I have that information can I calc amount of heat lost during non sunny and nighttime vs heat gain from solar, assuming I'm not going to use any kind of blinds day or night. Don't worry about heat gain in summer , will have roof overhang and shade trees to deal with that and I can live without air conditioning if I have to.
Stick with 2 x 4 walls and spray closed cell foam to 3" + thick (R-20+). Buy Marvin Windows with lowE 2 and Argon. Use plywood sheathing, not OSB and use felt not tyvek (foam acts as an air barrier).
Jeff
Much easier to simply go here:
http://www.efficientwindows.org/selection.cfm
And you can play around with any basic glass / window material design that you might want to consider.
i believe a thermal bridge is a reference to non insulation material having contact to outside weather (yes the 2x has some insulation) but you get the idea. so the foam sheathing on the outside seperates the the wood to wood (osb) contact and creates a thermal break. or stops a thermal bridge if you prefer. another classic thermal bridge example is where high rise buildings have the concrete floor slabs exposed on the outside wall, and then brick or glass or other material filling between the floors. but that concrete band on the outside will get cold in the winter and easily transfer that inside the building envelope since there is no thermal break to keep from doing so.
That's correct, Dick. A bit of a misnomer. REDUCING the thermal bridge. INTERRUPTING it.
People tend to be afraid or skeptical of 'new' techniques ... change is slow.
Just continuing with your thoughts on the calculations for adding exterior foam to a home that is built using conventional 2x construction. I was simply curious, so I did a quick (very quick) number crunch. <!----><!----><!---->
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Consider studs 2’ OC. 20’ wall @ 10’ for 200 sqft<!----><!---->
2x6 @ R1.2/†= 5.5 x 11 studs = 13.75 sqft @ R6.6
200 sqft – 13.75 = 186.25 @ R 19<!----><!---->
Wall = R19 or U.053studs = R6.6 or U.15 studs = 6.9% of wallWall @ 186.25sqft + studs @ 13.75 sqft, overall 200 sqftWall = 186.25 sqft x U.053 = 9.87 studs = 13.75 sqft x U.15 = 2.069.87 + 2.06 = 11.93/200sqft = U.0596 or overall wall R value of 16.77.By adding exterior foam @ R3.5: Wall = R22.5 or U.044studs = R10.1 or U.1 Wall = 186.25 sqft x U.044 = 8.195studs = 13.75 sqft x U.1 = 1.3758.195 + 1.375 = 9.57/200sqft = U.04785 or overall wall R value of 20.89.<!----><!---->
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23% improvement over the entire wall, not just the studs Preaching to the choir here, but the formula for computing heat transfer is (BTU/hr) = (area / R) * ÄT ----( I am typing a “deltaâ€, but the site is posting that funny “A†thing…) If ÄT = 10°, then (200 sqft / R 16.77) = 11.92 * 10° = 119 BTU/hrIf ÄT = 10°, then (200 sqft / R 20.89) = 9.57 * 10° = 96 BTU/hr<!----><!---->
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Then considering a more robust ÄT:If ÄT = 40°, then (200 sqft / R 16.7) 11.92 * 40° = 477 BTU/hrIf ÄT = 40°, then (200 sqft / R 20.9) 9.57 * 40° = 383 BTU/hr<!----><!---->
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And finally, if we happen to have a mind (and finger and toe) numbing ÄT of 100° (which does happen where I live), then:If ÄT = 100°, then (200 sqft / R 16.7) 1192 *100° = 1190 BTU/hrIf ÄT = 100°, then (200 sqft / R 20.9) 9.57 *100° = 957 BTU/hr<!----><!---->
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So, say that we average a ÄT of 50° for January and February – 60 days <!----><!---->
60 x 24 = 1440 hours <!----><!---->
1190 x 1440 = 1713600 versus 957 x 1440 = 1378080 <!----><!---->
1713600 – 1378080 = 335520 BTU difference<!----><!---->
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And, if the studs were 16" OC versus 24" as in this example and then to add 15% window space in the wall…<!----><!---->
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Edited 6/27/2008 7:53 am ET by Oberon
An option for you is 2x6 framing on 24 centers, and to insulate the wall cavities, a "veneer" coating of low-rise urethane foam is sprayed in, which when done right, gives a great seal against air infiltration.
Then the walls are meshed and filled with dens-pac cellulose.
The roof is designed so that you can get 16 inches of cellulose above the ceilings, and eaves with minimum 12-inch heel height to the trusses are sealed with sprayfoam.
Your biggest bang for the buck is to deal with air infiltration in a very anal way, using sealants, foam, backer rod, outlet and switchbox boxes, and more. Air infiltration is your biggest enemy, and minimizing it will do far more to raise your comfort level and lower your electric bills, than getting .02 lower on window U-value.
We are at elevation 2000 feet in the northern Adirondacks of upstate NY, with a winter heating design temp of -25F. The methods I have described here are being successfully used.
Another option for wallframes is to do the two-part "mooney wall" construction, well documented on this forum with some great photos in some total housebuilding from start to finish threads.
2x4 framing on 16 centers is done, then 2x2s are done horizontally on the inside, giving a total cavity depth of 5 inches. In the housebuilding threads shown here on Breaktime (Author: Mike Smith), the insulation was mesh and dens-pac cellulose. No sprayfoam.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Your winter design temp is only 25degF?? I'd be surprise that it is that high. Spokane, WA is -4 degF ... even down here near Death Valley it is under 10 degF, I think. Maybe you mean the average winter temp is 25? (Spokane is like 34)
Air leakage is a BIG factor to consider ... just do some calcs ... they are significant. I think the OP was specifically asking about doing good quality windows.
Remember, beyond simple heat loss ... windows improve comfort ... which can translate to additional reduction in calculated heat loss (i.e. a lower setpoint to achieve the same comfort). Heat Mirror is excellent in significantly reducing the 'cold wall affect' with large expanses of glass (e.g. floor to ceiling view type thing).
IMO - you only by windows once; size/place them right (which most do NOT do) and spend as much as you can possibly afford.
It's all good.
I didn't err in typing it. Look closer and you'll see the minus sign.
And remember that it is not how low your thermometer can sink on that winter night that sets the record. The definition of winter design temp has something to do with 99 percent.
I have seen it snap to almost 35 below zero here, but we still use a -25F for heat loss analysis and sizing systems.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Hey gene what is the lowest you have seen there?