Insulation information overload!

[Alan Gage]

So I'm in the process of planning my new house to be built this spring/summer and started doing a little research on what I thought was going to be one of the easiest decisions-insulation. A little research soon turned into a lot of research which branched off into vapor barriers among other things. I was hoping to get some opinions from some people that do this all the time to hopefully put me back on track. Right now my head is swimming with so many different ideas I'm lost.

I'm in climate zone 6 (Northern Iowa). The house will be a single story, open floor plan, no AC, wood heat (electric backup), and around 900 sq. ft.

The original plan was to just fill the 2x6 wall cavities with wet blown cellulose and be done with it. Cheap and easy.

The guy also gave me an estimate for 1" of dense spray foam in the wall cavity with with wet blown cellulose over that filling the rest of the cavity. A little more expensive but still pretty reasonable, more R value, and better air barrier. But the more I read on that technique the more it sounds like it can be problematic in cold climates if not enough foam is used. Too little foam and the inside surface of the foam gets too cold so condensation can occur. Sounds like I'd need at least 1 1/2" of foam for my climate.

Neither of the 1st two options however deal at all with thermal bridging through the studs. So I start thinking maybe I should add a little rigid foam on the exterior to help with that. But surprise, surprise, it's not that simple. You need the correct ratio of external (rigid foam) and internal (cavity) insulation. Too much cavity and too little external insulation makes the sheathing too cold and causes water to condense on it. So if I fill my 2x6 cavities with insulation I'd need something like R-11 to R-12 of exterior rigid foam (about 2.5 inches of XPS). Now we're talking some real money (and considerably more work) but it would give me R-30+ walls.

Another option along the same line would be to use 2x4 walls. Then I'd only need R-7.5 (1.5 inches) of rigid foam+wall cavity insulation. That would give me just over R-20 total. Pretty much what I'd get with my original plan of wet blown cellulose but no thermal bridging of studs.

The arguments for lots of external rigid foam are convincing but having no real world experience I don't know how much of a difference it would really make. Is it really going to be worth it for me to go to the extra work and expense? (I know no one can directly answer that for me) Is it going to be that much warmer? Is it going to keep everything drier and make it last that much longer? What's the real world difference between well sealed R-20 and R-30 walls? Would it really be that bad to just fill the cavities and use no exterior insulation?

Budget is definitely a concern for this house but I also don't want to start cutting corners. There's a good chance I won't stay at this location forever (early 30's now) but I might be here a good long time and I'd like the house to serve its future owners well. I'm not looking to build something that will still be standing in 200 years though. Energy conservation is important to me but I'm not obsessed with it. There's got to be a point of diminishing returns somewhere, that's about where I'm aiming.

Sorry for the ramble. Hope it made sense. Any input appreciated.

Alan

[glenn kangiser]

John knows a lot about insulation and wrote a book on superinsulation as I recall.

http://www.amazon.com/Superinsulated-Design-Construction-Building-Energy-Efficient/dp/0442260512/ref=sr_1_1?ie=UTF8&s=books&qid=1297926211&sr=8-1

Hopefully he will drop by this thread.  I'll message him.

[John Raabe]

With so many material options and potential issues, it can get confusing. What you want to avoid is condensation happening at the wrong place.  IE: moisture laden air being cooled enough to condense out water inside of materials that can't dry out.

In this example wall system - which I think is about as close as we will get to a relatively low-cost high-insulation universal wall - note where the air barrier/moisture barrier is. It is at the exterior sheathing and the foam board insulation. This is where moisture will stop and potentially condense - but wait, both sides of that barrier are kept warm and snug by insulation. Even with strong vapor pressure it would take some antarctic temperatures to ever cool these surfaces to the dew point. And even if it could happen this wall could dry out. On the inside you would refrain from adding a poly vapor barrier thus allowing drying to the interior. On the outside the siding will get wet and when the sun comes out the warmth will drive moisture out the backside that could potentially be a problem. But we can vent this moisture by using 1/4" to 3/4" vent strips that hold the back of the siding off the foam.

Exactly what levels of foam to use and what to put in the cavity can be another thesis problem but that one boils down to climate, fuel costs and economics.

[Squirl]

This seems to be a popular topic today.  I made a similar post in another thread.  I recommend an article named "heading for zero" in this month's Home Power Magazine.  The article was about a person building a net zero energy house.  It gives a detailed analysis on different insulation options, and value returned for each.  They had nice charts for you to compare return per option.  One of the key points they gave in the article was that air sealing is as important as insulation amounts themselves.  I didn't see anything mentioned of condensation.  This is the first I have heard of it.

It appears that you can read the article online.  I will try and post a link.
http://homepower.com/view/?file=HP141_pg88_Riggins

[Squirl]

I re-read your post, and I had a few more thoughts.  This topic is very fascinating to me.

Just to let you know, I am building in upstate NY.  Standard 2x4 or even 2x6 construction with cellulose alone will not meet our current energy code requirements for electric heat. (R26 for exterior walls)  IIRC this will be your full time residence, so comfort and cost over a 5-10 year period will be a factor.  Iowa is also an almost identical climate too the one I am building in.  Extra insulation is the cheapest and easiest addition when building from scratch with the greatest dollar value return. 

Personally I haven't even considered a 2x4 construction method.  Almost 60% more room for cheaper insulation for a 2x6 with almost half the studs, and a more rigid wall left 2x4's out of the equation.  The marginal cost to benefit was worth it.  Even with exterior foam, I would still go with a 2x6 stud.  Around me a 2x4 stud is $2 while a 2x6 stud is $3.  It also gives more room for insulation in headers. My thought on studs was that pine has an R value of around 1.25-1.5.  So in a 2x4 construction you would have a much larger area at R.4.2 with an exterior foam of R7.5 while with the original 2x6 method you would have much less of an area of R-7 studs for a significantly less cost.  Or if you went with 2x8 construction the studs would have an R value of R.9.1 getting close to what you would have for a 2x4 wall with foam and cost less.

All of this is with the idea that with proper venting condensation issues can be avoided from John's previous post.  If I have time today I wll post a chart based on local lumber prices.

[Windpower]

We hope to start construction on the cottage in WI this spring

this is a very timely topic as we will be forced to make decisions like this soon

thanks for all the good info

[Squirl]

I did this by an 8x8  (64 sq. ft.) wall for theoretical purposes.  I used the local Lowes as a price reference guide.

2x4 R-21 wall R-12 at studs. = $89.42
9 Studs @ $2.30 a stud = $20.70
2 sheets R-8 2" sheathing @ $24.66 = $49.32
2 rolls fiberglass insulation R-13 @ $9.70 = $19.40

2x6 R-19 wall R-7 at studs. =  $51.09
7 Studs @ $4.09 a stud = $28.63
2 bags cellulose @ $11.23 a bag = $22.46
  You could even add 2 sheets of 1" R-4 sheathing @ $10.50 for a greater R value and performance than the 2x4 wall for a total of $72.09.  This is still less than the cost of a 2x4 wall. I would stick with the 2x6.

For information purposes.

2x8 R-24 wall R-9 at studs = $66.70
7 Studs @ $6.32 a stud = $44.24
2 bags cellulose @ $11.23 a bag = $22.46

2x10 R30 wall R-12 at studs = $87.87
7 Studs @ $7.74 a stud = $54.18
3 bags cellulose @ $11.23 a bag = $33.69

What I find interesting about this option is that it would give you 50% more R value at the wall area than a 2x4 wall. It would have the same R value at the studs as the 2x4 method.  It would give you a much stronger house frame.  You wouldn't have to deal with the condensation issues you described and it would still cost you less.
Edit: Numbers revised for top and bottom plate.  Same conclusions.

[John Raabe]

Condensation is the ugly stepchild of air movement and air leakage. A perfect air barrier (very hard to do) will not allow condensation to happen if it's above the dew point temperature.

Theoretically, you could have an uninsulated house with a perfect poly air barrier on the inside and it would not get the framing wet, however it would soak the drywall and interior wall finishes. And any imperfections will carry moist air into the framing to condense on a cold surface, perhaps the inside of the wall sheathing.

If you keep all potential condensation surfaces warm and above the dew point you don't have to be perfect about airsealing.

Also, air leakage is not the only way to get the framing wet. It can come from the outside as well as I mentioned above.

[MountainDon]

Speaking of the dew point....   Might be interesting / helpful in understanding the issues at hand.

[Alan Gage]

It's good to know I'm not the only one going through this right now.

Still up in the air on just how much exterior foam I should go with. Some places say 50/50 and others 70/30 (percentage of in cavity to exterior R value). This article would seem to indicate I'd need more than 2" but I suppose the world wouldn't end if I shaved off a 1/2".

http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing

Any time I mention my quandary to someone they look at me like I'm an idiot for not just filling the 2x6 cavity with fiberglass and getting on with it. After all, look at all the old homes around. They have less than that with no rot problems. It's a tough argument to ignore. I assume the main reason for that is because there's not much to stop air from flowing through the wall to dry things out when they get wet?

Sounds like I should probably go with 2x6 walls filled with cellulose, house wrap of some variety over the sheathing, 2" of rigid foam, and furring strips to create a gap and give me something to attach the fiber cement siding too.

Or:  If the outside layers act as a good air barrier would I be better off going with fiberglass in the wall cavities? Seeing as how it's a bit more permeable than cellulose would it allow better drying to the inside?

For anyone interested here's a bunch of links I've been reading on the subject the past few days:

http://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall/

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-risky-cold-osb-wall-sheathing

http://www.buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh

http://www.greenbuildingadvisor.com/blogs/dept/musings/superinsulated-house-specs

http://www.jlconline.com/cgi-bin/jlconline.storefront/4d5dd72c04e454da27170a32100a0610/UserTemplate/69?s=4d5ae0cf0aae86e927170a32100a0694&c=82817a7d2e037bbf8d40db3b559caf21&p=1

http://www.jlconline.com/cgi-bin/jlconline.storefront/4d5dd7300ccdad8d27180a32100a0669/UserTemplate/69?s=4d57f7631175119c27180a32100a0651&c=cf6e9330206406dda640922be6253f18&p=1

Thanks for the great replies. Lots to think about.

Alan

[Alan Gage]

It appears that you can read the article online.  I will try and post a link.
http://homepower.com/view/?file=HP141_pg88_Riggins

Very interesting read, thanks for the link. Looks like they got a couple graphs backwards for the windows unless I'm reading something wrong. They show double pane clear glass outperforming double pane Low E.

Alan

[Alan Gage]

One more link:

http://www.buildingscience.com/documents/reports/rr-0903-building-america-special-research-project-high-r-walls

Haven't read that one yet. Just found it and my brain can only absorb so much in one evening.

Alan

[Squirl]

There is a second number with the windows. SHGC.  I believe this stands for solar heat gain coefficient.  I have seen conflicting reports, but the more trusted one that I had read (the solar home IIRC) said that Low E coatings reduce heat loss, but in a passive solar home for south facing glass, they also reduce solar heat gain.  I hear the opposite from retailers that want to sell me Low E coatings, but I don't trust the source.  The numbers in the chart seem closer to what I have seen from professionals in the passive solar market.

[MountainDon]

I think it is difficult to have the best of the all worlds, wanting to keep heat within the building in winter, keep the summer sun from heating the interior and yet permit the winter sun to provide solar gain. Planning the eve overhang correctly can help most with summer and winter desires.

Window label:



Interpretation:

If the values come from a member of the National Fenestration Rating Council then the entire window, frame and all, is taken into consideration for the U-factor and SHGC. If not from the National Fenestration Rating Council  then the numbers may only be the glass.

U-Factor:  Measures how well a window, door, or skylight prevents heat from escaping.  Ratings usually range from 0.20 to 1.20.  The lower the number, the more efficient your fenestration product.  U-Factor will change as window sizes change.

Solar Heat Gain (SHGC): Measures how well your new window blocks heat from sunlight – keeping your home cooler.  The lower the SHGC, the lower the heat gain through a window.  SHGC ranges from 0 to 1.  SHGC will change as window sizes change.

Visible Transmittance (VT):  Measures the amount of visible light transmitted through your new remodel window.  This will determine the amount of daylighting you will receive, ultimately reducing your need for lights.  VT is measured between 0 and 1.  The higher the value the more light.

Air Leakage:  Measures the amount of air that could pass through your window (yes, even when it's closed).  The lower the AL, the less air will pass through cracks in the window assembly.

Seems to me that for the best of everything a separate solar air collector system would be preferable.

Links:
http://www.nfrc.org/documents/SolarHeatGain.pdf
http://www.energysavers.gov/your_home/windows_doors_skylights/index.cfm/mytopic=13320
http://www.energysavers.gov/your_home/windows_doors_skylights/index.cfm/mytopic=13360
http://www.wascowindows.com/Documents/U-factor.pdf



Condensation Resistance:  Measure the products ability to resist moisture on the interior surface of the window.  The higher the rating number, the more resistant your new window will be to condensation forming.  CR is expressed as a number between 0 and 100.

[John Raabe]

U-value is a heat loss rating and is important in all climates, but especially in heating dominated areas.

U-value and R-value (resistance) have a reciprocal relationship, so the sample window with a U-value of 0.34 has an R-value of 1/0.34 or about an R-3. This makes it easier to compare to the insulation you are putting in other places.

Yes, in a house where you are wanting to store solar heat you do not want a low SHGC on the south windows. Most all climates would like better sun control (a lower SHGC) on the west facing windows

[MountainDon]

The ratings on windows available in different areas of the country will vary too.

http://www.energystar.gov/ia/partners/prod_development/archives/downloads/windows_doors/WindowsDoorsSkylightsProgRequirements7Apr09.pdf

scroll down for a climate map showing what has been calculated as best for different zones.


There is a window and door manufacturer performance database at
http://search.nfrc.org/search/SearchOption.aspx?type=W

[chancecarroll]

Thanks for all the links guys!
I'm also trying to fit my head around what insulation I'll need when we finally decide to build. I'm near wilmington NC so I'm in a 7-8 climate zone, however we want to make our house as energy efficient as we can afford. I don't usually see foam board on construction near here but I'm interested in learning more before I rule it out.

Thanks again!
Chance

[Squirl]

Sorry to revive this old post, but I have been researching this answer for a while and recently came to the information I was looking for with this.  Thank you for pointing me in the right direction.  I just thought I would apply it directly to Alan's question about the chart in the article.

First I found the difference of Low-E coatings that most sales associates don't know or won't tell you.  Low-E is a mild tinting that reflects heat waves.  The problem is that most coatings reflect heat waves coming from the inside and from the outside.  So a house designed for passive solar design would be hurt in performance if it has most types of Low E glass on the south facing windows.  One exception is a special type of high solar heat gain type of Low E coating.  The way this works is by allowing the wave lengths of heat from the sun, yet reflecting the radiant wave lengths of heat from heated objects and heaters.  This is exceptionally rare and has been very difficult for me to find.  None of the major manufactures make it standard if you look all their windows have correlation between a Low U value and a low solar heat gain coefficient.

If you notice the first column of the chart that you referred to about windows, it has Low E with a U value of .3 and a SHGC value of .57.  This means that it has an R-value of 3.3 and lets in 57% of the sun light heat that hits it.  If you compare this to the column next to it (no low E) has a U. value of .47 and a SHGC value of .67.  This means that the windows have an R-value of 2.12 and allow 67% of the sun light heat that hits it.  This means that the software he used with the variables of his location and his passive solar design the gain in heat from the sun outweighed the loss in heat from the lower insulation value.  But if you look at the next column (double pane) with an U value of .22 (R 4.5 ) and a SHGC of .39 the insulative value of the windows outweighs the heat gained from the higher amount in clear pane windows.  This balance seams to go back and forth between heat gained vs. heat lost.

I found this chart useful because I was able to find a glass with a SHGC with .69 which is higher than anything on this chart, and a U value of .26 which is .01 off the best performer on this chart.  This should mean that in a passive solar south facing design it is likely to perform better than all other options, if my climate performs similar (Colorado vs. New York)

[Alan Gage]

I found this chart useful because I was able to find a glass with a SHGC with .69 which is higher than anything on this chart, and a U value of .26 which is .01 off the best performer on this chart.

That's great. Who makes it? Double or Triple pane?

I was able to find some Marvin windows with Cardinal 179 coating in a triple pane but for me they were prohibitively expensive. (around $40/square foot). Most of the expense seemed to be upgrading to the high end wood windows it's offered on as opposed to the double pane vinyls I'll be getting (which are better than most vinyl). I think the 179 coating option added between 150-200 for a large picture window.

Today I called Gerkin, who will be supplying my windows, (midwest company) to ask about coatings. They said they get their coatings from Cardinal (good to hear) and that 366 is their standard. They can special order others but he was unsure about which ones. I asked about 179 and he said he doesn't think they can get it anymore. Basically it was either 366 or 272.

I see after doing some more research tonight that the 179 coating isn't listed on the Cardinal website but looks to be replaced with 180. Maybe that's why he said they couldn't get it anymore. I'll give them one more call before ordering to see if I can get it.

It's frustrating that windows with low U-factor and high SHGC are so hard to find in the states. The guy I talked to was nice and helpful but I believe he thought I was a bit daft.

Glad you found something that will work out.

Alan

[Alan Gage]

Just to note:

When looking around I did find a company in Wisconsin - Wasco Windows - that offers all the different cardinal coatings in a vinyl window. They look promising but they only sell through their personal dealers in Wisconsin and don't ship. Too far of a drive for me to go pick up windows, especially considering how big of a rig I'd need to haul them back.

Alan

[Squirl]

It was the Cardinal 180 that I had found.  Surfing all the passive solar websites I could find, they were the only one I found.  They are extensively used in Canada and there is a local marvin window dealer here. If not, I would try and go over the border to Canada.  They have a different energy rating system that takes into account SHGC. Thank you for the pricing info.  I was about to start calling around for that.  It saves me a lot of trouble for my estimates.  Anderson got back to me with a two line email, that they don't make any products for passive solar design at this time.  At least they were direct, honest, and responsive.  Let me know about the 180.  That is good news too.  I have seen a few advertisements for window manufactures to get other cardinal coatings.  It would be nice to know if some can order 180.

Hopefully you can still find the chart useful.  For your south facing glass, at least you know that clear glass is usually more energy efficient than a simple low E coating if you are going for passive solar.  The only time this is outweighed is if you are going for very low U value windows.

For my design I was shooting for 15% glazing to square foot ratio for 600 sq. ft.  If it was only an extra $200 for the type of glass in a large picture window (I plan on two) wouldn't be so bad.  For the rest of the windows I would be going for low U and not caring about SHGC because they will not be on the south wall and will be very few.  It might be the most cost effective to go with two large picture windows and a larger active solar system.  I was planning on an active solar component anyway.

[Alan Gage]

That certainly is something to think about, that sacrificing U value by going with clear glass might be offset by the higher SHGC. I'd never even considered that option, just assumed that once the sun went down I'd lose more heat than I'd gained. I'll have to look into it some more.

I am a little nervous since I'll have quite a few windows in my living room, which faces the south, so I'd like it to stay warm. The woodstove (main heat source) will be in the living room as well and I worry about all that radiant heat radiating right out through the clear windows. 

Since you're considering Marvin I dug up the quote I got a couple weeks ago.

32x40 casement:

LowE II (standard coating) - $414 ($562 list)
LowE 366 - $425
LowE 179 (triple pane) - $570
LowE 272 (triple pane) - $570

26x56 casement (same coatings as above):

$480 ($647 list)
$493
$655
$655

60x56 picture:

LowE 179 (triple pane) - $1020 ($1373 list)

In comparison the vinyl Gerkin double pane windows with the 366 coating that I'll likely be getting were:

26x56 single hung - $190
36x42 single hung - $196
36x42 casement - $140(!) The salesmen confirmed this wasn't priced wrong.
60x56 picture window - $278

The Gerkins have a U-factor of .29 and I just can't justify spending 3 times the money to get a .2 U-factor. It helps that I don't mind the way vinyl windows look. It was nice to talk to Gerkin the other day and find out that other coatings are an option, though maybe limited, even though there's no mention in the literature or online.

Since my heat is essentially free (other than labor involved with processing wood) it makes it even harder to justify spending a lot of money for a relatively little increase in energy efficiency.

Good luck with yours!

Alan

[Squirl]

Wow, that is a great breakdown.  I would probably go with double pane over triple pane for the 180 windows.  I read that adding an extra pane reduces SHGC.  So if the loe 180 window blocks 80% of the solar energy in the first layer, that 80% will be blocked by another 80% in the second layer letting around 64% of the solar energy through.  The $1600 price difference on two picture windows would be an interesting consideration.  I would have to go back and calculate the value.  I was most shocked  by the Mbtu differences over the .30 double pane low E and the .25 triple pane argon.  The 71 Mbtu to 55 Mbtu (30%) was the most dramatic difference in all options presented in the article.  I had never put that much emphasis on windows.  If I am willing to spend $1600 extra for wall insulation and air sealing, maybe I should consider it for windows too.  I am not one to put much emphasis on aesthetics in the vinyl vs. wood debate.  I like to worry most about performance and value.  Thanks for the help. I would never have spent that much time focused on that section without the discussion.  I have a lot to consider now.