Wow, only $4K difference in price! DH and I are building a 2800 sq. ft. home in Alabama, and spray foam insulatoin was over $25K more than blown cellulose.

You know of course that foam sheathing is far better and that you can not get r-20 with 2x4 construction without foam sheathing?

Thermal bridging is key and your total wall value will be better with sheathing.

That being said, the real issue is your fiberglass quote is way overpriced.

We have closed cell insulation and are very happy with it. Our house is tight, it adds structural rigidity, is not subject to absorbing moisture and has made the house extremely quiet. I don't know how our house would've performed with other insulation, but I can tell you that this has worked very well for us.

Hi Matt in Kansas. I am also building near your area and am anxious to know what you decide and watch your progress. Have you started building yet and if so, how far along are you? My crew started three weeks ago and they are doing great. good luck

the real issue is your fiberglass quote is way overpriced.

It does seem a small differential to the price for spf.

My preference is fg plus foam sheathing of, in your case, two inches. 2" XPS boards = R10 plus 3.2R per inch blown fiberglass (x3.5") = R21.2 (The XPS ages to R8 after 10 years.)

Switching to 2'x6' plus 1" XPS is another option.

For the fiberglass they call it white spider wall spray if that means anything. On the quote they claim they will get an r15 with that in the wall. Since the same company was quoting the two products maybe they're trying to make me "upgrade".

I've been asking folks about the huber r sheathing but it's not up here yet. I could see that working real easily.

I've been in homes with the closed cell and noticed how quiet it was and they did mention structural rigidity on the quote. It seems like a straightforward way to get a tight, relatively well insulated home. It sounds like I'd better get another quote on blown in fiberglass however.

Phoggie- I hope to start mid March, need to get our current house sold. I've noticed some of your posts and I'm a bit envious of the lot picture you posted. We'll be building on 11 acres between Lawrence and Olathe. Can't wait to let the little ones grow up out there!

We recently went through the same discussion. The link to my post is below. Our sprayed fiberglass and foam quotes are proportional to yours, so I am not sure that your fiberglass quote is high being that it is a sprayed application. In the end, that is what we decided to use. We just couldn't figure out how long the payoff for foam would be with $8000 difference. We have friends that have a 7000+ sqft house and they foamed... Power bills $170-220 monthly. Pretty amazing!

Here is a link that might be useful: Our insulation options

On the quote they claim they will get an r15

Indeed, that's the figure from Johns Manville for their low density spider spray. In that case, my preference would be the fg plus exterior XPS.

By contrast, if you use spf, every 16" you will have a strip of wall with R3.5 (the 2x4 stud), vs. R 8.5 with XPS. The framing factor--the portion of the wall, excluding windows, that is lumber--is 27%. So that's quite a difference.

You can make the wall even more energy efficient by using optimal value engineering (OVE) to reduce the section of the walls that are lumber. (See http://www.ornl.gov/sci/roofs+walls/NewRValue.pdf.) Very likely much too late in the design process to do that now.

JM Spider Low Density Nozzle sprayed fiberglass insulation designed for vertical installation

This post was edited by worthy on Sat, Dec 8, 12 at 2:10

The contractor is quoting blown fiberglass at an r-value of 4.3/inch and closed cell foam at 5.7/inch. The former seems unrealistically high and the latter seems unrealistically low. I would lower the effective R-value of 3 1/2" of blown fiberglass from 15 to 13 and raise the effective R-value of foam from 20 to 22 unless the contractor is using something I have not seen before.

I suspect the overall R-Value of the 2x4 stud and fiberglass wall might be 13 and the overall R-value of the 2x4 stud and foam wall might be 20 which is about what a 2x6 stud and fiberglass wall would be.

I find it odd that the 2x6 option and/or cellulose has not been considered. You should at least get a price for dense-pack cellulose in 2x6 studs.

The amount of additional heat saved is not directly proportional to an increase in R-value but because the cost of energy will continually rise now is the time to invest in the higher R-value and air sealing if you plan to live in the house for very long.

So it seems like if I do the fiberglass with 2" foam on the outside I will end up spending close to the same amount as the closed cell foam but get a higher r value and better performance if I do some sealing. After tinkering with the ornl whole wall calculator it seems like I might be able to get a whole wall value of 21 with fg and foam sheathing versus roughly 16 using just the closed cell foam.

Renovator- I'm curious to see how the cost of 5.5 " of cellulose compares to 3.5" of blown fiberglass. That plus foam could get me maybe r24 for the whole wall but then I've got an 8" thick wall plus stone veneer on my 8" basement walls. I'm assuming (just a dangerous amateur here) there are some additional costs here that could make this option significantly more. Of course I know you wouldn't have mentioned it if it wasn't a viable and economical option for many people so I probably need educated here.

Worthy- I found the table on pg 8 especially pertinent to this discussion. 6% savings on an average $250 electric bill amounts to about $15 a month.
It seems to me that the exterior sheathing is worth more than the close cell as long as I do a good job air sealing.

Thanks for giving we food for thought, this is great and I'd love to hear any additional thoughts or critiques on my thoughts above.

Edits: fixing iPad auto corrects :/

This post was edited by matt_in_ks on Sat, Dec 8, 12 at 11:46

I would lower the effective R-value of 3 1/2" of blown fiberglass from 15 to 13 and raise the effective R-value of foam from 20 to 22 unless the contractor is using something I have not seen before.

See the table below from Johns Manville for R Values. At 1.8 lbs/ft3 density, the spray-in R Value is 15 in a 2"x4" wall. The kicker, of course, is that unless you're micro-managing the install, the applicator may use the lower
density inadvertently or otherwise.

I find it odd that the 2x6 option and/or cellulose has not been considered.

There are so many permutations, you can't expect the builder to run more than a couple on any project.

It seems to me that the exterior sheathing is worth more than the close cell as long as I do a good job air sealing.

Especially when you factor in the relative costs. I still use ccspf at the rims on all floors.

Here is a link that might be useful: How the Same Wall Can Have Several Different R Values

"So it seems like if I do the fiberglass with 2" foam on the outside I will end up spending close to the same amount as the closed cell foam but get a higher r value and better performance if I do some sealing."

But with the sheathing on exterior you have same R-value
everywhere, unlike spray foam in walls. foam qoutes
'average' fill...meaning that if you average out the 1/4"
with the 3 1/2" you'll have an average 3" fill.
thats a deal breaker for me.
in addition, with foam sheathing, you have a thermal
break at studs & corners..add that up..its a lot of
insulation value over the 1 R-value per inch of wood.

insulate conventionally..then use air tight drywall approach. performs better than foam..I've done
the blower door testing long enough to know this for
a fact. and payback is shorter than foam spray for walls.

save foam $$ for attic & mastic seal of ducts.

instead of erv..what about whole house dehumidifier
that brings in fresh air. your location is not my area of expertiese...but go to hvac-talk.com you'd want to
talk to a guy who's screen name is teddy bear.

everyone wants to build a tight house. but unless
you test the house with a blower door..it is a wag
as to how tight house is.

Resnet energy raters & some bpi auditors
test both house & ducts for leakage.
as you explore your options..check into the
services offered by these org.

best of luck.
but

Started talking to my rough carpenters about the foam on exterior and got mixed reviews. The first (bid at $29,700) seemed to agree understand the benefit and said that it "wouldn't add much to the labor cost". No new numbers from him yet.

The second (bid at $21,700) said with the fiber cement siding (nichiha lap and shake) we will use you really need to do a rain screen and furring strips and that will really increase the cost. He sited the foam compressing and making siding look uneven and also the fact that the nails holding the siding are 2" away from anything solid and that he would rather do a 2x6 wall then use any foam. He's done it before but he charged some "green builder" a whole lot to do it. No new number on his framing cost yet.

Third framing bid hasn't got back to me yet but I'm a little surprised about the comments from the second contractor. He is definitely not lowest bidder type contractor, he mostly frames custom homes. Am I missing something here? I was thinking it wouldn't take long to put the foam and furring strips up.

Here's what the numbers are looking like to me:

Closed cell foam bid $10,000 (I'm budgeting this amount for insulation)

traditional insulation -$ 4,500
70 Sheets 2" xps -$ 2,000

Leaving $3,500 to pay for labor, and furring strips, and rain screen and if that covers it I can stay under my original insulation budget and get a better whole wall r-value.

Has anybody build with 2" foam on the exterior and if so what were your challenges, surprises, benefits, etc?

Thanks everyone!

we never see 2" down here in La. maybe a special order...
but the extruded polystyrene 1" @ R-7 plus R-15
conventional insulation in 2x4 wall R-22 suffices.
above code, and meets efficiency requirements.

in addition to the elimination of thermal bridging
that the foam sheathing brings to the structure.
air sealing is another side benefit. as long
as seams are taped and any holes sealed/repaired.
(and of course sole plate of walls is caulked
to slab or SillSeal is used)

we don't use closed cell in walls or rafters.
the only place we use it here is in floor
joists for homes on piers.

adding the furring strips will easily secure
the hardi siding. putting the furring strips
over the wall studs and using longer nails
to install siding..isn't a big deal. just like
decking the roof..someone needs to make sure
that the nails hit the studs and don't miss.
experienced carpenters & helpers can tell
by the sound if they hit or missed the stud.
and popping lines is always a good idea.

the only problem I have ever encountered with foam
sheathing is the door and window frames, once carpenters
are in line with what is going on. but if you get
a carpenter who don't want to do it..there will be
a lot of issues, simply because they don't want
to do anything different. just a fact of life.

avoid talk about 'green building' and price will
stay reasonable. lots of products for "green"
building entail a LOT of paperwork for the builder.
that is why they avoid it. and paperwork doesn't
make it green..smaller carbon footprint is green
enough. IMO

best of luck.

I talked to number 2 again and I think we're on the same page. He was referring to a leed home he'd done where they used 2 layers of tyvek mixed with huber zip and foam in some way that vented to the attic an it was a lot more work. Sounds like we'll just rip some plywood for the furring strips and use 2x6 around windows and doors. He said he'd get me a number this weekend so we'll see what that looks like.

Thanks for the words of wisdom from everyone, I feel pretty confident I'll be able to keep this below the cost of my spray foam.

If anyone else has thoughts or comments I'd love to hear.

SIPS are my go to above grade wall system. Here's why:
1.Airtight. One of the most consistent and easy to seal building envelope systems available.
2.Continuously Insulated. Thermal bridging is dramatically lower than most other options.
3.Strong. More capable of withstanding disasters than typical construction.
4.Pre-fab panelization. Using SIP panels offers many advantages of pre-fab in a more flexible and customizable system.
5.Most amount of R- value per inch. Keeping wall thickness smaller increases square footage which could also reduce cost per square foot and allow more light (and solar heating) in windows.
6.Less on-site waste and labor.

Of course they arent perfect for every situation but they are extremely competitive in my area. I find the sytrene product cost is simalar to conventional methods. The high performing polyurethane products are more pricey but come with some appealing upgrades like ZIP or LP exterior sheathing.

I did get a SIP bid but the cost was about the same as my lumber takeoff for the whole house and it didn't include any floors or interior walls. I'm sure I could have gotten more quotes but not many folks around here had worked with them and I didn't want to be a guinea pig. My neighbor did them himself but didn't get a tight house, he mentions that he can see daylight in places. I know that's not the norm with sips but the experienced contractors were too pricey for me.
The quote got me an r24 wall which I should be able to achieve if I use Polyisocyanurate sheathing which leads me to my next question:

The framer used 45psi foam when he has done this before and 25psi is what is commonly available around here. I will be using OSB sheathing on the walls so I'm not worried about structural rigidity but we don't want the nails to "suck into the foam" when we attach the siding causing it to look wavy. Is the 45psi what's commonly used or are most people happy with how the regular stuff looks when it's all said and done? I know people usually say XPS butis there a reason not to use Polyisocyanurate sheathing and get a little extra r value out of it?

Thanks!

This post was edited by matt_in_ks on Sat, Dec 29, 12 at 16:20

Polyisocyanurate is what I perfer. worth the extra
cost (same labor to install) for added R-value.
I find it very easy to work with, and the air gap
behind brick or siding on strip allows the foil
to work as radiant barrier.
the dow & corning products have T&G on the sides..
which is nice,but not top and bottom. my issue
with these products..and it is a personal worked with
it didn't like it issue..is that the plastic coating
can be a pita to cut. once razor knife gets the slightest
bit dull..the plastic film tears & messes up the cuts.
and, even with T&G..I tape all seams. just
me. I figure at this time..it is easy to take an
extra step to do this.

over the summer I replaced a roof on the addition of
my house. put 1" Polyisocyanurate on top of rafters
then furring strips & reflective metal.
this previously hot area is now easy to cool in
the summer & heat in the winter. before this it was
always uncomfortable in this area.

Please read link below that explains the following
excerpt.
There are three main types of insulating sheathing currently being used in the industry: Expanded
Polystyrene (EPS), Extruded Polystyrene (XPS), and Polyisocyanurate (Polyiso). Each of these products
all has a different set of physical properties that will affect the dynamic of the wall assemblies in regards
to the transmission and management of heat and moisture.
http://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing

this would be a good pdf for you to download & read
as you are chosing your materials.
buildingscience.com has a great site..specific
information for specific climates. even with
climate specific publications..foam sheathing
to exterior of walls is recommended for ALL
climates. backed up by building science studies.
just do a site search for building a perfect wall
on their site.

this link is about installing foam insulation.
while I don't agree with all of it..LOL! it
is pretty comprehensive. another must read
for you..
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing

your weekend homework!
best of luck.

Thanks for the homework, I actually got through about 20 pages of the building science doc before falling asleep last night.

Matt,
There have been some great posts here about insulation from several folks.
Glad you were lead to the BCS, and GBA site - great, great info and resources there.
I would also add that you should look at CCHRC.org (Cold Climate Housing Research Corporation) on the web - they have a whole builder's resource guide that outlines how to build with exterior sheathing (Using a technique known as REMOTE, based on the PERSIST technique). Dew Point calculators, and other building resources are vast at the CCHRC site.

You can insulate only on the outside (this is the most durable wall construction, healthy (as long as you manage interior RH) and energy efficient too). See the PERSIST and REMOTE walls for further info. For a builder of any value these are not hard to do - just different than throwing up conventional homes. Insulating on the exterior gives your
wall a solid layer of insulation (say 4" of Poly Iso) and a True high "R" value.

Let me add a few more thoughts:
Current RBC/IBC states you should have minimum R-5 on the exterior. As mentioned in several posts previously - this will reduce conductive heat losses through studs.

You CAN install Fiber cement over exterior foam with rainscreen, and it won't deflect - (BSC) did a study on this. Hardie Plank has construction details for this.

You can get XPS, EPS, and poly-iso rigid foam insulation that is aged (reclaimed), and far cheaper than retail - by sourcing it from a reclaimed insulation dealer - they are all over the US. Key is to find a dealer near you to reduce shipping costs - I am buying 14000 sq ft of insulation through this same market for my house renovation here in NH - Yes I did say 14,000 sq ft (yes three 000's) I will have 6" on my exterior walls, and 9" on my roof. Insulation Depot.com is one vendor I know of that sources insulation all over the US.

Search on craigslist, or google.......I am getting mine ISO for $.24/board ft and XPS for $.30/board ft so you can save a ton going reclaimed, and feel good about it also :).

It is true that Poly-Iso can have a reflective aluminized layer on it, and if placed against an airspace will increase the "R" value. (This foil was actually placed on Poly-Iso originally to reduce it's aged "R" value loss.

There is also a insulative board made by Roxul. It is a fire retardant rock-wool board (ComfortBoard IS). It allows walls to breath much more than XPS, EPS or Poly-Iso. This can be a benefit (depending on design). It is bug and pest resistant, and maintains it R value over time. It's has a lower "R" value than poly-iso, but doesn't "age". It also can't be sourced from reclaimed dealers -so you have to pay retail :(.

Know that you can actually do more harm though (to the durability of your walls, and you health), if you use too little foam on the exterior, while still insulating within the stud cavity - Check out the CCHRC.org decade long study on wall cavities and exterior sheathing. It is amazing how much mold grows in typical construction on the inside of exterior sheathing...... :(.

Good Luck and Happy New Year

Happy New Year

This post was edited by allhandsworking on Sun, Dec 30, 12 at 0:16

Matt,
I wanted to add that SIPS may be great but they do shrink (almost all petroleum based foam insulation shrinks).

if you do two layers of poly-iso on the exterior, overlaying, offsetting and taping seams - you get the best non structural air seal.

If you vapor/air seal your house from below the sillplate at the foundation all the way to your ridge you will have an airtight building (do this against your exterior sheathing). (See the PERSIST or REMOTE type wall system I spoke of previously). You can do this with Owens Corning Ice and water, IKO Ice and Water, or Grace (Ice and Water Shield). Grace is 2-3x times more expensive, but definitely the premium performer. You will also prevent any need to have an interior (6 mil poly) barrier (which seems to always get torn by ceiling strapping, or by sub contractors).

Good Luck

This post was edited by allhandsworking on Sun, Dec 30, 12 at 0:17

Matt,

It is my understanding that Poly-Iso is not graded on psi. The xps you would need would only need to be the 25 psi type (not the 45 psi).

If you check out the Hardie Plank pdf on fiber cement siding installation over continuous rigid insulation you will see how they recommend installation. See the link below....
Also as mentioned BSC has great articles on this also.

Here is a link that might be useful: Fiber Siding over Advanced Framing or Continuous Insulation

This post was edited by allhandsworking on Sun, Dec 30, 12 at 0:24

For the siding we are actually using nichiha fiber cement lap, and their "Sierra premium shake". Their installation manual states:

"When installing NichiBoard, it is recommended that an APA rated minimum 7/16" OSB or plywood sheathing be used. NichiBoard may be installed over non-structural sheathing such as foam, fiber builder board, and gypsum type panels. Non-structural sheathing thickness shall not exceed 1". Due to the compressive nature of some non-structural sheathings, care must be taken not to overdrive the fastener and compress the sheathing. The fastener length must be increased by the thickness of the non-structural sheathing"

On Home Depot's website they say neither the xps or poly-iso is structural but the hardie guide specifically states xps and poly-iso is acceptable. They mention to take great care to make sure everything is flat before attaching siding. The nichiha is thicker than hardie so I think that will help me. And my framers will just have to be careful...

I think I might double check with Nichiha before everything is up :)