Hello I have found this forum incredibly useful! Thank you to all who contribute! I have a 100-year-old Bungalow here in wonderful Minneapolis. Due to many issues, structural, livability and performance issues, I have decided after consulting with a few local builders and engineer to cut the top off of my house and add a new livable second story. Because I don't have the funds to move out and would like the first floor and basement to remain as undisturbed as possible I have settled on using sips for the new 2nd story walls and roof. They are familiar to local contractors and are very fast to put up -- But! an R60 roof and R40 walls seems minimum for an energy efficient house in this climate (I am going with Thermotech's triple pane fiberglass windows which I got a really good price on) but local SIPs max out at R48 for 12" and R24 for 6" wall. I am all for adding a 1.5-3" layer of polyisocyanurate to get to the recommended R40/60, but is it better to add this to the inside or outside of the sips? The inside (sandwiched between SIP OSB and 1/2" drywall) has lots of appeal because it would be easy to do myself, (potential to staple electrical to SIP face?), and then the exterior wall would stay in the same plane with the existing first story stucco. It also seams like this is where the vapor control should be. (The first floor walls are nominal 2x4s filled with 4" injected slow rise foam giving r-value of around 20). However, would be better to have the foam sheathing on the exterior of the sips, sticking out 2" over the 1st story stucco? This would motivate me to add 2" foam to the first floor exterior and redo the stucco, sooner…unfortunately I won’t have the funds/time to redo the first story stucco for 3-5 years. What would everyone’s advice be? (Builders & local SIP manufacturers have said it’s unnecessary for more then R24/R48 but don’t think it would be a problem to add 1-3” foam on either inside or outside)? I hope to add write-ups, pictures and videos to a website so I can contribute back and share this project with you all this summer. Thank you for your advice, -Jason

jasonrlord,

Find a SIP with a PIR/PU foam core they have an r value of about 7.5 per inch

http://www.eco-panels.com/

http://gefcollc.com/

Thanks for the reply Jeff,

Unfortunately, I have not been able to find anyone that makes PUT/PU core SIPS in the upper midwest, or any builders that have familiarity with them.
Do you happen to know of any resources up here in cold MN?

It does look like your Eco-panels are a good product, any idea how much shipping to MN would run?

-Jason

This is a good question even if it ultimately turns out that SIPS with higher r values are available for the OP.

What are the risks of adding additional rigid foam insulation to existing SIP walls? Is there a realistic chance of moisture somehow finding its way between the panel skin and the rigid insulation and degrading the skin?

I assume this would be a concern for either OSB or metal skins--the OSB could disintegrate, and the metal could rust, correct?

Jason,

I do not sell these SIPs but I think highly of them. You would have to contact these suppliers for shipping costs.

cj,

Metal skin SIPs do not rust except under very unusual circumstances. As to adding foam to a wood panel, it could very well trap moisture and cause the SIP skin to deteriorate.

Jason,
Wausau Supply Company is a distributor of Emercor panels, that a decently short jaunt to MN. R44 6- 1/2" panel.

Def more than R24 for walls!  Geesh you're in Minneapolis!  I'm using Eco-Panels, 50 mins west of Asheville, NC.  Whole house, 6.5" R-40.  Definitely recommend Eco-Panels!

Posted By jasonrlord on 27 Feb 2010 03:18 PM
Hello I have found this forum incredibly useful! Thank you to all who contribute! I have a 100-year-old Bungalow here in wonderful Minneapolis. Due to many issues, structural, livability and performance issues, I have decided after consulting with a few local builders and engineer to cut the top off of my house and add a new livable second story. Because I don't have the funds to move out and would like the first floor and basement to remain as undisturbed as possible I have settled on using sips for the new 2nd story walls and roof. They are familiar to local contractors and are very fast to put up -- But! an R60 roof and R40 walls seems minimum for an energy efficient house in this climate (I am going with Thermotech's triple pane fiberglass windows which I got a really good price on) but local SIPs max out at R48 for 12" and R24 for 6" wall. I am all for adding a 1.5-3" layer of polyisocyanurate to get to the recommended R40/60, but is it better to add this to the inside or outside of the sips? The inside (sandwiched between SIP OSB and 1/2" drywall) has lots of appeal because it would be easy to do myself, (potential to staple electrical to SIP face?), and then the exterior wall would stay in the same plane with the existing first story stucco. It also seams like this is where the vapor control should be. (The first floor walls are nominal 2x4s filled with 4" injected slow rise foam giving r-value of around 20). However, would be better to have the foam sheathing on the exterior of the sips, sticking out 2" over the 1st story stucco? This would motivate me to add 2" foam to the first floor exterior and redo the stucco, sooner…unfortunately I won’t have the funds/time to redo the first story stucco for 3-5 years. What would everyone’s advice be? (Builders & local SIP manufacturers have said it’s unnecessary for more then R24/R48 but don’t think it would be a problem to add 1-3” foam on either inside or outside)? I hope to add write-ups, pictures and videos to a website so I can contribute back and share this project with you all this summer. Thank you for your advice, -Jason

With all due respect, an R40 sip wall seems like a bit of overkill.  You mentioned "recommended" R40/R60.  Who recommended those values?  There are a couple reasons I'm saying that.  First, there is a point of diminishing returns.  When looking at payback times, you're going to reach a point where the savings are no longer in step with the extra costs.  That said, if you really want to get to R40. you may want to look at other options instead of SIPs.  Double-stud walls or truss walls may give you a better bang for you buck.  It's worth looking into, at least.

The other issue that I see with your plan is that you're adding on to the existing 100 year old house.  No matter how well insulated the 2nd story is, you're still going to plenty of heat loss from the existing construction.  I know you said that you don't want to disturb walls on the first floor, but I'm afraid you aren't going to see the result you're expecting.

Since the existing house is not being altered, it would seem that all the heat loss will be through the lower level. Use 24/48 and the saved money to add that 2" of styro to the first floor exterior. Then you get a place that looks new all over. With the studs in the way and the likely leaky airgaps in the first floor, that's where you want to spend - spend where the problem is worst. The cost difference on 40 in the walls vs 24 in the walls is not as high as the numbers suggest, as windows/vents/small problems will dominate heat loss.

jasonlord. first of all, kudos for your efforts to save a major portion of that 100 year old building. You mentioned that you're talking to a local engineer as well as contractors who are experienced with SIPs. Frankly, I wouldn't even attempt to override the advice of those people, who you will eventually depend upon to do this thing right. I guess that I'm not telling you anything new but you're talking about a major undertaking that requires a great deal of skill, and knowledge on the part of each member of your "team" . In regard to R-values, I've been involved with numerous projects in the Truckee, Ca./ Lake Tahoe area over the years. This area experiences some of the most severe winter weather in the U.S. and we usually use a 6 1/2" panel for walls, (R-22 to R-24) and and a 12 1/2" panel for roofs (R-44 to R-48) these figures are from the R-Control website and are shown for 75 df and 40 df. We have used 8 1/2" panels there on occasion for walls (R-29 to R-31). It seems that the addition of insulation on the SIP walls would not be necessary given the tight building envelope, which includes your very energy efficient windows. Of course, your plan to eventually do something to the lower level walls has to be a consideration here. It would seem that having to schedule this as a two phase project may complicate things a bit.

I am yet to see any credible evidence that you can achieve these types of R-values, and overall energy efficiency, at a comparable cost, with the double stud wall approach, or other methods that have been labeled "Alternatives to SIPs", in a previous thread on this forum not to mention the "green" issues of using twice as much dimensional lumber as with SIPs. The caveat here is whether or not you have a contractor aboard who is experienced with SIPs and understands the efficiencies of the system in regard to labor savings, less waste to deal with, faster close in time, etc. (Hopefully, my comments won't revive that somewhat "spirited discussion", if anyone is really interested it is easy enough to go back to that thread and see what that's all about

Of course, you're also getting recommendations for Foam and "Skin" options other than the more widely available OSB/EPS SIP. There are many factors that come into play here, and the pros and cons of the various configurations that are available have also been "discussed" to great length on several of the GBT forums.

In any event, it'll be interesting to follow the progress of your project. Good luck!

Thanks for the feedback,

To clarify a bit, the 1st story walls have had polyurethane Slow Rise foam injected into them so because they are a nominal 4" the R-value is around 24 but with thermal bridging at the studs. I am also installing double pane argon filled storm windows on the first story windows, which I wish to keep for historic reasons. The 2" of foam would be in addition to this existing R24. One main reason for the increase in r-value is that I would like to spend on the envelope in order to save by getting rid of the gas furnace (the house has a HRV) and using very little electric resistance heat through inline eliminates in the ventilation ductwork (I could easily program each room this way to, which is very handy when you have a SO who likes it 10degrees warmer . I talked to a HVAC guy who said this is a good way to save if I can get the loads low enough and I would use my small wood stove on the few really cold winter nights. The addition includes a lot of passive solar glazing as well. The entire living space is open to the vaulted ceiling, and keep in mind this is Minnesota, lots of beautiful lakes, just frozen solid half the year, a R40 sip roof is barely above energy code here.

I posted to building Green Building Advisor and got a quick reply from one of their experts that either way would work.
http://www.greenbuildingadvisor.com/blogs/dept/building-science/bs-podcast-perfect-wall-roof-and-slab

It seems that it would not be much cost or effort to add another R12 to the interior walls & ceiling, but are there negatives I am not thinking of?

if somehow you'll get moisture between SIP and the extra layer of foam will be very difficult for the SIP to dry. I wouldn't add rigid insulation to a SIP wall (interior or exterior) because the installation and detailing becomes critical.  If you really want to add consider some sort of spray foam. so water vapor doesnt represent an issue.

good luck
Adi

I think your R24 sip wall will out perform an R40 stick wall, so if that is where you got the R40/R60 numbers from, your R24/R48 SIPS are more than adequate. 

Jason,

To make life simple, I think a 6" SIP wall will be just fine. If you really feel that you need the extra R value, go to an 8" (R-32) SIP wall. Remember that one of the great things about SIP's are the combination of R value and air tightness. In fact, I think you would be pleased with a 10" SIP roof, and save a little money. Take the money you save and put a solar water heater on the roof.

Steve
GrandCountySIPs.com