We are getting bids for our new home and i am trying to decide what type of exterior walls will be best.  i am getting bids for the following:

2x4 - open cell foam
2x4 - cellulose

2x6 - open foam
2x6 - cellulose

4 inch Sips

I wanted to get peoples opinions on what is the best bang for my buck.  Obviously, the SIPS will be the more expensive but are they worth the xtra money.  We are located just west of St. Louis and are building a 2,100 sq foot ranch.

I would consider 2xs filled with cellulose plus 2" of EPS foam. Membrain on the inside, tape on the outside foam or sheathing (ie, a double air seal).

Either 2x4 option has a  whole-wall R (with the thermal bridging of the framing factored in) of about R10.  The open-cell foam will usually be slightly more air-tight, but air-sealing can be achieved easily & cheaply (and more effectively than just o.c. foam cavity fill) by other means.

Either 2x6 option will have a whole-wall R of ~R13 with 16" o.c. studs, or ~R14+ if the studs are 24" o.c. (which may not make for the flattest interior wall unless you have very fussy framers, but it's structurally sound & code-legal).

A 4 inch SIP with an EPS core comes in at ~R12-13, and is easy to air seal.

jonr's very good recommendation for 2x4 cellulose + 2" of exterior EPS insulation outside the sheathing (same wall thickness as a 2x6 studwall,  an easy thickness to handle with standard windows & doors) delivers a whole-wall R of about R18.  That's 50% uptick in R value from a 4" SIP, and closing in on 2x the R value of the 2x4 no-exterior insulation options.

If instead of EPS you used foil-faced polyiso (seams taped with FSK tape) you'd be at ~R22 whole wall.

If you build-in a 3/4" rainscreen gap between the siding & iso it would have an average performance close to ~R24 due to the radiant-barrier effect of the foil facer.  It's probably still cheaper than the SIP option, but has twice the R-value, and is probably the best bang for buck, even though it's slightly more expensive than the 2" EPS approach.

For an idea of what it takes to mount exterior foam, see:

http://www.greenbuildingadvisor.com...-sheathing

Air sealing is the cheapest energy efficiency upgrade you can do to any new construction. It's not rocket science, but you have to pay attention every step of the way or you'll lose the opportunity to get the tightest seal at the lowest cost.

Air sealing a wood framed building is much easier if done as you go. A bead of 1-part low expansion foam under the foundation-sill, acoustic sealant caulk between the foundation sill & band joist, and between the band joist & subfloor all count. Another bead between the subfloor & studwall plate as you tip the wall frames up, and between top plates when double-plated all counts.  A bead of caulk (or construction-adhesive or lo-expansion foam) between the framing and structural sheathing as the sheathing goes up is also good practice. Use a thin shot of low-expansion foam to seal around windows & doors, don't go all old-school with the crummy stuffed- fiberglass approach (some contractors still do that, or so I've heard.) It's cheap stuff, adds modestly to the labor cost, but makes for a much tighter wall than any cavity-only treatment of o.c. foam could achieve, and it can be made as tight as a SIP structure if you make the effort every step of the way.

It's important to foam-seal all plumbing & electrical penetrations of the exterior wall too.

There are lots of details to get right on the ceiling/attic interface too, but I'll spare that for now.

At R22-R24 whole-wall you're in the range but still below what's typically cost-effective in the long term. See table 2, p10 of this document- refer to the recommended whole-assembly R values for zone 4.  If you're heating with propane or oil you might even bump those a bit, but if gas or heat pump don't knock yourself out getting it to R25 rather than R22- concentrate on air sealing instead.   In a ranch your roof to wall area ratio is higher than a multi-story, and making up the performance difference on wall-R in deeper blown cellulose (say, R75 rather than the recommended R60) in the attic is pretty cheap compared to adding another half inch of foam on the walls.

Pay attention to window performance & placement too- it matters. eg:  a lot of west facing glass could nearly double the peak cooling load.

Any mechanical equipment or ducts planned for the attic?  If yes, banish that thought NOW!  Build taller walls with a mechanical chase between the finish ceiling and attic floor, or utilize crawlspace/basement under the first floor to accommodate the ducts & air handlers. If you keep it all inside the air-sealed & insulated space there will be but a fraction of the air-handler driven air infiltration, no direct conducted duct losses/gains, no condensation on air-conditioning ducts, and duct sealing & insulation become less critical. 

If by going to an R20+ wall and R50+ attic the heating & cooling loads are under 3 tons/36,000BTU/hr (as is likely the case), it may be cheaper and more efficient to go with a ductless solution to the heating & cooling (mini-split/multi-split) than separate heating & cooling systems or a ducted heat pump (and ductless is usually more comfortable & efficient than ducted air-source heat pumps too.)

Slab on grade, crawlspace, or full basement?

OK I quit, you were only asking about walls, eh?

Posted By cards66 on 23 Aug 2012 09:03 AM
We are getting bids for our new home and i am trying to decide what type of exterior walls will be best.  i am getting bids for the following:

2x4 - open cell foam
2x4 - cellulose

2x6 - open foam
2x6 - cellulose

4 inch Sips

I wanted to get peoples opinions on what is the best bang for my buck.  Obviously, the SIPS will be the more expensive but are they worth the xtra money.  We are located just west of St. Louis and are building a 2,100 sq foot ranch.

Have you considered getting a bid for ICF?

Insulated concrete forms (ICF) construction is usually more expensive than SIP and even easier to air-seal, and it's quieter & more durable than any of the aforementioned wall assemblies. The absolute minimum ICF available these days is ~ R16 whole-wall, but most vendors' offerings start at R20-R22.

While it's more money, there are benefits beyond thermal performance to factor in when looking at "the best wall for the money". The comparative cost will vary regionally/locally with the local cost of concrete, and the experience & skill level of the ICF contractor. (You don't want to be any contractor's first ICF project- particularly on a 2-story, but even on a 1-story house.)

Living in tornado country, while a tornado might rip the roof off, you won't have the walls collapsing on you in an ICF building should you find yourself in the direct path. But even in tornado country that the odds of being in that path over the lifespan of a house (100-200 years, say) is an extremely unlikely event.

Dana1...Thanks for all of the information.  We are looking at Thrmocore SIPS of Missouri.  There 4 inch SIP has a R24 value. (thermocroemo.com)   THis seems to be be a pretty good R value from what I can tell.  Just trying to figure out if the extra cost is worth it.   A lot of the options seem viable.  I am having a family member doing a majority of the building for me and i know he is only familar with standard framing and such.  The last house he built he had them do 2x6 with full fill of foam.

To answer some of your other questions, we have a basement and are trying to decide on our best window choices as well.  We priced Marvin Integrity and Anderson 200 and they are going to be probably a $10k differnce on that as well.  Just trying to figure out if all these big jumps in prices are worth the upgrade and trying to get as tight a house as possible. 

I've used SIPS extensively and both types of windows. Strongly recommend 2x4 or 6 with cellulose and 2" of exterior foam. Easier, less expensive and fewer future problems.
Andersen 200's are Andersen's cheapest line while Marvin Integrity is (IMO) one of the best windows made in the USA - no comparison.

Posted By cards66 on 24 Aug 2012 05:09 PM
Dana1...Thanks for all of the information.  We are looking at Thrmocore SIPS of Missouri.  There 4 inch SIP has a R24 value. (thermocroemo.com)   THis seems to be be a pretty good R value from what I can tell.  Just trying to figure out if the extra cost is worth it.   A lot of the options seem viable.  I am having a family member doing a majority of the building for me and i know he is only familar with standard framing and such.  The last house he built he had them do 2x6 with full fill of foam.

To answer some of your other questions, we have a basement and are trying to decide on our best window choices as well.  We priced Marvin Integrity and Anderson 200 and they are going to be probably a $10k differnce on that as well.  Just trying to figure out if all these big jumps in prices are worth the upgrade and trying to get as tight a house as possible. 

While I am a firm believer in SIPS and this is probably an isolated problem, it should be referenced because it was brought up here on this forum:

ThermoCore Issues

Make sure you install venting above your wood SIP roof. This involves furring the roof and then installing another layer of OSB to allow an air channel to help keep the OSB dry. This is highly recommended and should be standard practice when installing a wood SIP roof. It adds expense but if you don't want problems down the road, I recommend doing it.

BuildingScienceInfo

Is a SIP building OK for a first time builder? I would say no but others might disagree. I just wouldn't like someone learning/training on my home.

Posted By Dana1 on 24 Aug 2012 01:57 PM
Insulated concrete forms (ICF) construction is usually more expensive than SIP and even easier to air-seal, and it's quieter & more durable than any of the aforementioned wall assemblies. The absolute minimum ICF available these days is ~ R16 whole-wall, but most vendors' offerings start at R20-R22.

While it's more money, there are benefits beyond thermal performance to factor in when looking at "the best wall for the money". The comparative cost will vary regionally/locally with the local cost of concrete, and the experience & skill level of the ICF contractor. (You don't want to be any contractor's first ICF project- particularly on a 2-story, but even on a 1-story house.)

Living in tornado country, while a tornado might rip the roof off, you won't have the walls collapsing on you in an ICF building should you find yourself in the direct path. But even in tornado country that the odds of being in that path over the lifespan of a house (100-200 years, say) is an extremely unlikely event.

Good points. It should also be mentioned that with ICF systems you knock out numerous birds with one stone:

1 - You get your interior insulation & exterior insulation
2 - You get your air & water barrier
3 - You have a flat, solid & ready surface to mount your interior drywall

4 - Lbear quite possibly gets paid to tout ICF and trash alternatives. So, in the interest of fair play, here is the ICF horror story. http://www.askthebuilder.com/concrete-foundations-must-be-strong/

Of course, his horror story and mine aren't entirely the same. To fix cobbled-up ICF requires jack hammers.

As Dana says, if you can't find an experienced contractor, sip or icf, pass.

If I go with Sips I was going to let the company install them. This way I get someone who knows what they are doing. I was just going to do walls and then do regular trusses. I had seen the link about Thermocore some time ago where they had issues with the company out of Indiana. THis company is out of Missouri and seems to have a pretty good record from what ti can tell. I had looked at ICF but I just don't think it is going to fit our budget.

A hollow core SCIP where the interior is filled with blown (or built-in) cellulose would be interesting. You even get your interior and exterior finishes.

Posted By cards66 on 24 Aug 2012 05:09 PM
Dana1...Thanks for all of the information.  We are looking at Thrmocore SIPS of Missouri.  There 4 inch SIP has a R24 value. (thermocroemo.com)   THis seems to be be a pretty good R value from what I can tell.  Just trying to figure out if the extra cost is worth it.   A lot of the options seem viable.  I am having a family member doing a majority of the building for me and i know he is only familar with standard framing and such.  The last house he built he had them do 2x6 with full fill of foam.

To answer some of your other questions, we have a basement and are trying to decide on our best window choices as well.  We priced Marvin Integrity and Anderson 200 and they are going to be probably a $10k differnce on that as well.  Just trying to figure out if all these big jumps in prices are worth the upgrade and trying to get as tight a house as possible. 

That R24 is a center-cavity number, and there IS thermal bridging in their panels & construction not accounted for in their number, but the true whole-wall R is likely to be at least R20.

But I personally shy away from polyurethane SIPs on environmental grounds:

HFC245fa used as the blowing agent has more than 1000x the greenhouse impact of CO2.  This compares to about 7x CO2 for pentane, the blowing agent use for polyisocyanurate or EPS. 

With polyurethane blown with HFC245fa (which would include most of the R6-R7/inch products out there) any R-value more than ~R10 the total lifecycle greenhouse effect of the additional polyurethane exceeds that of the energy-use it offsets many times over, assuming a 100year useful life on the house.

With EPS or iso the crossover on greenhouse gas issues even at R50 is less than a decade.

SFAIK the only (relatively) benign 2lb polyurethane foam on the market is Icynene's MD-R-200 which only yields R5.2/inch of thickness. But it's blown with water, with a net greenhouse gas effect FAR lower than HFC245fa, lower than pentane, even lower than CO2(!). This is not to be confused with their MD-C-200, which is R6.75/inch, and blown with HFC245fa, just like most 2lb foam.

BTW: On the basement it probably IS going to be worth using ICF, and in your climate zone 1.5" of XPS or 2" of EPS under the slab is cost effective long term. With foam under the slab all the way up to the inner-EPS of the ICF you have zero thermal bridging to the ground and the (now floating) slab is fully within the thermal envelope of the house, enhancing the thermal performance of the house.

If not ICF, using 2" of fire-rated iso on the interior of the wall down to 4-6" above the slab, with XPS beween the iso and the footing (and the same sub-slab insulation) gets you there. You still have air-seal the foundation sill (and band-joist, depending on how you frame the thing) with spray foam to guarantee air tightness. It's better to use 2" of closed cell foam (even the nasty HFC blown stuff:-) ) there.

Don't want to seem antiICF. I used it for stem walls for my slab on grade, where it is superior in every way to typical cement block construction and cheaper besides.Be advised that your building inspector lkely will require drywall over the ICF foam for fire safety even if you aren't finishing out the basement. Depending on your soil type, water table and hvac choice, insulating the outer three feet of the slab is more cost effective than insulating the whole slab. Dirt being a poor conductor, btus lost in the middle of the slab aren't going anywhere quickly.

RE: insulating under your slab: on the other hand, you get one chance to do it right. Pretty hard to add insulation later.

In fact, it is quite easy to put foam boards over the concrete and float a floor on top of it. You'd still want the perimeter foam under the slab to break thermal bridging. As living space, interior insulation should be more comfortable if somewhat more expensive to condition. Exposed concrete would keep the AC from running much, but that's a mixed blessing in a humid climate.

Putting the foam over the slab puts the thermal mass of the slab outside the thermal envelope, which in most buildings would be a (very slight) hit in overall thermal performance.  Putting it under the slab now is the right thing to do rather than putting off on a "maybe". Build like it was 2030 with 2030 R/U values.

See Table 2, p10 of this document which is a middle-ground starting point for what can make economic sense with currently availble materials & methods, at 2010 energy prices.

For US zones 4 & 5 they're recommending R7.5 full-coverage for under slab foam, R10 if slab-edge.  EPS is R8 @ 2", and is usually cheaper than 1.5"/ R7.5 XPS. Either works.

When I talked to one of the insulation companies he showed me a product called Ecocell. (http://cmsgreen.com/) It is basically Cellulose Batts that seem like they would be very effective. Wanted to see what peoples thoughts were on it while we are talking about insulating the basement. We have no intention of finishing the basement ever. We have had issues in other houses and my wife wants no part of a finished basement.

Whether you finish the basement or not, without insulation it's still a large fraction of the heat load of a house with R20+ whole-wall values on the first floor. It's far easier to insulate and air-seal the foundation effectively than to get there with insulation under the first-floor. Experience with US climate zone-5 retrofits show that insulating and air sealing the basement walls alone usually take the heating fuel use down by 15-20%, even with R10 walls on the fully-conditioned space. The higher-R you make the rest, the bigger the fraction of the heat load the basement represents. R24 walls & R50+ attics would be wasted over an uninsulated unsealed foundation.

The better you air-seal & insulate the basement, the less issues you have with mold & moisture for storage purposes, since the basement air will then track the temperature & dew-point of the conditioned space air in summer. Humid summertime air leaking into a cool basement in summer to condense on the slab & lower portion of the foundation is a primary cause of that "musty basement" smell. Insulating the walls & slab and air-sealling to prevent stack effect from driving air infiltration really works!

Batts of any sort have to be installed PERFECTLY to perform to spec. Blown or sprayed goods yield far more reliable performance since it fills-in and conforms to every knot-hole, oddball framing, electrical box & plumbing/wiring without leaving performance-robbing gaps & compressions. Some performance-home builders all but refuse to use batts of any type since they always have to be re-worked to make them acceptable:

http://www.greenbuildingadvisor.com/blogs/dept/green-building-curmudgeon/should-batt-insulation-be-outlawed

Dense-packing cellulose to at least 3.2lbs/cubic-foot density (3.5lbs is better) is good enough to prevent settling in a zone-5 climate and will tighten a wall that hadn't been built with a well defined & implemented primary air barrier considerably. In a 2x6 24" o.c. construction it'll run ~ R14 after thermal bridging. But it would also takes another R7.5 of exterior insulation over the sheathing to keep the number of hours the sheathing spends below the dew point of the conditioned space air to be fully protective from wintertime moisture accumulation. A 2x6 cellulose-filled studwall with 1.5" of exterior iso (~R9ish) gives you enough margin, and a whole-wall R of ~R23.