Hello. I'm currently attempting to design a small efficient house and build it with ICFs. For the basement, instead of doing a traditional walkout, which involves stepping the footing and adding a frost wall, I'm putting the back door on the stair landing (kind of like a split-level entry but for the back door), which makes it about three feet above the basement floor (9ft ceiling). If I backfill up to that point, I have my required 4 feet underground, but still have lots of height above grade for windows to make the basement nice and bright. An ICF contractor has already said, "You will regret it." and that I'm complicating the basement. What does the forum think? I've attached the rear elevation. Thanks for any advice.

Posted By benman on 24 Apr 2013 10:36 AM
Hello. I'm currently attempting to design a small efficient house and build it with ICFs. For the basement, instead of doing a traditional walkout, which involves stepping the footing and adding a frost wall, I'm putting the back door on the stair landing (kind of like a split-level entry but for the back door), which makes it about three feet above the basement floor (9ft ceiling). If I backfill up to that point, I have my required 4 feet underground, but still have lots of height above grade for windows to make the basement nice and bright. An ICF contractor has already said, "You will regret it." and that I'm complicating the basement. What does the forum think? I've attached the rear elevation. Thanks for any advice.

Looks like a typical split entry or bi level (depending on what part of the country you are from) to me. There is no reason not to do this in ICF. It is done all the time. There is less lateral load on the walls so that would be a good thing. Make sure you keep your minimum four feet!! I assume the ICF is still going at least to the subfloor?

Yeah that's what I figured, it's just that most people usually do it for the front door, not sure if it's unheard of to do a split entry for the rear door. Also forgot to mention that I'm planning on both floors with icf.

That would be the proper way to do it!! But than maybe I'm a little bias (;+))
Where are you building, if I may ask?

I'm building in Orange County, NY. My main concerns are budget which leads me to try to avoid all the extra concrete and form work in a full walkout. I'll be posting some more info on the project soon for more feedback. I just wanted to see if anybody else agreed with this contractor. He's also frowned upon my use of roof trusses and said I should do the gables in ICF and spray foam the roof. I understand why, he's dealing with upscale clients with the money to do these things rather than me, someone looking for a small, high performance house.

R20-22- ish ICFs are on the thin side of "high performance" for a US zone 5 location like Orange County NY, but still way better than code-min.

Trusses have more flex issues than rafters & joists under snow loads and are more likely to have seasonal air leakage thermal issues at the transition from the concrete to the truss, but that's not to say you can't get there. If you're looking at R20-R22 ICFs it's not unreasonable to go with energy-heel trusses capable of handling 20-21" of blown cellulose (~R60 at a settled depth of ~17-18"). Air sealing details at the concrete/truss transition and the ceiling are critical, and it may take an OSB layer on the underside of the chords to handle the dead-load of the insulation if you're using 24" o.c. spacing. Even with the OSB and air sealing detailing it's still a LOT cheaper than code-min spray foam on the roof deck and an unvented attic approach.

It's also worth putting 2-3" of EPS under the slab in this climate zone, especially (but not exclusively) on a walk-out. Type-II 1.5lb nominal density is fine for the application, but don't be surprised if code inspectors insist on Type-IX 2lb goods (for no really good reason.) Using XPS would work from a thermal perspective, but is about 200x as damaging to the environment as Type-IX EPS due to the impact of the HFC134a blowing agent used (compared the pentane used to blow EPS.)

Hi Dana, thanks for the advice. My plan is to add 4 inches of foam on the exterior walls. Are there any issues with putting poly-iso on the exterior of the main level (with furring strips and cladding) and eps on the basement level (with eifs)? Obviously with some kind of trim detail to separate the two claddings. Your roof insulation and air sealing recommendations were what I had in mind. Thanks!

dana - would you care to look at this link? Click Environmental and it will take you down close to the bottom of the page. Do they actual use a different blow agent or is this just marketing?http://foamular.com/foam/faqs/#envir If they use a different agent would it result in less R value decay?

Benman, Are you building into a hill? What are you doing for the front door? Did the contractor elaborate on why he thought you would regret it?

Are you planning total ICF? or just the foundation? What part of the country are you building in? It would be far more efficient if you go deeper...

ron- I am building into a hill and I've attached the front elevation. The plan is to have the foundation 4 feet above ground in the front and 6 in the back. With only 5 feet below grade in the front, I can keep the normal rebar spacing with a 6 inch core, any deeper and you have to increase the thickness and/or frequency.
I think the contractor was saying that I would regret not building a full walkout, but as far as I can tell this is a good compromise to avoid doing a frost wall but still getting most advantages of a walkout.

Calamityj-for this post I was just looking for some quick feedback on the design. I'll being posting something more comprehensive soon. But I'm building in Orange County, NY Zone 5 and will be doing both floors ICF (but not the gable walls).

What ICF are you planning on using? I am drawing the plans for a similar project(walkout basement in hillside) and also want more insulation. From an ease of construction standpoint, I thought it best to put it on the inside in the form of a common stud wall. The ICF I am looking at (Arxx) has vertical crossties every 8" and the exterior cladding will screw right to it for a relatively fast exterior finish. Fabbing insulation and firring strips to the outside, that you then have to attach the cladding to, sounds time consuming. It will also make putting the windows flush with the outside for appearances a little more difficult.

A 2X4 on 24" stud wall will fab pretty fast on the inside(out of the weather), vapor barrier and sheetrock will go right up over it. The cavities will take standard less expensive batt insulation, and the wiring will be a little more conventional as opposed to routing all the wire runs and boxes into the ICF. It will also give you a little more ceiling insulation overlap at the roof-truss union... Of course your climate is a little colder in the winter than mine here in the northwest, so it may make more sense to put the concrete mass closer to the inside of the envelope

My .02

Benman, Check your private messages and call me if you need anything. Bruce

I don't see the complications. You will need a patform inside to access the door, so what. As far as the exterior walls they can be upgraded with more foam if you use the right system. It doesn't have to be the old 2.5 or 2.75 " foam. I just priced out a system that will use 3" iso ouside with a 2.5 iso inside with a 4" core. You could use 6" core for the lower section and a 4" concrete core for the upper section.

smartwall-what system was that?

I just check my e-mail and I have your number so I will call you, Don't want to give away all my trade secrets. I was given your contact info by a sales rep I deal with. I'm in upstate NY but cover your area

Posted By FBBP on 24 Apr 2013 06:18 PM
dana - would you care to look at this link? Click Environmental and it will take you down close to the bottom of the page. Do they actual use a different blow agent or is this just marketing?http://foamular.com/foam/faqs/#envir If they use a different agent would it result in less R value decay?

They state:

" All Owens Corning Foamular plants in the U.S. and Canada produce Foamular products using a proprietary blend of blowing agents which allow Owens Corning to manufacture Foamular products with Zero Ozone Depletion Potential and approximately 70% less Global Warming Potential than the blowing agents used before our blowing agent conversion in 2009."

OK, so they cut down on the HFC134a by mixing in something else to achieve that 70% reduction, dropping from ~1400 x CO2 GWP to "only" (0.3 x 1400 =) ~420 x CO2.

That's good and all, but is it really much to brag about? 

It's still more than 50 x the hit from pentane, the most common blowing agent for EPS and polyiso.  In Europe most XPS is blown with CO2, at only 1x CO2 GWP, but it has the same ~R4.2/inch as EPS of similar density.

The blended blowing agents may very well result in a different R-value decay, but they are only allowed to label it at lifecycle-average  (IIRC that's presumed by convention to be 25 years, but I could easily be wrong on that.)

Thanks Dana - kind of thought it would look like that. Hope they post some third party info.
Are you suggesting that it is "only" 30% worse then eps now?

Posted By Ronmar on 25 Apr 2013 12:04 AM
What ICF are you planning on using? I am drawing the plans for a similar project(walkout basement in hillside) and also want more insulation. From an ease of construction standpoint, I thought it best to put it on the inside in the form of a common stud wall. The ICF I am looking at (Arxx) has vertical crossties every 8" and the exterior cladding will screw right to it for a relatively fast exterior finish. Fabbing insulation and firring strips to the outside, that you then have to attach the cladding to, sounds time consuming. It will also make putting the windows flush with the outside for appearances a little more difficult.

A 2X4 on 24" stud wall will fab pretty fast on the inside(out of the weather), vapor barrier and sheetrock will go right up over it. The cavities will take standard less expensive batt insulation, and the wiring will be a little more conventional as opposed to routing all the wire runs and boxes into the ICF. It will also give you a little more ceiling insulation overlap at the roof-truss union... Of course your climate is a little colder in the winter than mine here in the northwest, so it may make more sense to put the concrete mass closer to the inside of the envelope

My .02

What do you need a vapor barrier for, if it's on the inside of the ICF?  A vapor barrier is just a moisture trap. The ICF has WAY more insulation than the minimum necessary to avoid condensation in the studwall, but if you put up a vapor barrier you're likely to hit pretty extreme moisture temps while the concrete is still curing & drying out after the pour. There's no rationale whatsoever for the vapor barrier, it can only cause, never cure problems in this stackup.

By adding more insulation to the interior you're isolating the interior from the thermal mass benefit, but it's still a net win.  It's far better from a performance point of view to add the additional R to the exterior, and keep the interior-side R at a minimum.

Posted By FBBP on 25 Apr 2013 11:03 AM
Thanks Dana - kind of thought it would look like that. Hope they post some third party info.
Are you suggesting that it is "only" 30% worse then eps now?

No, it's only ~6000% worse than EPS.

30% of ~1400 x CO2 is ~420 x CO2...

...compared to EPS @ ~7x CO2. 

420/7= 60, or 6000 %

Even with a 70% reduction in GWP, it's still a pretty bad hit.