I'm planning an ICF home near Sioux Falls, SD (zone 6). The 99% temps are around -10°F and 90°F with approx 7500 HDD. The home will be about 7ft in the ground on average and approximately 13ft out of the ground. My intention was the use the standard 8" ICF block for the basement and use a 2" foam insert at the height where I mount the floor trusses (9ft) all the way to the soffit. IE, R30 for the walls above grade. This saves some cost of concrete and will partially offset the cost of the foam insert. I intend to run the load calcs via a trial period of HeatCAD shortly, but I wanted to ask for any advice. My question is, has anyone realized a real-world benefit to using this type of construction? Is it worth the minor hassle or should I switch to a 6" block?

Generally it's a good idea do go a bit thicker on your foundation and sub-surface walls

The way you're looking to do it, you get a nice uniform facing on the insulation, making air sealing, waterproofing and wall covering much simpler.

Dil, Regarding foundation wall, thicker concrete or thicker foam? Plenty of 8" foundation walls in my area supporting homes if I'm not mistaken. I planned on an R22 below grade due to the relatively consistent temps most of the year.

For what it's worth, the load-calcs indicate just a 2000 btuh peak heating load difference with an additional 2" of EPS foam on the main floor. The HVAC equipment won't change size, but the cumulative costs over time might eventually make the additional 2" of EPS pay off. (plus a concrete savings initially.)

I was figuring base amount of insulation on the blocks and an 8" concrete core for the basement. So you get a nice strong sub-surface wall system.

Then on the first level, you still run an 8" core block. But you sub in an additional 2" insulation panel to the outside and continue with a standard (and totally acceptable) 6" concrete wall to the roof.

You sub insulation to the outside as that's where you're moving your dew control point in the wall. You lay out the block, and set the insulation panel(s) inside the block on the exterior facing.

And yeah, over time the additional insulation should pay itself off.
Just make sure to be rigorous about all your air and weather sealing details too.

Posted By Dilettante on 28 Feb 2020 05:15 PM
I was figuring base amount of insulation on the blocks and an 8" concrete core for the basement. So you get a nice strong sub-surface wall system.

Then on the first level, you still run an 8" core block. But you sub in an additional 2" insulation panel to the outside and continue with a standard (and totally acceptable) 6" concrete wall to the roof.

You sub insulation to the outside as that's where you're moving your dew control point in the wall. You lay out the block, and set the insulation panel(s) inside the block on the exterior facing.

And yeah, over time the additional insulation should pay itself off.
Just make sure to be rigorous about all your air and weather sealing details too.

This was my exact plan all along.

Unless you have some very long walls in the basement a 6 inches is more then strong enough for at 7 foot tall wall.

We did 6 inch for a 10 foot tall basement wall and 6 inch grid form R30 (global block) on the upper floor 10 foot tall.

Just use the rebar tables and get that right.

I have seen many 4 inch basements. We are in Michigan which has very soft ground.

There are many factors to consider when designing concrete basement wall structure. Seismic and wet soil loading for example.

There should be prescriptive ICF design info in your local building code that specs thickness and rebar schedule. All ICF manufactures also provide similar info. If in doubt, hire a structural engineer.

It's pretty hard to see ICF basement wall structural failure because the EPS insulation hides it...until you experience water intrusion or see actual wall bowing. We wouldn't consider going with less than 8" thickness for any basement wall where we build.

Can't let the 4" below grade fly. The only place that is accepted is for crawl spaces. Minimum for a back filled wall is 5.5". If your new to icf's use a 8" wall it's easier to consolidate because your using less rebar, it's what I usually suggest to my customers. Jesse not sure if your attaching the floor system inside the walls? Reread your post. Use Watkins hangers for the floor system and use an energy heel truss that is installed with the same hangers inside of the icf wall at the top

wall. This will allow you to blow celly against the icf and create a great seal.

Posted By sailawayrb on 04 Mar 2020 06:53 PM
There are many factors to consider when designing concrete basement wall structure. Seismic and wet soil loading for example.

There should be prescriptive ICF design info in your local building code that specs thickness and rebar schedule. All ICF manufactures also provide similar info. If in doubt, hire a structural engineer.

It's pretty hard to see ICF basement wall structural failure because the EPS insulation hides it...until you experience water intrusion or see actual wall bowing. We wouldn't consider going with less than 8" thickness for any basement wall where we build.

I always forget about the seismic stuff because we just don't have to worry about that in our area. The map does show South Dakota is similar to Michigan but yes very good catch to think about that....thanks.

Sure thing and be very happy that seismic is not a design issue for you. Although I do wonder with all the fracking for natural gas that is now going on, if seismic really should be considered everywhere. I would err on the side of more rebar and thicker basement walls as dealing with a failed basement wall would be very problematic and expensive.

Posted By sailawayrb on 06 Mar 2020 08:08 PM
Sure thing and be very happy that seismic is not a design issue for you. Although I do wonder with all the fracking for natural gas that is now going on, if seismic really should be considered everywhere. I would err on the side of more rebar and thicker basement walls as dealing with a failed basement wall would be very problematic and expensive.

I don't know that Seismic needs to be a concern EVERYWHERE.

But there ARE places in the US (especially around Illinois, Missouri, Kentucky, Missouri that should probably have some "oh shit!" provisions for seismic.

The last time the New Madrid Fault popped "for real", it literally sucked buildings down and rang church bells...IN BOSTON.

Back then, it sucked mightily.

Today?  You have major metro areas (INCLUDING CHICAGO) that are within the thing's area of effect.
Think the skyscrapers are quake-proof for even small ones?

We sell 5" and 7" blocks for a fraction of the price. Give me a call for a quick quote.

Kristina
Belco ICF
ICF4Less.com
(260) 367-2121

All:
To clarify, using an R22 8" below grade and an R30 6" wall above grade, HeatCAD indicates the increase in peak loss is under 2000 btuh. I realize the costs of heating/cooling will pay off over time, but it'll be slow. This cost increase would also be offset by removing 25% of the concrete upstairs as well.

Regarding a floor system, multiple local contractors have used a brick ledge block turned towards the interior and hung a top-chord truss from those. I like this idea better than all others.

That is certainly old school. It's the first time I have heard anyone use that in 15 or 16 years. What do they do about bracing? Hopefully they use a tie in system like the Fox brick ledge wire that keeps the concrete from shearing, wouldn't install brick ledge without it.

They have ICF braces. I felt the brick ledge block would be stronger and pretty easy to execute, honestly. Obviously willing to learn otherwise. One contractor uses a 3/4 piece of all-thread drilled and epoxied into the wall after the pour and an LVL attached via nuts and washers. I wasn't a fan of this as 3/4" all-thread is clamps the LVL against the foam and not to concrete. This seemed odd to me.

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/4/aft/78612/afv/topic/Default.aspx

The reason I asked the question about bracing is the brick ledge kicks the top of the wall in by at least 4" at the top. You need a flat wall to attach the bracing, so how do you do that with the top of the wall in 4" from the bottom? The second point is that in NY we are required to cover the icf with 1/2" dry wall with mud in the seams for fire code. It may be not required in your area but I still would do it if I'm living in the house or as a best practice for my customers. Which brings up the next question. What kind of pain in the butt are you causing yourself trying to cover the compound curve on the brick ledge with drywall? This is stone age icf construction that sounds like it will take more time and effort than it is worth. Been doing icf's for 30 yrs and this doesn't make sense. I'm not a spokesmen for the company but I use Watkins hangers since they save me time. By matching the type of hanger to you floor system, you can cast the hanger into the wall when you pour and skip the ledger board all together.

Agreed RE: brick ledge. This detail does work but it doesn't leave much margin of error. Installer must ensure to screed brick ledge concrete perfectly level (or shim 2x4 bolted on top) to achieve a level floor system. Several hanger options (eg, Simpson Strong Tie ICFVL, ICF-Connect) allow for adjustment of floor system while installing joists. Anchor bolts can also work, but the extra step of needing to remove EPS to allow ledger board to be in contact with concrete (to avoid bolt shear through EPS) seems like unnecessary work vs the hangers available).

As a side note an engineer looked at the hangers vs brick ledge on a project years ago and advised hangers are actually stronger for floor load than brick ledge. I assume this is because the brick ledge is designed to take a high vertical load (ie, brick stacked on top), while a floor load would impose a vertical load and a lateral load (due to floor deflection). Feel free to correct that assumption.....

Here is an article from ICF Magazine that explains various ways to support floor joist: https://www.icfmag.com/2006/08/installing-floor-joists/