Hey all,

I hope to start placing a basement about 4 years from now.  I have a lot to learn, but I've learned a lot, already.  I am leaning towards a saltbox-style, passive solar windowed, timberframed house with a sips envelope, metal roof.  For whatever reason, it's been hard to find passive designs that include a basement.

I plan on building on GeoFoam, double layered moisture barrier, then the footings/slab.  My wife's brother built his whole house, and cinder blocks were his basement.  I'm building on a Northfacing hill in Maine, so I obviously need more insulation than he would.

As I understand it, a poured foundation gives strength, well above what cinderblocks could.  I can't get a firm quote on what a poured basement would cost, and I think that I'd have to hire a contractor for that; he's got the expenses of the crew, placing forms...  I could build the forms of ICF, of course, but at what cost?  All those systems still require a massive network of braces while it all cures, etc.

Could I not get the same effect by simply building with cinderblocks, filling with grout between each layer, stick in rebar running up and down, and then spraying foam on either side?  It sounds significantly cheaper, but I have ZERO experience with basements.  I'd then backfill, etc...  What would make this an inferior solution to an ICF basement?  Is it necessarily weaker?  Too weak for my 2 story, passive, sip/timberframe home?

Thanks for any input.

You can design to any structural spec you like with CMU, but it takes a thicker wall if the loads are severe. A CMU foundation isn't as inherently air tight as poured concrete, but it's possible to make them air tight. If you do a CMU wall, putting all of thehigh-R foam insulation on the exterior, with 2x6 or 2x4 insulated studwall on the interior side would probably be the cheapest/best way of hitting your required R-value, and still get some benefit out of the thermal mass of the wall.

I'm not sure how cost effective a SIP + timber-framed structure is going to be compared to a double-wall/cellulose (or TJI-stud) approach with some exterior EPS.

Doing a PassiveHouse on a north facing hill is going to be tough- almost all PassiveHouses rely heavily in solar gain to meet their energy use numbers, and this my boost your R-values to something ridiculous. But if you get at least some winter sun on the south facing pitch of the roof you can probably hit Net Zero Energy at about R50 wall, R80 attic (and limited but high performance windows) with a rooftop PV array.

Thanks, Dana.

I understand that sips are more expensive than stick with blown cellulose(I don't know what TJI is, though). Another of my challenges, however, is that while I currently live in Philly, PA, I'm gonna have to build a little at a time 600 miles North, up in Maine; so I think big panels is the only way I'll get to a barely dried-in state before having to return home.

The solar situation practically keeps me up at night. There is a FAIR amount of sun, thankfully, but I would like to know what it'll take to take advantage of it. It sounds like all the R-value might even increase the weight pushing down on the basement, eh?

Would I be leaving the blocks hollow, or filled with foam, or filled with grout(where NOT anchoring the rebar, of course[pun not intended])? If I'm filling with grout, is it still significantly cheaper than a poured wall?

Thanks again...

I've seen lots of old cinder block foundations here in NH, and many of them are bowed in from the pressure of frost on the wall. Happens less frequently than with poured concrete. So the take away is that the backfill has to be very porus and the footing drains must be done well and drain to daylight. Not a place to cut corners anyway, but especially with cinder blocks. While they are standard construction for commercial buildings, we never see them on residential applications; probably because the cost of labor makes them more expensive than poured concrete.

Some of my projects have use CMU above and below grade in the southeast.  I would prefer to use almost anything else than CMU, especially below grade.  They are just too porous and require too much extra work and reinforcing for me.

CMU foundations are the standard in many parts of the upper midwest, so the frost heave issues CAN be managed.

TJI are truss-type assmblies often used for joists where large spans and floor flatness are an issue. Used as studs they offer much lower thermal bridging than dimensioned timbers due to the narrowness of the flange, and much deeper bays for insulation.



While they make R40-ish SIPs, it's a far more expensive way to go high-R.  TJI-stud walls can go up pretty quickly (more quickly than Larsen Trusses), but double-studwalls can get to a dried-in stage quickly by building the structural wall first, and most framing contractors don't need a lot of training to execute them reasonably well.

Before deciding on the wall assembly type, sketch out the footprint of the house and start running the numbers on what kind of U-factors you'll need to hit your PassiveHouse goals in that much colder and longer winter US zone-6/7 climate than your current zone 4 location. Philly's total annual heating degree days runs about 4500 to Millinocket's is about 8700 HDD/annum- even warm south-coastal Portland's climate average about 7500 HDD/annum.  Getting to PassiveHouse energy-use levels with SIPs might be affordable in Philadephia, but it could be a deal-breaker in central ME. 

Most high-R houses built in climate zones 6 & 7 use either Larsen trusses or double studwall approaches to wall assemblies for cost reasons, and it's not clear if there has ever been a PassiveHouse being built in that climate using a SIP approach, outside of the GoLogic's polyurethane-SIP built house outside of Belfast ME.  Given the extreme more than 1000x CO2 global warming potential of the HFC245fa used for blowing high-density polyurethane, I'm personally not a big fan of polyurethane SIPs at any R-value, let alone high-R.  EPS is blown with pentane at ~7x CO2 GWP, and is a far more benign material for use in high-R assemblies as far as foams go, but still nowhere near as low-impact as cellulose or rock-wool. If SIP it must be, please use an EPS-core product, despite the thicker wall.

Personally I'd favor grouted vs. ungrouted CMU, even if it meets the structural capacity if hollow. Grouting improves the air-tightness figure and adds to the thermal mass.  Insulating primarily on the exterior with Type-II EPS (1.5lbs density) is probably the right way to go, but fattening it out with a rock-wool insulated 2x4 studwall on the interior side would still get some of the thermal mass benefit of the wall.

Dana1, thanks for all of that information.

I can see a lot of room for error if I build with CMUs. Frost heave not being prevented is the scariest part.

What do you think of these? It basically makes a grid, instead of a solid wall, of concrete to build upon. I have my doubts; as all the examples are for southern climates. They never mentioned frost; but I thought I'd hit you with 'em, if you would, just to get your reaction. Just looking for cheapest/best solution that I can make the difference up in raw effort. Again--I'm only looking at the best BASEMENT technology, here.

http://apexblock.com/

Thanks again.

The Apex product has been discussed on this forum previously.

With the ASTM C518 results listed as "Results pending" in the spec, it's hard to say if you'll be able to meet your thermal performance goals without adding some rigid insulation on the exterior &/or interior finish wall.

They have an advantage over a mortared CMU by using expanding foam as glue/sealant rather than mortar between the blocks. Typical EPS-bead loaded poured concrete comes in at about R1.5-R2 per inch of thickness- not sure where it'll come in for them, after the thermal bridging of the concrete after the pour. A fly-by-caption on their video claims R35 at a 70F delta-T after the concrete is poured, which seems dubious in the extreme for a 10" thick EPS aggregate wall even WITHOUT the thermally bridging concrete.

That is at-best a dynamic-mass loaded performance number of the type bandied about by other ICF vendors, which needs some interpretation to fully assess for a particular site or climate. It might hit the high teens or even R20 steady-state under ASTM C518 test conditions- hopefully they'll be able to provide real test numbers, but I'm not holding my breath.  Analyzing the thermal bridging at the bond-beams and lintels etc might be tough without better characerization information.

Having both vertical & horizontal rebar means it'll be a stronger wall against frost-heave issues than a standard CMU wall in basement applications.

In general I like the look of the system, especially if they are in-fact primarily using scrap EPS as alleged in their marketing, and their practice of recycling their own cut scrap block from projects.  It looks quicker/stronger/cheaper than SCIP technolgy for above grade applications too, and just as easy to finish with stucco/hard-plaster. More complete information on the heating/cooling thermal performance would be useful.

Thanks again, Dana.

Why is the use of glue/sealant an advantage over mortar? Water resistance?

I was actually surprised to hear you think that you think they'll stand better against frost than CMUs. Come to think of it, now---that's the weakness of CMUs, isn't it--- You can't horizontally rebar it!!

What is/are SCIP? Structural Concrete insulated Panels? Another word for ICFs?

Then would come the issue of how to dam out the water/frost/mud from just oozing right through the limited resistance in the EPS component. Concrete-anchor steel sheets to the outside, or something?

I appreciate the time you take here to answer...

SCIP is basically a slab o' EPS with wire-reinforced shot-crete on both sides of it.  It makes better use of the thermal mass than ICF since there is no insulation between the interior side concrete and the conditioned space. The slabs go up quickly, but they are fairly customized, not as LEGO-blockable flexible as the Apex or ICF approach, and it's more labor & equipment intensive to apply shot-crete against the EPS and heavy-wire mesh than pouring more fluid slurries of concrete into forms.

Just about any standard exterior foundation waterproofing goop should stick pretty well to EPS aggregate CMU. The blocks are probably nearly waterproof to liquid water, and not nearly as wicking as the poured concrete, but fairly vapor permeable, with some wicking. I'm sure the manufacturer's guides spell out what can/can't be used for below grade waterproofing. 

The expanding foam joint sealer/glue is far more waterproof and air tight than any standard CMU or mortar, and it's typically R5-R8/inch of thickness, compared to R0.012 for typical mortar mixes.  Since EPS-crete block is at least R1.5/inch, a standard mortar mix would be a fairly severe thermal bridge, whereas the expanding foam joint sealer is MORE insulating than the blocks it's sealing/gluing.

I agree with Dana1 that SCIPs have traditionally been more labor and equipment intensive than most other technologies.  But now there is hope for the small, inexperienced contractor since the entry barrier has been lowered with less expensive equipment that operates at a lower pressure than gunite or shotcrete guns.  The equipment and SCIP panels from Gulf Concrete Technology are more user friendly and requires less training for the nozzleman.  Lower pressure guns result in less rebound which saves labor and materials.

No, I do not work for GCT but I do have to give them credit for moving the technology forward and keeping the cost reasonable.  I have found them to be very receptive to suggestions on how to add to their product line to meet unique requirements.

Posted By Pokletu on 28 Feb 2014 02:24 PM
Thanks again, Dana.

Why is the use of glue/sealant an advantage over mortar? Water resistance?

I was actually surprised to hear you think that you think they'll stand better against frost than CMUs. Come to think of it, now---that's the weakness of CMUs, isn't it--- You can't horizontally rebar it!!

What is/are SCIP? Structural Concrete insulated Panels? Another word for ICFs?

Then would come the issue of how to dam out the water/frost/mud from just oozing right through the limited resistance in the EPS component. Concrete-anchor steel sheets to the outside, or something?

I appreciate the time you take here to answer...

you can horizontally rebar CMU's with a KO block , its called a bond beam and does not need to be at the top of a wall

With CMUs, you can also use block ladder mesh or block truss mesh in the block joints for horizontal reinforcement.  I used the truss mesh for my garage foundation block walls that were >6' high on one side .

Thanks, Arkie6.

The truss mesh looks like it could make CMUs viable for my limited experience/resources. Since it's only in the grout, though: if I messed up the grout mix ratio, or something, wouldn't a flex in the wall just blow the grout apart, just passing around the wire?

Also: What's the weaker link: The CMUs themselves, or the grout?

Thanks again, guys...

Mortar for blocks is pretty hard to mess up. Generally, masonry sand is mixed with Type S cement in a 3:1 ratio for block walls - 3 parts sand to 1 part cement. The 28 day strength of this mortar is ~2000 psi which equals or exceeds the strength of most lightweight blocks (~1900 psi).

Another option with a CMU block wall is filling the cores with perlite insulation to increase the R value of the wall. You can fill 1 vertical block core every 24" (and at each corner and adjacent to each opening) with rebar and cement for strength with a bond beam at the top. Prior to installing the bond beam blocks, you can fill the block cores that will not have cement & rebar fill with perlite to increase the wall R value.

http://www.perlite.org/library-perl...lation.pdf

Okay guys, They are not cinder blocks, I don't know if anyone makes or uses cinder blocks anymore but you are not talking about them you are talking about CMUs or at least concrete blocks. And they aren't layers they are courses. And while we are at it, it's not Styrofoam it is EPS, Styrofoam is not even accurate, Dow not uses the name more on XPS than EPS.
For foundations CMUs are ridiculous for a foundation, lifting those damn heavy things up and why, to give them any tensile strength we have to core (cores are the big holes in them) fill them with rebar.

Take a breath.

Why aren't they cinder blocks any more?

I understand that Styrofoam is a brand name now, since Dow copyrighted it.

Most of us must be physically stronger than you; because the weight of a 'cinder block' is not all that bad.

The whole purpose of the thread is to measure it's viability for a foundation. You're not contributing anything but emotion with words like ridiculous for its use. I came here to be educated, not chastised. Maybe it IS a bad idea to use them for a foundation; but at least provide intelligent reasons.

As for your filling the cores-- Any ICF is filled, right? and doesn't any ICF application use rebar, too?

If your entry here is to be helpful, in some way; could ya turn it down?

a Canadian term because of the cinder fly ash content, and actually some US block may have a little fly ash in the mix as well as concrete does for workability. But predominantly the mix is cement, fravel and sand ............thus conrete blocks

Actually cinder blocks were made with cinders to make a light weight concrete. Not fly ash.

Pok, I did explain why CMUs are ridiculious in an easy to follow way without personal insult. When you have lifted as many CMUs as I have then we can talk about weight vs strength. But get your terminology straight so people know what you are talking about.
ICFs are not core filled. Core filling CMUs creates a non consistant column of concrete, somewhat trianglar. Like a chain it is only as strong as its weakest point. In terms of tensile strength it is hard to compare CMUs to a poured wall.

By definition: Those that use cinders (fly ash or bottom ash) are called cinder blocks in Canada, the US and New Zealand, breeze blocks (breeze is a synonym of ash)[1] in the UK and New Zealand, hollow blocks in the Philippines and are also known as besser blocks or bricks in Australia. Clinker blocks use clinker as aggregate. In non-technical usage, the terms cinder block and breeze block are often generalized to cover all of these varieties.