It is going to be much cheaper and conducive to having an unfinished basement to go with poured wall and attach Thermax foamboard insulation to the inside.

You will save the cost and inconvenience of finishing the basement when you may not be ready to finish the basement with respect to electrical and a drywall fire barrier.

Having the forms stripped will allow you to verify the pour and make sure the walls were properly vibrated.

Also keeps the cost of finishing the outer exposed ICF section out of the equation including the transition from exterior siding to a thicker surface underneath the siding. (you can undersize the foundation to accommodate some of the difference, most poured wall companies will probably give you the finger with that plan, and inspectors can differ on allowable overhang of a mudsill onto non structural foam). For example, say you are building a 10'x10' house with 2" foam on the outside foundation wall. 10' wide is framing, plus 1/2" sheathing plus siding of typically 3/4" means with a 10' wide foundation there will be 3/4" of foam sticking out past the bottom of your siding (2"-1/2"-3/4"=3/4") You could ask for a 9'8"x9'8" foundation to put the outside of the foam in the same plane as typical construction, however my inspector for example, will only allow the mudsill, which you need to be 10' for your 10' floor framing, to overhang off structural bearing (concrete) by half the thickness of the mudsill. So for a 9'8" foundation wall, I would need 3 plies of mudsill to get an ok on the 2" overhang. You could also ask for a 9'10 1/2" foundation wall to take advantage of your allowable overhang of 3/4" per side and at least have the foam flush with the bottom of the siding. Poured wall contractors can and will do this, but they are not exactly finish carpenters and you start to take 3/4" off every dimension in a typical not simple square house and it becomes ridiculous. So we simplified things and go with interior basement foam, and everything is reasonable.

Thermax is fire rated to be left exposed, put up whatever thickness of EPS foam board you want against the interior wall and clad over it with 1/2" of Thermax, you will want to do this because of the cost of Thermax.

Posted By FBBP on 01 Nov 2014 10:56 AM

Posted By arkie6 on 31 Oct 2014 11:50 PM

Posted By blacksunshine6973 on 31 Oct 2014 09:43 AM

Given the deep soil temperature in central Florida is approximately 72F to 75F, you don't really need any insulation on your basement walls if the top of the walls are at or below grade level.  If you have a portion of your basement walls exposed above grade level, you could insulate just that portion with a couple inches thickness of borate treated EPS foam.  A poured concrete wall would likely save you some money since with the ICF wall you would be paying for a lot of insulation that you don't really need.

Arkie - I wonder if there would be some significant advantage in using ICF as it might prevent condensation during times when the basement walls would be the coolest surface in the house?

Condensation occurs when the surface temperature is lower than the dew point of the air.  A wall temperature of 72F-75F is approximately the same temperature as the conditioned air temperature in most homes in the south, so no condensation will occur at that temperature unless the humidity level is approaching 100%.  Even if the indoor air temperature was allowed to rise to 80F, it would take a humidity level of over 77% to equal a dew point of 72F, which would be unlikely and infrequent in my opinion.

Posted By greentree on 02 Nov 2014 07:13 PM
It is going to be much cheaper and conducive to having an unfinished basement to go with poured wall and attach Thermax foamboard insulation to the inside.

If he was going to insulate the walls, it would cost much less to put the insulation on the outside of the poured wall.  Borate treated EPS could be used at ~1/4 the cost of Thermax.  Plus, foam insulation on the outside of the concrete wall would provide some protection for the waterproofing during backfill.

Arkie6, I disagree. Its true if your buying full 2" sheets of Thermax, not true if you're cladding over eps with 1/2" Thermax.
You have to pay to clad that exterior foam, and it becomes an ongoing maintenance item.

Posted By greentree on 03 Nov 2014 08:03 AM
Arkie6, I disagree. Its true if your buying full 2" sheets of Thermax, not true if you're cladding over eps with 1/2" Thermax.
You have to pay to clad that exterior foam, and it becomes an ongoing maintenance item.

My response was to address the basement proposed by blacksunshine6973.  Assuming this is a below grade basement, there would be no need to provide a clad on the exterior foam other than maybe the top foot or two above grade - for the below grade exterior foam just backfill and be done with it.  For any exposed exterior EPS foam above grade, just parge it with a low or no maintenance cementitious coating.

Cause this looks good..

Thanks all for the knowledge here! These are starting to get very technical and I am about to force my husband to start reading them! Another question we had was with the ICF - there must be gaps or seams between the foam blocks. Has anyone had issues with rodents, bugs or snakes getting into them?

There shouldn't be any sizable gaps in the ICF. If there are, concrete will ooze into the gap and fill it pretty much. On our build, there might be some gaps big enough for a few bugs, but they have nowhere to go; there's solid concrete in there. Also, the foam must be covered in some way, inside and out. On the inside, drywall is attached directly to the foam, so no gaps there. Outside, I put the siding over a drainage plane, with insect screening top and bottom. Below grade, the foam is protected by peel and stick membrane. Very, very few places for a bug to get in, and nothing big enough for a rodent or snake.