I am considering an ICF foundation as opposed to a cinder block or poured foundation wall. It will be a crawl space only, 5' from the bottom of the I joist to the floor and sealed/conditioned crawl space, not vented to the outside. Is it economical and practical to use ICF's simply for the foundation wall of a crawl space? Thank you. Phil

Maybe a dumb question but does the ICF foam have to be covered for fire protection in the crawl space?

Yes, and no. Depends on how it's used, what code you have to comply with, and if it's been tested as per below. Here's some paragraphs from the 2006 IRC. I don't know if any ICFs meet the requirements in Section 314.6. 1/2" gypsum may be the least expensive of all the alternatives even though it's more than is required in Section 314.5.4.

R314.4 Thermal barrier. Unless otherwise allowed in Section
R314.5 or Section R314.6, foam plastic shall be separated from
the interior of a building by an approved thermal barrier of minimum
0.5 inch (12.7 mm) gypsum wallboard or an approved
finish material equivalent to a thermal barrier material that will
limit the average temperature rise of the unexposed surface to
no more than 250°F (139°C) after 15 minutes of fire exposure
complying with the ASTM E 119 standard time temperature
curve. The thermal barrier shall be installed in such a manner
that it will remain in place for 15 minutes based on NFPA 286
with the acceptance criteria of Section R315.4, FM 4880, UL
1040 or UL 1715.

R314.5.4 Crawl spaces. The thermal barrier specified in
Section R314.4 is not required where crawlspace access is
required by Section R408.3 and where entry is made only
for service of utilities and the foam plastic insulation is protected
against ignition using one of the following ignition
barrier materials:
1. 1.5-inch-thick (38 mm) mineral fiber insulation;
2. 0.25-inch-thick (6.4 mm) wood structural panels;
3. 0.375-inch (9.5 mm) particleboard;
4. 0.25-inch (6.4 mm) hardboard;
5. 0.375-inch (9.5 mm) gypsum board; or
6. Corrosion-resistant steel having a base metal thickness
of 0.016 inch (0.41 mm).
The above ignition barrier is not required where the foam
plastic insulation has been tested in accordance with Section
R314.6.

R314.6 Specific approval. Foam plastic not meeting the
requirements of Sections R314.3 through R314.5 shall be specifically
approved on the basis of one of the following
approved tests: NFPA 286 with the acceptance criteria of Section
R315.4, FM4880,UL1040 orUL1715, or fire tests related
to actual end-use configurations. The specific approval shall be
based on the actual end use configuration and shall be performed
on the finished foam plastic assembly in the maximum
thickness intended for use. Assemblies tested shall include
seams, joints and other typical details used in the installation of
the assembly and shall be tested in the manner intended for use.

I used 1/2" exterior sheetrock on my crawl space wall because I put it on before I put down the floor sheathing and to withstand possible rains until the house was covered.

pduck,

since you are already 5' into the crawl space I would consider going all the way and add another 3' to a total of 8'. This way you have the option later on to expand into a "basement". The extra 3' will give you more bang for your buck than the 5' alone. I am not aware of your water table or your frost line. Your water table might be an issue in going down further than what you wanted to. It is definetly something to think about.