ICF Crawlspace Insulation
Hi All,
I’m building a small (900 sf) house in zone 5, eastern Oregon. The plans call for an ICF foundation forming a crawlspace approx 24″ high, with 6 mil vapor barrier (or thicker) covering the dirt floor, lapped and taped up the sides of the ICF foundation. The crawlspace will be sealed and conditioned.
I’m trying to figure out if I need to include any insulation between the floor joists, or if the ambient temperature in the ICF crawlspace will be high enough to keep the floors from feeling cold, and creating an energy penalty. Should I add rigid insulation below the vapor barrier? Will the ICF foundation keep the crawlspace as warm as a traditional basement?
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
If you actually install the ductwork to condition the crawl space to more or less the same temperature the floor will not be cold and insulating the floor would be a waste of time and materials.
Walta
Im trying to determine if a 15 minute rating (gyp board) is required in a conditioned / enclosed crawl space. Did you end up putting a fire resistant layer over your vapor barrier?
Ignition barrier minimum or full thermal barrier is absolutely required on the rigid foam. Anyone saying otherwise is trying to get around the code required way.
Two areas require it and it's not a recommendation, it's required;
-Every single manufacturer lists ASTM E 84 smoke and flame spread. No rigid foam meets the E84 of 1/2 drywall. You have to meet the install instructions of a product to pass code,
-All IRC Residential code required/s the minimum ignition barrier in an inaccessible crawl space. Your enclosed rigid foam requires thermal barrier (min 1/2 drywall with stud assembly, mineral wool, structural plywood, hardboard) But...all have to be installed as an assembly (ie studded or built to manufactures listing). You can't simply strap drywall to rigid. Drywall is only a thermal barrier when installed in an assembly--on studs. Rockwool 80 can be installed directly to rigid foam at 1.5" min with fastener schedule because it was tested this way.
Just know one thing can be Class 1 fire rated, but that doesn't mean anything as a flame or smoke protector. Cement board or bubble wrap insulation are Class 1. They cannot be used as a fire thermal barrier. All about assembly. They both will not burn in 15 minutes, but it will transfer heat so quickly and so hot that it will burn the products behind it. Like they don't even exist as a fire/smoke protector.
Your crawl space vapor barrier is only considered at ASTM E1745: is it a flexible/punctureless vapor barrier? That's it. Code is agnostic to the VB being a fire hazard.
Hello,
Building in zone 5 with an ICF (Insulated Concrete Forms) foundation for a crawlspace is a great choice for energy efficiency and durability. Since you're considering a sealed and conditioned crawlspace, here are some considerations regarding insulation and maintaining comfortable floor temperatures:
Insulation Between Floor Joists: Even with a conditioned crawlspace, insulating between the floor joists can further reduce heat loss, especially during colder months. This can help keep the floors warm and comfortable, which is particularly important in living spaces. Fiberglass batts or spray foam insulation are common choices for this application, with spray foam offering the added benefit of air sealing.
Crawlspace Ambient Temperature: An ICF foundation will indeed help maintain a more stable temperature in the crawlspace compared to traditional foundations due to its high insulation value. However, the effectiveness in keeping the floors warm will also depend on how well the crawlspace is sealed and conditioned. If the crawlspace is properly conditioned, the need for additional floor insulation may be reduced but not entirely negated, especially in colder climates.
Rigid Insulation Below the Vapor Barrier: Adding rigid insulation on the exterior of the ICF walls down to the footings or under the slab (if applicable) is a good practice in cold climates to further reduce thermal bridging and enhance the thermal envelope. However, placing rigid insulation below the vapor barrier inside the crawlspace might not be necessary if the crawlspace is sealed and conditioned. The primary insulation benefit comes from the ICF walls and any insulation between the floor joists.
Considerations for a Sealed and Conditioned Crawlspace:
Ensure the vapor barrier is well-sealed and taped to prevent moisture intrusion.
Consider adding a dehumidifier or integrating the crawlspace into the home's HVAC system to manage humidity and temperature effectively.
Evaluate local building codes and best practices for insulation requirements in sealed crawlspaces. Building codes may have specific requirements for insulation R-values in your climate zone.
In conclusion, while the ICF foundation will contribute to a warmer crawlspace environment, insulating between the floor joists is still recommended to ensure maximum comfort and energy efficiency. It's also advisable to consult with a local energy auditor or building professional familiar with ICF construction and local conditions in eastern Oregon to tailor the insulation strategy to your specific needs and climate zone.