Cold floors all winter long. An electricity bill that just keeps growing. And beneath the floors, pink fiberglass flapping from the joists like wet laundry. That’s what we see all too often in North Georgia.
Crawl space insulation makes the difference for the first two issues. Crawl space insulation gone wrong produces the third problem.
Here is your quick summary of crawl space insulation. It comes down to just one factor: is your crawl space vented or unvented? The vented crawl space uses crawl space insulation in the flooring, between the joists. The unvented crawl space uses wall insulation. That is the starting point; then everything becomes simple.
Should You Insulate Your Crawl Space?
For those who may be asking themselves the question, “Should I insulate my crawl space?” In a Georgia home, the answer is usually “yes,” though not immediately.
Insulation serves three main purposes:
- Warmer flooring: You’ll notice it before the thermostat does.
- Reduced load on HVAC equipment: The HVAC no longer has to battle the air beneath the home.
- Frozen pipes protection: Pipes close to outside walls won’t freeze on the rare freezing nights.
When to hold off: Should there be standing water in the crawl space, or the dirt remains wet days following rainfall, then insulation isn’t the immediate solution. Installing new insulation in a wet crawl space leads to wet insulation.
Address the water issue before installing insulation. Unclear how severe the water problem may be. Our 3-day rule for water in your crawl space helps you decide, and our guide to crawl space moisture covers the usual causes.
Crawl Space Floor Insulation vs Wall Insulation
This is a big decision, so start here. You pick one or the other. Not both.
Crawl Space Floor Insulation for Vented Crawl Spaces
Floor insulation in crawl spaces lies on the inside of the floor joists and below the subfloor. This is a feature of traditional houses in Georgia that have foundation vents.
The logic behind it is straightforward: the crawl space remains part of the outside, while the insulation protects the house from it.
However, there is a serious problem with this approach in Georgia: the summer heat and humidity come from the outside in through the vents, meet a cool floor thanks to the AC, turn to water, and lie on the insulation placed exactly at the site of condensation.
Crawl Space Wall Insulation for Sealed or Encapsulated Crawl Spaces
The crawl space wall insulation is installed inside the walls of the foundation. It is applied to situations where the vents are closed and the space is sealed, which is what happens in crawl space encapsulation.
This way, the crawl space becomes part of your house. You insulate around the space and not above it. You end up with your plumbing and ducts within the warm zone, and you insulate only the walls and rim joists and not the entire floor.
It works well in our humid climate, but it can work only in a fully sealed system. The wall insulation in a crawl space with vents is hardly effective. Can’t tell what type you have? Check out our page on encapsulated and sealed crawl spaces.
| Floor insulation | Wall insulation | |
|---|---|---|
| Where it goes | Between floor joists, under the subfloor | Inside of foundation walls and rim joists |
| Crawl space type | Vented (open foundation vents) | Sealed or encapsulated |
| Moisture risk | Higher. Summer humidity condenses right on it | Lower, as long as the space stays sealed and dry |
| Energy impact | Warmer floors, but ducts and pipes stay in the cold | Better overall. Ducts and pipes sit inside the insulated zone |
| Best fit | Dry vented crawl spaces with no ductwork below | Most humid Georgia crawl spaces, especially with ductwork |
Best Insulation for Crawl Spaces
The best insulation for crawl space use is the kind that does not care about water. In Georgia, that rules out a lot. Two materials do the job well. One usually does not.
Rigid Foam Insulation for Crawl Space Walls
Our preferred choice for crawl space walls is rigid foam board. This is hard foam insulation that is generally 1 to 2 inches thick and fastened with either screws or glue onto the foundation wall.
- This material does not absorb water.
- It will never sag.
- The thermal resistance (R-value) rating depends on the kind of board, but the range is about R-4 to R-6.5 per inch.
The use of rigid foam insulation for crawl spaces can also involve placing the material between joists in an open, vented crawl space if it fits well and all joints are properly sealed. This takes time but will last.
Note that, in general, foam boards require a fire barrier when used in crawl spaces unless the particular foam board itself is rated for exposed use.
Closed-Cell Spray Foam in a Crawl Space
Closed-cell spray foam goes on as a liquid and expands into hard foam that sticks to whatever it touches. On a spray foam crawl space job, it goes on the foundation walls, the rim joists, or the underside of the subfloor.
- It seals air leaks and insulates in one step
- It fills odd gaps around pipes and wires that boards cannot reach
- About R-6 to R-7 per inch, the highest of the three
- At the right thickness, it also slows water vapor
Make sure it is closed-cell, not open-cell. Open-cell foam is soft and spongy and holds water. Wrong pick for a Georgia crawl space.
Fiberglass Batts
Fiberglass is the pink or yellow insulation in most Georgia crawl spaces today, and it is the material we pull out the most. It works fine when it is dry. Under a humid house, it rarely stays dry. The next section explains why.
| Material | Moisture resistance | R-value per inch | Typical lifespan | Best location |
|---|---|---|---|---|
| Rigid foam board | High | R-4 to R-6.5 | Decades, if the space stays dry | Walls; tight-fit between joists in vented spaces |
| Closed-cell spray foam | High | R-6 to R-7 | Decades, if the space stays dry | Walls, rim joists, underside of subfloor |
| Fiberglass batts | Low | R-3 to R-4 | Can fail within a few years in a damp crawl space | Only dry vented crawl spaces. |
Why Fiberglass Insulation Falls Down in Georgia Crawl Spaces
Open the hatch on a vented crawl space in Gainesville or Woodstock in August, and you will often see the same thing. Batts hanging. A few lying on the dirt. The ones still up are dark on the bottom.
Here is what happens. Fiberglass is glass fibers with air between them. Air moves through it, and so does moisture. When humid summer air comes in through the vents and reaches the cool subfloor, it condenses, and the fiberglass soaks it up. Wet fiberglass gets heavy. The thin wire supports give out. Down it comes.
Wet insulation pressed against wood is a problem of its own. It holds moisture on the joists for weeks. That is how mold gets started, and then wood rot under your house.
Two local things make it worse:
- Long, sticky summers: A vented crawl space breathes in humid air all season.
- Red clay: Our clay holds water and drains slowly, so a bare dirt floor keeps giving off moisture long after the rain stops.
Fiberglass that fell once will fall again. Stapling the same batts back up does not fix anything.
How to Insulate a Crawl Space (Step by Step)
Here is how to insulate crawl space areas the right way. The order matters more than the material.
- Fix water and drainage first: Gutters, downspouts, grading, plumbing leaks. If water still gets in, no insulation will last.
- Remove old or wet insulation: Bag it and take it out. Fallen batts left on the dirt hold moisture and draw pests. If there is mold on the wood, deal with it before you cover anything.
- Get the ground cover in place: A crawl space vapor barrier on the dirt floor slows moisture coming up from the soil. In a sealed crawl space, the barrier and the wall insulation go in together, so plan them as one job.
- Install the insulation: Foam board or spray foam on the walls for a sealed space. Tight-fit foam board between the joists for a vented one.
- Leave a termite inspection gap: Georgia has heavy termite pressure. Keep about 3 inches open between the top of the wall insulation and the wood sill plate so an inspector can spot mud tubes. Check what your termite bond requires.
- Seal the rim joists and air gaps: The rim joist is the wood band sitting on top of the foundation wall, and it leaks more air than most people think. Seal it with spray foam or cut foam board sealed at the edges. Seal around pipes, wires, and the access door too.
Doing it yourself? Clearing out old insulation and sealing small gaps are fair DIY jobs. Spray foam and full wall systems are best left to a pro.
Signs Your Crawl Space Insulation Needs Replacing
You do not need to crawl under the house every month. But if you notice any of these, it is time to take a look at your crawl space insulation:
- Sagging or fallen bats: One fallen bat usually means the rest are wet too.
- Musty smell or visible mold: A musty smell upstairs after rain often starts with wet insulation below.
- Cold floors and rising energy bills: If nothing else changed in the house and the bill went up, the insulation may have stopped working.
- Dark, stained, or flattened insulation: Squashed insulation has lost most of its value.
Seeing more than one of these? Check how far things have gone with our guide, How Bad Is Your Crawl Space?
Crawl Space Insulation FAQs
Is spray foam safe in a crawl space?
That is correct, provided that it has been done right. Closed-cell spray foam remains stable once it has cured. During the application and the curing period, avoid any human or animal presence around the installation area.
The installer will provide the necessary re-entry period. Unless specified by the manufacturer, most crawlspace installations will need a fire-resistant covering for the foam.
Should crawl space insulation have a vapor barrier?
Because foam board and closed-cell spray foam are already resistant to water vapor, no additional layer is needed.
On the other hand, fiberglass does not block water vapor. The earth is different: every crawl space in Georgia should have a vapor barrier, regardless of what insulation is chosen.
Do you insulate a crawl space before or after encapsulation?
Neither, really. In a sealed crawl space, wall insulation is part of the encapsulation job. The crew fixes the water first, then installs the barrier, wall insulation, and rim joist sealing as one system.
What you should not do is add new insulation between the floor joists and encapsulate later, because that floor insulation usually comes out once the space is sealed. Encapsulated crawl spaces also need humidity control, which our crawl space dehumidifier post covers.
What R-value is recommended for a crawl space in Georgia?
The state of Georgia complies with the 2015 International Energy Conservation Code (IECC) as amended by Georgia. Crawlspace wall insulation for climate zone 3 (North Georgia, which includes Gainesville, Woodstock, and Atlanta) requires either R-13 in the wall cavities or R-5 continuous insulation (such as foam board).
Climate zone 4 is made up of the northern mountainous counties that will require either R-13 or R-10 continuous insulation. Floor insulation above a ventilated crawlspace requires an insulation rating of R-19.
Get a Free Crawl Space Inspection
Not sure if your crawl space is vented, sealed, wet, or just worn out? We will tell you. Tri-State Waterproofing has worked under homes across Gainesville, Woodstock, and North Georgia for over 20 years.
We check the insulation, the moisture, the wood, and the water source, then give you a written plan. Sometimes that plan is just “pull the wet batts and fix the downspout.”
Book a free inspection through our crawl space repair page or call (770) 869-7888.
