Pour Foundation Footings
Foundation footings are the concrete base that distributes the weight of your entire addition to the soil below. Getting them right is critical—footings that are too small, improperly reinforced, or poured incorrectly can lead to settlement, cracking, and structural failure.
Quick Summary
Time needed
1-2 days
Cost
$3,000-$8,000
Professional help
Concrete contractor
Why This Step Matters
Footings transfer the entire weight of your addition—walls, roof, contents, snow loads, everything—to the ground. They must be sized correctly for your soil type, placed below the frost line, and reinforced with steel to prevent cracking. A footing failure can cost $50,000+ to repair and may require demolishing completed work.
Critical Inspection Point
The building inspector must approve your footing excavation and rebar placement BEFORE you pour concrete. Pouring without inspection approval may require you to demolish and redo the entire footing.
How to Pour Foundation Footings
Prepare the Gravel Base
After excavation is complete, place a 4-6 inch layer of compacted gravel at the bottom of the footing trench. This provides drainage and a stable base for the concrete.
Key specifications: Use 3/4" crushed stone or gravel. Compact it with a plate compactor or hand tamper until it's firm and level. The top of the gravel should be at the designed footing bottom elevation.
Install Rebar Reinforcement
Rebar (reinforcing bar) prevents concrete from cracking under tension. Typical residential footings require two horizontal #4 or #5 rebar running the length of the footing, positioned in the bottom third.
- Rebar size: #4 (1/2") or #5 (5/8") per engineering plans
- Clear cover: 3 inches from bottom and sides
- Lap splices: Minimum 24" overlap where bars meet
- Vertical dowels: Install for wall connection per plans
Pro tip: Use rebar chairs or dobies (concrete blocks) to hold rebar at the correct height. Never let rebar rest on the ground—it needs concrete coverage on all sides for corrosion protection.
Schedule the Footing Inspection
Before pouring any concrete, call your building department to schedule the footing inspection. The inspector will verify:
- • Trench dimensions match approved plans
- • Depth is below frost line
- • Rebar size, spacing, and placement
- • Proper clear cover on all sides
- • Clean trench (no loose soil or standing water)
Warning: Never pour concrete before the inspector signs off. Uninspected footings may need to be removed entirely, costing you thousands in concrete demolition and disposal.
Order and Pour the Concrete
Order ready-mix concrete from a local plant. For footings, you'll need 3000-4000 PSI concrete—higher strength is required in cold climates or for larger structures.
Calculating quantity: Measure footing length × width × depth in feet, divide by 27 to get cubic yards. Add 5-10% for waste and spillage.
- Concrete strength: Minimum 3000 PSI, 4000 PSI for cold climates
- Slump: 4-5 inches for easy placement in trenches
- Weather: Don't pour if temps below 40°F or above 90°F
Place and Consolidate the Concrete
Pour concrete directly into the trench, working from one end to the other. Use a vibrator or rod the concrete to remove air pockets and ensure it flows around the rebar.
- • Fill trench to within 1/2" of the top
- • Screed the top level with a 2×4
- • Insert vertical dowels while concrete is wet
- • Verify rebar didn't shift during pour
Cure the Concrete Properly
Concrete gains strength over time as it cures. Proper curing is essential to achieving full strength and preventing cracks.
Curing timeline: Footings reach about 70% strength in 7 days and full design strength in 28 days. You can typically begin building walls after 3-7 days depending on conditions.
- • Keep concrete moist for at least 7 days
- • Cover with plastic sheeting in hot/windy conditions
- • Use curing compound if you can't water regularly
- • Protect from freezing for first 48 hours minimum
Concrete Strength Guide
Concrete strength is measured in PSI (pounds per square inch). Here's when to use different strengths:
| Strength | Best For | Cost |
|---|---|---|
| 2500 PSI | Non-structural, light-duty | Lowest |
| 3000 PSI | Standard footings, mild climates | Standard |
| 4000 PSI | Cold climates, heavy loads | +10-15% |
| 5000+ PSI | Commercial, special applications | +20-30% |
Common Footing Mistakes to Avoid
Pouring on Disturbed Soil
If soil was previously excavated and backfilled, it won't support loads properly. Dig deeper to undisturbed soil or compact thoroughly.
Inadequate Frost Depth
Footings above the frost line will heave in winter, cracking walls and doors. Know your local frost depth (12" to 48"+).
Rebar Too Close to Surface
Rebar needs 3 inches of concrete cover to prevent corrosion. Use proper chairs and spacers to maintain coverage.
Adding Water to Concrete
Extra water makes concrete easier to pour but dramatically weakens it. Never add water—use proper slump from the plant.
Frequently Asked Questions
How wide and deep should my footings be?
Typical residential footings are 16-24 inches wide and 8-12 inches thick, extending below the local frost line (12-48 inches depending on region). Your structural engineer will specify exact dimensions based on soil conditions and building loads.
Do I need a concrete pump or can I pour directly from the truck?
If the truck can back up within 10-15 feet of the trench, you can use chutes. For longer distances or difficult access, you'll need a concrete pump ($300-$500 extra) or wheelbarrows (labor-intensive for large pours).
What if it rains right after I pour?
Light rain after the concrete has set (1-2 hours) actually helps curing. Heavy rain on fresh concrete can damage the surface and weaken the mix. Cover fresh concrete with plastic if rain is expected within 4-6 hours of pouring.
How long before I can build walls on the footings?
In warm weather (above 50°F), you can typically start forming walls after 3 days. In cold weather, wait at least 7 days. Your engineer may specify a longer wait for heavy loads. The concrete will continue gaining strength for 28 days.
Ready for the Next Step?
Once your footings have cured for at least 3-7 days and passed final inspection, you're ready to build the foundation walls that will support your addition's floor system.