The foundation is one of the first big decisions on a new house and one of the hardest to change. It affects the construction budget, how the house handles your climate and soil, where pipes and ducts can run, and whether you get extra living or storage space below the main floor.
US builders have been moving steadily toward slabs. In 2024, 73% of new single-family homes started were built on slab foundations, 17% had full or partial basements and 9.2% had crawl spaces, according to NAHB analysis of Census data.[1] But the national split hides big regional differences, and the right choice for your lot may not be the most common one. This guide compares the three and explains what drives the cost of each.
Key takeaways
- Slabs were used on 73% of new single-family homes started in 2024, basements on 17% and crawl spaces on 9.2%.
- Foundations averaged $44,748, or 10.5% of construction cost, in the NAHB 2024 survey.
- Climate, frost depth, soil, slope, water table and flood rules usually decide the foundation before personal preference does.
- A basement costs more than a slab but can add finished or storage space at a lower cost per square foot than building out.
The three main foundation types
Slab-on-grade
A concrete slab poured directly on prepared ground, usually with thickened edges or footings around the perimeter. Plumbing drain lines are placed before the pour, so they end up under the concrete. It is usually the quickest and least expensive option on a flat lot in a mild climate.
Crawl space
Short foundation walls or piers raise the floor a couple of feet above the ground, leaving a space you can crawl into. Plumbing, ducts and wiring can run underneath and stay accessible. Crawl spaces need careful moisture control, whether vented or sealed and conditioned, depending on your climate and local code.
Basement
Full-height foundation walls below the house create a level that can be left unfinished for storage and mechanicals or finished as living space. A walk-out basement on a sloping lot has doors and windows at grade on one side. Basements need waterproofing and drainage, and they involve the most excavation.
| Slab | Crawl space | Basement | |
|---|---|---|---|
| Share of 2024 starts | 73% | 9.2% | 17% |
| Excavation | Least | Moderate | Most |
| Access to pipes and ducts | Limited (under concrete) | Good | Best |
| Extra usable space | None | Storage at best | Storage or living space |
| Main moisture concern | Vapor under slab, drainage around edges | Humidity in the crawl space | Water pressure on walls, drainage |
Where each type is used
The national numbers come from very different regional habits. In 2024, nearly all new single-family homes in the West South Central division (97.9%), the Pacific division (89.9%) and the South Atlantic division (85.7%) were built on slabs.[1] In colder northern divisions, where footings must reach below the frost line anyway, basements are much more common.
Slabs have also been gaining ground in the North. NAHB notes that their cost advantages led to increased use in some northern divisions after the pandemic, when rising material costs and supply problems pushed builders toward cheaper methods. The Mountain division has seen a gradual rebound in crawl spaces and now has the second-highest crawl space share.[1][2]
Where basements are built, they are large. The national average finished basement area in 2024 was 1,112 square feet, with the East North Central (1,119 sq ft) and Middle Atlantic (1,113 sq ft) divisions slightly above it and New England lower at 810 sq ft.[1]
What a foundation costs
In the NAHB 2024 Cost of Constructing a Home survey, the foundation stage averaged $44,748, or 10.5% of construction cost. Almost all of that, $43,002, was excavation, foundation, concrete, retaining walls and backfill.[3] That is an average across all foundation types, weighted toward slabs, so it is a starting point rather than a price for your house.
The factors that move the price most are:
- Footprint. Foundations are priced by the ground-floor area and perimeter, not the total floor area. A two-story house has a smaller foundation than a one-story house of the same size.
- Depth. Frost depth in your area sets how deep footings must go. In cold climates the extra depth makes a basement relatively less expensive to add, because you are already digging down.
- Soil. Expansive clay, fill or rock can require engineered footings, post-tensioned slabs, over-excavation or rock removal.
- Slope. Sloping lots may need stepped footings, taller walls or retaining walls, or they may suit a walk-out basement.
- Water. A high water table means more drainage and waterproofing, and may rule out a basement altogether.
- Finishing a basement. An unfinished basement and a finished one are very different budgets. Finishing adds framing, insulation, drywall, flooring, electrical, HVAC and often a bathroom and egress windows.
Get the foundation priced separately
Ask every builder to price the foundation as its own line, and ask for the alternatives if more than one type would work on your lot. In the calculator, enter the quote as a lump sum on the Foundations stage.
When a basement makes sense
A basement costs more than a slab under the same footprint, but compare it with the cost of the space it creates. Building the same square footage as an extra story or a larger footprint means more framing, roof, siding and windows. In cold climates with deep footings, the gap between a basement and a deep crawl space or frost wall can be smaller than people expect.
A basement tends to make sense when:
- You live in a cold climate where footings are deep anyway.
- The lot slopes enough for a walk-out with daylight on one side.
- You want storage, a mechanical room or future living space without a bigger footprint.
- The water table is low and the soil drains well.
- Local resale values reward basement space, which a local real estate agent can confirm.
- You may want a storm shelter or a protected space for mechanical equipment.
It is usually a poor fit on a high water table, in rock that is expensive to remove, or in a mapped flood zone. In zones A1-30, AE and AH, federal minimum rules require the lowest floor including the basement to be at or above the base flood level.[4] Our guide to building in a flood zone explains what that means.
Slabs and crawl spaces: trade-offs
Slabs are fast and economical and have no space under the floor for moisture or pests to build up. The main downside is access: drain lines are under concrete, so fixing or moving them later means cutting the slab. Plan bathroom and kitchen locations carefully, and consider running supply lines overhead where your code allows.
Crawl spaces keep the floor off the ground and keep plumbing and ducts accessible for repairs and changes. They can work well on gently sloping lots. Their weakness is moisture: a damp crawl space can cause mold, rot and energy loss. Ask your builder whether they will build a vented or sealed crawl space and how they will handle the ground vapor barrier, drainage and insulation.
Timing differs too. Concrete needs time to cure before framing loads it, and footings and foundation walls are usually inspected before backfill or before the slab is poured. A basement adds waterproofing, drainage board and a perimeter drain that must be in place and checked before the hole is backfilled. Ask your builder how many days each option adds to the schedule, because foundation delays push back every trade that follows.
Either way, good site drainage matters as much as the foundation type. Make sure the ground slopes away from the house, gutters discharge away from the foundation, and the final grade is checked after landscaping.
How to decide
- Start with the site. Get a topographic survey and, where needed, a soil report. Check the flood map. These may rule options in or out. See how to choose a building lot.
- Ask what local builders usually build. Regional norms reflect climate, code and the trades available, which affects price.
- Price the alternatives. Ask builders for the cost of each workable option, including drainage and waterproofing.
- Compare cost per usable square foot. For a basement, compare the extra cost against the space you gain, finished or not.
- Think long term. Consider access for repairs, future finishing plans and how the house will sell.
Foundation choices interact with framing and the number of stories. Our guides to framing costs and house size and cost per square foot explain how.
Plug your house size, land price and quotes into the free calculator. It uses the same NAHB 2024 averages as this guide.
Frequently asked questions
What is the most common foundation for new homes?
Slabs. In 2024, 73% of new single-family homes started were built on slab foundations, 17% had basements and 9.2% had crawl spaces.
How much does a foundation cost for a new house?
In the NAHB 2024 survey the foundation stage averaged $44,748, or 10.5% of construction cost. Your cost depends on the foundation type, footprint, soil, slope and frost depth.
Is a basement worth the extra cost?
Often in cold climates with deep frost lines, on sloping lots suited to a walk-out, or where you need storage or future living space. It is usually a poor fit on high water tables or in flood zones.
Is a crawl space better than a slab?
Neither is always better. Crawl spaces keep plumbing and ducts accessible and suit some sloping lots; slabs are usually cheaper and faster. Moisture control is the key issue with crawl spaces.
Sources
- NAHB Eye on Housing: Foundation Types in 2024: Slabs Continue to Rise, Crawl Spaces Decline Verified (third-party copy)
- NAHB Eye on Housing: Share of Homes Built on Slabs Surges to 72.4% Verified (third-party copy)
- NAHB: Cost of Constructing a Home 2024 Verified
- eCFR: 44 CFR 60.3, Flood plain management criteria for flood-prone areas Verified
Figures last checked October 18, 2026. National averages are a planning guide, not a quote. See our editorial policy and data sources.
