How to Pour a Concrete Driveway or Patio
Two of the four jobs on this page, footings and slabs inside a building, are written into the residential code in detail. The other two, patios and driveways, are named in it once, in a list of exemptions. That gap decides what an inspector can hold you to, which figures are yours to choose, and where the cost of a pour actually sits.
Two of these four words are in the code only as an exemption
Start with the absence, because it changes everything downstream. IRC Chapter 4 does not contain the word patio or the word driveway, and Chapter 5 uses them once, in the list of slabs exempt from the vapor retarder rule covered below. Neither chapter sets a minimum thickness for a patio or a driveway, and none of the other sources behind this page does either.
A footing is the opposite case. IRC Section R403.1.1 sizes it, three separate tables set the width and thickness, and the section is exact enough to disagree with. A slab on ground inside a building is prescribed too, by Section R506, which the slab guide reads line by line.
So the same afternoon of work is governed in detail or barely at all depending on which side of the house it is on, which is what tells you whether a figure is a requirement or a preference.
The code does have one thing to say about every pour here, and it is the mix rather than the geometry. IRC Table R402.2 sets porches, carport slabs, exterior steps and garage floor slabs at 2,500 psi where weathering potential is negligible, 3,000 psi where it is moderate and 3,500 psi where it is severe, and footnote d requires those last two columns to be air-entrained at 5 to 7 percent by volume. A driveway is not named in that row; a garage floor slab is, and it carries the same vehicles.
The plastic sheet you do not need, confirmed twice
IRC Section R506.2.3 requires a 6-mil polyethylene vapor retarder under a slab on ground, with joints lapped not less than 6 inches, and then exempts four cases. The third names this page directly: driveways, walks, patios and other flatwork not likely to be enclosed and heated at a later date.
NRMCA reaches the same place from the performance side. Its vapor retarder sheet argues for a retarder under every interior slab, recommending ASTM E1745 at no more than 0.1 perms and a minimum of 10 mils, and it still says plainly that vapor retarders are generally not necessary for exterior slabs on grade. A document that recommends a thicker sheet indoors still tells you a patio does not need one.
The same sheet describes the alternative layer for an interior slab placed without a retarder, and its terms are worth knowing. It asks for a minimum 4 inch layer of compactable, easy-to-trim material, names crusher-run graded from 1 1/2 inches down to dust as working well, and rules out concrete sand because it is easily displaced during construction.
It also says the granular layer should be dry when the concrete is placed, so that it works as a blotter and removes water from the fresh concrete. That sheet writes those terms for an interior slab rather than a patio, and it sets no base course for exterior flatwork.
A driveway is mostly edge
Lay 600 square feet out as a square and the perimeter is 98 feet. Lay the same 600 square feet as a 12 by 50 foot driveway and the perimeter is 124 feet, which in this site's arithmetic is 27 percent more edge for identical area. Everything that follows the perimeter follows that ratio: forming, isolation joints and a thickened edge if you pour one.
No code source behind this page requires a thickened edge, and none of the sources sets a width or depth for one. The volume table below uses an edge 12 inches wide and 8 inches deep purely as an example input, so the arithmetic shows how much concrete a perimeter strip adds; on a 4 inch slab that is 4 extra inches of depth over a 1 foot strip all the way round. Put your own section into the driveway calculator.
Volume and delivered cost, with the edge counted
This site's arithmetic, on example inputs this page chose rather than figures any source sets: a 4 inch slab plus a 12 inch by 8 inch thickened edge around the perimeter, and a 10 percent allowance rounded up to the quarter yard. Concrete is priced from HomeGuide's concrete price guide, written by Tom Grupa and published 6 January 2026: $119 to $147 per cubic yard delivered, with $53 per yard added under a full 10-yard load, and $1,169 to $1,444 for a full 10-yard truckload. That truckload total is HomeGuide's own figure and sits slightly below ten times its per-yard rate. Last price check: 2026-09-15.
| Pour | Area | Perimeter | Slab at 4 in, cu yd | Thickened edge adds | Ordered | Delivered |
|---|---|---|---|---|---|---|
| 10 x 12 ft patio | 120 sq ft | 44 ft | 1.48 | 0.54, up 37% | 2.25 | $387 to $450 |
| 14 x 20 ft patio | 280 sq ft | 68 ft | 3.46 | 0.84, up 24% | 4.75 | $817 to $950 |
| 20 x 20 ft patio | 400 sq ft | 80 ft | 4.94 | 0.99, up 20% | 6.75 | $1,161 to $1,350 |
| 10 x 40 ft drive strip | 400 sq ft | 100 ft | 4.94 | 1.23, up 25% | 7.00 | $1,204 to $1,400 |
| 20 x 30 ft driveway | 600 sq ft | 100 ft | 7.41 | 1.23, up 17% | 9.75 | $1,677 to $1,950 |
| 12 x 50 ft driveway | 600 sq ft | 124 ft | 7.41 | 1.53, up 21% | 10.00 | $1,169 to $1,444 |
Read the last two rows together, because they are the same 600 square feet of driveway. The one laid square orders 9.75 cubic yards and costs more than the one laid long at 10.00. A quarter of a yard is the difference between paying the short-load charge on every yard and paying none of it.
On these inputs the thickened edge is proportionally largest on the smallest pour: 37 percent on the 10 by 12 patio, against 21 percent on the 12 by 50 driveway.
The quarter yard that lowers the bill
The short-load charge is a step, not a slope, so somewhere below a full load the smaller order becomes the dearer one in absolute dollars. HomeGuide's concrete price guide puts that crossover in a place worth knowing before you round your order down. Last price check: 2026-09-15.
| Ordered | Cost as a short load | Against a full 10-yard truckload at $1,169 to $1,444 |
|---|---|---|
| 7.00 cu yd | $1,204 to $1,400 | Ranges overlap |
| 8.00 cu yd | $1,376 to $1,600 | Ranges overlap |
| 8.50 cu yd | $1,462 to $1,700 | Entirely above |
| 9.75 cu yd | $1,677 to $1,950 | Entirely above |
From 8.50 cubic yards upward, even the bottom of the short-load range is above the top of HomeGuide's full-truckload range. On the 9.75 yard row the gap is $508 at the bottom of the range and $506 at the top, for a quarter of a yard less concrete.
That is a pricing observation rather than a placing instruction, because concrete you have nowhere to put is its own problem. It is worth a spare path or a set of pier holes formed the same day, and it is worth knowing before somebody trims your order to save money.
Footings are prescribed, and there is more than one table
Here the code goes from silent to specific. R403.1.1 sets the minimum width, W, and thickness, T, of concrete footings by Tables R403.1(1) through R403.1(3), bases the footing width on the load-bearing value of the soil in Table R401.4.1, and says footing projections, P, shall be not less than 2 inches and shall not exceed the thickness of the footing.
Three things in that section are easy to miss. The first is that there are three tables, split by wall construction, and they do not agree.
| Wall construction | Table | Width x thickness | Against light frame |
|---|---|---|---|
| Light-frame construction | R403.1(1) | 16 x 6 in | Baseline |
| Light frame with brick veneer | R403.1(2) | 20 x 6 in | 25% wider |
| Cast-in-place concrete or fully grouted masonry | R403.1(3) | 29 x 9 in | 81% wider, 50% thicker |
Same house, same snow, same dirt. Pick the wrong table and the footing is wrong by a margin no allowance covers.
The second is footnote b. Every cell in all three tables is drawn for a 32-foot-wide house, and it instructs you to add or subtract 2 inches of width and 1 inch of thickness for every 2 feet of adjustment to the house width, never below 6 inches thick. A 40 foot house is four adjustments: 8 more inches of width and 4 more of thickness than the printed cell. The footnote is part of the table, not a suggestion.
The third is the projection rule, which tells you when the tables have run out. In this site's arithmetic, a 29 inch footing under an 8 inch foundation wall projects 10.5 inches each side against a printed thickness of 9 inches, so on that wall the cell already exceeds the limit set in the same section. On a thicker wall the projection shrinks and the cell holds; on an 8 inch wall the combination is a design rather than a table lookup.
Under all of it, R403.1 requires footings to bear on undisturbed natural soils or engineered fill, and Table R401.4.1 supplies the presumptive values, from 1,500 psf for clay to 12,000 psf for crystalline bedrock. Where the building official determines that soils below 1,500 psf are likely, footnote b to that table requires a soils investigation instead. Depth is separate again: R403.1.4 puts exterior footings not less than 12 inches below undisturbed ground, and R403.1.4.1 sends you to Table R301.2(1) for the frost line, which the jurisdiction fills in.
The order of the day, and the tools that are wrong
NRMCA's finishing sheet puts the whole argument in one instruction: complete all subgrade excavation and compaction, formwork, and placement of mesh, reinforcement or other embedments before concrete delivery, because delays after the concrete arrives reduce the final quality of the flatwork. Concrete starts on its own schedule and does not pause while you fix the base.
The rest of its placing guidance is short and specific enough to check yourself against:
- Compact the subgrade uniformly, avoid wet spots, and do not place concrete on a cold subgrade.
- Deposit concrete as near its final position as the chute, barrow, buggy or pump allows. Start at the far end, place each load against concrete already placed, and work back. On a slope, use a lower slump and work up the slope.
- Spread with a short-handled square-ended shovel or a come-along. Never use a garden rake or any tined tool to move concrete sideways, because it segregates the mix.
- Consolidate the edges by tamping along the form edges with a spade or a piece of wood.
- Strike off with a straightedge resting on the forms, tilted forward, drawn across with a slight sawing motion and a head of concrete kept ahead of it. No jitterbug or vibrating screed above a 3 inch slump, and do not overwork the surface.
Everything after strike-off belongs to the finishing guide, because the waiting is what decides whether the surface lasts.
Slope: one code figure, and only near the house
NRMCA requires the subgrade to be properly sloped for drainage and exterior slabs to be sloped to drain water with a texture that is not slippery when wet, and it sets no amount.
The code figure sits in IRC Section R401.3, which never uses the word driveway or patio. It requires the lot to be graded so the ground falls not fewer than 6 inches within the first 10 feet from the foundation walls. Where lot lines, walls or slopes prevent that, the exception requires drains or swales and adds that impervious surfaces within 10 feet of the building foundation shall be sloped not less than 2 percent away from the building. Two percent is about 1/4 inch per foot, in this site's arithmetic.
Past 10 feet from the house, none of the documents behind this page sets a fall for a patio or a driveway. If your inspection needs one there, it comes from your building department.
The hose is the only irreversible decision on the day
Everything else on this page can be fixed before the pour. Water cannot be taken back out.
NRMCA's sheet on jobsite water is the one to read before the truck arrives. ASTM C94 permits water to be added at the site only while the specified slump and the water-cementitious materials ratio are not exceeded. Past that point, added water delays setting, reduces strength, adversely affects durability and increases the potential for cracking, and if the purchaser asks for it anyway the purchaser owns the result.
The mechanics are worth having in your head, because they are countable:
- One gallon per cubic yard raises slump about 1 inch, which the sheet counts as roughly 10 lb of water per yard.
- No addition is permitted once more than about a quarter of a cubic yard has left the mixer.
- ASTM C94 requires 30 revolutions of the drum at mixing speed afterwards, and every gallon measured and recorded on the delivery ticket, which a representative of the purchaser should sign or initial.
On the 10 cubic yard driveway order above, this site's arithmetic on that rule of thumb makes one inch of extra slump 10 gallons, roughly 100 lb of water. The alternative, settled at a pre-pour conference rather than at the chute, is a water reducing admixture or a superplasticizer, which the sheet says usually will not alter concrete properties provided an excess amount is not used.
Joint spacing and curing duration are set out on the slab guide, and the surface operations, the waiting test and the defects that come from rushing them are on the finishing guide.
Run the numbers
- Concrete Driveway Calculator slab, thickened edge, apron and spoil
- Concrete Patio Calculator volume, base and excavated soil
- Concrete Footing Calculator pad size from load and soil bearing
- Foundation Calculator all three R403.1 tables with footnote b
- Concrete Calculator yards, bags and the R402.2 cell
- Gravel Calculator the base course, by the yard or the ton
Frequently asked questions
- How thick should a concrete driveway be?
- None of the sources behind this page sets a thickness. IRC Chapter 4 does not contain the word driveway, and Chapter 5 names driveways only to exempt them from the vapor retarder rule. What the code does set is the mix, through Table R402.2's row for porches, carport slabs, steps and garage floor slabs.
- Do I need plastic under a concrete patio?
- Not under the code and not under NRMCA guidance. IRC R506.2.3 requires a 6-mil vapor retarder under a slab on ground and then exempts driveways, walks, patios and other flatwork not likely to be enclosed and heated later. NRMCA's vapor retarder sheet says the same thing in its own words, that retarders are generally not necessary for exterior slabs on grade.
- How much concrete do I need for a 12x50 driveway?
- 7.41 cubic yards for the slab alone at 4 inches. With a thickened edge 12 inches wide and 8 inches deep around the 124 foot perimeter, used on this page as an example rather than a sourced size, it becomes 8.94, which is 10.00 cubic yards once a 10 percent allowance goes on and the order is rounded up to the quarter yard. That is this site's arithmetic.
- Is it cheaper to order less concrete?
- Not always. HomeGuide prices ready-mix at $119 to $147 per yard delivered, adds $53 per yard under a full 10-yard load, and gives $1,169 to $1,444 for a full 10-yard truckload. On this site's arithmetic, from 8.50 cubic yards upward the smaller order costs more in absolute dollars at both ends of the range, and at 9.75 yards the gap is just over $500. Last price check: 2026-09-15.
- What size footing does my house need?
- It depends which of the three IRC tables covers your wall construction, and they disagree. A two-story house over a crawl space on 1,500 psf soil at 20 psf snow is 16 by 6 inches in light frame, 20 by 6 with brick veneer and 29 by 9 in fully grouted masonry. Every cell also assumes a 32-foot-wide house, and footnote b adds 2 inches of width and 1 inch of thickness for every 2 feet over that.
- How deep do footings have to go?
- R403.1.4 puts exterior footings not less than 12 inches below undisturbed ground, and R403.1.4.1 requires frost protection, usually by going below the frost line in Table R301.2(1), which each jurisdiction fills in for itself. R403.1 also requires the footing to be supported on undisturbed natural soils or engineered fill.
- What slope should a patio or driveway have?
- The IRC sets one figure, in Section R401.3: where the lot cannot fall 6 inches within 10 feet of the foundation, impervious surfaces within 10 feet of the building foundation shall be sloped not less than 2 percent away from the building. Beyond that, NRMCA requires exterior slabs to be sloped to drain without giving an amount, and the figure comes from your building department.
- Can the driver add water to the truck?
- Only within the specified slump and water-cementitious materials ratio, which is what ASTM C94 permits. One gallon per cubic yard raises slump about an inch, all of it has to be measured and recorded on the delivery ticket, the drum needs 30 revolutions at mixing speed afterwards, and no water may go in once more than about a quarter yard has been discharged.
Check these numbers yourself
- 2018 Seattle Residential Code, Chapter 4 FoundationsSeattle Department of Construction and Inspections. Prints IRC Chapter 4 in full: Section R401.3 with the 2 percent slope for impervious surfaces within 10 feet of the foundation, Table R401.4.1 and footnote b, Table R402.2 and footnote d, Section R403.1.1 with the projection rule, Tables R403.1(1) through R403.1(3) with footnotes a and b, and Sections R403.1.4 and R403.1.4.1. The word driveway appears nowhere in it. Read 2026-09-16.
- 2015 Seattle Residential Code, Chapter 5 Floors, Section R506Seattle Department of Construction and Inspections, page 169. Source of R506.2.3, the 6-mil vapor retarder with 6 in laps, and of its third exception covering driveways, walks, patios and other flatwork not likely to be enclosed and heated later. Read 2026-09-16.
- NRMCA CIP 14, Finishing Concrete FlatworkNational Ready Mixed Concrete Association. Complete all subgrade work, formwork and embedments before concrete delivery; place from the far end working back; never move concrete with a garden rake or tined tool; no jitterbug or vibrating screed above a 3 in slump; exterior slabs sloped to drain with a non-slip texture, with no figure given. Read 2026-09-16.
- NRMCA CIP 26, Jobsite Addition of WaterNational Ready Mixed Concrete Association. ASTM C94 permits jobsite water only within the specified slump and water-cementitious ratio; 1 gallon per cubic yard raises slump about 1 inch; 30 revolutions at mixing speed after addition; no addition once about a quarter cubic yard has been discharged; water reducers or superplasticizers as the alternative. Read 2026-09-16.
- NRMCA CIP 29, Vapor Retarders Under Slabs on GradeNational Ready Mixed Concrete Association. Vapor retarders generally not necessary for exterior slabs on grade; ASTM E1745 at 0.1 perms or less and a minimum 10 mils where one is used; for an interior slab without a retarder, a granular blotter layer of at least 4 in of compactable easy-to-trim material, dry before placement, with concrete sand ruled out. Read 2026-09-16.
- HomeGuide, how much does concrete cost per yardWritten by Tom Grupa, published 6 January 2026. Ready-mix $119 to $147 per cubic yard delivered, plus $53 per yard added under a full 10-yard load; $1,169 to $1,444 for a full 10-yard truckload. Read 2026-09-15.
Figures here last checked against the source documents on 2026-09-16. Codes are amended locally; confirm against the edition your jurisdiction enforces.
Every guide on this site: Guides.