Table R702.1(1) thicknesses and the R703.7.5 curing schedule
The IRC does something for stucco that it does for almost nothing else: it sets a minimum duration. Three coat work cannot legally be finished in under nine days from the scratch coat, and no crew size shortens it.
Stucco takeoff
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Thicknesses are read from IRC Table R702.1(1) and coat counts from R703.7.2, as printed in the 2018 Seattle Residential Code. Bag coverage is your product's figure, scaled to the thickness the code requires for your base.
Specification summary
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Result
The minimum programme R703.7.5 sets
Worked example
A 40 ft by 28 ft two-storey house, wire lath over wood sheathing, on earth, with bags covering 25 sq ft at 3/8 in.
The area comes off the wall, minus what the weep screed takes. 2,448 sq ft gross, less 45 sq ft below the 4 in clearance R703.7.2.1 requires above earth, plus 229 for two gables, less 222 for openings: 2,409 sq ft.
The base sets the thickness, and wire lath is the thick end. Table R702.1(1) gives 7/8 in exterior over wire lath. A bag covering 25 sq ft at 3/8 in covers only 11 sq ft at 7/8, so the coverage figure on the bag is not the coverage on your wall.
That is 248 bags. Now put the same house on masonry instead. Table R702.1(1) drops to 1/2 in minimum and R703.7.2 drops to two coats, and the same 2,409 sq ft takes 142 bags. Same wall, same finish, 75% more material on lath.
And the programme changes with it. Three coats over lath is 48 hours to the brown coat and then seven days to the finish, so nine days minimum. Two coats over masonry is seven.
The barrier is doubled and nobody counts it. Over wood sheathing R703.7.3 wants two independent layers, each a separate continuous plane, so 2,409 sq ft of wall needs 4,819 sq ft of barrier.
The bag count is the easy half. The nine days is the half that decides whether the job fits the week you booked for it, and it is the half no stucco page prints.
The formula
Coverage does not survive a change of thickness, and that is the whole of the material arithmetic:
coveragewall = coveragebag × tbag / tcode
coveragebag
the square feet the bag claims, which is quoted at a thickness
tbag
that thickness, printed on the bag and routinely ignored
tcode
what Table R702.1(1) requires for YOUR base, which is not what the bag assumed
A bag quoted at 3/8 in covers 43% of that at 7/8 in. Every stucco calculator that takes the bag's square footage at face value is out by that ratio, and the ratio depends on a table most of them never open.
What the code prints, and what it hands to ASTM
R703.7 requires compliance with ASTM C926 for the plaster and ASTM C1063 for the lath. Neither is free to read, so neither can be quoted here. That is a real limit on this page and it is worth stating plainly rather than paraphrasing documents nobody can check.
What the IRC prints itself is quotable, and it is the part that changes quantities. Table R702.1(1) for thickness, R703.7.2 for coat counts, R703.7.2.1 for the weep screed, R703.7.3 for the barrier and R703.7.5 for the schedule. All of that is on this page verbatim.
What lives in ASTM and is therefore absent here: mix proportions, lath spacing against the framing, and control joint layout. Control joints in particular are the commonest cause of cracked stucco and this page will not guess at a spacing for them.
Read from Seattle's adopted code, which prints IRC Chapter 7 in full, because codes.iccsafe.org returns HTTP 403 to any automated request. Stucco is amended locally more than most chapters, because a render that works in Arizona behaves differently in a wet climate.
Prices for exterior wall finishes
The published figures for exterior wall finishes are on the siding calculator, with the byline, the publication date and the caveats that go with them. They are not repeated here, because the same table on two pages is worth less than one table you can find.
The thickness is set by what is behind it, and it nearly doubles
Ask how thick stucco is and you will be told three quarters of an inch. Table R702.1(1) does not have one answer, it has a column of them, and they are set by the base rather than by the finish.
Table R702.1(1), cement plaster, finished thickness from the face of lath, masonry or concrete
Half an inch over masonry against seven eighths over wire lath is 75% more material on the same wall, and the difference is decided before anybody picks a finish.
Two rows in that table are maxima rather than minima, and they are the concrete ones. Everywhere else the code is telling you the least you may apply. Over monolithic concrete it is telling you the most, because thick plaster on a smooth impervious substrate has nothing to key into and comes off in sheets. Read the third column before using the second.
Two coats or three is a different job, not a thinner one
Plaster shall be not less than three coats where applied over metal lath or wire lath and shall be not less than two coats where applied over masonry, concrete, pressure-preservative-treated wood or decay-resistant wood.
The split is the same one as the thickness: lath gets three coats, solid substrates get two. Scratch, brown and finish over lath; scratch and finish over masonry, concrete or treated wood.
The reason is what the first coat is for. Over lath there is nothing behind the plaster but wire and air, so the scratch coat has to be pushed through the lath and form keys on the far side of it. That coat is structural to the assembly and it is why the lath fastening in R703.7.1 is specified as tightly as it is:
Lath and lath attachments shall be of corrosion-resistant materials. Expanded metal or woven wire lath shall be attached with 1-1/2-inch-long (38 mm), 11-gage nails having a 7/16-inch (11.1 mm) head, or 7/8-inch-long (22.2 mm), 16-gage staples, spaced not more than 6 inches (152 mm) or as otherwise approved.
Fasteners at not more than 6 inches, of corrosion-resistant material. Over masonry none of that applies, because the wall itself is the key.
The code puts a minimum duration on the job
This is the part no stucco cost page has. R703.7.5 does not describe a material or a thickness. It describes a calendar.
The finish coat for two-coat cement plaster shall not be applied sooner than seven days after application of the first coat. For three-coat cement plaster, the second coat shall not be applied sooner than 48 hours after application of the first coat. The finish coat for three-coat cement plaster shall not be applied sooner than seven days after application of the second coat.
On three-coat work that is 9 days minimum from the scratch coat to the earliest legal finish coat. Forty-eight hours to the brown coat, then seven days before the finish. On two-coat work it is 7 days.
Those are floors, not estimates. They do not shorten with a bigger crew, a warmer week or a faster product, because what is happening in between is the plaster gaining strength and doing its shrinking before the finish goes over the top of it. A finish coat applied onto a brown coat that is still moving is a finish coat that will craze.
And R703.7.4 adds an obligation running the other way:
Each coat shall be kept in a moist condition for at least 48 hours prior to application of the next coat.
Each coat kept moist for at least 48 hours. So the wall is not merely waiting between coats, somebody is wetting it. That is labour on days when nothing visible is happening, and it is the line most commonly missing from a stucco quote.
Which is why a stucco schedule is not a stucco area. A single wall and a whole house take the same nine days if the crew can do the area in one pass. Doubling the house does not double the programme, and halving it does not halve it.
Where the stucco stops, and what has to be behind it
A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic weep screed, with a minimum vertical attachment flange of 3-1/2 inches (89 mm), shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C926. The weep screed shall be placed not less than 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas.
Not less than 4 inches above earth or 2 inches above paved areas. That is a hard stop, it comes off the bottom of the wall you are covering, and on a sloping site it is a different height at each end.
The screed is doing two jobs at once. It terminates the render, and it lets water that has got behind the stucco drain back out. Run the stucco to the ground and there is no exit, so the wall behind it holds water at the exact height where the framing meets the foundation.
The barrier behind it matters just as much, and R703.7.3 is unusually specific about how:
Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based sheathing, shall include a water-resistive, vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper. The individual layers shall be installed independently such that each layer provides a separate continuous plane.
Two layers over wood-based sheathing, installed independently. Not one heavier layer, and not two layers stapled up together. Each has to be a separate continuous plane, because the outer one is sacrificial: wet stucco bonds to whatever it is against, and the sacrificial layer is what lets the inner one stay a drainage plane instead of becoming part of the render.
Getting that wrong is invisible on the day and is the reason a wall rots ten years later with no crack anywhere in the stucco.
Where these figures came from
Read 2026-09-09. 2018 Seattle Residential Code, Chapter 7 Wall Covering, Seattle Department of Construction and Inspections. Prints IRC Chapter 7 in full, including Table R702.1(1) plaster thicknesses and Sections R703.7 through R703.7.5. Used because codes.iccsafe.org returns HTTP 403 to any automated request.
The code hands most of the detail to ASTM. R703.7 requires compliance with ASTM C926 for the plaster and ASTM C1063 for the lath, and neither is free to read. So what is quotable here is the part the IRC prints itself: thicknesses, coat counts, the curing schedule, the weep screed and the barrier. The mix proportions, the lath spacing against framing and the control joint layout all live in C926 and C1063, and this page will not paraphrase documents it cannot quote.
Your jurisdiction may have amended any of it, and stucco is amended more than most chapters because it behaves so differently in a wet climate from a dry one.
Frequently asked questions
How thick should stucco be?
It depends on what is behind it, and the range is nearly double. Table R702.1(1) gives 7/8 in as the exterior minimum over wire lath and over gypsum sheathing, 5/8 over expanded metal lath, and 1/2 in minimum over masonry. Over monolithic concrete it prints 7/8 as a MAXIMUM rather than a minimum, which is the opposite reading of the same column.
How many coats of stucco do I need?
R703.7.2: not less than three over metal or wire lath, not less than two over masonry, concrete, or pressure-preservative-treated or decay-resistant wood. The split is the same as the thickness split, and for the same reason: over lath the first coat has to push through and form keys behind the wire, which is work a solid wall does for you.
How long does stucco take to cure between coats?
The code sets minimums. R703.7.5: on three-coat work the second coat may not be applied sooner than 48 hours after the first, and the finish not sooner than seven days after the second. On two-coat work the finish is not sooner than seven days after the first. So three-coat stucco is nine days minimum from scratch to finish, and R703.7.4 requires each coat be kept moist for at least 48 hours during that.
Can a bigger crew finish stucco faster?
Not below those minimums. More people cover more area per pass, but the waits between coats are the plaster gaining strength and doing its shrinking, and they do not scale with labour. A one-wall job and a whole house take the same nine days if the crew can cover the area in one pass each time.
How much stucco do I need per bag?
Less than the bag says, usually. Bag coverage is quoted at a thickness, and if that thickness is not the one your base requires the figure does not transfer. A bag covering 25 sq ft at 3/8 in covers about 11 sq ft at the 7/8 in the code wants over wire lath.
How far above the ground does stucco stop?
Not less than 4 inches above earth, or 2 inches above paved areas, per R703.7.2.1. The weep screed sits at that line and lets water that has got behind the render drain back out. Running stucco to the ground gives that water nowhere to go, at exactly the height where the framing meets the foundation.
Do I need two layers of building paper under stucco?
Over wood-based sheathing, yes. R703.7.3 requires a barrier at least equivalent to two layers of Grade D paper, installed independently so each is a separate continuous plane. The outer layer is effectively sacrificial: wet stucco bonds to what it is against, and without it the drainage plane becomes part of the render.
Check these numbers yourself
2018 Seattle Residential Code, Chapter 7 Wall CoveringSeattle Department of Construction and Inspections. Read 2026-09-09. Prints IRC Chapter 7 in full, including Table R702.1(1) plaster thicknesses and Sections R703.7 through R703.7.5. Used because codes.iccsafe.org returns HTTP 403 to any automated request.
How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-09. Codes are amended locally; confirm against the edition your jurisdiction enforces.
The code hands most of stucco to ASTM C926 and C1063, and neither is free to read. So mix proportions, lath spacing against the framing and control joint layout are not on this page, and control joints in particular are the commonest cause of cracked render. What is here is what the IRC prints itself: thicknesses, coat counts, the weep screed, the barrier and the curing schedule. Your jurisdiction amends this chapter more often than most.