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Roof Tile Calculator

R905.3.2 and R905.3.6, and the weight nobody checks

A roof that takes asphalt shingles does not automatically take tile. The minimum slope is higher, and the covering weighs three times as much, which is a question for the framing before it is a question for the roofer.

Roof tile takeoff

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Slope and fastener rules are quoted from IRC R905.3. Tile dimensions and laps are yours, measured, because ASTM C1167 and C1492 set them and neither is free to read.

Specification summary

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Every minimum in R905, on one axis

Prices for roof coverings and tear-off

The published figures for roof coverings and tear-off are on the roof replacement cost 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.

This site publishes no price of its own. Why, and what that means for these figures.

Worked example

A 40 ft by 28 ft roof at 5:12 in concrete tile, 17 by 13 in with a 3 in head lap and 2 in side lap.

  1. Tile needs 2 1/2:12, not the 2:12 asphalt needs. That half unit is the difference between a roof that takes shingles and one that takes tile, and it is the first thing to check because nothing else on the page matters if it fails.
  2. One tile covers 1.07 square feet, not the 1.53 it measures. The head lap and side lap take 14 by 11 in out of a 17 by 13 in tile, so 30.3% of every tile is lapped out of sight. You pay for all of it.
  3. 1,405 tiles at 0.94 per square foot with 10% waste, on 1,365 sq ft of roof.
  4. Then the number that should have come first. At 9.5 lb per square foot this covering weighs 12,968 lb, six and a half tons, against about 4,095 for asphalt shingles. Swapping shingles for tile adds nearly nine thousand pounds to a roof whose rafters were sized for the old covering.
  5. And between 2 1/2:12 and 4:12 the underlayment doubles. Same band as asphalt, different lower bound, and it is easy to miss because the two coverings do not share the same numbers.

The tile count is the easy part. The weight is the part that decides whether the job is a re-roof or a structural alteration, and it is not a question a calculator can close.

The formula

Tile is counted on exposure, which is the tile minus both laps:

tiles per sq ft = 144 / [(l − head lap) × (w − side lap)]
l, w
the tile's own length and width, measured, because the ASTM standards are not free
head lap
how far each course overlaps the one below, up the slope
side lap
how far each tile overlaps its neighbour across the slope

The lapped fraction is one minus the exposure over the face, and on ordinary profiles it is close to a third. That is not waste and it is not a mistake: the lap is what makes the roof watertight, and it is the reason tile coverage figures never look like tile dimensions.

Three things the code says about tile and one it does not

R905.3.2 sets the slope at 2 1/2:12, and requires double underlayment from there to 4:12. Both numbers differ from asphalt, which starts at 2:12 and doubles below 4:12, so the bands overlap but do not match and a page that reuses the asphalt figures is wrong at the bottom.

R905.3.6 sets the fastener. Corrosion resistant, not less than 11-gage with a 5/16 in head, penetrating the deck not less than 3/4 in or through it, whichever is less. Attaching wire not smaller than 0.083 in where it is used.

R905.3.4 and R905.3.5 set the material standards, ASTM C1167 for clay and C1492 for concrete. Neither is free to read, which is exactly why this page takes the tile dimensions off your tile rather than publishing a profile.

And the thing the code does not say here: how much it weighs. Tile weight is a manufacturer's figure and it varies from around 6 lb per square foot for lightweight concrete to well over 12 for some clay profiles. That is the single most consequential number on this page and it is not in Chapter 9, because it is a structural question that belongs in Chapter 3 and, past a certain point, with an engineer.

The weight is the decision, not the tile

Everything else on this page is arithmetic. This part is not, and it is the reason tile re-roofs get stopped.

Asphalt shingles are roughly 3 lb per square foot. Concrete tile is around 9 to 11 and clay can be more. On a modest 1,365 sq ft roof that is nine thousand extra pounds, spread over rafters that were sized for what was there before.

Which is a dead load increase, and dead load is what span tables are built on. A rafter that spans comfortably under 10 psf of dead load may not under 15. The framing does not know the roof changed; it just deflects more, and it does so slowly enough that nobody notices until the ridge line sags.

Some houses were built for tile and are fine. If the roof is coming off tile and going back to tile, the framing has already carried it for decades. The dangerous case is the shingle roof being upgraded, which is also the most common reason people search for a tile calculator.

This page prints the total and the comparison so the question gets asked. It cannot answer it: whether your rafters take another four tons is a structural check on your actual framing, and the rafter calculator will show you what the span tables assume before you make that call.

Battens, and why the deck may not be the deck

Tile is often not fastened to the sheathing at all. It sits on battens, and that changes several things a shingle takeoff never has to think about.

The battens are a material line nobody counts. One run per course across the whole roof, which on this example is roughly 100 courses of batten at 42 ft each. That is more linear footage of timber than most people expect and it is not in any tile count.

They also lift the tile off the underlayment, which is deliberate: it creates a drainage and drying gap, and on a tile roof the underlayment is doing more of the waterproofing than the tile is. Which is why the double underlayment band matters so much between 2 1/2:12 and 4:12.

And they can dam water if they run unbroken across the slope. Counter-battens or notched battens exist for that reason, and whether you need them is a manufacturer and climate question rather than a code one.

None of that is in R905.3, which is short. It is in the manufacturer's instructions, and on a tile roof those carry more of the detail than the code does.

Frequently asked questions

What is the minimum slope for a tile roof?
Two and a half units in twelve, per IRC R905.3.2, and double underlayment is required from there up to 4:12. That is a higher bar than asphalt shingles, which are permitted at 2:12, so a roof that takes shingles does not automatically take tile.
How many roof tiles do I need?
Count on exposure, not on the tile. Exposure is the tile length minus the head lap, times the width minus the side lap. A 17 by 13 in tile with a 3 in head lap and 2 in side lap covers 1.07 sq ft, so 0.94 tiles per square foot, which is 1,405 for a 1,365 sq ft roof with 10% waste.
How much of a roof tile is hidden?
About a third on ordinary profiles. On a 17 by 13 in tile with 3 and 2 in laps the exposed part is 14 by 11, so 30.3% of every tile is lapped out of sight. That is not waste: the lap is what makes the roof watertight.
How much does a tile roof weigh?
Enough to matter. Concrete tile is commonly 9 to 11 lb per square foot and clay can be more, against about 3 for asphalt shingles. On a 1,365 sq ft roof that is nearly 13,000 lb against 4,000, so a shingle-to-tile change adds around four tons to framing sized for the old covering.
Do I need to strengthen my roof for tile?
Possibly, and it is a structural check rather than a calculator question. Dead load is what rafter span tables are built on, so a large increase can put an existing rafter outside the table it was sized from. If the roof is coming off tile and going back to tile the framing has already carried it; the risky case is upgrading from shingles.
What nails does the code require for roof tile?
R905.3.6: corrosion resistant, not less than 11-gage with a 5/16 in head, long enough to penetrate the deck not less than 3/4 in or through the deck, whichever is less. Attaching wire, where used, not smaller than 0.083 in.
Does tile need battens?
Often, and the manufacturer decides rather than the code. Battens lift the tile off the underlayment to create a drainage gap, which matters because on a tile roof the underlayment does more of the waterproofing than the tile does. They are also a material line that no tile count includes.

Check these numbers yourself

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.

Related calculators

The weight is the number that matters here and it is not this site's. Tile weight comes off the product and varies by a factor of two between profiles. Whether your framing carries it is a structural check on your actual rafters, not a calculation on this page. Tile dimensions and laps are yours because ASTM C1167 and C1492 set them and neither is free to read. Battens, underlayment type and high wind fixing are manufacturer requirements rather than code ones.