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Floor-Framing & Subfloor Details for Ceramic or Stone Tile Flooring
- How to frame and install subfloor to support ceramic tile, stone, marble, granite, and similar finish floor materials
- Floor Deflection Problems in Tile Floors Lacking Stiffness
- Subflooring Requirements for Tile Floors
- Two-Layer Subflooring System for Ceramic Tile Floors
- Floor Substrates for Ceramic Tile: Concrete, Cement Backerboard, Plywood, Drywall, Plaster
- Plywood Underlayment Specifications for Tile for Floors or Countertops: plywood type, fasteners, isolation membrane, etc.
- Questions & answers aboutfloor preparation for tile installation: framing, subflooring, underlayments, stiffness specifications or allowable deflection, and how to stiffen a floor that needs that improvement.
- References
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Floor framing for ceramic tile installations: this article discusses floor framing and subfloor recommendations for use under ceramic tile, stone, granite, marble, and similar floors. We discuss the stiffness of floor framing needed to avoid cracks or loosening of ceramic tile, stone, slate, and similar flooring and we describe alternative methods of floor preparation for tiling. We address the floor framing and subflooring details for each of these tile types. Also see flooring basics at Floor Designs: Kitchen & Bathroom and see Floor Tile, Ceramic for K & B.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Recommended Floor Framing under Tile to Avoid Cracks
 This article series discusses current best design practices for kitchens and bathrooms, including layout, clearances, work space, and accessible kitchen and bathroom layout, clearances, turning space, grab bars, controls, etc. We include advice on choosing and installing kitchen countertops, cabinets, and kitchen or bathroom flooring, sinks, and other plumbing fixtures and fixture controls such as faucets.
Tiles, stones, and grout joints crack easily from stresses
imposed by movement. For a successful installation, the
structure underneath must be very stiff.
On walls, 16-inch
on-center framing with 2x4s or steel studs is usually
adequate. Floors must be level and subject to minimal
deflection under uniform or point loads.
Our photo (above left) illustrates an exploration and repairs we made in the crawl area under a bathroom before installing ceramic tiles on the floor above.
Floor Deflection Problems in Tile Floors Lacking Stiffness
An insufficiently stiff floor will crack ceramic
or stone tiles. The Tile Council of America (TCA)
specifies a maximum deflection for floors of L/360 under
a 300-pound concentrated load. While building codes limit
deflection in living spaces to L/360 under uniform loads,
code-compliant floors may still have too much flexing
between joists under point loads. Many natural stone tiles
require stiffer conditions, ranging from L/480 to as stiff as
L/720.
Subflooring Requirements for Tile Floors
To meet TCA stiffness requirements, floor
framing should be no more than 16 inches on-center with
minimum 19/32
-inch plywood subflooring. Upgrading to 23/32-
inch plywood will stiffen the subfloor by almost 80% and
provide a more solid feeling floor. The subflooring should
be level to 1/8 inch in 10 feet. (TCA specs now permit 1/4 inch
in 10 feet, but this can be problematic for the large tiles
popular today.)
To avoid tile cracks caused by tight-fitting plywood
joints, it is best to use square-edged subflooring under tile
and leave an 1/8-inch gap between sheets (unless the setting
material specifications require tight joints). Lay the plywood
with its long dimension across the joists and use
solid blocking at all open joints.
Two-Layer Subflooring System for Ceramic Tile Floors
To meet the stiffness requirements
for natural stone floors may require two layers
of subflooring screwed and glued together, with the upper
layer serving as the underlayment.
Two layers of 19/32 inch
plywood glued and screwed together on 6-inch centers is
several times stiffer than a single layer (and over four
times as stiff as a single layer of 23/32-inch plywood). Offset
the upper layer so the joints do not line up with the joints
in the lower layer or the joists.
Also, screws in the upper
layer, which serves as underlayment for the tile, should
penetrate the subfloor only and not the joists. Use underlayment-
grade plywood or plywood rated C-C Plugged or
Plugged Crossbands, with a smooth face and no voids.
Floor Substrates for Ceramic Tile: Concrete, Cement Backerboard, Plywood, Drywall, Plaster
Ceramic tile can be installed over clean and sound concrete,
plywood, cement backerboard, drywall, or plaster.
Most substrates can be used with either organic mastic or
thinset mortar, but the installer should always check the
adhesive label for compatibility with the substrate.
Plywood Underlayment Specifications for Tile for Floors or Countertops
Because of its stiffness and
durability, exterior plywood makes an excellent substrate
for tile in relatively dry applications.
- Plywood type. The plywood should be free of internal
voids such as underlayment grade, CC-Plugged, or
Plugged Crossbands , and if tiling directly to plywood,
it should have a sanded face free of voids, surface
resin, or other surface defects.
While TCA specs allow
15/32-inch plywood underlayment over a 19/32 inch subfloor
in residential work, upgrading to 19/32 inch underlayment
is recommended for a trouble-free floor (Figure 6-32).
[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]
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- Plywood installation. Leave a 1/8 -inch gap between
sheets and make sure the edges of adjacent plywood
sheets are no more than 1/32
inch out of plane. Overall,
the surface should be level to 1/8 inch over 10 feet
(1/4 inch is allowed by the tile industry but is not
suitable for large tiles). Fasten with ring-shank nails
or screws at 6 inches on-center.
- Glue and screw. Where greater stiffness is required
in a floor, it is worth the effort to also glue the
underlayment to the subfloor and upgrade from
nails to screws.
- Isolation membrane. On large spans or where significant
movement is expected in the floor due to wide
moisture or temperature swings, a crack-isolation
membrane is recommended as a precaution against
cracking. Membranes, if sealed at seams, can also protect
the plywood from moisture that seeps through the
tile system. This is required in wet applications and
recommended in applications subject to occasional
wetting, such as bathroom floors.
- Countertops. Plywood also works well as a tile substrate
on walls and countertops not subject to regular
wetting (Figure 6-33). In applications subject to high
humidity or regular wetting, cement backerboard or
glass-mat gypsum are better choices.
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[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]
Kitchen and Bath Product Manufacturers, Sources, Associations
Ceramic Tile-Setting Material Manufacturer List
Bonsal American
www.bonsal.com
Setting compounds, grouts, preformed shower pans, curbs,
and niches. Also, distributor of backerboards, isolation
membranes, and other tile-setting products
Color Caulk, div. of Roanoke Companies Group
www.colorcaulk.com
Color-matched caulking
Custom Building Products
www.custombuildingproducts.com
Elastomeric and liquid-applied membranes, self-leveling
underlayments, setting compounds, and grouts
Laticrete International
www.laticrete.com
Trowel-on membranes, self-leveling underlayments, setting
compounds, grouts, and sealants
Noble Company
www.noblecompany.com
CPE sheet membranes, trowel-on membranes, clamping
ring drains, and preformed slopes, niches, and curbs
Mapei
www.mapei.com
Trowel-on and sheet membranes, self-leveling underlayments,
setting compounds, grouts, and color-matched
sanded caulks
Ceramic Tile Backerboard Producers
Custom Building Products
www.custombuildingproducts.com
Wonderboard cement backerboard, Easyboard cement and
polystyrene lightweight backerboard, and Rhinoboard
fiber-cement backerboard
Georgia-Pacific Gypsum
www.gp.com/build
Denshield gypboard backer with glass-matt facing
James Hardie Building Products
www.jameshardie.com
Fiber-cement backerboard
National Gypsum
www.nationalgypsum.com
Permabase lightweight cement and polystyrene
backerboard
Schluter Systems
www.schluter.com
Kerdi tile membrane goes directly over drywall or other
substrates
T. Clear Corp./Fin Pan Inc.
www.finpan.com
Util-A-Crete lightweight concrete backerboard
U.S. Gypsum
www.usg.com
Durock cement backerboard
W. R. Bonsal
www.bonsal.com
Extruded polystyrene backerboard with fiberglassreinforced
cement facing
-- Adapted with permission from Best Practices Guide to Residential Construction.
Frequently Asked Questions (FAQs)
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- "The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
- "Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
- Access Ramp building codes:
- UBC 1003.3.4.3
- BOCA 1016.3
- ADA 4.8.2
- IBC 1010.2
- Access Ramp Standards:
- ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
- ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
- ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
- America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
- American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
- ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
- 2005 ASHRAE Handbook : Fundamentals : Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
- 2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
- 1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
- Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
- How could homes be designed and built more efficiently?
- What kinds of construction and production techniques worked well and which did not?
- How did people use different kinds of spaces in their homes?
- What roles did community planning, zoning, and interior design play in how neighborhoods worked
- The Circular Staircase, Mary Roberts Rinehart
- Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
- "Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
- "Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
- "Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
- "Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
- Gypsum Construction Guide, National Gypsum Corporation
- Gypsum
Construction Handbook [purchase at Amazon.com] H17, Technical
Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
- Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and
- What Style Is It?: A Guide to American Architecture, Rev., John C. Poppeliers, S. Allen Chambers, Wiley; Rev Sub edition (October 6, 2003), ISBN-10: 0471250368, ISBN-13: 978-0471250364
- ...
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