Installation Guide
WOOD — Floors, Interior - Ceramic or Porcelain Tile 5
19.2" (488 mm) o.c. joist spacing, single layer OSB 
or plywood subfloor
DH-W19-T-14
Areas of Application
 over any even and structurally sound OSB or 
plywood subfloor with 19.2" (488 mm) o.c. 
joist spacing
 interior dry or wet areas
Limitations
 minimum 2" x 2" (50 mm x 50 mm) tile
 for natural stone, see detail DH-W-S (page 6) 
and natural stone discussion (page 22)
Requirements
 maximum spacing of joists, I-joists, or floor 
trusses is 19.2" (488 mm) o.c.
 minimum subfloor thickness – 23/32",  
3/4" nom. (19 mm) tongue-and-groove with 
1/8" (3 mm) gap between sheets.
Substrate Preparation
 verify that subfloor panels are properly 
fastened to framing members.
 any leveling of the subfloor must be done 
prior to installing DITRA-HEAT.
Movement Joints
 DITRA-HEAT does not eliminate the need for 
movement joints, including perimeter joints, 
within the tiled surface. Movement joints 
must be installed in accordance with industry 
standards and norms; see page 11 of this 
Handbook, TCNA EJ171, and TTMAC 301 MJ. 
Setting and Grouting Materials
 latex portland cement (p.c.) mortar –  
ANSI A118.11
 unmodified thin-set mortar – ANSI A118.1
 grout – ANSI A118.3, A118.6, A118.7, A118.8
Setting and Grouting Specifications
 tile – ANSI A108.5
 grout – ANSI A108.6, A108.9, A108.10
Other Considerations
 tightly butted and/or tented plywood or OSB 
seams must be addressed prior to installing 
DITRA-HEAT.
 vapor barrier on crawl space floors according 
to regional building codes.
 where a waterproof floor is required, all  
DITRA-HEAT seams and floor/wall transitions 
must be sealed with KERDI-BAND using 
unmodified thin-set mortar; see page 10.
DH-W24-T-14
24" (610 mm) o.c. joist spacing, double layer OSB 
or plywood subfloor
Areas of Application
 over any even and structurally sound double 
layer OSB or plywood floor
 interior dry or wet areas
Limitations
 minimum 2" x 2" (50 mm x 50 mm) tile
Requirements
 maximum spacing of joists, I-joists, or floor 
trusses is 24" (610 mm) o.c.
 double layer wood floor consisting of:
•  minimum subfloor thickness – 23/32", 
3/4" nom. (19 mm) tongue-and-groove
• minimum underlayment thickness – 
11/32", 3/8" nom. (10 mm)
Substrate preparation
 verify that subfloor panels are properly 
fastened to framing members.
 underlayment – minimum 11/32", 3/8" nom. 
(10 mm)-thick Exposure 1, plugged-face 
plywood or OSB with 1/8" (3 mm) gap 
between sheets; see page 14 for 
underlayment installation guidelines.
 any leveling of the subfloor must be done 
prior to installing DITRA-HEAT.
Movement Joints
 DITRA-HEAT does not eliminate the need for 
movement joints, including perimeter joints, 
within the tiled surface. Movement joints must 
be installed in accordance with industry 
standards and norms; see page 11 of this 
Handbook, TCNA EJ171, and TTMAC 301 MJ. 
Setting and Grouting Materials
 latex portland cement (p.c.) mortar –  
ANSI A118.11
 unmodified thin-set mortar – ANSI A118.1
 grout – ANSI A118.3, A118.6, A118.7, A118.8
Setting and Grouting Specifications
 tile – ANSI A108.5
 grout – ANSI A108.6, A108.9, A108.10
Other Considerations
 tightly butted and/or tented plywood or OSB 
seams must be addressed prior to installing 
DITRA-HEAT.
 vapor barrier on crawl space floors according 
to regional building codes.
 where a waterproof floor is required, all  
DITRA-HEAT seams and floor/wall transitions 
must be sealed with KERDI-BAND using 
unmodified thin-set mortar; see page 10.
Ceramic or porcelain tile
Unmodified thin-set mortar
DITRA-HEAT 
uncoupling membrane 
and heating cables
Latex p.c. mortar
Double layer of plywood 
or OSB
I-joists or  
trusses
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Ceramic or porcelain tile
Unmodified thin-set mortar
DITRA-HEAT 
uncoupling membrane 
and heating cables
Latex p.c. mortar
Single layer of plywood 
or OSB
Joists, I-joists, or  
trusses










