The best backer board for most tub and shower walls is Schluter KERDI-BOARD in 1/2 in: a waterproof foam panel that is light, cuts with a knife and seals at the seams with KERDI-BAND. Johns Manville GoBoard is the other strong foam choice, with a 1/2 in 3 x 5 ft sheet and its own sealant. If you prefer cement board, buy HardieBacker with HydroDefense, which James Hardie says meets the ANSI A118.10 waterproofness standard. Plain cement board like Hardie Backer 500 needs a membrane over it in a shower.
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Backer board goes up after the plumber sets the valve, tub and shower arm, and before the tile. The board you pick changes how deep the valve must sit, so choose it before rough-in. If you are still picking the valve and trim, see our shower system guide.
Quick comparison
| Check | Schluter KERDI-BOARD | Johns Manville GoBoard | HardieBacker with HydroDefense | Hardie Backer 500 |
|---|---|---|---|---|
| Core | Extruded polystyrene, reinforced faces | Polyisocyanurate, coated glass mat | Cement board | Cement board |
| Waterproof as installed | Yes, with KERDI-BAND seams | Yes, with sealed seams and screws | Maker says meets ANSI A118.10 | No, add a membrane |
| Common shower sheet | KB 12 1220 812 (1/2 in, 48 x 32 in) | 1/2 in, 3 x 5 ft | 3 x 5 ft | .42 in, 3 x 5 ft |
| Cut with | Utility knife | Utility knife | Score and snap | Score and snap |
| Choose it for | Full Schluter shower systems | Foam board with sealant seams | Cement board you can tile in a shower | Walls and backsplashes outside the wet zone |
| Exact purchase | Check the Schluter KERDI-BOARD kit (KBKIT) on Amazon → | Check GoBoard 1/2 in 3 x 5 ft (7-panel pack) on Amazon → | James Hardie dealer (no in-stock Amazon listing on Oct 14, 2026) | James Hardie dealer (no in-stock Amazon listing on Oct 14, 2026) |
BEST OVERALL · FOAM · 1/2 IN
Schluter KERDI-BOARD: light, waterproof, one system
Choose it when you want a waterproof wall with no cement dust and you may use a Schluter drain, niche or bench. Schluter describes KERDI-BOARD (maker page: www.schluter.com/schluter-us/en_US/Building-Panels/KERDI-BOARD-Panels/Schluter-KERDI-BOARD/p/KERDI_BOARD) as an extruded polystyrene panel with reinforcement on both faces and fleece for the thinset to grab. It is waterproof, thermally insulating, has no cement or fiberglass, and is for interior use only.
The KERDI-BOARD data sheet (maker page: assets.schluter.com/asset/570120892212/document_ssp6p29ns55s3ak2uaasbp467f/datasheet-kerdiboard.pdf) lists 1/2 in panels as KB 12 1220 812 (48 x 32 in), KB 12 1220 1625 (48 x 64 in) and KB 12 1220 2440 (48 x 96 in), and rates the 1/2 in board at 0.36 perms. Screws go in with KERDI-BOARD-ZT washers at no more than 12 in on center on walls and 6 in on ceilings. Screws must reach at least 3/4 in into wood studs or 3/8 in into metal studs.
Skip it if the wall is outside, or if you want the lowest cost per sheet. Cement board is cheaper and works when you add a membrane.
We found no in-stock new Amazon listing for single KB 12 1220 812 panels on October 14, 2026. The Amazon link below is a Schluter KERDI-BOARD kit sold as KBKIT, which the listing calls a bathtub and shower surround kit. Check what the kit includes against your wall area before you buy, or buy single panels from a tile dealer.
BEST FOAM ALTERNATIVE · 3 X 5 FT · SEALANT SEAMS
Johns Manville GoBoard: foam board with a simple seam system
Choose it when you want a foam board that seals at the joints with a gun-applied sealant instead of a fabric band. Johns Manville lists GoBoard (jm.com) with a polyisocyanurate core and a coated glass mat facer. It comes in 1/4 and 1/2 in 3 x 5 ft sheets, a 1/2 in 4 ft x 64 in sheet and 4 x 8 ft sheets up to 2 in thick. JM says the core passes ASTM D4068 and rates below 1.0 perm under ASTM E96, and that the board can meet ANSI A118.10.
Seal every joint and every fastener head with GoBoard Pro Sealant or GoBoard Sealant. On walls, JM calls for GoBoard fasteners at 8 in maximum spacing, within 1/2 in of supported edges, or GoBoard washers at 12 in. Framing must be no more than 16 in on center.
Skip it if your studs are 24 in on center. JM lists 16 in on center as the maximum.
The Amazon listing we link is a pack of seven 1/2 in 3 x 5 ft GoBoard panels, not a single sheet. GoBoard sealant is sold separately.
BEST CEMENT BOARD FOR SHOWERS · 3 X 5 FT
HardieBacker with HydroDefense: cement board rated for wet walls
Choose it when your tile setter wants cement board, but you also want the board itself to count as waterproofing. The James Hardie product sheet (form HB2501) (pdf.lowes.com) lists Hardie Backer with HydroDefense Technology for showers and tub surrounds and says it meets the ANSI A118.10 waterproofness standard. It also notes that some areas, such as shower pans, may need more waterproofing per local code.
James Hardie says to cut it by scoring and snapping. Cement board is heavy, so plan on two people for a ceiling or a tall wall.
Skip it if you are building a curbless or steam shower. Use a full system from one maker with a tested drain connection.
Buy HardieBacker with HydroDefense from a James Hardie dealer or home center; we found no in-stock new Amazon listing on October 14, 2026.
BEST BUDGET · .42 IN CEMENT BOARD
Hardie Backer 500: for walls next to the shower
Choose it when you are tiling a backsplash, a bathroom wall outside the shower or a tub deck you will waterproof separately. James Hardie’s backer board page (jameshardie.com) lists the .42 in Hardie Backer 500 as resisting moisture damage, and the product sheet lists it for walls and backsplashes. It is a fiber cement board.
Inside a shower, it is not the waterproof layer. Cover it with a liquid or sheet membrane listed to ANSI A118.10 and follow the membrane maker’s instructions at the tub flange and pipe holes.
Skip it for shower walls unless you will add a membrane.
Buy Hardie Backer 500 from a James Hardie dealer or home center; we found no in-stock new Amazon listing on October 14, 2026.
Foam vs cement vs fiber cement
- Foam boards (KERDI-BOARD, GoBoard, and others like wedi) are light, cut with a knife and are waterproof when the seams and screws are sealed. They cost more per sheet.
- Cement board is heavy, cheaper and familiar to every tile setter. Most standard cement boards need a membrane in the wet area. Cutting makes dust, so cut outside when you can.
- Fiber cement boards like Hardie Backer are a type of cement board with fibers in the mix. James Hardie says its boards score and snap with no special tools.
The board is only part of the system. The tub or shower pan, the seams, the screws and every pipe hole have to seal too. That is where most leaks start.
Thickness and stud spacing
| Board | Studs 16 in on center | Studs 24 in on center | Wall fastener spacing |
|---|---|---|---|
| Schluter KERDI-BOARD | 1/2 in minimum | 3/4 in minimum | 12 in max with ZT washers |
| Johns Manville GoBoard | Allowed (16 in max) | Not allowed | 8 in max with GoBoard fasteners, 12 in with washers |
| Hardie Backer | See James Hardie install guide | See James Hardie install guide | See James Hardie install guide |
Before you hang anything, check the studs with a straightedge. Foam boards follow the framing, so a bowed stud shows through as a bump in the tile. Plane or sister bad studs first.
Cutting for the valve and arm
This is where a plumber and a tile setter work together. Do it in this order:
- Check valve depth. Add the board, thinset and tile thickness. Compare it to the finished-wall range on the valve’s rough-in sheet or plaster guard. Fix the valve depth now, while the wall is open.
- Measure, do not guess. Measure from the tub rim or the last board edge to the center of the valve, the shower arm stub and the tub spout stub. Transfer those to the board.
- Cut holes small. Make each hole only as big as the trim plate or escutcheon will cover. A hole saw or an oscillating tool makes clean cuts in cement board. A knife works on foam.
- Seal every pipe. Use the board maker’s pipe and valve seals or its sealant. Schluter includes a 3/4 in pipe seal and a 4-1/2 in mixing valve seal in its KERDI-DRAIN kits. GoBoard uses its sealant.
- Leave the test cap on. If the valve has a test cap or plaster guard, keep it on until the tile is done.
Waterproofing the seams
Schluter says to cover KERDI-BOARD joints and corners in wet areas with KERDI-BAND, overlapped at least 2 in and set in unmodified thinset or a Schluter setting mortar. GoBoard joints and screw heads get GoBoard sealant, with optional seam fabric. Cement board needs a membrane over the whole wet area, lapped onto the tub flange the way the membrane maker says.
Where the board meets the tub, leave the gap the board maker calls for and seal it with a flexible sealant, not grout. Our silicone sealant guide covers the sealants plumbers use at tubs. If you are not sure the valve, tub drain or pan is right, call a licensed plumber before the board goes up.
Backer board FAQ
What is the best backer board for a shower?
For most tub and shower walls, a foam board such as Schluter KERDI-BOARD or Johns Manville GoBoard is the easiest to carry, cut and waterproof. Cement board such as HardieBacker is heavier but costs less per sheet and is the familiar choice for many tile setters. Either works when the seams, screws and pipe holes are sealed.
Is cement board waterproof?
Standard cement board resists water damage but is not a waterproof membrane. James Hardie sells HardieBacker with HydroDefense for showers and says it meets the ANSI A118.10 waterproofness standard. For other cement boards, add a waterproofing membrane over the board.
What thickness backer board do I need for shower walls?
Half inch is the common wall thickness. Schluter says KERDI-BOARD must be at least 1/2 inch on studs 16 inches on center and 3/4 inch on studs 24 inches on center. Check the maker’s chart for your board and stud spacing.
Can I use drywall or green board in a shower?
Not behind tile in the wet area. Use a board the maker lists for showers, and waterproof it the way the maker says. Drywall can go outside the splash zone.
How do I cut backer board around a shower valve?
Measure from a fixed point to the center of the valve and the arm, transfer it to the board and cut the holes only as big as the trim plate and escutcheon will cover. Then seal around each pipe with the board maker’s seal or sealant.
Does backer board thickness affect the shower valve?
Yes. The valve body has to sit at the right depth from the finished tile. Add the board, thinset and tile thickness and compare it to the depth range on the valve’s rough-in sheet before you hang board.
How we chose
This is a document-based comparison from a licensed plumber’s point of view. We looked at the boards plumbers see behind tub and shower tile and read each maker’s product page, data sheet or product sheet for core, sizes, waterproof claims and framing limits. We did not include boards whose current US data we could not read. Sources were read October 14, 2026; sellers and availability change. We do not publish prices or claim hands-on testing. More about our selection method and Plumbing Picks.
Primary sources
- Schluter KERDI-BOARD product page (maker page: www.schluter.com/schluter-us/en_US/Building-Panels/KERDI-BOARD-Panels/Schluter-KERDI-BOARD/p/KERDI_BOARD): core, thicknesses, interior use, seam treatment, fastener spacing, stud limits.
- Schluter KERDI-BOARD data sheet (PDF) (maker page: assets.schluter.com/asset/570120892212/document_ssp6p29ns55s3ak2uaasbp467f/datasheet-kerdiboard.pdf): item numbers and sizes, 0.36 perm rating, fastening and framing.
- Schluter KERDI-BOARD panels listing (maker page: www.schluter.com/schluter-us/en_US/Building-Panels/KERDI-BOARD-Panels/c/BP-KBP): panel family and accessories.
- Johns Manville GoBoard product page (jm.com): core and facer, sizes, ASTM D4068 and E96, ANSI A118.10, sealant seams, fastener spacing, 16 in framing.
- James Hardie backer board page (jameshardie.com): Hardie Backer .25 in and .42 in (500) boards.
- James Hardie Hardie Backer product sheet HB2501 (PDF, retailer copy) (pdf.lowes.com): HydroDefense for showers, ANSI A118.10, 3 x 5 ft sizes, score and snap.
- Schluter KERDI-DRAIN product table (PDF) (maker page: assets.schluter.com/asset/570120892212/document_nit795amql5tn0o7h1pl43s700/kerdidrain-products.pdf): pipe seal and mixing valve seal sizes.