Check compatibility of exterior insulation and drainage board over a waterproofing membrane

Steps

1. Confirm chemical compatibility between the insulation type (XPS, EPS, polyiso) and the specific membrane before specifying the assembly — some solvent-based or coal-tar-modified fluid-applied membranes can attack certain foam plastics; the membrane manufacturer's own compatibility list is the authoritative source, not the insulation manufacturer's general marketing claims.
2. Verify the drainage board/composite is on the membrane manufacturer's approved list, since drainage-board adhesives, coatings, or the plastic itself can also react with certain membrane chemistries — get written confirmation for any value-engineered substitution.
3. Confirm the manufacturer's assembly sequence (whether insulation goes directly against the membrane or a protection/slip sheet is required) to prevent both chemical attack and mechanical damage during backfill.
4. Verify the substitution doesn't compromise the below-grade insulation's own compressive-strength and moisture-absorption performance requirements, separate from the waterproofing-compatibility question.
5. If a full system/NDL warranty is desired, use only accessories explicitly on the membrane manufacturer's approved list — an unlisted but seemingly compatible product can void the warranty.