What is the minimum overlap required when laying bitumen felts?

A minimum overlap of 75 mm is required for longitudinal (side) joints and 100 mm for transverse (end) joints.

How should waterproofing be detailed at a parapet wall?

The felt must be taken up the parapet wall to a minimum height of 150 mm and securely tucked into a chase/groove cut into the masonry.

When is a six-course treatment preferred over a four-course treatment?

A six-course treatment, which includes an additional layer of felt and bitumen, is recommended for severe climatic conditions or areas with heavy rainfall.

IS 3384

: 1986

Code of practice for laying bitumen felt for roofing

CurrentSpecializedCode of PracticeArchitectural · Waterproofing and Damp Proofing

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This standard outlines the code of practice for preparing roof surfaces and laying bitumen felts for waterproofing. It specifies the methods for various multi-course treatments (e.g., four-course, six-course) based on climatic conditions, roof slopes, and base materials to ensure effective and durable moisture protection.

Provides recommendations for proper methods of laying bitumen felt for waterproofing of roofs.

Quick Reference Values

Minimum side (longitudinal) overlap75 mm

Minimum end (transverse) overlap100 mm

Minimum height for tucking felt into parapet wall groove150 mm

Recommended slope for flat roof drainage1 in 40 to 1 in 60

Groove depth in parapet for tucking feltMinimum 65 mm deep by 50 mm wide

Practical Notes

Blistering is a common defect; to prevent it, ensure the roof surface is bone-dry and free from dust before applying the bitumen primer.

Always unroll the felt completely and let it rest flat before laying to relieve internal stresses and prevent subsequent wrinkling.

Special attention must be given to critical junctions like rainwater outlets, parapet walls, and expansion joints, as these are primary points of waterproofing failure.