Our patented interlayment system will prevent a SlateTec slate roof from leaking even if a slate is missing. This is because the SlateTec system uses a traditional style head-lap with its interlayment. The slate on a SlateTec roof has a 4’’ overlap, and the interlayment is weaved into every course, resulting in multiple layers of protection above and below each piece of slate. Since the slate is 12’’ long and the interlayment is 18’’, the interlayment has three layers everywhere the slate overlaps. This means that if a piece of slate cracks or falls out of place, our interlayment system will continue to shed water over the course below and won’t penetrate the nails underneath either. What this comes down to is a SlateTec lightweight natural slate roof weighs 40% less than a traditional slate roof, has the same aesthetics of a traditional slate roof installation, and is a watertight roof even if a slate is missing.