How do you calculate protected days of supply?

Divide inventory on hand by daily usage to get unprotected days, then adjust by the weather-delay safety factor. With 1,200 units, 85 units/day usage, and a 1.1 factor, protected supply is 12.83 days versus 14.12 unprotected.

What is the difference between protected and unprotected days?

Unprotected days — 14.12 in the example — is raw inventory divided by usage. Protected days, 12.83, discounts that for weather volatility so you plan against the coverage you can actually rely on when demand spikes.

What is a good weather-delay safety factor?

Factors of 1.1 to 1.3 are common; higher values reserve more buffer for volatile storm seasons. A 1.1 factor trims about 1.3 days off the 14.12-day raw figure — modest protection for mildly variable demand.

How many days of buffer should roofing stock cover?

Enough to outlast a typical weather delay plus resupply lead time in your region. If storms routinely stall trucks for a week, 12.83 protected days gives comfortable margin; in a longer-delay market you would raise inventory or the safety factor.

When should I reorder using this buffer?

Reorder before protected days of supply falls below your resupply lead time. If a truck takes 5 days, 12.83 protected days means you still have roughly a week of cushion above the reorder trigger.

Roofing, Siding & Exterior Building Products calculator

Weather delay inventory buffer Calculator

Weather Delay Inventory Buffer tells a roofing or siding operation how many days of supply it truly has protected against weather-driven demand swings and delivery delays. Distribution managers and job schedulers use it because exterior building product demand is weather-sensitive — a rain-out stalls installs and then a clear-weather rush drains stock fast, while storms can delay the trucks resupplying you. By applying a safety factor to raw days of supply, this calculator separates the protected coverage you can count on from the unprotected figure that ignores volatility. That distinction keeps crews supplied through a weather-disrupted week instead of stranded waiting on backorder.

What this calculator does

Estimate weather delay inventory buffer for roofing, siding and exterior building products using production-ready inputs so teams can plan replenishment and safety stock using actual usage and lead time.
Use it when weather delay inventory buffer in roofing, siding and exterior building products is being sized for a buffer or safety stock review.
It computes protected days of supply by dividing inventory by daily usage and adjusting for a weather-delay safety factor.

Formula used

Weather delay inventory buffer cycle stock = weather delay inventory buffer daily usage × weather delay inventory buffer lead time
Required weather delay inventory buffer inventory = cycle stock + weather delay inventory buffer safety stock

Inputs explained

Finished product inventory on hand:
Daily install/ship usage:
Weather-delay safety factor:

How to use the result

Use it when setting reorder points or checking stock resilience ahead of a volatile weather window or storm season.
It assumes steady average daily usage; a genuine storm-driven demand spike can outpace the buffer the safety factor implies.

Current U.S. benchmarks

U.S. housing starts run at 1,177k per year (Census, May 2026), down 8.7% from a year earlier, the demand driver for building products.

Common questions

How do you calculate protected days of supply? Divide inventory on hand by daily usage to get unprotected days, then adjust by the weather-delay safety factor. With 1,200 units, 85 units/day usage, and a 1.1 factor, protected supply is 12.83 days versus 14.12 unprotected.
What is the difference between protected and unprotected days? Unprotected days — 14.12 in the example — is raw inventory divided by usage. Protected days, 12.83, discounts that for weather volatility so you plan against the coverage you can actually rely on when demand spikes.
What is a good weather-delay safety factor? Factors of 1.1 to 1.3 are common; higher values reserve more buffer for volatile storm seasons. A 1.1 factor trims about 1.3 days off the 14.12-day raw figure — modest protection for mildly variable demand.
How many days of buffer should roofing stock cover? Enough to outlast a typical weather delay plus resupply lead time in your region. If storms routinely stall trucks for a week, 12.83 protected days gives comfortable margin; in a longer-delay market you would raise inventory or the safety factor.
When should I reorder using this buffer? Reorder before protected days of supply falls below your resupply lead time. If a truck takes 5 days, 12.83 protected days means you still have roughly a week of cushion above the reorder trigger.

Last reviewed 2026-05-12.