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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Foam pipe sleeves come in fixed lengths sized to the pipe's outside diameter. Enter your run and this counts sleeves, fittings and cost.
With these inputs:
| Result | Value |
|---|---|
| Sleeve length to buy | 66 ft |
| 6 ft sleeves required | 11 pieces |
| Extra for fittings | 9 ft |
| R-value | R-3 |
| Tape / zip ties | 23 pieces |
| Material cost | $74 |
Sleeve length = pipe run × (1 + waste %) · Sleeves = length ÷ 6 ft per piece · Fitting allowance = elbows and tees × 0.75 ft
Hot water lines from the heater out (fastest payback), then any pipe running through an unheated crawlspace, garage or attic where freezing is possible.
It slows freezing dramatically but won't prevent it in a sustained deep freeze with no water movement. In very cold spots pair sleeves with heat tape.
Hot water lines first, especially the first few metres out of the heater, because that is where standby loss is greatest and where insulation pays back fastest. Cold lines in humid unconditioned space are worth doing for a different reason: they sweat, and the condensation drips onto whatever is below.
It slows freezing; it does not prevent it. Insulation reduces the rate at which a pipe loses heat, so a pipe with no flow and no heat source in sustained sub-freezing conditions will still freeze eventually. Where freezing is a genuine risk, heat trace cable under the insulation is the measure that actually prevents it.
It varies with pipe diameter and the temperature difference, and codes give minimums for hot water lines by pipe size. Thicker is not always better in tight spaces — sleeves that cannot close properly around a pipe leave a gap along their length, and a poorly closed thick sleeve underperforms a well-fitted thin one.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.