Tapered EPS comes in 1/8, 3/16 and 1/4 inch per foot. The Atlas tapered polyiso panels come in 1/8, 1/4 and 1/2 inch per foot.
Tapered Roof Insulation Systems
Slope-to-drain insulation, supplied to your plans
Tapered insulation gives a flat or low-slope roof the pitch it needs to move water to the drains. Source Mountain Supply supplies tapered EPS and tapered polyiso for new roofs and re-roofs, and we can quote from your roof plans.
Tapered EPS comes in slopes of 1/8, 3/16 or 1/4 inch per foot. Each piece is labeled to match the shop drawing, so the crew knows exactly where it goes. Need flat boards too? See our EPS roof insulation and polyiso roof insulation.
What You Get With Tapered Insulation
Water moves off the roof
Tapered pieces are laid out to carry water to the drains, so it does not pond on the membrane.
Labeled to the drawing
Each tapered EPS piece is labeled to match the shop drawing, which removes the guesswork about where it goes.
EPS or polyiso
Tapered EPS costs less and keeps a stable R-value. Tapered polyiso gives more R-value per inch. We price both so you can compare.
Tapered Insulation Specifications
Average R-values for tapered EPS at each slope, and the standard tapered polyiso panels, from the manufacturers' data sheets.
Tapered EPS: thickness and average R-value by distance from the drain
| Feet from drain | 1/8" per ft: thickness (in) | 1/8": avg R | 3/16" per ft: thickness (in) | 3/16": avg R | 1/4" per ft: thickness (in) | 1/4": avg R |
|---|---|---|---|---|---|---|
| 0 | 1 | 4.17 | 1 | 4.17 | 1 | 4.17 |
| 4 | 1.5 | 5.21 | 1.75 | 5.73 | 2 | 6.26 |
| 8 | 2 | 6.26 | 2.5 | 7.30 | 3 | 8.34 |
| 12 | 2.5 | 7.30 | 3.25 | 8.86 | 4 | 10.43 |
| 16 | 3 | 8.34 | 4 | 10.43 | 5 | 12.51 |
| 20 | 3.5 | 9.38 | 4.75 | 11.99 | 6 | 14.60 |
| 24 | 4 | 10.43 | 5.5 | 13.55 | 7 | 16.68 |
| 28 | 4.5 | 11.47 | 6.25 | 15.12 | 8 | 18.77 |
| 32 | 5 | 12.51 | 7 | 16.68 | 9 | 20.85 |
| 36 | 5.5 | 13.55 | 7.75 | 18.24 | 10 | 22.94 |
| 40 | 6 | 14.60 | 8.5 | 19.81 | 11 | 25.00 |
Computed from published K-factors for 1.0 lb/ft³ EPS at 40°F, starting at 1 inch at the drain. Higher density EPS gives higher R-values.
Tapered polyiso panels (Atlas ACFoam-II, 4 ft × 4 ft)
| Slope per ft | Label | Thickness min–max (in) | Average thickness (in) | Average R-value (LTTR) |
|---|---|---|---|---|
| 1/8" | AA | 0.5–1.0 | 0.75 | 4.3 |
| 1/8" | A | 1.0–1.5 | 1.25 | 7.1 |
| 1/8" | B | 1.5–2.0 | 1.75 | 10.0 |
| 1/8" | C | 2.0–2.5 | 2.25 | 12.9 |
| 1/4" | X | 0.5–1.5 | 1.0 | 5.7 |
| 1/4" | Y | 1.5–2.5 | 2.0 | 11.4 |
| 1/2" | Q | 0.5–2.5 | 1.5 | 8.6 |
LTTR is long-term thermal resistance per CAN/ULC-S770.
Sources: Cellofoam tapered EPS roof insulation sheet and the Atlas ACFoam-II product data sheet. Download the tapered EPS roof sheet and the ACFoam-II data sheet. Confirm your assembly with your roofing manufacturer and local code.
Where Tapered Insulation Is Used
New commercial roofs
Build the slope into the roof from the start, instead of relying on the deck.
Re-roofing flat roofs
Add slope to an existing flat roof that holds water.
Ponding problem areas
Direct water away from low spots and toward the drains.
Crickets and saddles
Lay out tapered pieces to send water around curbs and equipment and into the drains.
Send the roof plan. We will quote the taper.
Larger roofing bids with plans usually take about three to five days to price. Smaller requests are often answered faster.
Tapered Insulation Questions
What slopes are available?
Should I choose tapered EPS or tapered polyiso?
EPS usually costs less and keeps a stable R-value over time. Polyiso gives more R-value per inch, which helps where depth is limited. We price both. See the EPS vs. XPS vs. polyiso guide.
What do you need for a tapered insulation quote?
A roof plan or drawing with the drain locations, the deck type, your R-value or thickness target, and the delivery address. Larger bids with plans usually take about three to five days to price.
Are the tapered pieces marked for installation?
Yes. Each tapered EPS piece is labeled to match the shop drawing, so installers do not have to guess its position.
Do you supply flat boards and flute fill too?
Yes. See EPS roof insulation for flat boards and EPS flute fill for metal deck retrofits.
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