Posted by Spycor Building on Jun 15th 2026
If you're installing or replacing a pitched metal roof, the underlayment you choose underneath the panels matters almost as much as the panels themselves. DELTA®-TRELA is a vapor-permeable underlayment purpose-built for metal roofing and metal cladding, and it's one of the most specified products for contractors who've dealt with condensation, corrosion, or "tin roof rattle" complaints on past jobs.
This guide covers what DELTA-TRELA is, who it's for, its full technical specifications, what you need to install it correctly, and where to buy it — including current pricing and availability.
What Is DELTA-TRELA?
DELTA-TRELA is a vapor-permeable roofing underlayment manufactured by Dörken Systems, designed specifically for pitched metal roofs and façades with metal cladding — whether the assembly is ventilated or non-ventilated.
It's built from two bonded layers: an 8mm randomly oriented studded fiber mat (polypropylene), thermally bonded to a tear-resistant, vapor-permeable, watertight spunbond fabric/film. That combination gives it three jobs at once: separating the metal panel from the substrate, channeling residual moisture out and away from the roof deck, and allowing trapped vapor inside the roof assembly to diffuse safely to the exterior.
In plain terms: it's the layer that stops your metal roof from sweating on the inside.
Why Metal Roofs Need This Layer
Metal roofing and metal cladding are not sealed tight to the deck or sheathing underneath. That gap allows moisture — from condensation, minor leaks, or vapor drive from inside the building — to collect between the metal and the substrate.
Left unmanaged, that trapped moisture causes two problems:
- Substrate damage. Moisture sitting against roof sheathing or rafters leads to rot, mold, and structural deterioration over time, often requiring the metal panels to be removed for repair.
- Metal corrosion. Condensation forming on the underside of metal panels accelerates corrosion, shortening the service life of the roofing material itself — sometimes well before the panel's expected lifespan.
DELTA-TRELA is engineered to prevent both. The studded structure keeps the underside of the panel ventilated and creates a drainage channel for any moisture that does collect, while the vapor-permeable membrane lets that moisture escape through diffusion rather than getting trapped.
Who This Product Is For
DELTA-TRELA is most often specified by:
- Metal roofing contractors and installers working on standing seam, corrugated, or architectural metal roof systems — residential or light commercial
- General contractors and builders managing new-construction projects with metal roofing or metal façade cladding
- Architects and specifiers writing roofing assemblies that require a separation/drainage layer under metal panels per manufacturer warranty requirements
- Roofing supply buyers and distributors sourcing Dörken DELTA® products for stock or job-specific orders
- Homeowners and property managers replacing a metal roof who've had prior issues with condensation, rust, or noise
If your project involves metal panels going down over a deck or sheathing — ventilated or not — this is the underlayment category you're shopping in.
DELTA-TRELA Key Features and Benefits
- 8mm studded fiber mat creates continuous airflow underneath metal panels, preventing moisture from sitting against the panel underside
- Vapor-permeable, watertight membrane allows residual moisture from the roof cavity to escape via diffusion while blocking liquid water intrusion
- Drainage course channels any moisture that collects down and out, away from rafters and sheathing
- Noise dampening — the studded structure helps reduce rain and hail noise transmission through the metal roof
- Non-slip studded surface improves footing safety during installation
- Omnidirectional studs mean the membrane works correctly regardless of roof pitch or panel orientation, including around detail work like valleys and penetrations
- One-step installation — no separate underlayment plus separation layer needed, reducing labor time on the schedule
DELTA-TRELA Technical Specifications
| Specification | Detail |
|---|---|
| Material | PP spunbonded fabric/film combination with studded fiber mat |
| Fire behavior | B2 rating (DIN 4102) |
| Studded structure height | Approx. 0.3 in (8mm) |
| Cover width | Approx. 1.4 m |
| Temperature range | -40°F to +176°F (-40°C to +80°C) |
| Weight | Approx. 270 g/m² |
| Roll size | 3'3" x 98.6' (323 sq ft) |
| Roll weight | Approx. 37 lbs (17 kg) |
| SKU | 22600411 |
What You Need to Install DELTA-TRELA
A correct DELTA-TRELA installation requires a few additional components — make sure these are part of your order so you're not waiting on a second shipment mid-job:
- DELTA-SEALING NAILS — required for fastening DELTA-TRELA and sold separately. Don't substitute standard roofing nails; the sealing nails are matched to the membrane for a watertight fastener penetration.
- Standard roofing tools for cutting and overlapping the membrane
Basic Installation Steps
- Lay DELTA-TRELA parallel to the eaves, with the studded structure facing up.
- Overlap each subsequent course in shingle (clapboard) fashion so water is shed toward the eaves, not channeled underneath the membrane.
- Fasten using DELTA-SEALING NAILS at the manufacturer's specified spacing.
- Install metal panels directly over the membrane — the studded surface provides ventilation and a non-slip work surface during panel installation.
For full step-by-step instructions, download the official installation guide and product brochure linked on the DELTA-TRELA product page.
DELTA-TRELA Pricing and Availability
| Item | Detail |
|---|---|
| Product | DELTA-TRELA, 3'3" x 98.6' roll (323 sq ft) |
| Price | $679.58 |
| Availability | In stock — usually ships in 3-5 business days |
| Where to buy | Spycor Building Products |
Spycor Building Products stocks DELTA-TRELA as part of its full line of Dörken DELTA® moisture management products, alongside related accessories like DELTA-SEALING NAILS, DELTA-VENT S, and DELTA-MULTI-BAND tape for sealing and flashing details.
View current price, stock status, and order DELTA-TRELA →
DELTA-TRELA vs. Standard Roofing Felt or Synthetic Underlayment
Standard roofing felt and many synthetic underlayments are designed for asphalt shingle assemblies, not metal panels. They don't provide a ventilation gap, which means condensation on the underside of metal panels has nowhere to go and nothing to channel it away.
DELTA-TRELA's studded mat creates that missing airflow and drainage layer in a single product — eliminating the need to install a separate underlayment plus a separate separation/ventilation layer. For metal roofing specifically, this is the functional difference between a roof that stays dry underneath and one that develops hidden corrosion and rot over years of service.
Get DELTA-TRELA for Your Next Metal Roofing Project
Whether you're a contractor specifying a complete metal roof assembly or a property owner replacing an aging roof, DELTA-TRELA gives you a single-product solution for ventilation, drainage, and vapor management under metal panels.
Order DELTA-TRELA (323 sq ft roll) from Spycor Building Products →
Frequently Asked Questions
What is DELTA-TRELA used for?
DELTA-TRELA is a vapor-permeable underlayment used underneath pitched metal roofing and metal wall cladding. It separates the metal from the substrate, ventilates the underside of the panels, and channels residual moisture away from the roof deck while letting trapped vapor escape.
Where can I buy DELTA-TRELA?
DELTA-TRELA is available at Spycor Building Products in 3'3" x 98.6' rolls (323 sq ft), priced at $679.58 and typically shipping within 3-5 business days.
What size does DELTA-TRELA come in?
The standard roll size is 3'3" wide by 98.6' long, covering 323 square feet per roll.
Do I need anything else to install DELTA-TRELA?
Yes — DELTA-SEALING NAILS are required for installation and sold separately. They're specifically designed to create a watertight fastener penetration through the membrane.
Can DELTA-TRELA be used on a non-ventilated metal roof?
Yes. DELTA-TRELA is designed to work on both ventilated and non-ventilated metal roof assemblies, providing drainage and vapor permeability in either configuration.
Does DELTA-TRELA help with roof noise?
Yes. The studded structure helps dampen the sound of rain and hail hitting the metal roof, reducing noise transmission into the building below.
What is the fire rating of DELTA-TRELA?
DELTA-TRELA carries a B2 fire rating under DIN 4102.
What temperature range can DELTA-TRELA withstand?
DELTA-TRELA is rated for -40°F to +176°F (-40°C to +80°C), suitable for most North American climate zones.
