2026-05-07 00:23:11

Leak-free roof penetrations with curb systems — Installation and applications

You sealed the base of a pipe, solar panel, or HVAC unit on a roof, and after a while, the leak came back. You added more product but it came back again. Every roof waterproofing inspection is pretty much the same story over and over. It costs you time, materials, and credibility with the client who hired you.

More often than not, roof penetration leaks happen because the job was done with generic sealants that were never designed for that level of detail. These products shrink, crack under thermal movement, and lose adhesion under constant sun and ponding water. The solution isn’t more sealant. It’s to switch to a penetration sealing system with specific components designed for each penetration scenario.

The curb system, for example, combines preformed curbs, adhesives, and high-performance sealants that work together as a waterproofing system built for these critical points. We’ll break down how the components of a penetration sealing system work, which configuration matches your roof penetration.

Why do some sealants fail at penetrations?

Every pipe, HVAC duct, or solar anchor that passes through a roof surface creates a break in the waterproofing system. That break concentrates mechanical stress from thermal movement, direct UV exposure, and (on flat or low-slope roofs) ponding water that sits for hours or days after a rain event.

The problem in question here is that many generic acrylic sealants shrink as they cure, harden, lose volume, and crack with every sun-and-rain cycle. Off-the-shelf silicones offer slightly more flexibility, but they tend to lack lasting adhesion on asphalt substrates and often can’t be painted or top-coated.

That’s why roof pipe sealing and HVAC roof leak repair aren’t issues you fix by repeating the same application. What’s needed is a penetration sealing system that combines a physical barrier with adhesives, high-performance sealants, and accessories engineered for a specific type of penetration.

How does a penetration sealing system work?

A curb is a preformed ring that a certified roofing contractor installs around the roof penetration to create a raised physical barrier against water. Unlike a bead of sealant that relies solely on chemical adhesion, the curb adds structural protection. Water has to rise up and over the ring before it can reach the penetration. That’s what separates a penetration sealing system from randomly improvising a fix.

Danosa’s curb system combines GPX, SLX, and NSX. Each component plays a role within the system:

Preformed curbs. These snap together quickly around pipes, ducts, and anchors. Sizes vary based on the penetration diameter.
GPX (multi-purpose adhesive). Bonds the preformed curb to the substrate on flat roofs. It delivers 300% elongation (ASTM D412), has passed over 4,000 hours of QUV weathering testing (ASTM G26), and operates in a service range of −50°F to 220°F. GPX also works as flat roof flashing in the transition zone between the penetration and the membrane.
SLX (self-leveling sealant). Poured inside the curb on horizontal applications, it levels on its own to create an airtight seal with a smooth finish, no manual tooling required. Elongation of 900–1,000% (ASTM D412), service range of −40°F to 200°F, ASTM C920 Class 50 rating.
NSX (non-sag adhesive). Designed for sloped roofs and vertical surfaces where a self-leveling product would run off. Same elongation as SLX (900–1,000%) and the same Class 50 rating, but with a non-slump consistency that holds its position.

All three share a polyester base, are moisture-cured, 100% solids (meaning zero shrinkage), and free of solvents and isocyanates. This is a system where each component addresses a specific variable.

Step-by-step installation of a curb system

One of the advantages of a curb system for roof penetrations is that it standardizes roof pipe sealing into four clearly defined steps. All three chemical components come in 20 oz cartridges and roofers apply them with a standard caulk gun. No mixing, or specialty tools, or heat equipment required.

Step 1: Surface preparation. Remove any previous sealant and clean the entire surface. Don’t use petroleum-based solvents. Once the surface is clean, apply GPX (on flat roofs) or NSX (on sloped roofs) to the base of the penetration, covering up to 3" above the roofline.

Step 2: Adhesive application. Apply a ¼" bead of GPX or NSX along the base of the first curb section. Position the preformed curb around the penetration and press firmly until the adhesive extrudes from the edges. That extrusion confirms full contact.

Step 3: Complete the curb. Join the second curb section to close the ring. Again, press until the adhesive extrudes from the base. Apply an additional bead of GPX or NSX around the edges and smooth for a clean seal. Tooling time is approximately 30 minutes with GPX and approximately 15 minutes with NSX and SLX.

Step 4: Seal the penetration. On flat roofs, pour SLX inside the preformed curb. The sealant self-levels and creates an airtight seal with a smooth finish, functioning as flat roof flashing. On sloped roofs, apply NSX, which holds its position without sagging on vertical surfaces.

Keep a couple of restrictions in mind. Membranes require a compatible primer before applying any of the adhesives. The system shouldn’t be installed at temperatures below 32°F (0°C) without consulting the manufacturer’s cold-weather procedures. All surfaces must be clean and dry before application, with the exception of GPX, which cures over damp surfaces without affecting performance

Understanding these kinds of restrictions before you start prevents rework and protects the warranty. Although the process is straightforward, installation by certified roofing contractors ensures that every step follows the manufacturer’s guidelines, which is a required condition for the warranty to apply.

Application scenarios: Solar, HVAC, pipes, and more

The variables differ by penetration type (diameter, vibration, roof orientation, exposure level) and by the sealing system. These are the most common scenarios in roofing projects across the Caribbean.

Solar panel anchors

Photovoltaic installations create dozens of small, repetitive penetrations in the same area of the roof. The typical configuration is a 3" preformed curb + GPX + SLX on flat roofs. Each point is exposed to continuous UV radiation and ponding water on the roof between panels, where drainage is reduced. GPX is built for that demand with 4,000 hours of QUV weathering testing, and the complete system is designed to withstand these conditions without degrading.

HVAC Units

HVAC penetrations are larger in diameter and subject to constant vibration from equipment operation. Here, a 4" or 5" curb is combined with GPX, whose 300% elongation absorbs mechanical movement without losing adhesion. For anyone who regularly deals with leaks on roofs with equipment, this configuration replaces the seal-fail-repeat cycle with a system that works with the movement instead of resisting it until fracture.

Residential pipes and antennas

This is the scenario for the homeowner who’s been watching water come in around a pipe or antenna for months. On sloped roofs, a 3" curb is combined with NSX, a non-sag adhesive with 900–1,000% elongation that holds its position on vertical surfaces without sliding. On flat roofs, the combination is curb + self-leveling SLX. In both cases, installation is handled by a certified contractor who knows the correct configuration for each property type.

New construction vs. Repairs

On a new build, curb can be specified at the design stage alongside the asphalt membrane system that will serve as the waterproofing base. For repairs, it can be installed over the existing system once the surface is prepared. The NSX and SLX components are directly compatible with SBS-modified membranes, allowing curb to integrate with the current roof without replacing the entire membrane.

How penetration and sealing systems work together

The curb system works in sync with membrane-based roof sealing systems. Its GPX, NSX, and SLX components are compatible with SBS- and APP-modified asphalt membranes.

For example: an Esterdan R-36 as the base layer, a Glasdan AL-80-4 as the cap sheet, flashings at parapets and terminations, curb at penetration points, and KnuckleHead for equipment supports. Every component covers a specific zone of the roof to eliminate vulnerabilities.

Membranes with a white or aluminum finish offer high reflectivity that reduces heat buildup, and their thickness adds an extra layer of thermal protection for the property.

The curb components complement this profile. GPX, NSX, and SLX have VOC levels below 17 g/L and contribute to LEED 2.2 credits as low-emission materials, which is aligned with environmental goals and useful for projects seeking green certification and accurate material takeoffs.

What’s your situation right now?

Roof penetration leaks persist when they’re treated with products that don’t work with the membrane system. Or worse, when they’re handled by an uncertified roofer. Danosa’s curb system includes preformed curbs in three sizes, polyester-based adhesives and sealants with up to 1,000% elongation, documented UV resistance, and more. Every part of the penetration seal addresses a variable based on roof type, penetration, and substrate, backed by a 10-year warranty against material defects.

If you happen to be evaluating whether to repair or replace an existing waterproofing system, specifying materials for a new roof waterproofing project, or getting fixed an urgent leak, Danosa Caribbean’s technical sales team can recommend configurations for your specific case.

Reach out to the Danosa Service Agent (a chatbot that appears on this page) to connect with a Danosa rep, or email us at sales@danosapr.com mentioning this blog post so we have some context for your request. Every roof has critical points. Danosa Caribbean has the sealing system you need.