Why are GRP Valley Troughs Replacing Traditional Materials?
For centuries, lead was the default material for critical roof valley drainage, but it is now being rapidly replaced by Glass Reinforced Polyester (GRP), a modern composite that outperforms traditional options. This industry-wide shift is driven by GRP’s superior advantages in cost efficiency, durability, lightweight properties and ease of installation, making it the go-to choice for new builds and renovations where reliable, high-performance drainage is important.
What are GRP Valley Troughs?
A GRP valley trough is a pre-formed, rigid channel made from Glass Reinforced Polyester (GRP), a composite material known for its strength, lightweight nature and corrosion resistance. Fabricated off-site to precise specifications, it is designed as a finished product that installs seamlessly into the roof structure, creating a continuous, watertight pathway from the valley to the gutter.
The Advantages of GRP v Traditional Material Valley Troughs
There’s a steady shift to GRP valley troughs. Discover the advantages of GRP as a roofing material below.
| GRP Valley Troughs | |
| Weight | Extremely lightweight. Easy for a single installer to handle, reducing personal physical strain and structural load on the roof structure. |
| Installation | Quick and simple. Pre-formed sections are simply nailed in place and installed quickly. |
| Durability and Lifespan | Exceptional. Highly resistant to corrosion and UV degradation. |
| Maintenance | Virtually maintenance-free. The non-porous surface prevents moss and lichen growth, eliminating the need for painting or sealing. |
| Cost | Low installed cost. The material cost is competitive, and the significant savings in labour time and reduced need for highly specialised skills make the overall project cost low. |
| Weather Resistance | Performs consistently in all temperatures. Will not become brittle in cold weather nor soften in intense heat. |
| Health and Safety | Inert and safe to handle without special protective equipment beyond standard site PPE. |
| Theft Risk | No scrap value, making it a very low-risk target for theft on-site. |
| Environmental Impact | A long lifespan and low maintenance reduce the long-term impact. |
GRP has many advantages over traditional materials in most practical categories.
Why GRP is Replacing Traditional Valley Materials?
The ‘why’ behind the industry shift to GRP is a combination of the advantages outlined above and pressures to ensure modern homes and buildings are sufficiently protected from the elements. The reasons for the move towards GRP over traditional materials include:
The drive for efficiency and cost-effectiveness
The construction industry is under constant pressure to build faster and more cost-efficiently without compromising on quality. GRP valley troughs are a perfect example of Design for Manufacture and Assembly (DfMA). By relocating fabrication from a wet, windy and unpredictable roof site to a controlled factory environment, the process becomes vastly more efficient. The drastic reduction in on-site labour time is the single biggest financial driver for builders and contractors, making projects more profitable and predictable.
A shortage of specialised skills
GRP installation can be mastered quickly by most competent roofers and general builders as it requires no specialised traditional skills. This ease of installation future-proofs projects against the growing skills gap in traditional roofing trades.
Enhanced performance and peace of mind
For homeowners increasingly focused on long-term building performance, GRP offers a definitive ‘set-it-and-forget-it’ solution. Its resistance to thermal movement, corrosion and UV damage eliminates common failure points found in traditional valley trough materials, guaranteeing decades of reliable, maintenance-free operation and providing unparalleled peace of mind.
Safety and security concerns
GRP’s inert nature removes potential health risks associated with other materials. Also, specifying GRP for a roofing project significantly reduces the risk of theft as there is no scrap value in GRP, unlike other materials, thus protecting the project budget and timeline.
Suitability for modern building methods
GRP valley troughs represent a modernisation of the entire roofing process. It aligns with contemporary priorities of speed, safety, cost certainty and long-term, low-maintenance performance. While traditional materials will always have their place in heritage restoration and certain architectural styles, for the vast majority of new build and retrofit projects, GRP valley troughs are the logical choice.
FAQs
Are GRP valleys strong?
GRP has very high tensile strength and is impact-resistant. The UV-absorbing layer on the outer face is also highly scratch-resistant.
Can GRP valleys be used on any roof pitch?
GRP valleys are highly versatile and can be used on a wide range of roof pitches, including low pitches where efficient water runoff is critical. Always consult the manufacturer’s specifications for the minimum recommended pitch but most GRP valley troughs are suitable for roof pitches from 17.5 and up to 60 degrees.
How are GRP valleys joined together?
They are simply dry lapped, ensuring that the lap length is at least 150mm when measured vertically. Sealants are unnecessary.
Advantages of GRP over lead valley troughs?
Lead is a very common application. The dated lead valley material can replaced, removed and the new pre-formed can GRP trough is installed directly onto the prepared valley board. It’s often a quicker and more cost-effective solution than repairing or replacing with a new lead trough. GRP is more flexible than lead and can last longer.