Exposed CPVC in Homes & HMOs? GFS Sprinklers

Published on 23 January 2026 at 11:36

Can CPVC Sprinkler Pipework Be Installed Exposed? The Truth for UK Homes & HMOs

Retrofitting a sprinkler system into an existing property often raises the same question:


“Do the pipes have to be boxed in?”

 

It’s a fair concern. Homeowners and HMO landlords want fire protection without compromising the look and feel of their property. The assumption is usually that CPVC pipework must always be hidden, but modern fire‑rated CPVC systems tell a different story.

Recent testing and manufacturer guidance shows that exposed CPVC can be safe, compliant, and fully approved in certain environments.

Why Exposed CPVC Can Be a Smart Retrofit Option

For many retrofit projects, exposed CPVC offers:

  • Lower installation cost
  • Faster installation (no need to open ceilings or walls)
  • Less disruption to tenants or homeowners
  • A clean, paintable finish when aesthetics matter

Exposed installations can significantly reduce labour and material costs, especially in existing buildings where opening up ceilings is impractical.

📞 Need Advice on Your Retrofit Project?

Whether you're upgrading an HMO, converting a loft, or improving fire safety in your home, we can advise on the most practical and compliant installation method including when exposed CPVC is appropriate.

 

Common Questions:

Where Exposed CPVC Is Permitted

BlazeMaster®’s published listings allow exposed CPVC in several specific scenarios under UL/FM and NFPA standards. 

 

  1. Beneath Smooth, Flat, Horizontal Ceilings

Exposed CPVC can be installed below finished ceilings when paired with listed residential or light‑hazard sprinklers.

 

  1. Unfinished Basements with Solid Joists (NFPA 13D)

BlazeMaster® became the first CPVC system approved for exposed installation with 16‑inch solid joists, allowing:

  • Pipework parallel or perpendicular to joists
  • Extended blocking distances up to 40 ft
  • More flexible layout options

 

  1. Unfinished Basements with Open‑Web Joists

A unique UL listing allows exposed CPVC beneath open‑web joists when:

  • Sidewall sprinklers are used
  • Sprinklers are installed below the joists
  • Minimum K‑factor 4.2
  • Maximum temperature rating 155°F (68°C)

 

  1. Exposed Risers in Residential Buildings

Risers may be installed exposed beneath smooth ceilings or unfinished basement ceilings, provided spacing and temperature requirements are met.

What the Testing Shows: CPVC CAN Be Installed Exposed

CPVC pipework has undergone extensive UL and FM testing, including:

  • Exposure to fire plume temperatures between 370°C and 483°C
  • Sustained exposure for at least 10 minutes
  • Follow‑up pressure testing at 175 psi

These tests demonstrate that CPVC can maintain structural integrity and performance even when installed beneath ceilings without additional protection.

This directly challenges the common belief that CPVC is “just plastic” and must always be boxed‑in.

Can Exposed CPVC Be Painted?

Yes — water‑based latex/acrylic paint is acceptable, provided:

  • The Authority Having Jurisdiction (AHJ) approves painting over identification markings
  • Painting is done after installation and after solvent cement has fully cured

This is particularly useful in retrofit projects where exposed pipework needs to blend into the room.

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What This Means for UK Installations 

While testing is based on UL/FM and NFPA standards, the underlying principle is the same:

If the manufacturer lists the product for exposed installation, and the installation follows their guidance, exposed CPVC can be safe and compliant.

In the UK, exposed CPVC may be appropriate in:

  • Lofts and attic spaces
  • Utility rooms
  • Certain HMOs with accessible service routes
  • Areas where boxing‑in is unnecessary or impractical

 

 

This blog post includes summarised information from:
BlazeMaster® Fire Protection Systems — “Truth Uncovered: BlazeMaster® CPVC Can Be Installed Exposed”
https://www.blazemaster.com/en-us/blog/truth-uncovered-blazemaster-cpvc-can-be-installed-exposed

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