Should non-combustible metal pipes with a diameter of below 160mm be firestopped? Firestopping FAQs

The simple answer is yes.

However, there is a long-standing myth in the construction industry that non-combustible metal pipes (cast iron, copper, and steel) with an internal diameter of 160mm or below do not need to be firestopped.

Section 9 of Approved Document B (England & Wales), vol. 1 for dwellinghouses, requires non-combustible metal pipes of 160mm internal diameter [table 9.1, p.71] or less to meet one of the provisions in alternatives A, B or C:

Alternative A:

Provide a proprietary, tested sealing system that will maintain the fire resistance of the wall, floor, or cavity barrier.

Alternative B:

Where a proprietary sealing system is not used, firestop around the pipe, keeping the opening for the pipe as small as possible.

Alternative C (applicable to uPVC):

A pipe with a maximum nominal internal diameter of 160mm may be used with a sleeve made from a high melting point metal.

Similar to Approved Document B’s section 9 is Scotland’s Technical Handbook, section 2.2.9.

The information in both of these documents is misleading as it could be interpreted from Alternative B that services do not require the use of a ‘proprietary sealing system’.

However, with decades of fire testing experience, we know that additional service penetration sealing elements are required when it comes to metal pipes and maintaining the fire rating of compartment walls and floors – no matter the size of the service.

> See also: How should metal pipes be insulated and firestopped?

Why is Alternative A the most suitable solution?

The main issue with non-combustible metal pipes is that they transfer heat at a rapid rate. Because of this, it is unlikely that an EI (integrity and insulation) fire-resistance rating will be achievable without a proven fire test.

This is exemplified when comparing details QSS-FW120-03 and QSS-FW120-02:

QSS-FW120-03: When the 40mm uninsulated copper pipe is sealed with just QuelStop Intumescent Acrylic Sealant, it achieves an integrity rating of 120 minutes but only an insulation rating of 15 minutes.

QSS-FW120-02: Take the same 40mm copper pipe, but this time firestop it with QuelStop Intumescent Acrylic Sealant and insulate it using interrupted rock fibre, this results in an integrity rating of 120 minutes. Additionally, it significantly improves the insulation rating to 90 minutes.

The fire-resistance requirement itself is often overlooked. If, for instance, the compartment wall requires an EI60 rating and detail QSS-FW120-03 is used under the notion that non-combustible pipes can use Alternative B as described in Approved Document B, then this would effectively be non-compliant.

Although the metal pipe is non-combustible and easily achieves the integrity requirement of 60 minutes, it is also a very good conductor of heat and, therefore, fails the insulation rating at 15 minutes. So, although you have followed the guidance in Approved Document B (Alternative B, seal only) you have not met the actual building regulation requirement itself.

Service penetrations typically require both integrity and insulation fire-resistance ratings. The most reliable method to achieve an insulation rating is by using a tested system, such as Alternative A.

Hence, Alternative A is the preferred solution as manufacturers, like ourselves, have test evidence, comprehensive technical support, and a clear understanding of its application in scenarios like this, making it the most suitable choice.

It is important to note that the guidance in Approved Document B and Scotland’s Technical Handbook are only used to help meet building regulations. However, following this guidance does not guarantee the building work complies with the requirements of regulations. The only way to ensure you have complied is by using products in applications with specific fire test evidence.

For advice on which tested service penetration seal to use on your application, please get in touch at

> Read should plastic pipes with a diameter of below 40mm be firestopped? 


Alec Purdie

This question was answered by Alec Purdie

Technical Manager

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