How do I specify a cavity closer?

Saving energy, protecting life, health and property

An architect and specifier essential guide to cavity closers and fire cavity barriers

Choosing and specifying the correct product for your projects

Background

The primary function of cavity closers and fire cavity barriers is to save energy, protect life, health and property. They both operate based on the simplest ideas but are an essential component in the construction of homes, places of work, indeed, anywhere we build.  So, where should a cavity closer or cavity fire barrier go? In principle anywhere with a cavity that needs to be closed.

This can be around door and window reveals, or internally at party wall junctions, they all need to be close with some form of barrier.

There are two types of cavity barriers outlined in this guide:

• Cavity Closers – used anywhere where there is a cavity that can allow heat loss or spread of fire. They are used in traditional brick/block, timber frame, rainscreen cladding in new and refurbishment projects. It is comprised of an insulated profile, closing off the cavity at reveals, acting as a DPC.

• Fire Cavity Barriers – Approved document B of the building regulations, Fire Safety, defines a cavity barrier as: “A construction, other than a smoke curtain, provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space”

Relevant cavities include party wall junctions, wall plate junctions, at the eaves, between fire compartments both horizontally and vertically.

with a fire rating, to stop fire spreading into different areas of a building – these can be installed retroactively or in new builds.

Functions of Cavity Closers and Fire Cavity Barriers

• Prevent water penetration–in compliance with Building Regulations Part C. It is critical to set back the frame of a window a minimum of 30mm into the cavity and use a recognised sealant around the frame. Also, a cavity closer with ridges on will further help prevent water penetration.
• Prevent heat loss and cold penetration– Cold bridging is when an area of a building has significantly higher heat transfer than the surrounding materials resulting in an overall reduction in thermal insulation of the building. The problems of cold bridging are recognised in the Building Regulation Part L. Insulated Cavity Closers are used to overcome thermal loss that occurs around unprotected cavities and reveals. Thermal loss can result in problems of condensation, staining and mould growth at the reveals of these openings. Prolonged exposure to such factors will lead to a deterioration of the internal plaster and paint work. The use of cavity closers will help to prevent the occurrence of such factors.
• Create a fire barrier– To comply with Building Regulation Part B a fire rated cavity closer should be used. A fire rated cavity closer can prevent the spread of fire for up to 1 hour. A purely insulted cavity closer without a fire rating will not actually comply with Part B.
• Comply with Part L – Building Regulation Part L compliance is ever more important with sustainability being prioritised and reductions in heat losses. The minimum thermal resistance path through the cavity closer must be at least 0.45m2k/W (the higher this number the lower the heat loss).
• Not all cavities that need closing are at reveals. Other cavities include party wall junctions, wall plate junctions and at eaves. In timber frames and SIP construction, fire sock products are often used. These are fire rated compression fit products that stop fire spreading into adjacent areas of a building (can be installed retroactively or in new builds).

Failures from lack of/insufficient of Cavity Closers and Fire Cavity Barriers

Cold bridging occurs where an element of a building has significantly higher heat transfer than surrounding materials, resulting in an overall reduction in thermal insulation of the building.

This leads to excessive heat loss, condensation and mould growth, damaging to human health, property and value.

In the Grenfell Tower catastrophe, one of the findings showed no cavity barriers were installed. Part B requires compartmentation at floors and between apartments with fire cavity barriers. Fire penetrated the cavity and was drawn up the building, with nothing to stop it. The speed of spread of the resulting fire was too rapid to enable effective firefighting and rescue services to act, resulting in the loss of 71 lives.

Types of Cavity Closers and Fire Cavity Barriers

There are two types of cavity closers in use:

Bar length cavity closers

Bar length cavity closers are available in two forms:

1. ‘Check reveal’ – External structural opening is smaller than the window frame

• External face of the window frame butts against back of external skin.
• Weather seal is formed between front face of the window and opening.
• Used in areas of severe exposure to driving rain – e.g., Wales, Scotland and Northern Ireland

2. ‘Standard’ – Weather seal is formed by outer perimeter of window in a ‘flush’ reveal.

Frame former cavity closers

*Push fit can be retrofitted to existing buildings whereas fixing tie method and frame formers can only be used in new build

Relevant Building Regulations & Standards

Legislation and industry standards can be traced back to part L 2013, conservation of fuel and power; Part C2 on resistance to moisture; Part B (updated in 2017)and BS5350 and Robust Detail 262.

Part L – Conservation of Fuel and Power

• Cavities should be closed off around window and door reveals with a closer which will: Provide a Minimum
  Thermal Resistance Path (MTRP) of at least 45m2K/W.
• Specify an insulated closer with this MTRP. This will meet the guidelines contained in the Building Regulations
  (Part L) – 2013 amended “Conservation of Fuel and Power”

Part C – Water Ingress

Water Ingress  can lead to damp, mold growth & condensation. This is unattractive and can cause health issues.

• Specification should ensure the window is set back at least 30mm into the reveal.
• A recognised sealant should be used internally and externally.
• The cavity closer should have grooved flanges – when the water comes into contact with the cavity closer it is drawn down the closer and into the cavity

BS 5250 + Robust Detail 262

New guidance recommendations:

• To reduce condensation risk to floors, walls and roofs reference should be made to revised BS 5250,
• Limiting thermal bridging and air leakage: robust details and BRE Report BR 262 Thermal insulation – avoiding risks.
• BS 5250 control of condensation in buildings
• Robust Details 262 – thermal insulation avoiding risks

* Complying with Parts L and C2, also means meeting BS5250 and Robust Detail 262

Fire Safety (Part B)

Fire can be undetected in cavities for extended periods. There needs to be sufficient protection
to allow time for occupants to escape.

• “Window and door reveals should be closed off with a fire ‘barrier’ with an integrity rating of at least 30 minutes” (BR Part B)
• Specify a cavity closer with at least 30 minutes fire integrity.
• Becomes a barrier with the approved fire rating

• 8 of B4 of the 2019 Approved Document B Vol 1 Section 8:

In this context cavity barriers relating to ‘relevant’ buildings as described in 7(4) of the Building Regulations must be addressed. Also those described as ‘other’ buildings, see 10.3 of ADB1

• 8 of B4 of the 2019 Approved Document B Vol 2 Section 9:

In this context cavity barriers relating to ‘relevant’ buildings as described in 7(4) of the Building Regulations must again be addressed and also those described as ‘other’ buildings, see 12.3 of ADB2

Specifying the correct cavity closer and cavity fire barrier – key considerations

• What is the width of the cavity?
• How wide should the cavity be?
• Is there a maximum and minimum?

Cavity closers can vary in width from 40mm up to 200-300mm. As a rule, the wider the cavity, the better the thermal value, but this can introduce additional costs.

Improvement in insulation performance has allowed the cavity reveal to decrease to 150mm.

Fire rated cavity closers of 170mm and a fire rated cavity sock type barrier to 300mm are now available.

When specifying a cavity of 100mm, the barrier or closer will be supplied slightly bigger as a push fit, to achieve fire rating. Cavity closers are available in 5mm increments, whilst fire barriers are available in 10mm increments.

Detail Examples: Cavity Closers

Detail Examples: Fire Cavity Barriers

Environmental Considerations

Cavity closers and Cavity fire barriers do not actually come under BREEAM or the green guide. Dacatie products have 0% ozone depletion potential, 0% global warming potential, and we use a high percentage of recycled compounds where possible.

Life Cycle Considerations for a good Insulated Cavity Closer:

• Zero Maintenance during the life of the building. But it is advised that cavity closers should be replaced if/when windows are changes or removed for any reason. To increase thermal efficiency or upgrade to meet new standards with newer technology.
• Carrier is made from part recycled uPVC and can be recycled in full at end of life
• Mineral wool is non pollutant – no formaldehyde
• ISO 9001 and ISO14001 source
• Produced using LEAN processes – least waste – best value

* For further guidance see: Site Waste Management Plans Regulations 2008

Specifying the Correct Product – Summary

• Cavity widths – How wide should they be?

Specify an insulated cavity closer to accommodate the cavity width of the building design   (available in 5mm increments).

• Heat loss/ cold penetration – How can it be controlled?

Specify an insulated cavity closer to give MTRP of at least 0.45m²K/W and window/door
set back of 30mm (BRE Part L).

• Water Ingress & Air Infiltration – How can it be restricted?

Ensure frame set-back is a minimum of 30 mm for severe weather rating

• Fire protection in cavities – What is the best solution?

Specify an insulated cavity closer with a fire rating of at least 30 minutes integrity to act
as a barrier in cavities around window and door reveals (BRE Part B).

• Sustainability – How do these affect cavity closers?

BREEAM does not directly affect cavity closer choice, however, specify a closer with
green credentials which will enhance the environmental aspects of any construction.

Specifying the Correct Product for your Project:

You can find everything you need to specify the correct product for your project here:

https://quantumprofilesystems.com/dacatie/

 Simply follow the links to services and follow the drop-down menu:

Alternatively, please feel free to contact us here:

• email:    [email protected]
• visit:       www.dacatie.co.uk
• follow:  @Dacatie
• tel:         +44 (0) 161 627 4222
• fax:        +44 (0) 161 627 4333

Quantum Profile Systems Ltd, Salmon Fields, Royton, Oldham, OL2 6JG, UK

About us:

Dacatie make the widest possible variety of cavity closers, fire rated barriers and fire barriers in the UK.

We are also part of a bigger group- Quantum Profile Systems Ltd and have been operating for over 50 years:

• The largest range of PVC contract flooring accessories in the UK, including stair nosings, entrance matting, transition profiles and skirting profiles.
• We also manufacture, under the Qwood brand, a range of products that go into the joinery market. Eight out of ten joiners use our profiles in their windows.
• Qwood looks like timber, acts like timber, paints like timber but without the small timber profile. QWood is a timber composite, it enhances the performance of windows, it will not bow, crack or rot.
• We also make profiles in QLean, where we supply bespoke PVC and uPVC extrusions to the offsite marketplace.

QPSL are Lean, Green, Safe and Clean – our principles:

• To create value for customers; generate flow to eliminate job queues; let customer pull decide what is made; strive for perfection; and never be satisfied, always learning to be better.
• We don’t have an order book; we wait for the phone to ring, get it on the system, manufacture it that day and then ship it out that night.
• We are green, we are heading towards a 0% waste site, we have environmental sustainability in all we do.
• We are ISO14001 certified. Its more than that, it’s a culture, we do waste walks and turn bins upside down to see what is in them and question everything in there.

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