What Are Cavity Closers and How to Install Them?

What Are Cavity Closers and How to Install Them?
Loading... 11444 view(s)
What Are Cavity Closers and How to Install Them?

When dealing with work inside the home, you may have come across the term ‘cavity closer’ but are not quite sure what they are or what their purpose within the home is. Insulation Express are here to explain all and tell you how you’d go about installing a cavity closer yourself when working with cavity wall insulation.


What is a Cavity Closer?


Essentially, a cavity closer makes up part of a cavity wall, where windows and doors are fitted. Their main purpose is to protect the building from things such as damp, condensation and heat loss.


The cavity closer takes the form of a seal to prevent any water and damp from entering the cavity wall and building. That’s not all though, as they also stop heat from exiting the building through the gap, so they are also important for insulation purposes.


These cavity closers can be used in many different constructions, such as timber frame, steel frame and masonry systems.


Cavity Closer


What are Insulated Cavity Closers?


Insulated cavity closers are built the same as most other cavity closers, featuring a damp-proof membrane to stop water and damp from infiltrating into a building, as well as PVC extrusions and a flexible seal. An insulated cavity closer also features an added layer of insulation, to increase the amount of heat retained.


Why Install a Cavity Closer?


There are plenty of reasons to use cavity closers, such as:


Preventing Water Leaking


The cavity closer will prevent any ingress of water from occurring around the edges of any windows and doors, thus vastly reducing the chances of any damp, condensation, or mould from occurring.


Reducing Heat Loss


Heat transfer is often much greater around windows and doors. Adding a cavity closer prevents the thermal loss from occurring, reducing the amount of energy needed to keep the building warm.


Improve Fire Safety


Fire-rated cavity closers can prevent the spread of fire for up to 30 minutes or an hour, which can be crucial if a disaster does occur.


How To Fit a Cavity Closer


When installing standard cavity closers, it’s best to follow this step-by-step guide.


  1. Measure the width of the cavity wall, as this will decide the size of the cavity closer you’ll need to use.
  2. Fix the cavity closer with the flange against the inner leaf wall, with the fixing ties slotting into the cavity side and the key into the mortar bed of the outer masonry skin.
  3. It’s important to ensure that there’s a 50mm minimum overlap between the flange and the masonry skin, with a tight fit of the closer with no gaps left between it and the walls.
  4. Then, secure the fixing through the holes provided.
  5. Install a lintel and damp-proof course cavity tray at the head along with weep holes.
  6. If an insulated lintel is used, a head closer section is not needed. The jamb sections of the closer will butt up against the lintel.
  7. If needed, use a cavity closer at the head where a separate lintel is used for each leaf.


If installing as individual sections, follow these steps:


  1. Cavity closer sections should be built in as the wall is constructed.
  2. For the sill, cut the cavity closer precisely to the frame width.
  3. For the jambs, make sure that the sections overhang the bottom of the closer sill by 50mm.
  4. Cut off the fixing flange as required to allow fitting the closer into cavity.
  5. If used at the head, also cut the closer to extend 50mm beyond each vertical jamb section.
  6. If fixing the window, follow conventional frame fixing procedure.



If installing a cavity closer on a window and door replacement or refurbishment, follow these steps.


  1. Cut out and clear away any masonry that closes the cavity.
  2. Secure the closer in position with wedges and fixings to ensure that there’ll be no movement.
  3. Offer up the window or door frame and secure it to the masonry.
  4. Use frame straps or frame fixings to fix the frame to the masonry.



If the cavity closer sections are butt jointed, it should be limited to no more than one joint per frame side. To make sure things align properly, give preference to machine cut ends ahead of those cut on site. Then, use a joint strip to help connect and align the abutting sections on site. Use adhesive aluminium foil around the joints to prevent water tracking.



There you have it. Follow these steps and you can enjoy the benefits of these cavity closers in your home. If you’re looking for more advice, our guide to installing wall insulation may help point you in the right direction.