A PPT on Openings in cavity walls

1. Cavity Walls
Openings in
Cavity walls

2. Tutor Copy

3. Door and window openings
Door and window openings are formed during
the construction of the cavity wall. The
openings can allow the door and window
frames to be:
• Fitted as the work progresses so that the
frame is built into, and encased by, the wall.
• Fitted into a preformed opening after the
wall is built.

4. Frames built into the wall as
work progresses
A bricklayer often has to build in frames as
the work proceeds. The frames are usually
pre-made of timber and they act as a profile
for the required opening as the wall is built.
The frames are usually plumbed, squared
and held in position before the brickwork
begins, and the wall is built around the
frame, encasing it within the wall.

5. Frames built into the wall as
work progresses
Weight applied
to base to hold
frame in place
Batten nailed
to the frame

6. Built-in frames
Built-in frames are fastened in place as the brick courses of
the wall are being built. The frames, whether window frames,
or door frames are manufactured so that the head and the
sills are longer than the width of the frame. The extensions to
the frame are called ‘horns’ and before the frame is fitted, the
horns at the head have to be trimmed and shaped or ‘splayed
back’ to allow the facing bricks to cloak the head.
Door
Frame
DPC
‘Horn’Facing
brickwork
BlockworkInsulation

7. Securing frames in place
Metal cramps
This method of securing the frames makes
use of specially designed metal cramps which
are fixed to the back of the frame and
positioned so that the cramp
coincides with a horizontal
joint. The cramp is laid on
top of the bricks and then
the wall is built on top of it.
Care must be taken when using this method
that the frame is plumb and level.
Metal cramp
in line with
brick bed
courses

8. An alternative method of securing
frames is to use wooden fixing
pads or ‘slips’.
These pads are small pieces of
timber 90mm x 90mm x 10mm
thick. The pads are placed within a
horizontal joint at intervals of 4–6
courses. The pad should be placed
so that the grain of the timber is at
90˚ to the fixing edge of the
brickwork. These pads can be built
in as the work progresses and the
frame can be fitted at a later date.
Securing frames with wooden pads or ‘slips’
It is still advisable to splay cut the horns at the head of the
frame and build them in to secure the frame at the head.
Frame screwed or
nailed to the slip
Wooden slip built
in as the work
proceeds

9. Forming pre-formed openings in
cavity walls
With the increase in
Upvc windows and door
frames it has become
common practice to form
openings in cavity walls
to allow the frames to be
fitted at a later date. This
method is also preferred
when hardwood windows
are to be fitted.

10. To form the opening, dummy frames called profiles are
made to suit the door or window openings. These frames
are then built into the walls to form the correct size openings
for the doors and windows selected.
The frames consist of sawn softwood pieces held together at
the corners by plywood gussets which are nailed or screwed
to the frame. The frame is usually made slightly larger than
required so that the new frames can be fitted easily.

11. Fixing frames to pre-formed
openings in cavity walls
The fixing of the frames will depend
upon the construction specification of
the building.
The development of, and
improvement of, modern fixings has
led to most frames being fixed in
place using these types of fixings.
The commonest type consists of a
plastic sleeve which encases a
toughened zinc screw. When the
screw is tightened the sleeve
expands, securing the frame in place.

12. Jambs, sills and thresholds
Jambs
The sides of openings are called jambs, with the actual
face known as the reveal.
In cavity walls, the reveals can be constructed either
square or rebated. The cavity can be closed at the
opening by using a suitable frame or by returning the
inner leaf towards the outer leaf. When the inner leaf
abuts the outer leaf, a vertical DPC must be inserted to
prevent moisture from passing through.
Note: The vertical DPC
should extend into the
cavity to avoid mortar from
bridging. When 100mm
blocks are used, the DPC
must be 150mm.

13. Other Methods of Closing the Cavity

14. Sills
The function of the sill is to shed rainwater
from the window frame and away from the
wall below.
A cavity closer block is bedded below the
inner window board to provide a larger, more
solid base on to which to fix the window
board. This must be insulated from the
external face.

15. Sill Detail
Brick on
edge sill
Window sill bedded
onto the face brickwork
Cavity
closing
block with
DPC and
insulation
Window
board
Window
board
Window sill bedded onto
the face brickwork
Cavity closing
block with
DPC and
insulation

16. Thresholds
As with window frames, door frames are integral
components of a building. The door frame usually
has a base component called a threshold, but
some frames are available without an attached
threshold and will therefore require a concrete or
brick-on-edge threshold. Bricks used for thresholds
should be engineering bricks or bricks well burnt to
withstand severe weather conditions. The mortar
used for this type of work should be a 1:3 mix
which will make it of equal strength to the bricks.

17. Thresholds
Door frame
with threshold
Hardwood
threshold
Water bar
Water bar
Concrete
step