Cavity walls are constructed with an inner and outer leaf separated by an air gap, or cavity. This construction helps prevent dampness by allowing water that enters the outer leaf to drain out before reaching the inner leaf. Cavity walls are reinforced with wall ties to bind the two leaves together. Properly installed wall ties and other components are needed to bridge the cavity at openings while preventing water transfer. Mortar droppings in the cavity can form bridges for water to pass through, so the cavity must be kept clean during and after construction.

1. Cavity Walls
Cavity Wall Construction

2. Tutor Copy

3. What is a cavity wall?
A cavity wall is made
up from:
• An outer leaf
• An inner leaf
• Air gap between
these leaves which
usually contains
insulation
Outer leaf
Cavity wall construction
Inner leaf
50mm minimum width of air gap
Section through a cavity wall

4. Solid Walls can let dampness
into buildings.
Section through a solid wall

5. Why do we use cavity walling?
Cavity Walls
were originally
introduced to
prevent Damp
penetration.
Section through a cavity wall

6. Problems?
• Weakness: Two slender half brick / block
skins are not as strong as a one brick thick
solid wall.
How can this Kind of walling be
strengthened?
The use of Cavity Wall
Ties

7. Cavity Wall Ties
The walls are supported and tied into one
another by means of specially designed
metal ties called ‘wall ties’.
Wall Ties are usually made from stainless
steel but can also be made from Plastic or
Galvanised Steel.

8. Cavity Wall Ties
Problems can occur when bridging the cavity, such
as water penetrating from the outer leaf to the
inner leaf.
Outer leaf
brickwork
Inner leaf
blockwork
Wall tie
Moisture drips off wall tie
Cavity
Section through a cavity wall

9. Common Faults
Wall tie bent (sloping
down towards Inner leaf)
Wall tie upside down
Wall tie drip touching inner
leaf

10. Wall tie spacing’s
Building Regs state wall ties must be positioned
450mm vertical 750mm horizontal (100mm
cavity) and no more than 300mm vertically on
un-bonded reveals.

11. 5 wall ties per m2
Wall ties every course
up a reveal

12. Bridging the cavity can create
problems.
Preventing
Water
Transfer.
The Tray DPC
prevents water
crossing along
the top of the
air-brick liner.
Section through a cavity wall

13. Typical components needed for
bridging cavities at openings.
Tray DPC
DPC stop end
Vertical DPC
Weep hole

14. Keep the cavity clean.
Mortar droppings
can gather on wall
ties and at the
bottom of the cavity
creating a bridge
for water to pass
through to the inner
leaf.
Section through a cavity wall

15. Clean
Cavities
Keep the cavity
clean to
prevent water
penetration
Section through a cavity wall
Water
cannot
pass the
drip on the
wall tie

16. Ensuring Cleanliness
• Core Hole

17. Ensuring Cleanliness
• Cavity Batten

18. Wall construction below ground
level
Cavity walling below ground level:-
• Cavity wall formed with two leafs of
common bricks. The external leaf will revert
to facing bricks 2 course below ground level
to allow the bricklayer to ensure that bond is
worked out

19. Broken Bond
If Broken Bond can not be avoided the piece
should be placed in the centre of the wall, or
against the reveal.
No cut should be less than ½ brick
If bastard sized window and doors are used
then the piece is better placed under the
opening if possible.
ANY CUT SHOULD ALWAYS STAY IN THE
SAME POSITION