Cavity Walls

Cavity Wall Construction

Tutor Copy

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

Solid Walls can let dampness into buildings.

Section through a solid wall

Why do we use cavity walling?

Cavity Walls were originally introduced to prevent Damp penetration.

Section through a cavity wall

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

Cavity Wall TiesThe walls are supported and tied into one another by means of specially designed metal ties called ‘wall ties’.

Wall Ties are made from stainless steel

Cavity Wall TiesProblems 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

Common Faults

Wall tie bent (sloping down towards Inner leaf)

Wall tie upside down

Wall tie drip touching inner leaf

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

5 wall ties per m2Wall ties every course up a reveal

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

Typical components needed for bridging cavities at openings.

Tray DPC

DPC stop endVertical DPC

Weep hole

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

Clean Cavities

Keep the cavity clean to prevent water penetration

Section through a cavity wall

Water cannot pass the drip on the wall tie

Ensuring Cleanliness• Core Hole

Ensuring Cleanliness• Cavity Batten

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

Broken BondIf 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