Design considerations for wall ties

When selecting which wall ties to use a number of factors must be considered ie cavity size, building type, height and location. To determine the correct wall tie to use guidance must be sought from several main documents covering wall tie usage.

These include:
BS 5628: The Use Of Masonry: Part 1: 1992
Provides recommendations on density, positioning, embedment and length of ties.
Allows ties from BS 1243 and DD140 to be used.

Least Leaf Thickness	Nominal Cavity Width	Permissable Tie Type		Tie Length
Least Leaf Thickness	Nominal Cavity Width	BS1243 Shape Type	DD140 Tie Type	Tie Length
75	75 or less	Butterfly, double triangle or vertical twist	Types 1,2 & 4	175
90	75 or less	Butterfly, double triangle or vertical twist	Types 1,2 & 4	200
90	76 to 90	Double triangle or vertical twist	Types 1 & 2	225
90	91 to 100	Double triangle or vertical twist	Types 1 & 2	225
90	101 to 125	Vertical twist	Types 1 & 2	250
90	126 to 150	Vertical twist	Types 1 & 2	275

Least Leaf Thickness	Nominal Cavity Width	Spacing of Ties		Ties Per Metre Square
Least Leaf Thickness	Nominal Cavity Width	Horizontal	Vertical	Ties Per Metre Square
65 - 90	50 - 75	450	450	4.9
Above 90	50 - 150	900	450	2.5

BS 5628 recommends that the embedment into each leaf of the cavity wall should be a minimum of 50mm.
Ties at vertical edges of openings or unbonded edges ie: movement joints, should be placed at 300mm centres vertically at a maximum 225mm from the open edge.

BS 1243: 1978: Specification Of Metal Ties For Cavity Wall Construction
Largely a manufacturing standard specifying the size, material and tolerances for three types of tie, butterfly, double triangle and vertical twist. The standard contains no guidance related to the ties performance or recommended usage.

Figure 1: Butterfly Tie Ref: GA7	Figure 2: Double Triangle Tie Ref: GA7	Figure 3: Vertical Twist Tie* Ref: GA5
		*Supplied with 3 hole saftety end

DD140: Part 2: 1987: Recommendations For The Design Of Wall Ties
Part 2 of the DD140 document gives recommendations on the design requirements of wall ties used in masonry and timber construction. There are 6 classifications each specifying requirements depending on end use. Class types 1 to 4 relate to masonry construction, class types 5 and 6 relate to timber construction. This document rather than BS 1243 is now used as the primary reference when considering wall tie usage. For more information about DD140 please select this link.