Wall Ties & Restraint Fixings
EC6, EN845, PD6697 and BS5268
The selection and spacing of wall ties depend on many factors. These include type of masonry to be tied, cavity width, type and height of building, location, and design life. There are several documents which need to be consulted and are summarised here.
Eurocode 6 – Design of Masonry Structures (BS EN 1996-1-1: 2005)
In 2010, Eurocode 6 became the main code for the design of reinforced and unreinforced masonry. Eurocode 6 refers to EN 845-1 for wall ties and sets the density of ties per square metre based on the declared value of the tie, the material factor and the design wind load. The material factor of 3.0 for detailed calculations is specified in the UK National Annex.
BS EN 845-1: 2013 Specification for Ancillary Components for Masonry - Part 1: Ties, Tension Straps, Hangers and Brackets
This European Standard specifies the requirements for wall ties used for interconnecting masonry and for connecting masonry to beams, columns or other parts of the building. Materials, tolerances, tie variations and the requirements for declared values, are all covered in this standard. For tie Types and qualifying criteria refer to PD 6697.
PD 6697: 2019 Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2
Published Document 6697 contains noncontradictory, complementary information from the withdrawn British Standard BS 5628, which was not included in the BS EN 1996 series.
It includes recommendations on tie lengths, embedment, density, material and positioning. Masonry-to-masonry ties are classified as Types 1 to 4; the relevant classification is determined by strength, function and use. Minimum declared values for tension and compression are listed for each tie Type.
BS 5628, Code of Practice for the Use of Masonry
BS 5628 was withdrawn when the Eurocode became the accepted National code in March 2010. The majority of information in this British Standard has been reproduced in PD 6697: 2010.
BS 5268-6.1: 1996 (Incorporating Amendments No. 1 and 2): Structural use of timber - Dwellings not exceeding seven storeys
BS 5268 provides recommendations for wall ties for timber framed buildings. Information is provided for the type of structure, location, embedment, density and positioning. These ties are classified as Types 5 to 7; minimum declared values in tension and compression are listed for Types 5 and 6.
Although BS 5268 was officially withdrawn on the full implementation of Eurocodes in March 2010, timber frame wall ties should continue to be selected from Types 5 to 7 as given in Annex B of BS 5268 Part 6.1: 1996, until further guidance is made available.
Masonry-to-Masonry Wall Tie Types to PD 6697: 2019*
| Tie Type | Application | Density | Max. Building Height | Geographical Location |
|---|---|---|---|---|
| Type 1 e.g. ST1 |
Heavy duty tie suitable for most building sizes and types. Not very flexible and not recommended for applications where there is expected to be excessive differential movement between leaves. |
2.5 ties/m2 3-4 ties/m at unbonded edges |
Any height | Suitable for most sites. However, for relatively tall or unusually shaped buildings in vulnerable areas such as coastal sites, the tie provision should be calculated. |
| Type 2 e.g. RT2 |
General purpose tie for domestic and small commercial buildings made with box-form masonry walls | As Type 1 | 15m | Suitable for flat (less than 1 in 20) open sites where the fundamental basic wind velocity does not exceed 31m/s and altitude is not more than 150m above sea level. Could be adequate for higher altitudes and sloping sites exceeding 1 in 20, if calculated. |
Type 2 ties are suitable for use outside the parameters stated e.g. sites over 150m above sea level, buildings exceeding 15 metres etc, if shown to be adequate by calculation. Contact us for more information.
| Tie Type | Application | Density | Max. Building Height | Geographical Location |
|---|---|---|---|---|
| Type 3 | Basic wall tie generally as Type 2 above | As Type 1 | 15m | As Type 2 but fundamental basic wind velocity limited to 27m/s. |
| Type 4 e.g. HRT4 |
Light duty wall tie suitable for box-form domestic dwellings with leaves of similar thickness | As Type 1 | 10m | Suitable for flat sites (less than 1 in 20) in towns and cities where the fundamental basic wind velocity does not exceed 27m/s and altitude is not more than 150m above sea level. |
Note: Fundamental basic wind velocity must be calculated for the specific altitude of the site, refer to Clause NA.2.4 in NA to BS EN 1991-1-4:2005. The table above provides only a brief summary of information. *Refer to PD 6697:2019 and NA to BS EN 1991-1-4:2005 for complete information.
Masonry-to-Timber Tie Types to BS 5268-6.1: 1996**
| Tie Type | Application | Density | Max. Building Height | Geographical Location |
|---|---|---|---|---|
| Type 5 | Timber Frame. Domestic, industrial and commercial developments of up to three storeys | 4.4 ties/m² 3-4 ties/m at unbonded edges |
15m | Suitable (at a density of 4.4 ties/m2) for buildings on flat sites in towns and cities where the basic wind speed does not exceed 25m/s and altitude is not more than 150m above sea level. In more severe situations the tie density should be increased to 7 ties/m2. |
| Type 6 e.g. STF50 |
As Type 5 but suitable for developments of up to four storeys | As Type 5 | 15m | Suitable (at a density of 4.4 ties/m2) for buildings on flat sites in towns and cities where the basic wind speed does not exceed 25m/s and altitude is not more than 150m above sea level. In more severe situations the tie density should be increased to 7 ties/m2. |
| Type 7 e.g. TFMT |
As Type 5 but suitable for developments of between five and seven storeys, being designed to accommodate the increased vertical differential movement | Calculated for actual performance required for each site location | 18m | Calculated for actual performance required for each site location. |
**Refer to BS 5268-6.1: 1996 and BS 6399-2: 1997 for complete information.
Minimum Requirements for Wall Ties to PD 6697: 2019 (Table 12) and BS 5268-6.1: 1996 (Annex B)
| Type of Tie | Minimum Mortar Class and Designation | Tensile Load Capacity (N) | Compressive Load Capacity (N) |
|---|---|---|---|
| 1 | M2 (iv) | 2500 | 2000 |
| 2 | M2 (iv) | 1800 | 1050 |
| 3 | M2 (iv) | 1100 | 650 |
| 4 | M2 (iv) | 650 | 350 |
| 5 | M4 (iii) | 600 | 425 |
| 6 | M4 (iii) | 630 | 440 |
| 7 | M4 (iii) | To be declared by the Wall Tie Manufacturer | |
Bracketed compression values are those confirmed for inclusion in the next issue of PD6697 following a change to test procedures in BS EN 846-5:2012, which affects wall tie tests from August 2015 and are applied by us as appropriate.
Approved Document E: Resistance to the Passage of Sound
This document specifies the acoustic performance requirements of ties suitable for use in separating walls (Type A ) and external walls (Type B) of new build dwellings. Click here for further information.
Lime Mortars
Ancon stainless steel wall ties and Teplo-BF wall ties are suitable for use with lime mortars (minimum strength HLM2); tie selection should be based on the general guidance here. Preference should be given to the most flexible wall tie that meets the structural load i.e. wire ties over strip/bar ties.
Wind Code Variations
Masonry wall ties should be selected from the Types in PD 6697 and timber frame wall ties should be selected from the Types in BS 5268. These two documents use different Wind Codes.
The maximum wind speeds referred to in PD 6697 are based on ten minute return periods according to the current Wind Code BS EN 1991-1-4: 2005.
The geographical locations in BS 5268-6.1 are based on hourly return period wind speeds according to BS 6399-2: 1997.
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