Wall Tie Densities and Spacing
Why is wall tie replacement required ?
There are two reasons why one might need replacement wall ties. The first is when the walls of a cavity wall structure have been built defectively. For example where the original built-in tie installation system has been incorrectly fitted, fitted with ties that are too short or fitted with ties at incorrect spacings. The second is where the original cavity tie system comprises metal connectors that exhibit corrosion.
In both cases installation of a cavity wall tie replacement system will ensure that the outer brick facade wall is firmly anchored to the buildings inner and main structural masonry wall, allowing applied loads to be transferred and shared.
How many ties do I need & what wall tie spacing is recommended ?
Provided that your walls are of a typical masonry cavity wall make-up, with each leaf being at least 90mm in thickness, you will need to install the remedial tying system at the rate of 2.5 wall ties per m2.
Wall tie spacing should be at 900mm centres vertically by 450mm centres horizontally, in a staggered 'domino 5' pattern. An additional vertical row of wall ties should be inserted at open reveals (gable apexes, windows, door openings, etc.) so that there is 1 wall tie per 300mm (height) of wall.
In the unlikely event that either wall is less than 90mm thick, wall tie spacing should increase from 2.5 ties / sq. metre to 5 ties per m2 (450 x 450mm). For wall tie replacement in brick clad timber frame construction wall tie installation should be spaced at 4.4 wall ties / m2.
Which is the correct type of wall tie for my property?
This will require investigation by you. You should first check to see whether you have cavity wall insulation. If you have, you should avoid using chemically reactive resins and choose a wall tie system that uses the smallest installation bore in order to minimise any effect on thermal efficiencies. You will need to drill at least one investigation hole to each elevation and determine whether the bricks or blocks are solid (drilling rate will be constant) or whether they have perforations (drilling rate will be inconsistent).
- For tying solid brick and masonry walls select a Mechanical Tie, Resin Grouted Tie or Helical Screw-in Tie.
- For tying walls with perforated bricks or blocks choose from a Resin Grouted Tie in a sleeve or a Helical Screw Tie.
- For cavity insulated walls choose from a Mechanical Tie or a Hammer-fix Screw-in Tie.
- For buildings requiring greater than half hour fire performance use a Helical Screw in Wall Tie