Professional Installation Tips: Cavity Screw Ties
The incorrect use of cavity screw ties is a common construction problem, whether it involves the wrong type of tie, an insufficient number of ties or simply improper installation (such as hooking ties together, retaining insulation with the use of masonry pieces or not maintaining the correct cavity width, all of which lead to cold bridging, dampness and sometimes complete failure.
Here are some tips to help ensure professional results when installing cavity screw ties:
- The correct length of wall tie can be ascertained using Table 5 of Approved Document A of the Building Regulations
- Each square metre of masonry will require 2.5 wall ties and so proper measurement in advance is essential in order to ensure the correct amount of ties is sourced
- Cavity wall insulation boards usually have a maximum dimension (on the short edge) of 450mm. This is because the maximum vertical spacing of ties is also 450mm (horizontal spacing should not exceed 900mm)
- Each tie should be set a minimum of 50mm into BOTH leaves of masonry
- Ties should be installed with a slight outward fall; this will prevent water being transferred to the inner leaf and possibly causing damp issues
- Only compatible accessories (such as plugs and insulation retaining clips) should be used with cavity screw ties. BS Fixings supply the correct accessories with each box of 10 ties
- Around openings (such as doors, windows, movement joints and roof verges), change the wall tie pattern. Vertical spacing is here reduced to 330mm maximum and should always be withing 225mm of the opening
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