Incorrect use of cavity wall ties is one of the common problems found on site by our building control surveyors. The wrong choice of cavity wall tie, not enough ties, and wrong detailing around openings are frequently spotted.
Hooking wall ties together, using masonry chunks to retain the insulation and not maintaining the cavity width will all lead to cold bridging and dampness meaning the wall would have to be demolished and rebuilt.
Here are some easy steps to get your wall ties right:
- The length of wall tie needed is specified in table 5 of Approved Document A of the Building Regulations, reproduced below.
- You need two and a half wall ties per square metre of masonry. The maximum horizontal spacing is 900mm and the maximum vertical spacing is 450mm. That’s why cavity wall insulation boards usually have a maximum dimension on the short edge of 450mm.
- Set each wall tie a minimum of 50mm into both masonry leaves.
- Lay the wall ties to a slight ‘outward’ fall to prevent water passing to the inner leaf.
- Only use insulation retaining clips that are compatible with your tie.
- Change the wall tie pattern around openings such as windows, doors, roof verges and movement joints. Here the vertical spacing is reduced to a maximum 300mm and should be within 225mm of the opening. So realistically, that’s a wall tie every course of blocks within 225mm of the opening, which means you need to carefully cut (and clip) the insulation.
- Cavity wall ties should be stainless steel.
Follow these simple rules and you’ll meet the Building Regulation requirements every time.