Wall ties and cavity insulation
What is a butterfly wall tie, and how is it different from a strip tie?
A butterfly tie is a wire tie with a twist in the middle, used in many cavity walls. A strip tie is a flat metal tie. Both are there to hold the two leaves together. The name does not tell you whether this wall’s ties have corroded. Only an inspection that can see them, such as a borescope where that is agreed, can do that.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
From the outside, a cavity wall looks like brickwork. The ties are in the cavity. A visual home survey does not remove bricks as standard. It looks for the clues that ties may be failing: horizontal cracks in regular courses, a bulging outer leaf, or ties that have already been replaced and pointed. Those clues are not the same as seeing the metal.
The Energy Saving Trust’s cavity-insulation advice assumes a cavity that is suitable to fill. It is not a wall-tie survey. If the report suspects tie failure, filling the cavity first can hide the evidence and add a material you then have to work around. Ask which inspection would actually see the ties.
What should you ask your surveyor?
- Are you naming the type of tie, or only saying the wall is a cavity?
- Did you see ties, or only the clues on the face?
- Would cavity insulation be sensible before the ties are known?
What are the typical next steps?
- Do not drill insulation into a wall the surveyor has flagged for ties.
- If you need the metal confirmed, instruct a borescope inspection and agree how many openings.
- Ask the lender what they want in writing if the report mentions wall ties. Their rule is not the survey.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Are butterfly ties immune to rust?
No. Wire ties corrode, particularly in damp or exposed walls. The shape is not a guarantee.
Does a strip tie mean the house is pre-war?
Not reliably. Dating a wall from one tie you have not even seen is a guess. Ask the surveyor what they could date, and what they could not.