We’ve had a run of clients who have had a survey carried out by local residential surveyors for additional works that for whatever reason they haven’t been able to offer there client and they have come to us as we offer a full range of additional and specific defect surveys, for Damp, Drone Surveys for Roofs etc.
One of the more common is an endoscopic survey of a cavity for confirmation of cavity wall Insulation or to review for cavity wall tie failure.
Wall Tie Failure Survey
When it comes to the latter we use the guidance of BRE Digest 401 and that is using an endoscope or boroscope to review the condition of wall ties. As almost all our investigations are pre-purchase and although this is still intrusive it is much less intrusive than removing several wall ties for physical study and we take the advice contained within 401 as allowing this “For single dwellings or parts of dwellings, it is not normally sensible or economic to carry out chemical analysis or even to remove ties from walls against the wishes of the owner because of the likelihood of damage“
Now some professionals use the sampling rates table (Image Below) and the highlighted section to justify that a sample must always be taken but the same document above this table contains the statement above verbatim and to me and other professionals this means when dealing with a single dwelling we should use visual inspection in situ if its likely to cause issues with the building owner.
To make it clear in situ isn’t a substitute for removal, but in 99% of circumstances, we don’t do it, unless specifically asked and it’s agreed by all parties and one of them is required to supply a qualified builder to work under there instruction to remove the ties for us to inspect. When your selling a house you don’t want someone removing a tie from the top and bottom of your wall and ideally from every elevation on a terrace this is two but on a detached this is four elevations
Suggested Minimum Sampling Rates BRE Digest 401
Cavity Wall Tie Inspections
Usually, there is a report of suspected issues the most common being minor cracking in the mortar bedding where wall ties are expected to be, On our surveys, we would usually already have confirmed metal as we would have scanned the wall if reachable with a White Knight Metal detectors or one of our handheld detectors to confirm that where the cracks are likely in an area with metal ties.
We will scan a wall where the problem is, marking anywhere where there is metal detected in chalk this allows us to see where the likely location of ties are and once we’ve found them we will then usual select two per elevation as per Table 1 in BRE 401 we prefer one at ground level and one up high if they are all showing signs of issues, if they are not we will usually pick the most exposed corner too.
We then proceed to drill a 14mm hole to allow our endoscope in to the cavity above the suspected wall tie, allowing us to look at it from above and see the condition of the wall tie which we will then grade against Table 2 in BRE 401. We would do this as required for elevations and this would indicate if you need the work to go ahead.
Once we have the on-site inspection undertaken we will then fill in the holes using a cartridge mortar in most cases which isn’t guaranteed to match and we will leave site to compile the Specific Defects – Wall Ties Report.
Physical inspection and removal may still be required particularly if the wall is insulated as we won’t be able to see the wall ties given them a reference grading. Example of a cavity insulated from an Endoscopic Survey to confirm Cavity Wall Insulation is below:
Our Specific Defect Surveys and Endoscopic Surveys start from £450 as a stand-alone survey and report and can be even less if bolted on to a single visit. Each survey comes with a custom specific defect report.
Home Heroes Limited are a Construction Consultancy based in Canterbury, Kent Specialising as Party Wall Surveyors, Building Surveyors Canterbury and Historic Building Consultants you can contact us by filling in the contact form, emailing info@home-heroes.co.uk or calling 01227 806334
We cover Canterbury, Margate, Ramsgate, Whitstable, Herne Bay, Folkestone, Dover, Deal, Ash, Sandwich, Faversham, Sittingbourne and Other Kent Locations for all Our Party Wall, Building Surveys, Level 1, Level 2 and Level 3 Surveys