Specific Structural Inspection Report on External Cracking to The Existing Chimney at Ground Floor
The structural inspection report has been prepared on the instructions of Gemma Bell our client. We have been requested by our client to carry out an external inspection of the existing chimney with a view to inspecting some cracking and dislodged brickwork to the base of the chimney. The visual survey was undertaken on the morning of the 12th of June 2020 The inspection took place externally and the weather was warm and overcast.
An intrusive investigation was carried out in the form of a small trial hole. The following other limitations in respect of this report should also be noted: The inspection was carried out externally at ground level. The inspection was of a purely visual nature.
Services within and to the property have not been inspected. In accordance with our standard practice we must point out that this report is based upon our inspection of the premises and any other information made available to us, both written and oral, which we have assumed to be correct.
This report is intended primarily for information and is to be read in conjunction with any other specialist reports and investigations. The report is for the benefit of Gemma Bell our client. Structural Engineering Services cannot accept any liability to any third party for the whole or part of its content.
Description of The Existing Building
The existing building is a two-story detached property located in Winkfield Row, . The existing property is constructed with masonry facades with the 1st floor formed in timber joists we assume supported off the internal central masonry load bearing wall as would be the roof structure. The roof is a pitched timber roof covered with clay tiles and the internal walls are a combination of timber and masonry stud partition walls. The surrounding properties are of a similar age and construction
There is cracking and dislodged brickwork to the base of the chimney breast with some bricks loose and easy to move by
hand. These cracks currently are up to 10.0mm in width (Refer to pictures 1 to 6) and the wall has also moved outwards at its base. There are two manholes located one to the front of the property and one to the rear and the drain run runs parallel with the flank wall to the house where the chimney is located. There are no major trees within close proximity to the property.
Based upon the British Geological Survey Maps the superficial deposits indicate Alluvium which is made up of clay, silt, sand and gravel with bedrock geology indicating the Bagshot Formation which is sand. A trial hole was dug to the corner of the chimney and wall and this indicated that the chimney appeared to be built off paving slabs and there was no foundation below this. (Refer to picture 5). The close proximity of the drain run is also a concern as there may be issues with this and there is an indication that the external ground has lifted around the manhole covers and drain run.
- We would suggest the following investigations/works are carried out:
1. A full CCTV survey report is carried out on all the local drainage to assess for any damage or leaks. If damage or leaks are found, they will need to be repaired as per the drainage report.
2. The trial hole dug indicates there is no discernable foundation so localized underpinning will be required to
stablilise the chimney. This can be carried out externally with minimal disruption to the existing property.
- Once the underpinning has been completed, we would suggest the following remedial works be carried out on the damage to the property:
1. Localized rebuilding works to the base of the chimney to reinstate the damaged and loose brickwork. It may be
feasible at this stage to try to realign the brickwork where it has moved previously and this may involve some
temporary propping to facilitate this.
Based upon the BRE digest 251 Table 1, Classification of visible damage to walls with particular reference to the ease of repair of plaster and brickwork or masonry and this information is listed out below for your information. Damage categories with descriptions of typical damage. Ease of repair in italics.
0 – Hairline cracks of less than about 0.1 mm which are classed as negligible. No action required.
1 – Fine cracks that can be treated easily using normal decoration. Damage generally restricted to internal wall finishes; cracks rarely visible in external brickwork. Typical crack widths up to 1 mm.
2 – Cracks easily filled. Recurrent cracks can be masked by suitable linings. Cracks not necessarily visible externally; some external repointing may be required to ensure weather-tightness. Doors and windows may stick slightly and require easing and adjusting. Typical crack widths up to 5 mm.
3 – Cracks that require some opening up and can be patched by a mason. Repointing of external brickwork and possibly a small amount of brickwork to be replaced. Doors and windows sticking. Service pipes may fracture. Weather-tightness often impaired. Typical crack widths are 5 to 15 mm, or several of, say, 3 mm.
4 – Extensive damage which requires breaking-out and replacing sections of walls, especially over doors and windows. Windows and door frames distorted, floor sloping noticeably. Walls leaning or bulging noticeably, some loss of bearing in beams. Service pipes disrupted. Typical crack widths are 15 to 25 mm, but also depends on number of cracks.
5 – Structural damage that requires a major repair job, involving partial or complete rebuilding. Beams lose bearing, walls
lean badly and require shoring. Windows broken with distortion. Danger of instability. Typical crack widths are greater than 25 mm but depends on the number of cracks.
In general, categories 0, 1 and 2 with crack widths up to 5 mm can be regarded as ‘aesthetic’ issues that require only redecoration. Categories 3 and 4 can generally be regarded as ‘serviceability’ issues, that is, they affect the weathertightness of the building and the operation of doors and windows. Category 5 presents ‘stability’ issues and is likely to require structural intervention. BRE Digest 251, and in particular the information above, is now used widely in the industry as a way of categorising cracks and determining whether any intervention is necessary.
It should be stressed that these comments are a simplification of the assessment needed to properly classify damage to housing. Several factors, including whether the widths of the cracks are increasing with time, can affect the classification. BRE Digest 251 should be consulted when carrying out any assessment and a building professional should be consulted where damage is significant.
This letter report is considered professional opinion and is not a warranty or guarantee as regards to the works undertaken and no liability shall be attached to us except to the extent that we have failed to exercise reasonable skills, care and diligence in the provision of our structural design services.