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Thornton Avenue

Proposed Internal and External Inspection of Front Bay Window and Surrounding Structure

Project Details:

Completion Date:

February 2020

Building Type:


Project Type:

Structural Reports


Thornton Avenue, London

Structural Engineer:

John Murphy


The structural inspection report has been prepared on the instructions of Ann Jones, our client. We have been requested by our client to carry out a site visit with a view to looking at the current condition of the front bay window structure to the property and to carry out a general internal and external inspection of the property to inspect some cracking and movement that has taken place, this has been highlighted as being an issue in the Clients Homebuyers Report carried out by Wonnacott Chartered Surveyors. The visual survey was undertaken on the afternoon of the 3rd of February 2019. The inspection took place internally and externally and the weather was cold and sunny. No intrusive investigations were carried out at this stage.

The following other limitations in respect of this report should also be noted: The inspection was carried out from within the property at all floor levels and at Ground floor level externally. The inspection was of a purely visual nature.

Services within and to the property have not been inspected. A Homebuyers report has been carried out in the past by Wonnacott Chartered Surveyors. 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 Ann Jones, 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 property is a three-story end of terraced house located in London. The property was built circa 1830. The property is formed of ground, first and second floor levels with the 2nd floor level being formed within the roof.

The property is formed in load bearing masonry walls typically 225mm wide (Possibly wider walls may be in place as its end
of terrace and three stories in height) with timber floors and roof construction. The internal walls are a combination of timber and masonry. The adjacent property No 43 is of a similar form of construction as is the rest of the Avenue. To the front of the property is a large tree which is located within the pavement and based upon the British Geological  Survey Maps the bedrock geology indicates London Clay Formation made up of clay and silt is the subsoil beneath the property. The existing foundations would be relatively shallow in nature and based upon the subsoil and mature tree location may be susceptible to tree root influence.

The elevations comprise fair faced brickwork and there are numerous areas of spalled brickwork and areas of previous repointing. Also, there are missing sections of the corbelled banding course where down pipes have been repositioned which need to be replaced. To the front of the building is a full height bay window which has been highlighted within the Homebuyers Report as being of concern. The front bay window at 1st floor level we would assume has been built in a half leaf of brickwork with external timber battens and pebble dashed render making it a substantially heavy form of construction.

At 2nd floor level to the bay window is a balcony area accessed from 2nd floor level and above the balcony is a timber
pitched roof with concrete tiles over. The roof structure to the bay window is supported off timber framing which
continues down to 1st floor level where the bay window structure cantilevers out.

Internal Inspection

Bay window structure at ground, 1st and 2nd floor levels

There are areas of internal cracking and movement generally at all floor levels. The cracking is more prevalent at 1st and 2nd floor levels and this can be seen in pictures 2 to 5 for the 2nd floor level and pictures 6, 7 and 8 for the 1st floor level where the cracking is worse to the left hand side of the window as viewed externally. At ground floor level there is also cracking around the bay window and ceiling.

External Inspection

Bay window structure at ground, 1st and 2nd floor levels

There are areas of cracking, movement and distortion generally at all floor levels as viewed externally. The bay window cantilevers out at 1st floor level and the loads from the structure above are supported on some form of framing within the bay window construction at 1st floor level. The support framing is unknown at present but with the level of distortion and  downward movement evident within the bay window structure would indicate that the supporting structure is suffering from excessive deflection.

We understand that the ground floor bay windows have been replaced within the last five years. The original window framing would have been in timber construction and its highly likely that the original window framing and mullions would have been offering some form of support to the cantilever supporting structure in place. The new window installation may have weakened the original support framing which has in turn then had a knock-on effect on the retained structure above.


Due to the level of internal and external cracking evident and localized distortion and movement to the bay window
structure we would recommend the following: Opening-up of the bay window structure at 1st floor level to establish the existing framing beams to confirm their condition and what form of support is in place to the bay window. This can be done both internally and externally. Following this exposure works some form of additional framing may be required to stabilize the bay window and limit any further movement.

The bay window masonry sills are in a poor condition and have suffered from rotation and slope inwards which is not a good design as this will allow excess rainwater to fall against the window structure. The amount of distortion and rotation to the sill will need further investigation works and can be tied in with the bay window framing exposure works. It’s quite possible that the sill may need to be replaced.

Externally the bay window structure has numerous defects and areas may need to be replaced due to excessive water penetration. It would be worth contacting a damp specialist to get their views/comments as to the amount and type of repairs required. A full timber specialist inspection should be undertaken to fully confirm what repairs and replacement works may be required.

There has been some obvious movement taking place to the bay window structure where it abuts the main house and there are vertical cracks to both sides of the bay. The left-hand cracking has been repaired in the past, but this has opened -up again and needs to be repaired to limit any further water ingress. This repair should be coordinated with the bay window opening-up works.

The window to the right of the bay window (Refer to pictures 20 and 21) has cracking and damage both below and above it. The lintel needs to be replaced and the cracked brickwork stitched using stainless steel heli-bar or similar with the areas repointed after to suit.

The extent and pattern/shape and locations of the cracking would suggest downward movement. We are unsure if this has now ceased or is an ongoing issue. This can be confirmed with movement monitoring undertaken for a period of say six months.

There is also a two-story bay window to the Criffel Avenue elevation which has also suffered from historic movement as there is evidence of cracked bricks and joints and fractures to the window sills ad lintels. Settlement is not unusual to bay  windows as the foundations tend to be shallow in nature compared to the main house foundations which can lead to differential settlement. As above we are unsure as to whether the movement is ongoing and movement monitoring would confirm if it’s an ongoing issue.


  • 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.



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