Greenford Avenue

Structural Letter Report: Two-Storey Detached Property

Structural Letter Report: Two-Storey Detached Property

This structural inspection letter report was prepared and commissioned under the instructions of our client, Mahomed Ashraf Jussab. We have been requested by our client to carry out a localised structural site inspection of cracking occurring in the first floor window bays, located at Southall, London. A single, non-disruptive site visit inspection was conducted on the Friday 10th of July 2020. The weather condition at the time of the inspection was clear and dry. This report is intended primarily for information and is to be read in conjunction with any other specialist reports and investigations.

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. Structural Engineering Services will not accept liability to any third party for any loss, consequential or otherwise, for whole or parts of the conclusion and recommendations provided in this report

Internal Crack Flank Wall

Project Details:

Structural Letter Report: Site Inspection 

Completion Date: July 2020

Building Type: Residential

Project Type: Structural Report

Location: Southall, London

Structural Engineer: John Murphy

Brief Description of The Existing Property

The property is a detached house built approximately in the early 1890s. The property is formed with a solid 225mm brick walls, suspended timber flooring and a traditional cut roof which has been replaced by bespoke support structure to allow for a rear loft conversion. First floor side/rear extension and single storey rear/side extension have been added within the last decade.

The local geological map has been highlighted in the figure indicated below. The underlying superficial deposit are indicated to be Langley Silt Member which is a combination of clay and silt. The bedrock geology is indicated to be London Clay Formation, which is a combination of sand, silt and clay. We carried out a non-intrusive general site inspection of the property. In order to provide a structural assessment on the cracking that has occurred and recommendations for any necessary structural repair work.

Observations Recorded:

Upon inspection of the interior:

  • Several cracking were observed to have developed during building works to replace the ground floor bay window frame. Additional notched timbers were installed above and existing first floor joists in the front bedroom.
  • In the ground floor reception room, vertical crack appears from the celling level between the interface of the left side of the bay windows and the main wall of the property. The cracking extends up to the first floor bedroom and is approximately 1-2mm wide. No signs of excessive deflections or cracking have been observed in the ceiling above the front elevation of the bay window.
  • In the first floor bedroom, cracking has occurred at the base of the wall on both the sides of the bay window.
  • On the right hand side the cracking has occurred in the plaster which are approximately 1-5mm wide and appear to be larger at the top that at the bottom.
  • Horizontal hairline cracking is observed along the bearing level of the window sill and vertical cracking have propagated along the side of the window sill.
  • Similar cracking pattern can be observed on the left hand side of the bay window. However, the vertical and horizontal cracking are propagating more boldly around the outline of what may be lintel(s) used to support the bay window walls at the first floor
  • No excessive deflections have been observed at the top of the first floor ceiling above the bay window.
  • The timber floor appears to have slightly dipped below the first floor bay window. No excessive deflections or vibrations outside the permitted tolerance allowance have been observed. Several cracking were observed to have developed during building works to replace the ground floor bay window frame. Additional notched timbers were installed above and existing first floor joists in the front bedroom.
  • In the ground floor reception room, vertical crack appears from the celling level between the interface of the left side of the bay windows and the main wall of the property. The cracking extends up to the first floor bedroom and is approximately 1-2mm wide. No signs of excessive deflections or cracking have been observed in the ceiling above the front elevation of the bay window.
  • In the first floor bedroom, cracking has occurred at the base of the wall on both the sides of the bay window.
  • On the right hand side the cracking has occurred in the plaster which are approximately 1-5mm wide and appear to be larger at the top that at the bottom.
  • Horizontal hairline cracking is observed along the bearing level of the window sill and vertical cracking have propagated along the side of the window sill.
  • Similar cracking pattern can be observed on the left hand side of the bay window. However, the vertical and horizontal cracking are propagating more boldly around the outline of what may be lintel(s) used to support the bay window walls at the first floor.
  • No excessive deflections have been observed at the top of the first floor ceiling above the bay window.
  • The timber floor appears to have slightly dipped below the first floor bay window. No excessive deflections or vibrations outside the permitted tolerance allowance have been observed.

Upon inspection of the exterior:

  • The cracking to the window sill describe above are also visible on the external face of the first floor bay window corners. This occurs on both sides of the bay windows and appear to be 1-5mm wide.
  • The front elevation of the first floor window bay appears to be slightly deflected around the mid-span. However, no signs of cracking have been observed.
  • No cracking or signs of ground movement have been observed around the base of the ground floor bay window.

Conclusion

  • Despite the age of the building, the structure appears to be overall in reasonably fair condition. Various cracking have been observed around the first floor bay windows and are considered to be category 1 and 2 of damage, as defined by the BRE Digest 251 – Assessment of damage in low-rise buildings. The cracking would require further opening up works to determine the extent of the cracking and the condition of the bay window support. The bay window is not considered to be in high risk of collapse but monitoring of the cracking will be require to ensure the cracking does not propagate further.
  • Although it is difficult to ascertain the exact cause of the cracking observed, the manner in which the cracking have propagated are indicative of potential structural defect in the support structure of the first floor bay window. This conclusion is reinforced by the dipped floor joists in this location and deflected front elevation of the bay window externally.
  • It should be pointed out that cracking had appeared during building works to replace the ground floor bay window frames due to slight deformations. This would could suggest that the window frame was possibly subjected to loading from the first floor bay. In such case, carefulness should be adopted to provide adequate temporary supports during the replacement stage in order to prevent damage.
  • Although the property is situated above superficial deposits containing both clay and granular material such as silt and sands, the cracking are unlikely to have developed as a result of ground and foundation movement. Although one relatively large tree is situated approximately 10m away from the front bay window, no signs of cracking or movement have been observed around the ground.

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