technical report on a subsidence claim

TECHNICAL REPORT ON A SUBSIDENCE CLAIM

Crawford Reference: SU1801348

J G Jones

3 Parkfield Stillington

York YO61 1JR

prepared for

RSA - MORE TH>N 6th Floor

Bowling Mill Dean Clough

Halifax HX3 5WA

Claim Reference 201804009786

SUBSIDENCE CLAIM

16 May 2018

Subsidence Division

Cartwright House, Tottle Road, Riverside Business Park, Nottingham, NG2 1RT

Tel: 0115 943 8230 Fax: 0121 200 0309

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TECHNICAL REPORT

Chartered Loss Adjusters

Cartwright House, Tottle Road, Riverside Business Park, Nottingham, NG2 1RT. Tel 0115 943 8260 www.crawfordandcompany.com Registered Office Crawford & Company Adjusters (UK) Ltd, 70 Mark Lane, London, EC3R 7NQ Registered in England No 2908444

Site Plan This plan is Not to Scale

This plan is diagrammatic only and has been prepared to illustrate the general position of the property and its relationship to nearby trees etc. The boundaries are not accurate, and do not infer or confer any rights of ownership or right of way. Position of utilities is only indicative and contractors must satisfy themselves regarding actual location before commencing works.

© Bluesky International & © Infoterra 2006. Map Reproduced with the Permission of Ordnance Survey License Number ########

Key:

Tree: Deciduous Tree: Conifer Shrub

Hedge Area of Damage Bore Hole

Trial Hole Trial & Bore Hole Level Monitoring

Rain Water Manhole Rain Water Gulley Rain Water Pipe

Waste Water Manhole Waste Water Gulley Toilet Pipe

Rain Water Drain Waste Water Drain Electricity Cable

Water Supply Pipe Gas Supply Pipe

Incoming Gas Pipe

Incoming Water

Incoming Electrics

5 Parkfield

Garage

TECHNICAL REPORT



INTRODUCTION We have been asked by RSA - MORE TH>N to comment on movement that has taken place to the above property. We are required to briefly describe the damage, establish a likely cause and list any remedial measures that may be needed. Our report should not be used in the same way as a pre-purchase survey. It has been prepared specifically in connection with the present insurance claim and should not be relied on as a statement of structural adequacy. It does not deal with the general condition of the building, decorations, timber rot or infestation etc. The report is made on behalf of Crawford & Company and by receiving the report and acting on it, the client - or any third party relying on it - accepts that no individual is personally liable in contract, tort or breach of Statutory duty. Where works address repairs that are not covered by the insurance policy we recommend that you seek professional advice on the repair methodology and whether the works will involve the Construction (Design & Management) Regulations 2015. Compliance with these Regulations is compulsory; failure to do so may result in prosecution. We have not taken account of the regulations and you must take appropriate advice. We have not commented on any part of the building that is covered or inaccessible. TECHNICAL CIRCUMSTANCES

We are advised following a recent drain blockage, damage to the drains was discovered. Damage to the main house and garage was also noted. We understand that some of this damage may have existed for a number of years. The Insured and his wife are both elderly and were not in a position to investigate the damage earlier. PROPERTY

Two storey detached house of traditional construction with part rendered brick walls surmounted by a pitched tiled roof. There is a large attached garage with brick walls and a flat felt roof. HISTORY & TIMESCALE

Date of Construction ................................................... Circa 1970 Purchased .................................................................... 1975 Policy Inception Date .................................................. 09/09/2005 Damage First Noticed .................................................. April 2018 Claim Notified to Insurer……………………… .................... 10/04/2018 Date of our Inspection ................................................. 10/05/2018 Issue of Report ............................................................ 16/05/2018 Anticipated Completion of Claim ................................ December 2019

TOPOGRAPHY

The property occupies a reasonably level site with no unusual or adverse topographic features.

TECHNICAL REPORT



GEOLOGY

Reference to the 1:625,000 scale British Geological Survey Map (solid edition) OS Tile number SENE suggests the underlying geology to be Sandstone. Sandstones comprise cemented sand particles. They have an average porosity of around 30% or more, depending on the degree and nature of the cementitious material that binds the grains. Although not shrinkable, the superficial weathered deposits may be. The superficial deposits are thought to be Clay Soils.

Clay soil superficial deposits are a cohesive soil characterised by their fine particle size and are usually derived from weathering of an underlying “solid geology” clay soil such as London Clay or Oxford Clay.

Like the solid geology sub-soil from which they are derived they shrink when dry, and swell when wet and can be troublesome when there is vegetation1 nearby and Gypsum and selenite crystals can be encountered (particularly in the south east). Protection using Class II Sulphate Resisting cement is therefore recommended for buried concrete.

Geology. Reproduced with consent of The British Geological Survey at Keyworth.

Licence IPR/34-7C CSL British Geological Survey. ©NERC. All rights Reserved.

1 DriscollL R. (1983) “Influence of Vegetation on Clays” Geotechnique. Vol 33.

TECHNICAL REPORT



VEGETATION

There are several trees and shrubs nearby, some with roots that may extend beneath the house foundations. The following are of particular interest:- Type Height Distance Ownership Ash 14 m 9 m Owners Ash 14 m 10 m Owners Deciduous 14 m 8 m Owners Sycamore 12 m 9 m Neighbour (No.5) Deciduous 12 m 11 m Neighbour (No.5) Deciduous 12 m 12 m Neighbour (No.5)

Tree roots can be troublesome in cohesive (clay) soils because they can induce volumetric change. They are rarely troublesome in non-cohesive soils (sands and gravels etc.) other than when they enter drains, in which case blockages can ensue. Ash (Fraxinus) are deciduous and can reach heights between 20-30m depending on health, environment and soil conditions. They have a fast growth rate of around 500mm per year, medium root activity2 and medium water demand. It is naturally vigorous and large growing, preferring light, fertile soils, but will grow on heavy clay. The maximum tree-to-damage distance recorded in the Kew survey was 21mtrs, and 50% of recorded cases occurred within 6mtrs3.

root affect 0.75m

H

H

0.25H

1.25H

'drip' line

H/3

0.2H

Typical Propert ies of a Broad Leaf Tree

Typical proportions of an Ash. Note the potential root zone.

Young and old trees are tolerant of quite heavy pruning and crown reduction, but the timber is not particularly decay resistant and re-growth will need periodic cutting to keep weight and wind resistance down. Life expectancy > 100years. Root pruning can leave tree vulnerable to disease.

Broadleaf trees typically have wider spreading roots and higher water demands than coniferous species and many are better adapted to growing on heavy clay soils. Some are capable of sprouting from cut stumps or bare wood and most will tolerate pruning better than conifers.

2 Richardson & Gale (1994) "Tree Recognition" Richardson's Botanical Identifications 3 Cutler & Richardson (1991) “Tree Roots & Buildings” Longman Scientific

TECHNICAL REPORT



root affect 0.75m

H

H

0.25H

1.25H

'drip' line

H/3

0.2H

Typical Propert ies of a Broad Leaf Tree

Typical proportions of a broadleaf tree. Note the potential root zone. It must be noted that every tree is different, and the root zone will vary with soil type, health of the tree and climatic conditions.

However heavy pruning of any tree should be avoided if possible, as it stimulates the formation of dense masses of weakly attached new branches which can become dangerous if not re-cut periodically to keep their weight down. Sycamores (Acer) are deciduous and can reach heights between 20-30m depending on health, environment and soil conditions. They have a fast growth rate of around 600mm per year and medium root activity4. The Sycamore is a hardy tree, and can withstand quite aggressive environments. Maximum tree-to-damage distance recorded in the Kew survey was 20mtrs, with 50% of cases occurring within 6mtrs5. They are deep rooting on clay soils and have a life expectancy > 100 years.

root affect 0.75m

H

H

0.25H

'drip' line

H/2

0.2H

They can usually tolerate quite heavy pruning or crown thinning, although this can create large wounds which decay rapidly. OBSERVATIONS

The Main House and Garage are the focal points of the Insured's concerns / movement. The following is an abbreviated description. Photographs accompanying this report illustrate the nature and extent of the problem.

4 Richardson & Gale (1994) "Tree Recognition" Richardson's Botanical Identifications 5 Cutler & Richardson (1991) “Tree Roots & Buildings” Longman Scientific

TECHNICAL REPORT



INTERNAL

Crack to rear wall of rear left bedroom Cracking/heave to garage floor slab Rear Dining Room – 2mm wide diagonal crack to external wall near front left corner. 2mm wide vertical crack to top left of rear window. 1st Floor Office – 3mm wide vertical crack to bottom right of window. Circa 3mm wide cracking to top left of window and to left wall/ceiling junction. Front Left Bedroom – 1mm wide cracking across ceiling. Front Right Bedroom – 1mm wide previously repaired crack across ceiling. Landing – hairline cracks to walls and ceiling. Kitchen – hairline cracks to walls and ceiling. Lounge – 1mm wide cracks in ceiling/coving. Garage – upward heave of concrete floor, particularly in the centre of the floor. Cracking to floor up to 15mm in width. Salts visible around edges of cracks. EXTERNAL

Crack to top corner of rear left bedroom

window Cracking/movement to brickwork at rear of

garage Rear Elevation – diagonal crack to top right of office window 4mm in width. Cracking up to 2mm wide below window. 1mm wide horizontal crack between office and bedroom windows. 1mm wide crack to top left of bedroom window.

TECHNICAL REPORT



Left Elevation – 1mm wide diagonal crack in render below 1st floor window. Right Elevation – hairline diagonal crack in render to front right corner. 1mm wide vertical crack in render below 1st floor window. Circa 15mm wide crack to top right of rear door opening. Garage – cracking up to 12mm in width to brickwork at low level around rear right corner. Displacement of brickwork by around 10mm. Diagonal 1mm wide crack to rear elevation. CATEGORY In structural terms the damage falls into Category 3 of Table 1, Building Research Establishment6 Digest 251, which describes it as “moderate”.

Category 0 "negligible" < 0.1mm

Category 1 "very slight" 0.1 - 1mm

Category 2 "slight" >1 but < 5mm

Category 3 "moderate" >5 but < 15mm

Category 4 "severe" >15 but < 25mm

Category 5 "very severe" >25 mm

Extract from Table 1, B.R.E. Digest 251

Classification of damage based on crack widths.

DISCUSSION

The pattern and nature of the cracking to the rear left of the main house is indicative of an episode of subsidence. The cause of movement appears to be either clay shrinkage or an escape of water. The likely presence of shrinkable clay beneath the foundations and the proximity of vegetation where there is damage indicates that clay shrinkage will most likely be root induced. This is a commonly encountered problem and probably accounts for around 70% of subsidence claims notified to insurers. Fortunately, the cause of the problem (dehydration) is reversible. Clay soils will re-hydrate in the winter months, causing the clays to swell and the cracks to close. Provided the cause of movement is dealt with (in this case, vegetation) there should not be a recurrence of movement. Water escaping from drains or from other sources in non-cohesive soils can cause localised erosion as the finer particles of soil are washed away. It can also soften cohesive soils by reducing their shear strength. Usually, the building stabilises following repairs to the damaged service. We note that the condition of the drainage in the immediate vicinity of the subsidence movement was not possible to ascertain during the recent CCTV survey.

6 Building Research Establishment, Garston, Watford. Tel: 01923.674040

TECHNICAL REPORT



DAMAGE NOT RELATED TO THE SUBSIDENCE CLAIM The damage to the garage floor slab and cracking to the garage walls is indicative of sulphate attack. Unfortunately, this is a commonly encountered problem in houses of this age and style of construction. Symptoms include cracking, crazing and bulging of the slab, and traces of white salts on the surface. The problem is the result of a chemical reaction between the sulphate contaminated fill on which the floor has been cast, and the cement paste in the slab. The reaction also causes expansion of the fill material, with the slab breaking down gradually, with a consequent loss in strength. The external walls can also be affected due to the pressure created by the expansion. A water source is required for the reaction to take place. However, if the supply of water stops, or is diverted, the reaction ceases. The cracks in the ceilings appear to be due to normal deterioration, shrinkage, and differential movement. Ceilings crack for many reasons. For example, older lath and plaster ceilings suffer as a result of seasonal shrinkage of the underlying laths or fail simply due to age. Modern ceilings are, by comparison, relatively thin and brittle structures, and they often crack because of shrinkage. Shrinkage of the material itself, or of the joists onto which they are fixed. Also, if the joints between boards have not been adequately taped, or the boards have not been properly edge fixed, then cracks will appear. The pattern and nature of some of the cracks tends to suggest they are the product of the form of construction, rather than foundation movement. Timber shrinks and swells seasonally, and some cracking is inevitable from time to time. In addition, brickwork and timber expand and contract at differing rates, which can exacerbate damage. The cracking to the rear elevation above the entrance door is likely related to corrosion of the steel lintel. There is no corresponding internal damage, which indicates that the issue is not subsidence related. Cracking to the render coating to the left and right elevations is the result of thermal movement and gradual deterioration.

TECHNICAL REPORT



RECOMMENDATIONS

Further investigations are required to determine the exact cause of subsidence damage. This will involve excavation of exploratory trial pits/boreholes, as well as examination of the drainage to the rear left of the property. We note the vegetation is subject to a Preservation Order. Unfortunately, current legislation requires certain investigations to be carried out to support an application for the tree works. Typically, these investigations would involve monitoring to establish the rate and pattern of movement. The monitoring data provided must be sufficient to show a pattern of movement consistent with the influence of the vegetation and therefore it may be necessary to carry out the monitoring for up to a 12 month period. It will also be necessary to obtain a specialist Arboricultural Report. We will report further once these investigations have been completed. Craig Nicholson BSc (Hons) MCIOB Dip CII (Claims) Crawford & Company Subsidence Division Direct Dial : 07917 584059 [email protected]

mailto:[email protected]

TECHNICAL REPORT



PHOTOGRAPHS

Cracking to top corner of rear doorway Vegetation to rear of property

Crack to left wall of rear dining room Crack to rear wall of dining room

Cracking to rear left corner of rear left bedroom

Non subsidence cracking to front right bedroom

technical report on a subsidence claim

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