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Disclaimer

The content of this book is in the nature of general comment and cannot be project specific advice. While it may be possible for some readers to draw useful conclusions from following the investigations and processes described in this book this should not be relied upon and appropriate professional advice should be sought as and if required.

FIRST EDITION 2012

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system in any form other than that provided, or transmitted in any form by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission from the publisher.

Distributed in Australia by Irwin Structures Pty Ltd

Please do not copy this book.

The author spent several hundred hours on its preparation,

so please reciprocate our trust by sending your friends to the following link:

www.crackinginhouses.com

rather than pirating this copyrighted work.

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11. Symptoms of Distress

This chapter is a grab bag of common symptoms of distress with explanations of common causes. In your investigation, you may be able to match some of your observations with these typical cases, keep in mind that I have oversimplified for clarity and often there can be more than one mechanism operating:

Corner Settlement Cracking. When footings move, they may heave or settle.

Settlement is generally more common. Corners tend to go ﬁrst with consequent

cracking around openings. Heave immediately in from such a corner may produce similar symptoms. Figure 11.1 shows some typical patterns and presentations:

Figure 11.1 - Corner Settlement Cracks

Typically a vertical or diagonal crack widening with height at a point of weakness, often over openings

settlement widest crack

gap

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Footing Rotation. When foundation conditions vary from one side of a footing to another, the footing may rotate and rotate the wall it is supporting. Small rotations in footings can cause major distress at tops of walls; a 1mm rotation in a 450m deep footing will grow to a 7mm gap at ceiling level, usually seen at the cornice. A common cause of such rotation is a change in foundation moisture, which may fluctuate on the outside of the footing but be comparatively stable on the inside. Most building structures effectively resist inward rotation, so its’ the outward

rotation that produces the distress we see. Also, in the case of cyclic movement, once a building cracks, the crack will distress and resist closure, repeated inward and outward footing rotation (with seasonal fluctuations for instance) will tend to ratchet a crack open.

rotation of footing in ground tilts walls outward gap or crack at cornice line wall cracks result

Figure 11.3 - Wall Rotation Distress

Look for the gap or crack at the cornice line. Check wall verticality with a spirit level.

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Other Wall Rotation. While most wall rotation is due to footing rotation due to differential foundation conditions, it can also occur

due to applied loads, retaining actions in particular. Figure 11.4 shows what can happen with an under done retaining structure. Small retaining structures are often not appropriately constructed:

Cracks in Footings. Although usually unseen below ground, cracks in walls may well continue down into footings although not always on the same alignment. In the case of old fashioned weak masonry footings this will greatly reduce the strength of the footing. Reinforced concrete footings will usually retain significant strength, even if cracked, but crack widths of more than about 2mm may be a problem. Investigating footing cracks below ground can be inconvenient and is often best done as part of a geotechnical investigation.

Figure 11.4 - Wall Rotation, Special Case

The retaining actions, not the foundation, are causing the problem

Retaining forces

Rotation

Figure 11.5 - Footing Cracks

Wall cracks may continue into footings below ground weakening them and making further movement more likely

at the weak point

settlement

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Out-of-Plane Distress. This is when the element, usually a wall moves sideways, either locally or by bodily rotation. There are many possible reasons for this but the most common is footing rotation. When the wall is rotated low down but hung onto by the roof structure at the top, it can lead to either a bow or rotation with a local step such as illustrated at Figure 11.6 below.

In brick veneer or cavity brick construction such a mechanism may also be

associated with failure of cavity ties that tie the outer brickwork, either to the inner skin or to the timber frame. If significant displacement has occurred between the outer masonry leaf and inner structure, there is likely to be an issue with the ties, although this may be the symptom rather than the cause.

Figure 11.6 - Out-of-Plane Movement of Masonry

Here we see a brick veneer skin rotating at the side of an opening. This kind of rotation is most commonly caused by footing rotation.

Rotation

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6. One of the most common factors affecting foundation performance is trees. Common guidelines for tree and shrub placement on reactive sites are to keep them well away, at least their mature height distance, from buildings. This does not accord with most peoples’preferences which means that vegetation too close to a building is very common.

How close is too close? This depends upon the species of planting, root

distribution, soil, plant size and maturity, depth of foundation, availability of water and many other factors. In this book I am trying to provide broad guidelines that will cover many common cases rather than complicated or rigorous analysis so the key things that I recommend assessing are the canopy size, distance and

availability of likely water sources.

You will have to take a guess at where the tree may look for water unless you have access to site investigations of some complexity, such as radar investigations of roots.

A clue here is that leaking storm-water lines are greatly sought after by trees and roots can follow such lines for a considerable distance.

Trees and shrubs most commonly cause settlement of the part of the building closest to them and outward rotation of strip footings towards the plant. Watering, particularly over-watering of plants can cause heave or in extreme cases saturation settlement.

If a large tree is removed, the foundation may heave and re-bound, perhaps leaving part of a building permanently slightly high, particularly if it was built when the plant was sizeable.

Figure 12.1 - Foundation Moisture Influences

Reactive foundations swell when excessively wet and shrink when excessively dry

Clay foundation swells & heaves

Underneath the house is often stable and dry.

movement & cracks Common sources:

Overflowing & leaking stormwater & plumbing, adverse drainage

Common sources: Trees and shrubs, adverse drainage

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13. Building Investigation

There are a variety of building investigation techniques and methods ranging from a casual look around to sophisticated remote sensing or destructive investigation. The investigations discussed in this chapter will be the more useful if you have already covered the background and site investigations outlined in Chapters 10 & 11. In the case of

foundation movement issues, there will invariably be interaction between site and building investigations; after looking at the building you might decide to review the site in more detail and vice versa.

1. Before commencing specific investigation, be sure you understand what you are looking at, whether it be from background information [Chapter 10] or a preliminary inspection, be aware of the type of construction both above and below ground and review the descriptions in chapters 6 & 7.

Start with a preliminary walk around and review signs of distress and related symptoms such as cracks, gaps and leaks.

Sketch a floor plan and mark on the defects like so:

Figure 13.1 - Sample Building Inspection Notes

Showing a grab-bag of minimal but vital information Bed 1 Bed 2 Study Living Dining Kitchen w.c. Ldry/bath Infil l sla b

slab settled approx 15mm, 2mm crack 15mm rotation wall crack 0 to 10mm> previous repair 20mm rotation 1 0 m m c ra c k @ w in d o w bouncy & soft floor tiles drummy 10mm crack @window Articulation joint 10mm at btm, 20mm@ top subﬂoor vents covered up <100mm freeboard!! tim ber f loor 1 10 crack at cornice crack at cornice plaster repaired at corner downpipe leaking at junction

New downpipes & stormwater drains at front

solid brick lightweight

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16. Remedial Siteworks

This chapter provides some common examples of remedial works that can be conducted outside the building to relieve structural distress problems. Many of these works are good practice in any case and should be conducted on a preventative basis, particularly those aimed at reducing foundation movement problems and especially those aimed at reducing reactive foundation movement.

1. Damp Foundation Issues

In most cases the best treatment for damp foundation problems is removal of the cause of the dampness. This is because it is extremely difficult to accurately control a source of damp and thus more reliable to simply remove it and accept a drier condition. In the case of reactive foundations this exposes the structure to the risk of further shrinkage settlement so this must be carefully considered. In many cases there is little choice but to accept this risk, the alternative being to attempt to manage the state and source of the dampness. Common causes of dampness that are readily solvable include the following:

Leaking plumbing. Fairly obvious but not always that easy to identify. Also see Page 44, but keep in mind that some leaks such as overflowing gutters may only be apparent under extreme rainfall and that leaks in sewers and stormwater systems can be difficult to identify. Plumbing checks should include at least checking supply lines by referencing the water meter over several hours when the building is unoccupied to rule out leaks. Stormwater should be checked by

blocking the outlet and holding head at least back to the bottom of the lowest downpipe. Sewers are generally difficult to check other than via camera investigations but are not common problems due to their depth and general soundness of construction compared to stormwater systems; also sewer leaks often make their presence felt by smell.

Detrimental site fall. If the site proﬁle falls towards the foundation and there is

evidence of this affecting the foundation performance, the usual remedy is to alter

the proﬁle to fall away from the building and install any necessary drainage

system. If the detrimental fall is in an adjacent sit,e it will be necessary to involve the neighbour. If cooperation cannot be obtained, legal advice may be sought to

confirm what action, if any, can be taken. The ﬁnal and least attractive option is to

install a subsurface cut-off drain near the foundation in an attempt to control the moisture; this is often a messy job and subsurface drains can be unreliable so is a last resort.

Detrimental subsurface drainage occurs when water is conducted by sloping impervious surfaces underground such as the bases of garden beds or service trenches. Faulty subsurface drains can occur when a pipe or geotextile drain is installed above the base of its trench: The pipe may be set to fall, but the trench

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requires local repointing of both skins it is often not practical. Proprietary remedial systems are designed to reduce such works and be applied from one face only. 9. Underpinning

Underpinning is the process of excavating beneath existing footings and pouring deep concrete pads in order to reach a more stable foundation. This can be an effective solution but there are numerous issues:

Advantages include the stability of the deeper foundation, the permanent nature of the works and the prospect of recovering movement by jacking.

Disadvantages include cost, (both for the underpinning and associated works such

as to the site and to ﬁnishes) lack of effectiveness against rotation, the likelihood of

ongoing differential movement between the underpinned and original parts of the Building.

Underpinning of any scale needs to be approached with caution and should only be specified after professional structural engineering and geotechnical engineering investigations and recommendations.

Perhaps because of its tangible nature underpinning is often considered before a complete investigation is even complete. There are very many cases where

appropriate attention to site development and maintenance and some compromise in expectations of building performance can avoid costly underpinning.

10. Grout Injection

Expanding grout injection is a method that can be used to raise or stabilise some structures, which have voids beneath into which the grout can be injected.

Situations in which this can produce an assured result are limited; for instance ﬂat

ground slabs under which voids have formed by subsidence. This technique should not be mistaken for a solution to foundation reactivity problems which are entirely different [Chapters 12 & 17]. If you are considering such works, carefully review what assurances are being offered and ensure you understand how the method can work and be effective in your case.

11. Structural Ties

Steel rod ties across or along a building suitably fixed to steel plates outside can be effective in reducing ongoing distress due to building movement. However, they need to be specified and detailed sensitively by a structural engineer familiar with such conservation works and with understanding of the frailty of the old building which may be extreme. The usual application is to old masonry buildings with chronic cracking. Masonry, more so old masonry, is very weak in comparison with even light gauge steel tie rods. If foundation movement persists a steel tie and plate can easily tear the corner out of old brickwork. Thus it is important that such systems are specified in conjunction with other conservation works and that there limitations are properly understood. Despite these limitations I have had great success with these systems over some decades.

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About the Author

Patrick Irwin is a structural engineer who specialises in forensic investigation of problems in building.• A graduate of the University of Melbourne, Australia, he has 30 years experience as a consulting structural engineer and is currently the principal of Irwin Structures, Consulting Structural Engineers.

Over the course of his career, he has conducted over 500 investigations of buildings with structural problems and provided extensive practical advice to clients.

He currently applies this expertise by acting as an expert witness on structural matters, providing authoritative reports and witness services to courts all over Australia. In addition to his consulting activities, Patrick sits on the Building Appeals Board in Victoria, Australia, the body that makes determinations on appeals against matters of building regulation and authorises modifications of the local building regulations.• From within the board and its subcommittee, he also advises the department and minister on building regulation matters.

Patrick and his practice have won numerous design awards from the steel industry, Building Commission and consulting groups.

He is currently deputy chairman of the Building Dispute Practitioners Society and writes regularly for their journal of record “The BDPS News”, winning their 2010 essay prize for an article on building movement causes and responsibilities.

Patrick is also on the committee of the Forensic Engineering Society of Australia in which he is encouraging the formation of a structural chapter.

This e-book summarises some of the important information relating to cracking in houses and other small buildings that he has collated and learnt in his many years of practice.

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Contents

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Figure 11.1 - Corner Settlement Cracks

Figure 11.3 - Wall Rotation Distress

Figure 11.5 - Footing Cracks

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Figure 13.1 - Sample Building Inspection Notes

About the Author