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  • Desain Rumah Minimalis Terbaru 2015

    Common Causes For Residential Building Failures



    By Damien Swart
    A/Overview
    This document has been written to give clients of Property Protect an understanding of the most common types of building defects that can be found in buildings whilst doing an AS 4349.1 inspection. This list gives the reader a basic outline of the more common defects and the reader should be aware that there are literally thousands of forms of building defects. The items which we have listed are the more common ones only.

    B/Abstract

    The report lists some of the more common residential building failures including the causes based on the case studies carried out by the writer as a licensed Builder. The writer has also included some of the causes of the failures.

    Purpose
    The purpose of this report is to give the reader a summary of the types of residential building failures and the suggested remedies to these defects.

    Method
    This report is presented as a case study based on the experience and personal records of the author over the last 15 years as a licensed Builder.

    Findings
    A large proportion of structural building failures listed in this report have in my opinion been caused by the mismanagement of stormwater around houses leading to movement in the homes. The remainder of the failures are caused by poor building practices and or poor maintenance.

    C/Introduction

    The most common forms of Building failure noted during AS 4349.1 house inspections by the writer in Adelaide are as follows.

    Slab Edge wetting
    This is the horizontal ingress of moisture and salts in solution from the soil which enter into footing edges through the capillary action (Suction caused by the concrete) of the concrete. It is caused by a number of factors including, Concretors pushing down the Fortecon membrane with edge forms prior to pouring a floor slab, relatively poor cement concrete in the footing (Many engineers have called for 32 MPA concrete to resist the ingress of salts in lieu of 20 to 25 MPA currently used), Concrete over pours caused when concretors edge forms are not placed low enough to stop a horizontal over pour which can lead to water ponding on the top face of the over pour creating a pool of water. The final cause is the lack of a plastic membrane to be placed between the paving and the footing edge.

    The damage that can be caused though this problem includes, mould and rotting to the underside of floor coverings internally and the fretting of the concrete through the salt attacking the cement matrix through a hydraulic action both internally and externally. (Salt crystals expand inside the concrete matrix thereby causing it to fret and crack).

    Rising Damp in walls
    This is a similar problem to Salt damp detailed below. The main difference is that Salt damp is generally a 90 to 100% break down of the Damp Course in the wall whilst rising dampness is a partial failure of the Damp Course and the partial failure generally means that the damage to the masonry wall is not as bad as Salt damp. There is a good chance that rising dampness may be found in most pre 1950 homes and the Rising dampness could be limited to erosion of the mortar joints by as little as 1 to 2 mm from its original face. The treatment is the same is Salt damp.

    The client should be aware however that in most cases the rising dampness is not treated as the erosion of the masonry is very slow and it may have taken 50 years for the mortar to erode 4mm deep from the face of the brickwork. I would advise clients to monitor this if the damage is not major.

    Salt Damp in Walls
    This is caused through the vertical ingress of moisture and salts into a wall which can lead to the wall fretting and not being able to take structural loads. The damage caused to the masonry is from the salt crystals inside the masonry expanding leading to the bricks and or mortar fretting. In some cases the salt damp can render the masonry unstable.

    It is caused by a number of factors including the full breakdown of the damp course (Pre 1910 homes had pitch or bitumen between the footing and bricks and this becomes brittle with age), paving and or render bridging the damp course also causes this.

    Breacher piece failures in showers This is where the breacher piece fails through metal fatigue via thousands of heat cycles inside the wall (This is where the hot and cold water meet inside the wall in the shower). Water then flows into the walls. Generally a breacher piece will fail in a shower every 25 to 30 years or so and it is quite common. A tell tale sign of a breacher which has been replaced is two off different tiles to the walls of the shower.

    During inspections carried out by Property Protect the company carries out a survey of the wet area walls in its premium report using an electronic moisture meter to identify this defect. High moisture levels to the walls next to the shower generally indicate that it is leaking.

    Brick Growth
    Cracks in walls Older homes can have brick growth cracks which usually occur at the end of a wall in a vertical plane. Clay bricks will actually expand as they are porous. If a house does not have control joints in the wall the bricks can exert a compression load on one another leading to cracking.

    Terracotta roof tiles
    Fired clay roof tiles will fret when exposed to moisture for long periods of time and this generally occurs at the laps of the tiles. The tiles can also fret in seaside environments due to salt attacking the tiles. It is not uncommon to see these roof tiles fretting to the laps on the underside of the roof tiles. As these tiles age they can also become very brittle and are easily cracked.

    In most instances when the tiles are fretting they will need replacing within the short term. Concrete cancer in footings and precast concrete lintels. This occurs when the steel bars inside the concrete rust due to moisture/salt/Carbonation ingress into the concrete. As the bars rust they expand causing the concrete to crack. This can cause cracking in the surrounding concrete elements. The client should be aware that it is very expensive to repair this defect.

    Tree damage
    Although some tree roots can cause hydraulic damage from the roots physically moving the building element, most Building failures are caused by the tree withdrawing moisture from the soil. This then leads to the soil contracting which can cause Building elements to drop or move.

    In a large number of inspections over the years the writer has observed walls and footings dropping or moving due to soil contraction when a tree is too close to the base of a wall. In most instances the writer would advise clients to keep large trees well away from the house. If this is not possible an impermeable root fabric can be used to stop the tree roots growing under a house.

    Stormwater damage and Soil movement
    This is caused when gutters, stormwater pipes and downpipes overflow/leak causing the soil around and under the footing to be saturated. Once the soil becomes saturated it then loses its ability to take load and the soil can collapse leading to the Building element dropping or moving. In some instances reactive soils can expand also leading to cracking. This then places uplifting loads on a house which can lead to significant cracking and movement as well.

    In Adelaide reactive (fine soils such as clays) can be found at the base of the foothills where fine silts run off the hills. The fine reactive soils can generally be found in Rostrevor, Athelstone and Campbelltown.

    Lack of Paving around the external perimeter. This can cause expansion and contraction in the soil around the footing leading to movement in the Building. ie Expansion in soil after heavy rains and contraction in the soil in the summer. In some instances the contraction of the soil under the footing (on the external portion) can lead to the footing rotating on the external side as it drops. The author has seen many instances of this occurring and this leads to the whole wall leaning out or in. (Bows out at the base and then leans in at the top). In these instances the wall generally needs to be pulled down and rebuilt.

    In many of the Property Protect reports you may see a note detailing seal gaps at the footing paving junction. Many houses inspected by this company have gaps at this junction and this can allow moisture to enter both under the house and also under the paving. Where the water enters under both elements it can erode the soil away and or cause the soil to either expand or contract. In this instance the gap should be sealed off with a flexible sealant.

    Older style wiring.
    The author has seen electrical failures from the following during inspections over the years., -Canvas coated and vulcanised rubber power cables. In the first instance the canvas can be eaten by rodents or just physically ages leading to the cables being exposed which can result in fires. The same can happen with older rubber cables which can split.

    -Power cables not in conduit in contact with steel frames. I.e. If the cables are damaged the frame becomes live. A number of houses over the years have been inspected by Property Protect and found to have new wiring in all areas of the house but not inside the existing hard plaster. During the premium house inspections this company uses a high powered torch to identify wall patches and chases to the walls. An existing house without wall chases above the light switches and power points would generally indicate that the original wiring has not been removed. In this instance Property Protect would advise the client to engage an electrician to carry out a survey of the house to confirm if the wiring is original to these areas. Hard plaster cannot be removed during a house inspection as the vendor would not generally approve this.

    Leaking pipes in wet areas This is generally caused through corrosion of lead or galvanised steel waste pipes under or in floor slabs. As the pipes corrode this leads to a leak which can wash away sub fill in a floor leading to the floor and or footing dropping.

    This is very expensive to repair as generally the pipes are cast into the floor slabs in the wet areas and they need to be jack hammered up. This is a common defect as a large number of houses in pre 1970 properties have galvanised steel pipes cast into the floor slabs. For these steel pipes it is not a matter of if but when the pipes need to be replaced . Having stated this steel pipes although not draining as well as they should do can function for many years until funds can be found to replace them.

    If you have steel waste and or water supply pipes in a pre 1970 house and you are contemplating a wet area renovation with new tiles etc we would strongly advise you to remove the steel pipes prior to the renovation.ie If you renovate the wet areas without removing the steel pipes a failure of the pipes could result in you having to re renovate the wet area at great cost again!

    Cracks/Movement in walls
    Movement in any home is hard to control. In most instances cracks are caused by changes in soil moisture levels around the footing although trees can also cause significant movement. Horizontal cracks can occur in walls if a window lintel sags or if a footing/wall drops.

    Diagonal cracks radiating away from window and or door heads are the most common form of cracks. Lateral movement cracks can occur with a shear load if a footing rotates (Drops) on one side. Due to Adelaide's dry climate soil shrinkage related cracking in homes is causing many problems. This leads to footing settlement (Dropping of the footing) and cracks in all building elements.

    Roof frame failures
    The first type of failure is for an older style roof which does not have under purlins and or struts. In this instance the failure is generally from the frame not being able to take the dead loads from the weight of roof tiles. It is common to see the frame sag heavily and split and this instance repairs may need to be carried out. If a roof frame is sagging from the weight of the roof tiles and the timber frame is not splitting or showing any signs of stress our advice to you is to closely monitor the roof frame.

    In the second instance the writer has seen heavy splitting to timber around defective gang nail trusses manufactured in the 1970's. In some instances the trusses could not take roof loads and sagged.

    White ant attack
    Property Protect does not carry out a survey for white ants in our inspections and we would advise that you engage a pest controller to do this. White ant attack is a very common problem in Buildings with the ants literally eating any form of timber in a home. As the timber wall frame is load bearing in a brick veneer home this can led to structural failures. The ants will normally enter a home where voids are close to the ground. One example of an entry point is where the paving bridges the Damp Course allowing ants to enter a wall cavity through weep holes (i.e. the paving is poured above the Damp Course in the wall).

    A second example is where garden beds are placed up against walls without any paving and in this instance we would advise on removing the garden bed and then installing paving all around the house.

    Poor Workmanship
    The following defects are caused by poor workmanship which does not comply with the Building Code. -Render in brick wall weep holes This stops condensation from draining out of a cavity. The writer has seen fretting render caused by blocked weep holes. -Bricks overhanging the footing. BCA allows a tolerance but in many instances concreters' set out the slab incorrectly. As the wall is not supported the bricks can bow out.

    -Render bridging wall Damp Courses In many instances plasterers do not strike a horizontal line through render which can result in ground moisture and salts rising up into the wall by passing the Damp Course. This can cause Salt damp in a wall.

    -Concrete slabs poured up against brickwork. In some instances around porch slabs builders sometimes place the Damp Course one brick course above the footing and pour the porch slab up against the first course of clay bricks. In this situation clay bricks are not designed to be exposed to ground moisture and salts for extended periods of time and this leads to fretting of the bricks.

    This is sometimes seen in older houses and it is hard to fix this if the fretting of the walls is heavy. Subject to a site visit sometimes the best option in this instance is to jackhammer up the floor slab and then repour the concrete below the Damp Course. At the end of the day this is an expensive problem to rectify. The writer has seen this in many garages in pre 1980 houses.

    -Puddle flanges to wet areas not installed correctly. Puddle flanges are designed to drain any water caught between the waterproof membrane and the floor tiles. In some instances the flanges are laid proud of the floor and the trapped water cannot drain into the waste pipe. In a second floor building this ponding water can bypass the membrane leading to the timber floor swelling and door, wall and window frames jamming up from compression loads. If this has occurred it is very expensive to repair.

    -Waterproof membranes to showers This is probably the largest of the observed failures mentioned in this article in my opinion. If a shower leaks this can cause heavy damage to the timber wall frame via wood rot and water damage. In masonry wall long term moisture leaks into the surrounding walls can lead to fretting of the masonry brick walls and render. In a metal wall frame heavy rusting can occur.

    In a timber wall frame long term leaks into the shower walls can also cause swelling of the wall cladding and wall tiles debonding and cracking. In a masonry wall the high moisture levels can lead to the tiles cracking and or debonding off the walls.

    The BCA (Building Code) requires silicone to the internal wall corners of a shower and many tilers still grout these areas which leads to cracking as the grout is rigid. The BCA also requires an angle to be installed at the wall floor junction in the shower and in many instances this is not installed.

    Many waterproof membranes are not installed correctly or the wrong materials are used.ie Bitumen membranes to showers which leach into the grout, liquid membranes not reinforced with polypropylene gauze fabrics. Etc.

    Asbestos
    Most homes built before 1988 would have some cement asbestos based cladding in the house. Property Protect can carry out a survey to identify this based on our opinion only in our premium report. This can only be verified by analysing samples under a microscope in a laboratory so any survey is based on our opinion only and would need to be confirmed by the Lab. Our premium report does not analyse the samples in a Laboratory.

    If this material is disturbed by grinding, drilling or cutting it can be fatal. Areas where it can be found in a house include.

    -Backing sheet for the power board -Old floor coverings -Eaves cladding externally. -Wet area cladding Etc.

    D/Discussion

    In terms of the remedies to the failures identified above these are as follows.

    Slab edge wetting
    This can quite easily be solved by stopping the transfer of moisture horizontally into the slab by placing an impervious membrane between the paving and the footing or directly onto the full depth of the footing. Plastic, waterproof membranes (Liquid or sheet) are the best remedies.

    Salt damp
    This can be repaired by forming a new Damp Course by undersetting (removing bricks and inserting a new plastic membrane) or chemical injection (Silane siloxane injection) where the Damp Course has failed. Where the paving bridges the damp course the paving should be lowered. If render bridges the Damp Course the render can be removed.

    Breacher piece failures
    In this instance generally four off wall tiles, the affected render and the original fitting are removed. The reverse is then carried out with new materials.

    Brick Growth cracks
    This form of cracking can be stopped by forming control joints in the wall above the windows and doors to allow the bricks to expand from long term moisture absorption.

    Terracotta roof tiles
    Generally if these tiles are fretting at the laps they should be removed and then replaced with new concrete roof tiles or metal roof cladding.

    Concrete Cancer
    The only way that this can be repaired is by physically removing the affected concrete fully exposing 360 Degrees of the bar, placing saw cuts , grit blasting steel, prime steel with zinc cold galvanising, prime and then replace concrete with a polymer modified shrinkage compensated repair mortar. In order to stop contaminants (Chloride ions and carbon dioxide) entering the concrete, a coating (Acrylics) should be applied to stop water and contaminant ingress. This is applied after the repair is carried out.

    Trees
    Once minor damage to homes has been caused generally it is not viable from a financial perspective to carry out major repairs. In some instances this may happen but this is rare. If a wall has dropped from soil shrinkage the most common rectification is to under pin the footing. This involves excavating under the existing footing, propping, pouring a new footing and then grouting between the new and existing footings. Under pinning is very expensive.

    If trees cannot be removed a trench approx 2m deep can be dug between the house and the tree and then lined with an impermeable root fabric to stop the tree roots growing under the house.

    Stormwater damage
    If the gutters and downpipes are leaking they should be repaired and or replaced. In most instances these elements do not drain out to the street. If this is the case the stormwater should be diverted out to the street via stormwater pipes.

    Lack of Paving.
    The essential elements to control cracking in older homes is to keep the soil around the footing in a stable moisture range. This can be achieved by installing paving .It is important however to water gardens consistently during summer for a fixed duration and intervals in areas adjacent to the paving. This keeps the soil moist adjacent to the paving (Best to use an electronic watering system).

    Older style wiring In order to stop the chance of an electrical fire, older wiring should be removed and replaced with new PVC wiring together with the installation of earth leakage circuit breakers.

    Leaking pipes
    In order to check if existing pipes are corroding a plumber can pressure test the pipes or use a CCTV system. Generally any older steel or lead pipes should be removed and replaced with PVC however this can be expensive as concrete floors need to be jack hammered to access the pipes.

    Cracks in walls
    Generally the best way to control movement is to articulate a house. This allows it to move by installing wall control joints above windows and doors and slip joints between the hard plaster and the brickwork. To form a slip joint remove render, install mesh onto bricks and replaster with a lime rich mortar. A lime rich mortar is used to reduce the cement content and hence the rigidity of the render with a 1 cement, 10 sand and 2 parts lime mortar).

    In relation to soil shrinkage cracks a number of soil engineers in Adelaide have instigated the direct injection of water into the soil around the footings to the external perimeter of homes (Mainly to Parkside). This keeps the soil in a stable moisture range via the computer controlled injection of water into the soil.

    Roof Frame failures
    In most instances roof frame failures are easy to rectify by propping the sagged or damaged area and either lapping the member either side with new timber or inserting additional props (The props generally run from the under purlin to the internal wall). In the case of gang nail failures lapped timber bolted either side of the affected timber can also solve this defect.

    White ant failures.
    Ants can be prevented from entering a house via chemical sprays , Ant caps (Stumped homes) or stainless steel mesh barriers (Termimesh). If existing homes are infested, the homes can be sprayed with chemicals or have bait stations inserted placed around the external perimeter of the home which are literally baited with poisoned timbers (Sentricon system).

    Property Protect does not carry out a survey for white ants in our pre purchase inspections and we would advise that you engage a pest controller to do this.

    Poor workmanship In each instance the work should be carried out as per the requirements in the BCA ie.

    -Weep holes During rendering cut the render out of the weepholes
    -Bricks Overhang footing Set out floor slab correctly.
    -Render bridges damp Course Cut a horizontal line in the render over the DPC
    -Concrete slab poured up against bricks Ensure that the i.e. porch slab is poured up against the edge of the main footing.
    -Puddle flanges Ensure that the flange is flush with the top of the floor. The timber/concrete needs to be rebated down to allow the flange to sit flush with the floor.
    -Membrane to showers Ensure that the membrane is installed in accordance with the BCA.

    E/Conclusions
    The bulk of the causes of Building failures as detailed in this cast study are due to changes in the moisture conditions in the soil around the footings due to seasonal change. The remedies discussed revolve around keeping the soil in a constant moisture state. The measures discussed include installing paving and electronic garden watering systems, diverting stormwater away from the house, ensuring plumbing does not leak, Keeping tree roots away from footings and articulating older homes to enable them to move.

    Of the remaining failures many are due to poor maintenance and or construction techniques. Ie Damp Courses bridging paving (Non BCA compliant) can cause white ant infestations and or Salt damp.
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    1 comments:

    1. F-a-n-t-a-s-t-i-c ! I was looking for similar projects last week, and now i see this post. I normally use breadboard to do this type of work, with one of these, job will be more easy.
      Sarasota Roofing

      ReplyDelete

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