Browse Forums DIY, Home Maintenance & Repair 1 Jul 19, 2010 11:00 am Hi all, sorry for the long post, however here goes. Have a double brick house that has quite a bit of minor cracking (barely 1mm) but a couple of major cracks (5mm). Am looking to renovate, but want to minimise the amount of cracking that will occur. So basically what appears to be happening is that the house appears to be sinking/moving toward one side. We also have a large tree (40 years old) on our nature strip, approx. 6 meters from the front of the house. Archicentre mentioned that the major reason of cracking was due to the drought and the tree's roots searching for water, encroaching on our property. The fix was, where there was cracking, to cut out a section of the wall around the crack, afix some metal sheets to strengthen the walls and then replaster over, however they mentioned that this could just move the cracking elsewhere. The mentioned underpinning was an option, but that it's not that effective for the cost (to underpin the whole house). An interior designer mentioned that down the side of the house we have a concrete path which was preventing the the soil on that side of the house from getting moisture and breathing and suggested that we rip up the concrete, place down some weave-mat, then pebbles and then water the area once a week which would allow the soil to breathe and also re-moisturise the dried out clay soil. I am intrigued by the weave-mat approach (as the wall fixing one doesn't appear to attack the cause) and would like to know if anyone has done something similar, or if anyone can recommend a Hydraulic Engineer (or someone similar) who could come out and sample the soil around the house and setup a mechanism for us to monitor the clay soil and hydrate if necessary. Your help is greatly appreciated.!! Re: Double Brick - Cracking, clay soil and hydraulic enginee 2Jul 20, 2010 4:47 pm About 10 years ago I used to inspect a lot of residences like yours. What needs to be established is where the damage is coming from? Is it the tree? Is the clay drying out? Something else? A combination of the above? The tree first. The tree is 6 metres away from you house. What type of tree is it? We need to find out where the roots are. There are basically two types of tree roots, tap roots and running roots. Tap roots basically go straight down (Pines are good example). Running roots stretch out (Gum trees, figs etc). It is very unlikely that a tap root tree will be doing damage 6 metres away. A running root tree could be doing damage. As a general rule, the length of the roots out from the tree are the same as the length of the crown (branches) of the tree. How close are the braches from your house, this may indicate where the roots are. Can you see big roots or ground lifting near your house? Several companies can install a “root barrier” between the tree and your house. It works like a wall (that is underground) that keeps the roots out (a cheaper option than under-pinning IF the tree is the problem. Cut a few branches off the tree, a smaller tree will search less for water. The clay. If the clay is drying because of the drought, the easiest way is to hydrate the soil (you know this already). Look at your neighbours houses, do they have the same cracking, this could indicate the clay your area is the problem. I don’t like the weave-mat approach because I believe the water you place on the surface will evaporate before it absorbs into the clay. We used to recommend drilling 100mm dia holes at angles under the footings (like under pinning). Then placing a piece of ag-drain into the hole, finally fill the ag-drain with blue metal. Place these holes (about 1200 deep) at 1 metre spacing around the areas of the walls with cracks in them. Finally, twice a week (in the evening), walk around with your hose and fill each of the holes (water your house). The water will expand the clay and the cracks should close (this may take up to 18 months – if you do this, measure the cracks at a set location and log the results to see if working). Concrete path and other issues. Have you got any broken pipes under your house? If you have a broken pipe, that area around the break will have a high water content and the clay will expand, a nearby area that doesn’t have a cracked pipe will have a lower water content clay and thus will tend to shrink. It is the boundary area of the two that you will see cracking in your walls because one side is expanding whilst the other is contracting. The concrete path is much the same, a “shaded” area under the path will have a different water content to exposed area which will be different to the area under your house. I don’t a copy of the code in front of me but off memory any crack up to 5mm is considered MINOR in brickwork. I have seen cracks I have put my hand into that have been fixed by the house water technique. A structural engineer should be able to give you advice on this (try to find one that deals with residences as opposed to big buildings, bridges etc). Some of the smaller engineering practices specialise in residential work only. Hope some of this helps Cheers Bluey Re: Double Brick - Cracking, clay soil and hydraulic enginee 3Jul 21, 2010 7:45 am In regards to OP's house, "the house appears to be sinking/moving toward one side" - what is on that side? The tree? What is different? My signature is distracting people from my wise posts ... Re: Double Brick - Cracking, clay soil and hydraulic enginee 4Jul 24, 2010 11:53 am BLUEY494 About 10 years ago I used to inspect a lot of residences like yours. What needs to be established is where the damage is coming from? Is it the tree? Is the clay drying out? Something else? A combination of the above? The tree first. The tree is 6 metres away from you house. What type of tree is it? We need to find out where the roots are. There are basically two types of tree roots, tap roots and running roots. Tap roots basically go straight down (Pines are good example). Running roots stretch out (Gum trees, figs etc). It is very unlikely that a tap root tree will be doing damage 6 metres away. A running root tree could be doing damage. As a general rule, the length of the roots out from the tree are the same as the length of the crown (branches) of the tree. How close are the braches from your house, this may indicate where the roots are. Can you see big roots or ground lifting near your house? Several companies can install a “root barrier” between the tree and your house. It works like a wall (that is underground) that keeps the roots out (a cheaper option than under-pinning IF the tree is the problem. Cut a few branches off the tree, a smaller tree will search less for water. The clay. If the clay is drying because of the drought, the easiest way is to hydrate the soil (you know this already). Look at your neighbours houses, do they have the same cracking, this could indicate the clay your area is the problem. I don’t like the weave-mat approach because I believe the water you place on the surface will evaporate before it absorbs into the clay. We used to recommend drilling 100mm dia holes at angles under the footings (like under pinning). Then placing a piece of ag-drain into the hole, finally fill the ag-drain with blue metal. Place these holes (about 1200 deep) at 1 metre spacing around the areas of the walls with cracks in them. Finally, twice a week (in the evening), walk around with your hose and fill each of the holes (water your house). The water will expand the clay and the cracks should close (this may take up to 18 months – if you do this, measure the cracks at a set location and log the results to see if working). Concrete path and other issues. Have you got any broken pipes under your house? If you have a broken pipe, that area around the break will have a high water content and the clay will expand, a nearby area that doesn’t have a cracked pipe will have a lower water content clay and thus will tend to shrink. It is the boundary area of the two that you will see cracking in your walls because one side is expanding whilst the other is contracting. The concrete path is much the same, a “shaded” area under the path will have a different water content to exposed area which will be different to the area under your house. I don’t a copy of the code in front of me but off memory any crack up to 5mm is considered MINOR in brickwork. I have seen cracks I have put my hand into that have been fixed by the house water technique. A structural engineer should be able to give you advice on this (try to find one that deals with residences as opposed to big buildings, bridges etc). Some of the smaller engineering practices specialise in residential work only. Hope some of this helps Cheers Bluey +1 Just completed build with Hallmark Homes Re: Double Brick - Cracking, clay soil and hydraulic enginee 5Aug 10, 2010 9:20 pm Hi, thanks very much for your reply. Stupid question, but are you still in the business? I will get some pictures uploaded tomorrow to show the extent of the problem and also the layout of the house. I have some questions inline if you have the time!. Quote: About 10 years ago I used to inspect a lot of residences like yours. What needs to be established is where the damage is coming from? Is it the tree? Is the clay drying out? Something else? A combination of the above? The tree first. The tree is 6 metres away from you house. What type of tree is it? We need to find out where the roots are. There are basically two types of tree roots, tap roots and running roots. Tap roots basically go straight down (Pines are good example). Running roots stretch out (Gum trees, figs etc). It is very unlikely that a tap root tree will be doing damage 6 metres away. A running root tree could be doing damage. As a general rule, the length of the roots out from the tree are the same as the length of the crown (branches) of the tree. How close are the braches from your house, this may indicate where the roots are. Can you see big roots or ground lifting near your house? Several companies can install a “root barrier” between the tree and your house. It works like a wall (that is underground) that keeps the roots out (a cheaper option than under-pinning IF the tree is the problem. Cut a few branches off the tree, a smaller tree will search less for water. Will get a picture of the tree. I think it's an Elm Tree, quite old (40+ years) and am pretty sure the roots spread out instead of down as it's quite large. There is a mound in the lawn, will take a pic and I also notice the concreate skirting around the front of the house, on the side with the big crack, is leaning/falling towards the lawn, so it may be the tree roots have extended that far now. I'm guessing the only way to check for roots is dig up some of the lawn ? Quote: The clay. If the clay is drying because of the drought, the easiest way is to hydrate the soil (you know this already). Look at your neighbours houses, do they have the same cracking, this could indicate the clay your area is the problem. I don’t like the weave-mat approach because I believe the water you place on the surface will evaporate before it absorbs into the clay. We used to recommend drilling 100mm dia holes at angles under the footings (like under pinning). Then placing a piece of ag-drain into the hole, finally fill the ag-drain with blue metal. Place these holes (about 1200 deep) at 1 metre spacing around the areas of the walls with cracks in them. Finally, twice a week (in the evening), walk around with your hose and fill each of the holes (water your house). The water will expand the clay and the cracks should close (this may take up to 18 months – if you do this, measure the cracks at a set location and log the results to see if working). Thanks for the advice. Have read a few people do this, but wouldn't know where to start, nor have the tools to do it. Does a structural engineer do this, or do they just give advice ? If so, what type of contractor would perform this work ? No cracks on the neighbours houses. The side of the house with the concrete path, and the big crack, has the neighbours driveway going all the way down from the front of the property to the back, and I believe those houses (there's 2 of them) are on concrete slabs. Quote: Concrete path and other issues. Have you got any broken pipes under your house? If you have a broken pipe, that area around the break will have a high water content and the clay will expand, a nearby area that doesn’t have a cracked pipe will have a lower water content clay and thus will tend to shrink. It is the boundary area of the two that you will see cracking in your walls because one side is expanding whilst the other is contracting. The concrete path is much the same, a “shaded” area under the path will have a different water content to exposed area which will be different to the area under your house. Not sure about broken pipes. I don't believe so, but don't have access under house (no cut out in the wall and no manhole). Quote: I don’t a copy of the code in front of me but off memory any crack up to 5mm is considered MINOR in brickwork. I have seen cracks I have put my hand into that have been fixed by the house water technique. A structural engineer should be able to give you advice on this (try to find one that deals with residences as opposed to big buildings, bridges etc). Some of the smaller engineering practices specialise in residential work only. Hope some of this helps Cheers Bluey Thanks very much. I'll look up a structural engineer and get some quotes for an investigation. I'll take some pics tomorrow and upload them tomorrow night if you are still able to provide advice (when you get a chance). Re: Double Brick - Cracking, clay soil and hydraulic enginee 6Aug 10, 2010 9:24 pm Lex In regards to OP's house, "the house appears to be sinking/moving toward one side" - what is on that side? The tree? What is different? I will take a pic, but in terms of ascii art ... |Neighbours Driveway |Neighbours Driveway |Neighbours Driveway |Strip of soil with a couple of small trees |Concrete Path -------//---------------------------------- House wall // = large crack Re: Double Brick - Cracking, clay soil and hydraulic enginee 7Aug 10, 2010 11:11 pm I am trying hard to decipher the ASCII art, but it's not going that well I think a photo would work better for me ... And get all those pics, like the 'concrete skirting' leaning away, etc. etc. ... If you call around for a structural engineer, make sure he/she/they have the word "residential" mentioned somewhere ... My signature is distracting people from my wise posts ... Re: Double Brick - Cracking, clay soil and hydraulic enginee 8Aug 11, 2010 10:02 am Thanks. Yeah, ascii art was a bit of a long shot! I'll get some pics tomorrow morning, forgot this morning (as usual). Has anyone had any dealings with Site Geotechnical http://www.sitegeo.com.au/index.php Quote: Footing Inspection & Assessment of Distressed Buildings Some minor cracking and movement will occur in a significant proportion of buildings, particularly those on reactive clays. Generally, the remedial action for such damage should start with an investigation to establish the cause of the damage. Based on the findings of our investigation general treatments consist of stabilizing moisture conditions by physical barriers or paths or replenishing moisture in dry foundations. This can be followed by repair of the masonry and wherever possible added articulation should be included while repairs are being effected. Structural repairs to the footing system such as deep underpinning is generally only considered as the last resort. Re: Double Brick - Cracking, clay soil and hydraulic enginee 9Aug 18, 2010 11:20 pm Hi, finally got around to taking some pics. This is a side on view of the tree. Edit: Had to remove pics while I re-organise Photobucket account. The tree is about 10+ meters from the front of the house, so could it really be an issue? Would the roots travel that far? In any case, I'm organising for an inspection of the tree roots and installation of a root barrier first and also an inspection of the footings with a view to underpinning that section of the house, but always appreciate any advice people can impart. Thanks Re: Double Brick - Cracking, clay soil and hydraulic enginee 10Oct 27, 2010 9:20 am As a structural engineer giving advice on such matters in Canberra for the past 27 years I'd say 'bluey' is pretty much on the money. Although I would suggest that assessing the situation without local knowledge of the founding conditions can be a little difficult. If you are confident that you are on a reactive clay site we have a lot of free advice of a generic nature at www.structuraldesigns.com.au. Pics were not up when I viewed the site so cannot be more specific. Best of luck with it! Thanks. I wish there was a youtube video explaining this concept. 10 27350 I’m not a structural engineer but I’m free. you still need an engineer for the plans. I only have part of your plans, but you seem to have a 850mm drop from the side… 3 10330 |