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In any typical month, Partridge receives somewhere between two and five phone calls from homeowners who are concerned about major structural cracks in the walls of their house. Sometimes these have “suddenly” appeared; other times they’ve been present for a while but worsened more recently.
Many homeowners first engage a building inspector or local builder to assess the situation, often receiving the advice that the footings have settled and will need to be “underpinned”. Nine times out of ten, this is misguided (or blatantly inappropriate) advice, leading homeowners to spend thousands of dollars on work that fails to fix the problem and, often, will actually exacerbate the damage!
Underpinning is simply a fancy term for strengthening or re-instating the foundation material underneath the footing. Or transferring the footing down deeper to a more stable material. If the foundation material (e.g. sand, loam, fill, natural ground, etc) has washed away or consolidated over time, causing the footing to drop locally, then this can indeed cause cracking in the walls above. Similarly, if the house is founded on reactive clay, it’s possible the clay may have dried out and shrunk, causing the footing to drop. (Alternatively, it may have become saturated and swelled up, causing a local rise in the footing and creating the illusion that the walls/footings each side have dropped). Underpinning seeks to either re-instate the loose/missing material, or to transfer the weight of the house down to deeper, more stable foundation materials.
The two big problems with this are that (1) in the vast majority of cases, merely underpinning the footing will not address the cause of the foundation movement, and (2) if you locally underpin just one part of the house down to deeper, more stable foundations, you’ll then leave the rest of the house on the higher-level footings, which means the house is now on varied and non-uniform foundations. This creates a high probability of differential settlement – meaning the walls immediately adjacent to the underpinning will now start to crack!
So…in assessing the cracks in a wall and deciding upon the best course of action for repair, the key is to actually first determine the cause of the foundation movement. There’s no point treating the symptom without attempting to find and fix the cause. And, 90% of the time, we find that the cause of the cracking is actually water! An inspection of the site almost invariably reveals that there is a leaking or disconnected downpipe in the vicinity of the cracking. In older houses, we often find downpipes simply discharge onto the ground, with no connection to a drainage system. Or, occasionally, the cracking is near/adjacent to a bathroom, and it transpires that there’s a cracked plumbing pipe in the ground. (Sometimes also associated with tree roots that have punctured/damaged the plumbing pipes. Either way, water is effectively being injected into the ground, either flushing away or consolidating loose material (e.g. sands/soils); or causing reactive clays to swell. The solution, therefore, has nothing to do with underpinning, but instead involves getting a plumber to repair the gutters, downpipes, and in-ground plumbing pipes – taking care to ensure that all stormwater is effectively transferred to the street, easement, or the detention system.
If your house is on reactive clay (most of western Sydney and parts of the North Shore), then the reality is that the foundation clays will continually shrink and swell with the cycles of dry and wet weather. It’s common to see cracks appear in houses in summer when we have prolonged hot, dry spells and the clays subsequently shrink as the moisture in the clay dries out. Correspondingly, the cracks often close up of their own accord when the rains come and the clays swell as their moisture content is restored. Such foundation movement is “natural” and comes with the territory. However, homeowners should ensure they’re not adding to or driving the problem with defective downpipes or damaged plumbing.
The moral of the story? If you see a crack, first check that your plumbing’s not slack!