Old Houses Move

[@brucef]

This deserves to be more popular, it assuages the (unneeded) worries that all owners of houses have when they see cracks.

[@Matt.Cornell.Photography]

Thank you Bruce!!

[@RolandElliottFirstG]

A couple of years ago I was doing and extention on a home in the northern beaches area of Sydney, the walls had been stripped of old plasterboard, the new extension was a room 4x 4 to the rear, the engineer specified engaging strip footings into rock, interesting though was the fact I could stand at the rear of the house and look straight through to the front eyeing the floorboards, which were the most perfect flat level you could imagine. The original home was set on sand ( the whole block was sand with rock at varied levels lower than about 1 metre) the old house footing was 1 metre x 2 metre sandstone blocks set into the existing sand about 20 cm. It's amazing how some people over engineer to the extreme and when a home of 80 yeras or more has not moved at all they come along and decide to try and make things stronger, in my opinion if I was to go there tomorrow and look at that extension I bet it has moved in relation to the old section of home.

[@kimuoi85]

Would it be expected for there to be exacerbated seasonal movements caused by the Feb 2022 Brisbane floods? About one year later we noticed a wider than usual crack in one corner of house - only 2mm wider

[@CornellEngineers]

Hi Kim Flood waters and heavy rains do a couple of things to houses and each house is affected differently. A lot of water around a house can either soften the soil and turn it to mush (ie reduce the capacity of the soil to carry load), erode the soil (ie wash it away), cause the clayey soil to swell and lift (moreso in areas where the soil has always been dry) or any combination of these issues. Repairing a home straight after floods waters is problematic because the soil that has never been wet before is wet and has swelled. The soil that changes season to season is wet and has swollen too. Builders making repairs under these circumstances are locking unevenness into the house structure that has never been there before. As the always dry soil dries back out it shrinks and the ground surface drops. The wet soil around the outside continues to shrink and swell with the seasons. None of this will help you diagnose your 2mm wider crack - but it shows the complexities in the assessment with many factors unable to be accounted for (ie how deep the wet soil extended under the house where it can't be tested). So, an old house that used to move will eventually go back to moving just like it was. Occasionally the unevennes will be greater (or less) after a flood and occasionally th repair work will lock this unevenness in and result in cracks that had never existed before. At the end of the day - old houses on old foundation styles will continue to move season to season and also as the ground (that has never been wet before) dries out.. Rarely will the movement be so extreme that the house will be deemed unsafe. Allow your home to flex. Monitor it by all means. Understand that it is going to move again and again and modify your attitude and rectification methods to suit. Best of luck Matt Cornell