If your house is crack­ing up it could be in need of ther­apy

Yorkshire Post - Property - - PROPERTY - Jonathon Wing­field

to make good. In older build­ings hair­line cracks can ap­pear around June to Septem­ber but then close up in the win­ter when the build­ing fab­ric ab­sorbs mois­ture. These are gen­er­ally harm­less and are called “sum­mer cracks”.

It is more likely that sub­si­dence is tak­ing place. This is more se­ri­ous and oc­curs when the ground be­neath the house is lit­er­ally un­able to sup­port the load. The shrink­age re­sults in both hor­i­zon­tal and ver­ti­cal ground move­ments. Al­though there are sev­eral causes, sub­si­dence oc­curs most fre­quently in ar­eas of clay, par­tic­u­larly when there are trees close to build­ings. In nor­mal cir­cum­stances the mois­ture con­tent of the ground at deeper lev­els re­mains fairly con­stant. How­ever, dur­ing ex­tended dry pe­ri­ods the trees re­move wa­ter from the soil al­low­ing the clay to shrink, caus­ing foun­da­tions to sink. This re­sults in crack­ing, which when se­vere, can be seen from both in­side and out­side. It is par­tic­u­larly ap­par­ent in the weak points of the build­ing struc­ture such as be­tween the ground and up­per floor win­dows. The cracks are wider than those at­trib­ut­able to set­tle­ment and are gen­er­ally wider at the top.The im­pact of mine work­ings on the in­tegrity of sup­port­ing ground is well doc­u­mented in the York­shire area but sub­si­dence also oc­curs when drains or cul­verts col­lapse. The pres­ence of rot­ting or­ganic ma­te­rial can also desta­bilise all or part of a foun­da­tion. It is im­por­tant to get the ad­vice of a struc­tural en­gi­neer who can mon­i­tor the ex­tent of crack­ing over a pe­riod of time and pro­vide the best so­lu­tion for you. At it’s sim­plest you may have to do very lit­tle other than some mi­nor re­point­ing. If it is se­ri­ous then some form of un­der­pin­ning will be re­quired.

Un­for­tu­nately this will be ex­pen­sive and can re­quire the ex­ca­va­tion of trenches, ap­prox­i­mately 1m in length and 1.5 mdeep, ev­ery other me­tre along the af­fected sec­tion of wall in­dent­ing be­neath the ex­ist­ing foun­da­tion. Steel re­in­force­ment bars are in­serted at 90 de­gree an­gles into the side walls of the trenches be­fore they are back­filled with con­crete. This process is then re­peated along the in­ter­ven­ing sec­tions cre­at­ing a sin­gle ho­moge­nous foun­da­tion. It’s a labour in­ten­sive ex­er­cise and may eas­ily cost £1,000 per lin­ear me­tre. How­ever, sub­ject to cir­cum­stances there are other op­tions avail­able. Pres­sure grout­ing be­neath the foun­da­tion by in­ject­ing chem­i­cals ef­fec­tively turns the sub­soil into an ag­gre­gate, thereby con­sol­i­dat­ing the ground. Al­though favoured by in­surance com­pa­nies be­cause it is sig­nif­i­cantly cheaper it’s largely in­ef­fec­tive in clay soils with a low poros­ity.

I would also urge you to con­sider the re­moval of any trees planted close to the house. Non in­dige­nous species such as Eu­ca­lyp­tus are par­tic­u­larly dam­ag­ing and can also dis­rupt ser­vices com­ing into the house.

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