Is it possible to lower a concrete sub floor that has been laid 40mm to high in a single storey extension? Will the vibrations of its removal cause problems with the structural integrity?

how did this happen ,i see your questioning cost already ,i suspect you got amateurs to carry out this work to cut costs ,and have ended up with a step up into new build ,this makes me wonder if the new damp course is also too high ,as i always say pay cheap pay twice ,taking off 40mm on a subfloor will probably cause damage to the insulation if they bothered to put it in ,check the damp b4 you do anything else ,has it been inspected !!!!!!

Structure should be fine but the entire floor will have to come up and be relaid - lots dust/disruption so if you can work round the 40mm its advisable

If the extension isn't to old and comply's with building control standards you should'nt have a problum, but you may have to fit a new DPM damp prof membrain, if the sub base needs lowering to maintain a minum 100mm thick finished floor. TDR Building Services.

best option is to break out floor, lower the ground by at least 90mm (allowing for a minimum 50mm screed top layer) and re concrete with minimum 100mm thick concrete. expensive way but who laid the concrete 40mm high in the first place is my question????? you could take 40mm off the concrete depending how deep the concrete base is but if it is a sub base then it should be screeded on top to bring it to level. the basics of laying a concrete sub floor is as follows.....lay hardcore fill, layer of d.p.m membrane, layer of insulation, layer of concrete min 100mm thick and finished off with layer of screed to finished level. anything else is probably not conforming with up to date building regs.

This depends on what needs to go on top of the sub floor It may be that other products mean the need to remove the 40 mm is not required If this is not the case then breaking it out should not affect the structural integrity It will be costly to break out and relay Hope this helps

Hi, We are local if you would like we can come & have a look. Kind Regards Mark