Groundwork & Foundations Question

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?

Is it costly? Area 34 sqm approx.

6 Answers

Best Answer

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 !!!!!!

Answered 3rd Jun 2011


Member since 7 Jun 2008

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

Answered 3rd Jun 2011

AJ Plastering & Building Services

Member since 14 Jan 2010

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.

Answered 4th Jun 2011

TDR Building Services

Member since 19 May 2008

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.

Answered 4th Jun 2011

ibuild building services

Member since 28 Jun 2008

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

Answered 4th Jun 2011

C Jackson Builder

Member since 12 May 2008

No feedback


We are local if you would like we can come & have a look.

Kind Regards


Answered 5th Jun 2011


Member since 6 Jan 2009

Need help with your project?

We have tradesmen ready to help you. Post a job, read reviews and hire today.

Post a job

Need some help?

Post a job on MyBuilder to find quality, local Groundworkers who can help you with your project.

Search all questions