A little bit of construction knowledge is dangerous! So are YOU one of those who would tackle the job yourself rather than pay a professional?
These articles are aimed at improving your knowledge as well as making you aware of the dangers and pit falls… YES, FREE info! With a Q&A follow up.
This issue we can start by looking at foundations, for an extension perhaps?
For some reason everyone tries to get away with digging out the most minimal of earth possible and using every trick in the book to fool the good old building inspector… Why? Firstly the surveyors are not stupid, secondly why would you want to cheat? The outcome at best can be subsidence!
The minimum depth you want to be digging is 900mm, 90cm or 36″ in funny money, regardless if the existing house foundation is but a gesture of cement tucked under the turf. Most existing house foundations are around 900mm in depth so finding the bottom of the existing house footing will suffice.
What you are looking for is a solid chalk or stone base, a good test is if you throw your digging fork into the ground and it stops dead which then sends resonation up thru your body and makes your teeth fall out! You get this gist…
The depth of concrete wants to be no less than 225mm… so once you have worked out your concrete depth (obviously work back from DPC so your top of concrete works out to be brick or block height equivalent) and you are now ready to peg out a level through the foundation, if you are finding that driving wooden pegs into the ground too hard, try using metal rods.
***top tip – get some surveyors spray paint and spray up the side of the trench in line with your pegs so when the concrete is poured you don’t need to be Shirlock Holmes to find them when tamping*** ………yes tamping, always give it a light tamp to vibrate any air out the mix, this will eliminate any weak spots and potential breaking points.
Allow to cure for 24 hours prior to loading.