Building on Existing Footings?

[NRMartin]

I have recently had planning approved to knock down a garage & rebuild it, on the same footprint with a pitched roof and to new spec. 

 

The footings used for the garage are the same as they are for the rest of the bungalow - around 300mm deep and just carry on from the main building under the garage, aside from a gap where the garage door was. 

 

Can I re-build on the existing footings, and if not, who determines whether I can or cant - do i need a structural inspection by an engineer or can building control give the go ahead?

 

Thanks in advance,

[Discoeye]

To determine the suitability of the footings an inspection hole dug alongside the garage footings is usually done but you have stated you know the depth to be 300mm deep. Is this a guess or confirmed depth a usually suitability is checked first before being given the go ahead.

The inspection hole can be dug by yourself but will need to be confirmed by an expert as proof.

[Carrerahill]

43 minutes ago, NRMartin said:

I have recently had planning approved to knock down a garage & rebuild it, on the same footprint with a pitched roof and to new spec. 

 

The footings used for the garage are the same as they are for the rest of the bungalow - around 300mm deep and just carry on from the main building under the garage, aside from a gap where the garage door was. 

 

Can I re-build on the existing footings, and if not, who determines whether I can or cant - do i need a structural inspection by an engineer or can building control give the go ahead?

 

Thanks in advance,

The first thing I would look at and consider is the existing building, make up, materials and how long has it been there. Assuming it has been there a while, is there any damage or cracking, subsidence etc. etc. that is caused by the existing foundations failing in some way? I would give the foundations a bash with a hammer and a cold chisel to see how hard the concrete seems, I would expose sections of the foundations and check for big cracks, bits that have fallen off etc.

 

If the existing foundations are suitable in size, and pass all the other common sense checks above, then I would consider the new structure weight. How does it compare to the existing, if the walls are basically the same as before, with only a pitched roof going on, I would not be too concerned as the new roof load is supported round the whole build. 

 

Assuming you are pretty sure the founds are OK, and if not, even get an SE to come and have a look (dig some test pits and let them have a look), then I would probably just crack on and do it. Do you actually have building control on your garage or just planning? If the garage is small enough then BC won't be involved in which case do your checks above and carry on.

 

If BC are actually involved, then it depends on your inspection schedule with BC. If they want to see the trench and founds then you need to raise it, if they don't really care as it's just a garage then on you go. 

[nod]

If you’ve had to go to planning I assume it’s attached to to house and you will need building control Who will want to see the depth of the  concrete and what’s under them 

By the time you have buggered about with test holes You could have dug the old strip out in a couple of hours 

Check with building control 

He will probably make the decision for you 

[Carrerahill]

Will the new garage be connected to the house? If it is, I would make the case to retain the existing founds based on the fact they are tied into the house and will therefore provide a better connection at found level.

 

New founds can cause issues with differential settlement, if you dig them up and pour new ones, which are for example, much deeper or bigger, then that part of the building will start to behave differently to the rest and that can often lead to issues.

[Discoeye]

Test holes a must