Building regulations for attached garage

[Randomiser]

Our site has a few challenges with regard to foundations.  There is a root protection area under part of the footprint, the are many trees around the house, the soil is clay and the water table is high.  The discussions with the structural engineer have therefore been along the lines of piled foundations.  However, he has suggested it may make financial sense to go with a raft foundation for the attached garage.  At a recent meeting I suggested that while the main house is likely to be brick and block construction maybe we could construct a timber frame garage, I raised this as I thought that this would be lighter than a brick built garage and therefore help in terms of the cost and complexity of the garage foundation.  The structural engineer said he did not think that building regulations would allow this.

 

I've had a look on the internet and while I can find the building regulations documents I can't find anything that relates specifically to an attached garage.  I wondered if anyone knows if there is anything specific on an attached garage or are the requirements embedded in the regulations for houses?

 

Many thanks in advance,

Randomiser.

[Mr Punter]

My brother has a house on clay with piled foundations. Later he had an orangery built attached to the house using a raft foundation. I looked fine at first. Now none of double doors operate correctly and he is thinking of demolishing it.  Mixing foundation types on shrinkable soil is very risky.

[Jeremy Harris]

I'd agree with the above, as I had a workshop on a concrete raft, built alongside a house with conventional deep foundations, on very shrinkable clay.  The workshop moved up and down relative to the house a fair bit.

 

The garage will need to meet the fire resistance requirements, but a timber frame is OK, just needs to meet the internal spread of fire requirements in Part B, which aren't hard to comply with. 

[Ferdinand]

I put a building on a concrete slab - sort of conservatory - next to a Victorian brick building on clay, but cannot remember how I handled that.

 

I rather suspect that I improvised a movement joint to allow a modicum of slip, but the new building was timber, and the slab was not rigidly attached to the other building.

 

Any stresses would appear where the roof plate or side joints occurred - all of which were timbers.

 

F

[nod]

It strange how some SE like pile foundations Others don’t 

We are on simalar conditions to you and went for deep strip and clay board 

[Randomiser]

Many thanks for the replies everyone, I will consider and raise the differential movement point with the SE.

 

2 hours ago, nod said:

It strange how some SE like pile foundations Others don’t 

We are on simalar conditions to you and went for deep strip and clay board 

 

Our SE said his 'gut feel' is that if you end up below 2 metres with strip foundations it starts to become more economic to use piles.  Add to that the water table is less than 1 metre below ground, he said we would also need to pump the water out of any trenches before they can be filled with concrete.  Given our main consideration for the foundations is cost (structural soundness is obviously a given) I hope his initial view is correct.  Even if we went with strip foundations for most of the house we would almost certainly be made to use piles where the root protection area is, I guess there is a fixed cost for mobilising the piling team, equipment, etc. so once they are there the cost to do the rest with piles becomes relatively less.

 

There is a secondary issue in that with part of the site over a root protection area if we have to put large machinery in that area we would need to spend a lot protecting the ground from compaction, with the helical piles my understanding is that they can be installed (is that the right term?) with a relatively small digger with an appropriate 'head' attached.

 

 

[vivienz]

It's worth checking out mini piles as well. We are on highly shrinkable clay that was also dessicated. By the time the costs of muckaway and associated labour are accounted for, piles may not be more expensive. I had 37 in total, for tte house and attached garage and it came in at 14.7k. All installed in 1 week.