Garage/Car port slab on pre-laid foundations.

[swinster]

Hi all,

I have somewhat of a dilemma. Our house backs onto an access lane and we want to build a garage/car port to take advantage of this. The area available to us is approx 4.5m x 5m, and a concrete foundation has already been laid around this perimeter. The slab itself would need to come above this foundation height (by at least 4” or so) so I am wondering what the best course of action would be.

Should I lay a course of bricks on the foundation then lay the slab to the brickwork (so using the brickwork as an effective shuttering), or should I lay the slab over the foundations and lay any further brick work directly on the slab?

The foundation were laid with the idea to a brick built garage but if we were to get a garage no it would probably be of a wooden construction (with a log cabin effect facing the house and the back of the cabin (facing the lane) housing some up and over doors. For the time being however, we just want the slab laid to we can get some off street parking.

The last thing I am concerned with is laying a slab this size in one go. I was thinking of doing this in quarters but am not sure how to butt the edges of the slab up to each other, or whether this is simple more work than necessary.

Any idea or thoughts welcome.

Chris

 

[masona]

Here

 

[swinster]

Interesting - I have a feeling I came across this site a while back. Unfortunately, I have not heeded it advice as it looks as though the wall foundation and slab should be laid together, which cannot now be done. I will have to lay the slab over the existing foundation but will separate them with a dpm.

I will excavate an area within the foundation to lay a sub-base then lay the new slab directly over this base and on top of the concrete foundations (separate with a dpm). I will also lay the base in 4 bays which is going to take a bit more work, oh well.

 

[noseall]

if the foundation is say, 9 inches below finished ground level, i would be inclined to lay 3 or 4 courses of bricks, then use these as a shutter for my slab.

i would definitely set the slab height above finished ground level by say, 4-6 inches or so, and have a slight ramp up into the garage. this will facillitate a water run off, thus preventing a flooded garage floor.

my finishing course of bricks would be solid (as opposed to frogged or perforated) as these will not have the problem of holding water. use engineering bricks too.

 

[swinster]

It is not quite as easy as that. The ground and access road have a relatively steep gradient. The slab will follow this gradient to provide run off but cannot be as exaggerated.

The net effect of this gradient is that the foundation is almost exposed at the lowest point but nearly 1.5' below ground level at the other (4.5m away). what I props it to lay a further 4" slab on the foundations height which will mean a compromise of downward ramp at one side and slight upward (unfortunately not the best) on the other.

I'll see if i can to a quick sketch to show this in better detail.

 

[swinster]

Ok, lets see if this works

I hope that you get the gist. There are two sketches - one plan, one 3D. The access road is around 15" above the foundations on the left side (looking at the sketch) yet drops slightly below the top of the footing at the right side.

Due to the nature of the land, I will also be building a wall to terrace the land to the bottom of the foundations (i.e. the rest of the garden). The ground level on the rear side will be approximately 3' higher that the slab level. A path and steps on the right side will lead down to the slab area.

Does this make sense?