Foundations for small porch - Need clarification on requirements

[Jim S]

Hi
I am attempting to build a small entrance porch 2.2m wide x 550mm projection (over a recessed front door)

I have dug trench for foundation 600 deep x 400 wide. Soil at foot of trench is firm clay.

My intention is to fill this trench with correct grade concrete to finish 1 brick below ground level then lay 3 courses to DPM to support structure.

Am I going about this sensibly?

Will this safely support the structure? Which is like a very small conservatory with a tiled lean to roof, central Rockdoor, two side panels and two return panels.

Any advice appreciated.

Thank you
Jim

Ps I am a bit confused about foundations v footings.

[TheRockConcreting]

If the wall is going to be free standing and not retaining then I would only be putting down a footing of 225mm C20, theres no need to go any deeper in this case, footings are just another word for foundations.

[lutonlagerlout]

jim that sounds fine as long as you retain your existing front door internally
if you choose to remove it the porch become part of a habitable dwelling and must conform to building regs
which requires a 1 m deep foundation

generally (just me maybe)
foundations are the concrete
footings is the brickwork below DPC

cheers LLL

[Jim S]

Thank you for replies.

TRC, the wall is only 3 courses and will be concreted to form the new base, with membrane, jablite etc. I'll be back with questions on this aspect

The minimum readymix I can get delivered is 1m3 so I thought it best to try to use near that amount for foundations.

LLL, that's very reassuring. Yes I'm retaining the front door. The reason the porch is so small is because my garage corner is in front of it and building control said if there is minimum 1 metre to garage I don't need planning consent or building warrant, provided other permitted development requirements are met (max height, max area, no electrics, no tapping heating system, etc.)

Less than 1metre needs firewalls etc. Costly and difficult.

Your explanation of foundations/footings was my interpretation also.

Thanks again
Jim

[Jim S]

Finished the dig out now and put in some shuttering. Do I need to line with any membrane or plastic before filling?

Thanks
Jim

[Dave_L]

Nope, just trench fill it with that wonderful grey stuff, make sure it's to level!

[Jim S]

That's great. Thanks Dave.

[Jim S]

Said I'd be back again with more questions

I've got the 3 course dwarf wall up now and backfilled leaving a depth of 140mm for insulation and concrete slab.

Should it be 100mm insulation and 40mm concrete or some other ratio, or more backfill to reduce the depth first?

Any recommendation on insulation product? ie Jablite, Celotex , Kingspan etc.?

I've got the 1200mm DPM. does it go under the insulation or under and over (I've got enough)?

Thanks for your patience
Jim

[lutonlagerlout]

him jim

if using any of the solid insulation it has to have DPM below and on top,as they reckon that concrete can rot it
140mm isnt really enough

how far are you from finished floor in the house?
100mm concrete is minimum for any slab
40 insulation is not enough normally we use 100-125 kingspan

and finally a 70mm screed and floor cobverings

cheers LLL

[Jim S]

Hi LLL
Thanks for your reply. I also have the original slab and new footings as well.

Here's a couple of pics (I hope)





Cheers
Jim

[seanandruby]

Think some DPM against house walls would be a good idea.

[Jim S]

Think some DPM against house walls would be a good idea.

Where? Sean

Jim

[Jim S]

A few more details...

I'll remove the uPVC facing under the front door to expose the original brickwork. Intention then is to fit DPM as a tray in the cavity coming up to original DPC which is just at the bottom of the render. Then the insulation and slab.

After LLL's reply I'm wondering if it may be better/easier to do a suspended timber floor using 4"x2" joists and noggins.

What do you think?

Jim

[seanandruby]

....DPM against the brickwork inside your slab.
If your planning on suspending the floor the you need air vent bricks.

[Jim S]

If your planning on suspending the floor the you need air vent bricks.

Oops - back to concrete, then.