ᐅ Foundation for Post-Supported Patio Roof

Hello everyone,

we are about to order a patio roof with wall mounting.

Two posts obviously need to be secured on the patio with foundations.

Our patio has a concrete slab laid on a gravel bed.

The manufacturer of the roof recommends two isolated footings with a diameter of 45cm (18 inches) and a depth of 80cm (31 inches).

I remember how heavily the gravel for our patio was compacted (which is of course a good thing) – I’m just wondering how I am supposed to dig 80cm (31 inches) down here.

Could I possibly use the compacted gravel as a foundation already – or is it really necessary to go 80cm (31 inches) deep? How would you approach this?

This can be easily excavated by hand. Use a digging bar (or shovel) and a crowbar to loosen the ground. The manufacturer's recommendation is standard. At a depth of 60 cm (24 inches), you probably won’t find any gravel anymore.

As my predecessor already mentioned, crowbar, small spade or similar tools, and a lot of manual work. Our foundations were really poorly constructed by KD Roofing. They probably only dug about 40-50cm (15-20 inches) deep, placed a shallow but wide aluminum profile in it, set the post on top, poured concrete, and soaked it with a hose. Fortunately, we also received sliding glass elements whose rail profiles were mounted on another support profile, which in turn was screwed to the posts. Otherwise, it certainly would have already sunk.

Better follow the guidelines and accept the effort involved. The gravel might be removed faster than what appears beneath it. The foundation needs to be frost-proof to prevent lifting caused by the expansion of frozen moisture under the foundation.

Allthewayup schrieb:

As my predecessor already said, crowbar, small spade or similar, and a lot of manual work. Our foundations were really poorly done by KD Roofing. They probably only dug 40-50cm (16-20 inches) deep, placed a flat but wide aluminum profile inside, set the post on it, poured concrete, and saturated it with a hose. Fortunately, we also received sliding glass panels whose track profiles were mounted on another support profile, which in turn was screwed to the posts. Otherwise, it would probably have already sunk.
Better stick to the specifications and take on the effort. The gravel is probably excavated faster than what appears beneath it. The foundation should be frost-resistant so that frost does not cause heaving due to the expansion of frozen moisture under the foundation.

Okay – thanks so far!

I was planning to dig 80cm (31 inches) deep and then insert a concrete foundation tube made of plastic, which I would fill with concrete. After that, place the concrete patio slab back on top and then drill through the slab into the foundation using ground anchors. Make sure to reach about 8cm (3 inches) deep into the foundation, and that should do it. Does that seem appropriate?

Prager91 schrieb:

I would have dug 80cm (31.5 inches) deep, then placed a plastic concrete footing tube filled with concrete. Put the concrete patio slab back on top, and then drilled through the patio slab into the foundation with lag screws to secure the post. Make sure to go about 8cm (3 inches) deep into the foundation and that should do it, right?

That method for creating the foundation is fine. You can also add leftover reinforcement bars, it won’t hurt.
However, I strongly recommend setting the posts directly onto the footings and cutting out the patio slabs around the posts using an angle grinder. Otherwise, you will be putting pressure on the patio slabs and they will crack. Also, the screw or anchor heads won’t be visible that way, which looks much better visually!

Simon-189 schrieb:

I strongly recommend placing the supports directly on the foundations and cutting out the terrace slabs around the supports with an angle grinder. Otherwise, the slabs will be under pressure and may crack.

We didn’t cut out the slabs; instead, holes were drilled through them. Nothing broke in our case, but our terrace slabs are 8cm (3 inches) thick.

Simon-189 schrieb:

Also, the screw and anchor heads won’t be visible anymore, which looks much better!

Aren’t those usually recessed? At least in our case, you can’t see them.