Wooden terrace substructure

Dear forum readers,

I am looking for a fastening tip for the substructure of a terrace. I want to build a terrace (approx. 5 x 3 m, wooden decking 25 mm on support beams 45x70 both Bangirai) in front of our terrace door (approx. 40 cm above ground). The substructure consists of holes 35x35 approx. 30 deep, in them a sidewalk slab 30x30, on top a drainage pipe DN150 standing up to approx. 25 cm above ground, filled with concrete, embedded post shoe. Does anyone know suitable post shoes for the beams only 45 mm wide and preferably not higher than 60 mm? Or should one first put a "substrate wood" in the post shoe and place the support beams on it, since I only find post shoes with width 71/61 mm and height 100 mm? Or does anyone have another suitable idea? L-post shoes are usually too high (80 mm).

There will certainly be many foundations, but because of the access, I cannot bring in an excavator and also cannot remove the terrain (sandy soil) and completely fill with gravel etc. An advantage is also that I can build the foundations gradually alongside. The problem is just finding the right post shoes. Does the wooden beam have to sit tight on the base in the post shoe or is it sufficient if it is held by the side screws?

The terrain under the terrace will be leveled with a slope of 5-10% away from the house and covered and weighed down with fleece/foil.

Many thanks for tips

Does anyone know suitable post shoes for beams only 45 mm wide and preferably not higher than 60 mm?

Grab a grinder and the suitable height is quickly there. Place concrete bags* in the post shoe (they can be shaped accordingly), put terrace pads on top and lay the substructure. That's how I build my terraces, although not yet with post shoes. *Concrete bags = suitable freezer bags filled with wet concrete (bagged material from the hardware store, which can be mixed well with a little water)

Have you already built the foundations? I have just finished this myself, even on unprepared ground, level about 20-40 cm below the upper edge of the terrace covering.

My approach:
Point foundations, up to ground level, with plastic pedestals on top. The pedestals have threads for height adjustment, they come in various heights from about 2 cm and with a self-leveling head. You don't need to work to the exact centimeter with them. If necessary, you can also concrete a paving stone or similar onto the foundation to gain additional height. For the substructure, I used aluminum square tubes, 40x60 upright and in two layers, i.e., with counter battens, to gain height and stability, but above all to require fewer foundations than with wood.

The terrace does not need to be screwed to the substructure. So you could place beams made of KDI pine or similar into the post shoes, lengthwise to the house, then place the substructure on pads on top of that, crosswise to the house, and then the decking boards again lengthwise to the house. For safety, you can then drive a Spax screw through each corner.

Alternatively, Spax Freelift, but 40cm height is almost too much for that.

Thanks for the hints,

I will now insert short wooden beams (also Bangirai) 71 mm across 45x70 into the U-post holders, screw them in, and then screw the substructure 70x45 on top.

What speaks against screwing the substructure onto the concreted-in post holders?

Height adjustment for slope of the decking boards of 1.5% by first screwing the post holders to the substructure, placing them exactly at height into the pipes, and then concreting them in.

What speaks against screwing the substructure onto the concreted post supports

Nothing. Just make sure the wood does not lie in water = place terrace pads underneath. Otherwise, your Bangkirai can quickly rot away.