Casting support beams

[Hantlangaren]

I was thinking about building a large rectangular decking (composite) at ground level, but what bothers me and makes me hesitant is all the preliminary work and hassle of getting the beams properly aligned and leveled.

The "right way" to do it is probably to dig out, pack some gravel or build up the beams on pillars and level it, etc., but I find it troublesome

My thought was that it would be much easier to dig some trenches, place the beams in the trenches, and then simply fill the trenches with concrete (perhaps only in selected areas), I might also place some garden slabs under the beams for larger support surfaces. That way, all I need to do is ensure that the first and last beams are level and at the correct height, and then I can hang the other beams using temporary braces that I place between them. That would be a straightforward solution.

Do you think that would work? I live in Skåne and have sandy soil.

 

[Kane]

With such a base, garden tiles should suffice as support for the beams. Do you need beams, or can you just lay the joists on the tiles?

 

[seniorkonsult]

Completely okay and sufficient. Add a black plastic as well for less weeds through the decking gaps. It's good if water doesn't run down under the decking.

 

[Oldboy]

There's no reason to make it more complicated than necessary. Just like Kane says, use some garden slabs for support. Either adjust the slabs in the sand or shim with roofing felt (which should be placed between the stones/slabs and the joists). (However, the felt should be about 40 mm wide for 45-joists, otherwise it may collect water.)

The ground under the slabs should be hard and strong. You must level the joists no matter what you do if you want it to slope in the right direction across the entire deck. Use a level and a stiff and straight (eyeballed along the length) board/joist on its edge, and align from the house foundation outwards. Then three times across*. Ready for laying and boarding. It's advisable to allow for a little extra slope. Slopes are not noticeable unless you're there with a level or billiard balls, and it provides a bit of a buffer if the slabs/ground settle slightly over the years. (This can happen, for example, with frost heave.)

* If the board/joist isn't long enough to reach from side to side, do an extra leveling check in the middle so you don't risk creating a dip there if the worst luck occurs.

Edit: black plastic/ground cover/weed barrier underneath is good, as mentioned in the previous post.

 

[Hantlangaren]

Thank you! I want to make it as simple as possible, which is why I am considering beams. Let's say my deck will be 8x10 m.

If I do as in Kane's picture and as you suggest, I need to excavate a large area of 80 sqm, manage to get it reasonably level, and then fill it with stones and pack it. After that, I need to measure all my beams (cc 40 cm = 26 per 10 m) and adjust the height of hundreds of bearing points by shimming with roofing felt and digging in the sand, which would weaken the load-bearing ability if I'm sloppy and don't pack properly under each point (I know myself).

My proposal essentially involves digging 4 channels (at cc 267 cm over 8 meters), placing garden tiles at the bottom of the trenches on undisturbed soil that nature has already packed over millennia. Then I lay down 45x145 and leave an air gap between the garden tile and the beam for easy adjustment/direction and then pour concrete in the gap. Only the first and last beams require minimal measuring; the other beams are aligned based on them. Ready to place beams and decking!

I only excavate where the beams and joists will lie, and backfill gradually to minimize excess soil.

I might be wrong, but I still think my method feels much simpler, although a disadvantage is that it requires more material. Specifically, 248 meters of beams and joists in the above example. 45x145 NTR/A might be on the low side, but if so, it would have cost a total of 6000 at Byggmax, which I think is okay.

 

[seniorkonsult]

I also see Kane's suggestion as advanced. Remove sod for larger than slab size, add some gravel, pack a little 16/34, and lay btg-slabs c/c 1.8 m. Level off, plastic foil, bearers along the length, maybe 3 pieces 45x230 are enough. Then 45x170 c 6-700 mm cc across depending on span. Screw decking battens 28x120 mm. Cover the edge where necessary. Done.
The height seems to be sufficient compared to the floor inside.
Alternatively, you can use lecablock to achieve the height.

 

[Hantlangaren]

Even Kane's suggestion I see as a bit advanced. Remove sod for areas larger than the slab size, add some crushed stone, compact a little 16/34, and lay concrete slabs c/c 1.8 m. Level off, plastic sheeting, bearing beams along, maybe 3 pcs 45x230 is enough. Then 45x170 c 6-700 mm cc across depending on the span. Screw down decking batten 28x120 mm. Cover the edge where needed. Done. The height seems to be sufficient compared to the inside floor. Or you can use lecablocks to raise the height.

Today there's an old wooden deck sitting on concrete slabs. It's about 10 cm too high. I want to level with the slabs and therefore need to place the bearing beams about 40 cm below the existing slabs so I want to go DOWN in height. I want to replace the work of compacting crushed stone and getting the slab to the right height by pouring concrete between the beam and the concrete slab. I find it heavy and difficult to get the slab at the exact height otherwise, but I might change my mind depending on how it looks under the slabs. If I'm lucky, there's a packed layer of stone, but I have a hard time believing the concrete slab would move downward even without crushed stone. The beams will also be supported by the soil I backfill with.

I want composite decking and hence cc 40.

 

[seniorkonsult]

Wood against concrete or soil = a sure mold bomb! This also applies to pressure-treated wood. In other words, it is rather the studs that should be made of composite material.

 

[Hantlangaren]

Wood against concrete or ground = guaranteed mold bomb! This also applies to pressure-treated timber. That is, it is rather the studs that should be made of composite material.

As I mentioned, I have sandy soil (almost like a beach under the topsoil) with good drainage. How many years would you estimate that NTR/A can last when buried? The entire frame will lie against the ground, so there's a lot of material that needs to rot away before the deck falls down, and the fall won't be that high

By the way... is it possible to remove individual composite planks afterward, or do they need to be removed in the reverse order they were laid? I assume it varies from brand to brand, but is it generally possible?

 

[seniorkonsult]

Buried will smell.? Sand is wet most of the time except at the top.
Is the decking made of composite tongued and grooved? Where does the water go then)

 

[Hantlangaren]

Buried will it smell.?

I don't know. What do you think?

Is the composite decking tongued and grooved? Where does the water go then

I haven't decided which decking to use yet, but either the water stays on the board until it evaporates or it drains into the ground through the gaps

 

[SBH]

I was thinking of building a large rectangular deck (composite) at ground level, but what holds me back and what I'm a bit hesitant about is all the groundwork and the hassle of getting the beams at the right slope, etc.

The "right way" to do it is probably to dig out, pack gravel, or build up the beams on pillars and level them, etc., but I find it troublesome

In my opinion, it would have been much easier to dig a few trenches, place the beams in the trenches and then simply fill them with concrete in the trenches (possibly only in selected places), I could also place some garden tiles under the beam to get a larger bearing surface. Then I only need to make sure that the first and last beam are level and at the right height, then I can hang the other beams on temporary rails between them. It would have been a simple solution.

Do you think it would have worked? I live in Skåne and have sandy soil.

never embed any type of wood in concrete

 

[Hantlangaren]

never cast any kind of wood

Because it smells, or because it rots? After how many years do you estimate the problems begin?

 

[Oldboy]

It will probably last 20 - 25 years, then you'll be left with concrete trenches filled with rotten pressure-treated wood that needs to be disposed of.

I tore up our old deck last year. It consisted of 45x70 joists at 60 cm centers with 22x95 decking and was laid over a mix of cobblestones, gravel, and propped up with joist and decking pieces where needed. It had presumably been there for 20-25 years. The decking was finished, but the joists were still okay, except in places that had a bit of contact with the soil. It never smelled, as far as I noticed. Not even when I tore it up.

Despite the small joists, the floor was heavy and stable. The joists were quite heavy. I assume it was because they were moisture-saturated. With sufficiently close support points, small joist dimensions work perfectly.

The joists should be free in the air. Neither soil, sand, nor concrete is suitable against them. I believe your method, which mostly matches my description, can work. The only difference is that you skip the concrete and backfill against the joists. Using a double cross-laid joist framework with beams is probably not a bad idea. The heavier the construction, the more stable it will sit, and any settling will probably not be an issue.

 

[SBH]

Is it because of the smell, or because it rots? After how many years do you estimate the problems start?

problems start after the first frost heave. also depends on how humid it is where you live.
and pouring on sand is not ideal
preferably set deck adjustable pillars.