The depth of deck pillars ?

[kick3n]

Hello.

It's time to plan the deck construction as the time for it is approaching.

But what depth do you feel the footings should be? Frost-free is 2 meters here.

One row of footings will need to support the weight of a roof over part of the deck.

 

[justusandersson]

It is a trade-off between frost-free depth and the condition of the ground. Without knowing the latter, it's not possible to make a statement.

 

[gaffa]

Work on and off with this, and we typically don't dig to frost-free depth but instead insulate. Hole - 2 pcs 100mm styrofoam boards at the bottom. Pillar on that - 2 pcs 100mm styrofoam boards just below ground, carefully cut around the pillar. Usually not a problem but as mentioned, the nature of the ground affects it. Personally, I see no reason to dig 2 meters down to frost-free when there is effective ground insulation (which didn't exist before). Moreover, you can dig down a three-meter-long pillar that still freezes up because the frost grips it and pulls it up instead of pushing it up from below. Insulation is the most important.

 

[Kane]

I work on and off with this, and we usually don't dig to frost-free depth but instead insulate. Hole - 2 pcs 100mm Styrofoam boards at the bottom. Foundation on that - 2 pcs 100mm Styrofoam boards just below ground, carefully cut around the foundation. Usually not a problem but as mentioned, the nature of the soil affects it. Personally, I see no reason to dig 2 meters down to frost-free depth when there is effective ground insulation (which didn't exist before). Moreover, you can dig down a three-meter-long foundation that freezes anyway because the frost grips it and pulls it up instead of pushing it up from below. Insulation is the most important.

How large are the insulation boards?

 

[gaffa]

Standard size, 60x120 cm. This provides 60 cm insulation in every direction.

 

[Strip]

Insulation under the plinth seems at least counterproductive?

 

[justusandersson]

If the ground consists of a well-draining material such as gravel and the elevation conditions are such that one can assume that water in the ground drains away, the foundation depth can be reduced to half of the frost-free depth. The best results are achieved if one can combine this circumstance with the insulation method that gaffa describes excellently.

 

[gaffa]

Insulation under the footing seems counterproductive, to say the least?

It is customary. Imagine frost creeping in under the insulation at approximately a 45-degree angle, which means that about 60 cm down, you can expect frost to reach the footing. You definitely do not want frost underneath the footing, so you insulate there as well.

If you are in a location with significant frost heave problems, you might want to use more insulation or use a pipe around the casting tube itself which, like a telescope, can be lifted by the frost without lifting the footing.

 

[KJD]

It's customary. Imagine the frost creeping in under the insulation at about a 45-degree angle, which means that approximately 60 cm down, you can expect the frost to reach the footing. You definitely do not want frost beneath the footing, which is why you also insulate there.

If you're in an area with significant frost heave problems, you might want to use more insulation or use a pipe outside the actual casting tube, which can be lifted like a telescope by the frost without lifting the footing.

How does a sandy soil affect the depth of the footing? We have 30-40 cm topsoil, and then 120 cm of sandy soil before reaching gravel (Halland).

How should one reason here?

Frost-free depth is 120 cm according to husgrunder.se in our area.