finished plinth or cast your own

[TreeMonkey]

The plan is to build a 1.8m fence - 30+m long in a windy area

Trying to decide if I should use ready-made foundation blocks 700mm or cast my own... Have always just set the posts directly in the ground before.

Looking for advice / advantages / disadvantages. The ground is sandy with lots of small stones

 

[hapazard]

If it is a dense fence, in my experience, you must place supports at an angle against the fence. The moment in the fastening becomes enormous and can break screws and snap post shoes if the footing isn't displaced instead.

If you set a reasonably large number of supports, you might manage well with earth anchors or the like, so you don't have to dig.

 

[TreeMonkey]

Wondering if casting tubes with a 150 mm diameter are large enough for 95x95 posts...

I will use supports regardless. 30m/s + wind in winter storms is not uncommon.

 

[vectrex]

Wondering if casting tubes with a 150 mm diameter are large enough for 95x95 posts...

I will use supports regardless. 30m/s + wind in winter storms is not uncommon

150mm is more than enough for 95x95 posts.

Properly cast footings won't be the weak link. Do not use post shoes but cast at least 3 (preferably 4) post anchors instead. It will be much sturdier.

 

[Janus82]

Cast your own foundation piers so you can make them deeper than standard piers. If you use an earth auger, it often goes quickly to drill holes that are about 1.2m deep. This way, you avoid frost heave and get a solid resistance against all torsional forces. The most convenient method is to cast directly into the hole and only use a casting tube in the top third so that the part sticking out of the ground looks nice.

You should absolutely not use post shoes, but you should use plintjärn. Cut off stumps of the type of post you are using, and screw together two plintjärn with through-screws so the holes align perfectly. The plintjärn should preferably be in the lengthwise direction on the fence to prevent sharp screw ends from sticking out towards the property. Additionally, it becomes easier to align all posts so that the fence is arrow-straight since you can adjust each post by a few centimeters. Some claim that the fence becomes weaker with the plintjärn in the lengthwise direction, but that is an unfounded concern.

I have nearly 40 m of fencing around my house built with 150mm pipes and plintjärn in the lengthwise direction along with 70x70 posts, and it is sturdy and good. It's not wrong to use 95x95 posts, but personally, it feels like overkill and mostly risks making everything look big and bulky.

Edit: Of course, two plintjärn per post is sufficient.

 

[TreeMonkey]

Cast your own foundations so you can make them deeper than standard ones. If you use a soil auger, it often goes quickly to drill holes about 1.2m deep. This way, you get below the frost line and achieve significant resistance against all twisting forces. The easiest method is to pour directly into the hole and only use a casting tube in the top third so that the part protruding from the ground looks nice.

You should absolutely not use post shoes; instead, you should use foundation iron. Cut off pieces of the type of post you will be using and screw together two foundation irons with through bolts so the holes align perfectly. The iron can preferably be oriented in the longitudinal direction of the fence to avoid sharp screw ends protruding toward the property. It also becomes easier to align all the posts so the fence is perfectly straight because you can adjust each post a few centimeters. Some claim that the fence becomes weaker with the iron in the longitudinal direction, but that is unwarranted concern.

Unfortunately, I've already applied for the building permit, and changing the sizes of the services would mean submitting a new application—and a fee, I believe.

Would you use regular coarse concrete in the hole?

And would reinforcement be needed to go from the casting tube section into the base, or how would you do it?

 

[Janus82]

Use the 95-posts in that case. It's never wrong to make something too stable.

Regular coarse concrete from a bag works excellently. If you have many footings, make sure to borrow/rent/buy a concrete mixer. For just a few footings, you can mix concrete in a wheelbarrow, but it quickly becomes tedious. It's possible to vibrate footings with a wooden stick, but again, it becomes boring quickly if there are many footings, so consider renting a vibrator so everything goes faster and becomes more enjoyable.

The footing absolutely must have reinforcement. Cut pieces of 8 mm rebar to a suitable length so that they are about 10 cm shorter than the finished footing. This way, the rebar will have 5 cm of concrete above and below, so they are well protected from the elements. Fill the entire footing with concrete and vibrate them down so that they are about 5 cm below the top to ensure they are positioned adequately from the bottom. I usually use 3 pieces of rebar and place them in a triangle in the footing. It may be unnecessarily much, and there might be better ways to place the reinforcement, but my footings for the fence still hold well even after 7 years.