Play fort on stilts

[dance]

I'm building a play fort on 4x4 posts for my son. We're thinking of it as a treehouse without a tree.

At the moment I've got two posts in concrete curing and two more to do tomorrow. I have a few questions, if I may? I know 1 & 1b aren't really woodworking questions but I hope it won't offend anyone if I pose them before a few woodworking questions.

1) How long should I give the concrete before I start whacking nails into the posts and hanging joists off them and 'disturbing' them? I was thinking two days? But is that enough? Don't want to compromise the concrete...
1b) I used those bags of sharp sand & cement mixes and added gravel because there didn't really seem to be any aggregate in with the sharp sand. I added water until I got the desired consistency but now I'm fretting (and fretting probably is the right word for it) I've messed with the magic formula and my concrete won't be strong....really don't want this thing to fail! I mixed and poured it at about 5pm and it's not 11pm and I've just been out and given it a prod and it's definitely hardened some, but if I prod it with my finger I can make an indentation. The top of the concrete is also a tad sandy, it's not sort of 'solid'. But I've not really worked with concrete before so I don't know what to expect at this stage.

So at the moment I've got a rectangular layout and four posts coming out of the ground. The footprint is roughly 2m x 1m. We do not have a big garden and my only wish really was that my son would be able to sleep out in it with a friend in the summer months and otherwise it would just be a 'lookout post'.

2) I've seen online a few different methods for how to lay a floor. This guy screws boards either side of his posts then lays the floorboard joists on top of the boards perpendicular to them.
Then there's the joists themselves - some people seem to use joist hangers (I guess to avoid screwing into end grain?) whereas others seem to just nail the joists into the floor framing without using joist hangers. I'm sure there must be other questions and other methods I'm not even considering here.

Another big question I have is whether to chop off my four posts at the height of my platform as many people seem to do with their builds or somehow incorporate them into the framing of the walls? They seem like they should be hugely useful as a structural member so I'm minded to keep them but the prevailing wisdom seems to be chop 'em off and just frame four walls on top of the floor?

Given the footprint (again, 2m x 1m roughly) should I be going 2x6 for the beams which will support the floor or would 2x4 suffice? Also for the framing of the walls - I see lots of (eg) Americans who are building huge treehouses using 2x4s for the wall framing whereas here if you look at treehouses you can buy as a kit, the wall framing seems to be a lot less substantial.

As you can probably tell....I would really love some guidance at this juncture..! If people are interested in really following along I can post pictures and like a daily 'build' with queries that crop up!

many many thanks everyone :-D :-D

 

[Tris]

Hi Dance, surprised no one has jumped in here. I'm no expert on carpentry but here's a few thoughts as I've built a few of these sorts of things over the years.
As long as your post holes aren't much more than double the width of your post (so up to 10 inches say) you should be OK with the concrete but I would use the mix straight from the bag for the next two. Make sure you get the concrete level above soil level and slightly sloped so water flows away from the post otherwise you will be replacing them sooner than you want to.

I would leave the posts full height and fix 6x2 along all sides using coach screws or similar. Screw a 2x1 batten along the lower edge of the 2m side then rest 4x2 joists at 16 inch centres on the batten before screwing them in place through the 6x2. Lay the floor of your choice over that.

The framing of the upper parts will depend a bit on what you want to clad it in.

Hope this helps
Tris

 

[dance]

Thanks Tris - brilliant, thank you. I've already been out this morning to have a prod and the concrete is much harder so I'm relieved a bit there. I'm sure it will continue to harden. Thank you.

 

[Beanwood]

I would be putting the legs at 18 inches deep, and I wouldn't be concerned about the concrete mix particularly. (Try to keep the holes narrow though) It's only going to stop it rocking side to side, or blowing over in the wind - and what you have will cope with that I'm sure.

I'm interested in the other questions you raised though.

 

[dance]

Thanks Beanwood. Can I query why you suggest to keep the holes narrow? Is that to reduce cost of bags of cement? I ask because I sadly DIDN'T keep my holes narrow (I tried but bush and tree roots foiled that plan) and the cement was eye wateringly expensive and took about 13 bags for all four post holes!! I'm HOPING though that means my posts aren't going anywhere even though three of them are not 2' deep. They ARE all 1.5' deep though... so I was relieved to hear you quote 18".


Next question if anyone's got the time (and I've taken the hint not to post the daily pictures!! ) how would you join the brace I want to extend from the play platform at a right angle to the brick wall?

Imagine this is my play platform (it isn't) and imagine that wooden fence is a brick wall - the relationship between the fence and the platform is more or less the same as what I'll end up with.

THANKS ALL

 

[Tris]

The most important thing with post holes is to make the sides straight, I have seen fences blown over where the holes were like bowls, which makes them easy to roll out. That's often easier when the holes are kept narrow, as well as using less concrete.

To fix to the wall cut your 6x2 so it passes the post and reaches to the wall, then use heavy duty L brackets to attach them on the inner face. Tool station will have something to suit.

I don't think you will need wall fixings for this, but it is worth housing in your 6x2 by an inch to help resist any racking forces, that should still leave plenty of strength in the upper section for the roof etc.

 

[Beanwood]

A drainage shovel is useful if you’re going to dig many more. Mine gets used quite a bit, then goes back in the shed for months.

 

[wsb1207]

I'm building a play fort on 4x4 posts for my son. We're thinking of it as a treehouse without a tree.

At the moment I've got two posts in concrete curing and two more to do tomorrow. I have a few questions, if I may? I know 1 & 1b aren't really woodworking questions but I hope it won't offend anyone if I pose them before a few woodworking questions.

1) How long should I give the concrete before I start whacking nails into the posts and hanging joists off them and 'disturbing' them? I was thinking two days? But is that enough? Don't want to compromise the concrete...
1b) I used those bags of sharp sand & cement mixes and added gravel because there didn't really seem to be any aggregate in with the sharp sand. I added water until I got the desired consistency but now I'm fretting (and fretting probably is the right word for it) I've messed with the magic formula and my concrete won't be strong....really don't want this thing to fail! I mixed and poured it at about 5pm and it's not 11pm and I've just been out and given it a prod and it's definitely hardened some, but if I prod it with my finger I can make an indentation. The top of the concrete is also a tad sandy, it's not sort of 'solid'. But I've not really worked with concrete before so I don't know what to expect at this stage.

So at the moment I've got a rectangular layout and four posts coming out of the ground. The footprint is roughly 2m x 1m. We do not have a big garden and my only wish really was that my son would be able to sleep out in it with a friend in the summer months and otherwise it would just be a 'lookout post'.

2) I've seen online a few different methods for how to lay a floor. This guy screws boards either side of his posts then lays the floorboard joists on top of the boards perpendicular to them.
Then there's the joists themselves - some people seem to use joist hangers (I guess to avoid screwing into end grain?) whereas others seem to just nail the joists into the floor framing without using joist hangers. I'm sure there must be other questions and other methods I'm not even considering here.

Another big question I have is whether to chop off my four posts at the height of my platform as many people seem to do with their builds or somehow incorporate them into the framing of the walls? They seem like they should be hugely useful as a structural member so I'm minded to keep them but the prevailing wisdom seems to be chop 'em off and just frame four walls on top of the floor?

Given the footprint (again, 2m x 1m roughly) should I be going 2x6 for the beams which will support the floor or would 2x4 suffice? Also for the framing of the walls - I see lots of (eg) Americans who are building huge treehouses using 2x4s for the wall framing whereas here if you look at treehouses you can buy as a kit, the wall framing seems to be a lot less substantial.

As you can probably tell....I would really love some guidance at this juncture..! If people are interested in really following along I can post pictures and like a daily 'build' with queries that crop up!

many many thanks everyone :-D :-D

I wouldn't nail anything, screw or bolt it all together. Wrap 6x2 around the posts at floor level and use 4x2 joists. Set the joists on top of the 6x2, they're plenty strong enough for a 1m span. The posts should run up to roof level, it'll be stronger than 2 seperate structures. Wrap the posts with 4x2 at roof level and screw rafters in between, make sure you have a slight fall. Short elbow bracing from posts to floor level 6x2's will give enough stability but you can put them at roof height too.