the yesyes observatory - let the planning begin

[fwm891]

Thanks Francis, I'll have a look there.

...Thinking about 20x20 cm and 75cm tall (50 under ground and 25 over ground).

Concrete blocks are about 40 x 20 x 10 cm why not just cut a few blocks in half or use as-is and get a larger footprint - better load bearing....

Some of the lighter cellular block (theralite etc) can be used 'in the ground', you can cut them with a hand saw

[Gina]

As it's an exposed site here I made my six shed support blocks about 15" square and about a foot deep. I didn't use rebar but did bulk out with stones excavated from the site. I also concreted ties into the blocks to fasten to the 3 main bearers (8" x 3"), onto which the joists are screwed and the main uprights bolted. This means any wind would have to lift not only the weight of the "shed" but also a fair weight in concrete bases. You shouldn't need to go that far Chris

[opticalpath]

Hi Chris ..... really making progress - great!

Rebar: It was several years ago, but If I remember correctly I got mine from Travis Perkins, very near you.

Adrian

[yesyes]

Hi Chris ..... really making progress - great!

Rebar: It was several years ago, but If I remember correctly I got mine from Travis Perkins, very near you.

Adrian

I shall pay them a visit soon. I though, and their website implies, that they only supply the trade, not individuals. But I have now heard from someone else that they would sell to the public as well.

[yesyes]

Concrete blocks are about 40 x 20 x 10 cm why not just cut a few blocks in half or use as-is and get a larger footprint - better load bearing....

Some of the lighter cellular block (theralite etc) can be used 'in the ground', you can cut them with a hand saw

That is a good idea as well.

But come to think of it, couldn't I just use some of these rocks and some cement / mortar and build little posts that way? Most of them are quite flat so it should be fairly easy to lay them like bricks. It would also help to get rid of some of them and it would go well with the remaining walls in the garden.

[yesyes]

As it's an exposed site here I made my six shed support blocks about 15" square and about a foot deep. I didn't use rebar but did bulk out with stones excavated from the site. I also concreted ties into the blocks to fasten to the 3 main bearers (8" x 3"), onto which the joists are screwed and the main uprights bolted. This means any wind would have to lift not only the weight of the "shed" but also a fair weight in concrete bases. You shouldn't need to go that far Chris

I was planning to concrete in some threaded rod in the middle of each post and use that to bolt down the main floor frame.

How may posts do you think I would need for a 5m x 2.70m obsy? Is 4 along the longer 5m sides enough or should I add one more in the middle of each shorter 2.70m side?

[Chris]

If I remember rightly I got my rebar from Wickes and I think it was cheaper than B&Q. I think using existing pre made concrete blocks sounds like the easiest option, however, similar to what you're thinking of I recycled some old paving slabs for my base and built them up on morter to raise them up and had gaps between them for airflow. Sounds like harder work making supports out of flattened rocks and morter but recycling is a good thing now days:)

[opticalpath]

I shall pay them a visit soon. I though, and their website implies, that they only supply the trade, not individuals. But I have now heard from someone else that they would sell to the public as well.

Like a lot of builders merchants, they have a retail counter too. You see cars as well as white vans there!

BTW, if you want heavy timber for joists etc., check out their prices. They have a big stock and I found them quite a bit cheaper than Wickes/ B&Q etc. The trick if you can is to buy full lengths (4-5 metres.) It's always a lot cheaper per metre that way than asking for pieces cut to size. That way you pay for any waste of course, but it's a good deal if your dimensions mean you can use their stock lengths efficiently. They'll even help you cut it up in their yard. Wickes multi-packs are quite good value if the lengths match your requirements but the quality of some of the timber in the DIY stores can be poor.

Adrian

[yesyes]

Thanks Adrian. I shall go there as soon as I can. Knowing their standard sizes / lengths I can then finalise the size of the obsy.

What size timer should I use for the main floor frame and the corner posts? Would 10x10cm (4x4") be enough?

[opticalpath]

What size timer should I use for the main floor frame and the corner posts? Would 10x10cm (4x4") be enough?

You should take advice from other members, Chris, since I did not build my observatory-shed with this kind of framing.

My guess is that 100x100mm would be good for corner posts, but for floor framing you want something thinner but deeper with a bigger vertical dimension to resist deformation better in that direction. Size will depend on the length of unsupported spans.

Adrian

[JamesF]

What size timer should I use for the main floor frame and the corner posts? Would 10x10cm (4x4") be enough?

100mm square would be fine for the corner posts I'd have thought. If you have diagonal bracing in the walls you could probably go smaller. I might be tempted to go 75mm square for the corners and 75x50mm in between. For floor joists I usually look up what the building regs suggest for a clear span and make a decision from there. For 2.7m clear span I think the suggestion would be to go for 6"x2", but as the static load is probably never going to be very high you'd probably get away with 5"x2" at 16" centres.

(Apologies for the mixture of units. I'm at that awkward age

James

[yesyes]

Thanks for that, James.

So at the moment I'm looking at

- 4x4" (100x100mm) for the floor frame

- 5x2" (125x50mm) for the floor joists

- 3x3" (75x75mm) for the outer obsy frame (6 uprights, one in each corner and 2 on either side of the dividing wall and the frame on top of the uprights)

- 3x2" (75x50mm) for remaining uprights in the walls.

Does that sound about right?

[r3i]

So at the moment I'm looking at

- 4x4" (100x100mm) for the floor frame

- 5x2" (125x50mm) for the floor joists

- 3x3" (75x75mm) for the outer obsy frame (6 uprights, one in each corner and 2 on either side of the dividing wall and the frame on top of the uprights)

- 3x2" (75x50mm) for remaining uprights in the walls.

Does that sound about right?

That sounds like it should be nice and solid. Would recommend putting in some bracing on the walls at 45 degree angles - this really helps to make the framework rigid.

For the record I used the following:

Anchor posts: 4x4"

Floor joists: 6x2"

Wall framework: 3x2"

Internal partition wall & rolling roof framework: 2.5*1.5" (63x38mm)

[yesyes]

Quick update on my progress.

I've had a rather productive day yesterday getting more of the ground work done. Despite the hard work there's not much to see on pictures. But here's a few anyway...

1 - removed bamboo roots in 2 places (on the far left in front of the neighbour's water butt and further to the right in front of the fence post). 2 of the concrete foundation blocks will be where the bamboo was.

2 - moved all rocks from pile 1 to pile 2 leaving a single pile, taken out any nice flat pieces that can be use for paving the path between the 2 remaining walls. That remaining bit of wall on the right is my biggest problem at the moment. It appears to be a solid block of concrete. I'll need to rent one of those electric breaker hammers to get rid of that. This is where the tool shed will stand.

[yesyes]

How should I do the corners of the floor frame and corner posts. option 1 or option 2 or completely different?

[Gina]

Quick update on my progress.

I've had a rather productive day yesterday getting more of the ground work done. Despite the hard work there's not much to see on pictures. But here's a few anyway...

1 - removed bamboo roots in 2 places (on the far left in front of the neighbour's water butt and further to the right in front of the fence post). 2 of the concrete foundation blocks will be where the bamboo was.

2 - moved all rocks from pile 1 to pile 2 leaving a single pile, taken out any nice flat pieces that can be use for paving the path between the 2 remaining walls. That remaining bit of wall on the right is my biggest problem at the moment. It appears to be a solid block of concrete. I'll need to rent one of those electric breaker hammers to get rid of that. This is where the tool shed will stand.

Coming on nicely, if gradually, Chris A lot of work, isn't it, particularly this time of year with the bad weather - not that it was much better in the summer! Good luck

[Gina]

How should I do the corners of the floor frame and corner posts. option 1 or option 2 or completely different?

Well, I did mine differently. Overlapped the corners with two coach bolts , washers and nuts for each joint. I'll see if I can find a photo or two or do a diagram.

[yesyes]

That would be great, Gina. Though I think I do remember roughly how you did yours.

I think I need a different approach as my obsy will be very close to the fence on 3 sides; too close to access the outsides of these walls once installed. So my idea was to build a rigid frame and then build and insert pre-clad wall panels between the corner posts of the frame. The wall panels will not need to have any structural strength.

I assume that option 1 would be better as that would protect the end-grain of the corner posts better. With option 2 on the other hand I could use shorter timber for the horizontal ones. If I made the corner posts 100x100mm, then that would add 20cm per length. With standard 2.40m and 4.80m lengths that would bring me to the desired 5 x 2.60m size.

[Gina]

A scan through a my photos (hundreds and hundreds of them) and I think this one shows the underfloor structure about the best. The whole floor rests on 3 barn roof beams of 8"x3" which sit on 6 concrete pads and fastened to them with stainless wall ties. The 4 corner posts are coach bolted onto these beams and also onto the north and south floor joists (5"x2" ie. 125mmx47mm)) though not yet in this photo. This is at the stage of spacing everything out to see how it was going to fit together.

[opticalpath]

I'd go with option 1, Chris, for the reason you mentioned and because the joints in the horizontal frame would be more rigid; even 4.8 x 2.4 is a good size.

If you choose option 2, I would reinforce all the corners with triangular gussets or diagonal braces (good to do anyway) and ensure the whole base frame and vertical end grains are wrapped from underneath with DPC, and that the outer cladding goes low enough to completely overlap the DPC and shelter the vulnerable areas from rain and water running down the walls.

Adrian

[fwm891]

How should I do the corners of the floor frame and corner posts. option 1 or option 2 or completely different?

Hi Chris - Happy New Year!

On mine I made each wall as an independent panel and then screwed each panel to the corner posts before adding the inner osb cladding.

[yesyes]

Hi Chris - Happy New Year!

On mine I made each wall as an independent panel and then screwed each panel to the corner posts before adding the inner osb cladding.

Happy new year to you too! ;-)

This is exactly what I had in mind. Though that does not allow for diagonal bracing of the corner posts as Adrian recommended.

The cladding on the 3 walls next to the fence will be 300mm wide PVC cladding. Being 300mm wide it will allow for plenty of overhang well below the floor frame and DPC.

[JamesF]

With the childrens' tree house I didn't bother with separate corner made the short sides the full width of the building and the longer sides fitted between the end uprights of the short sides. Each side has a diagonal brace at each end. It has put up with being eight feet up a tree in quite fierce winds, so I don't think the design compromises the structure at all.

James

[Gina]

I made my walls as separarte frameworks fastened together with coach bolts, washers and nuts. What I mean is the frames were 3x2 (75x47mm) fastened together with wood screws and then fixed to the corner posts or the next frame with coach bolts.

I'm planning to write up a shortened version of my build with many fewer photos and far fewer posts. That great big long build thread needs a precis!

[Gina]

The south wall frame with roof runner forming the top. It sits on top of the floorboards which in turn are supported at the ends with the outerrmost floor joist. The ultimate rigidity is obtained by screwing through the bottom wall frame member through the floorboards and into the joist. The east end frame is awaiting diagonal members.