Obsy build for the summer...

[fwm891]

1 hour ago, JamesF said:

And you had to completely take that down when you left?

James

No James - it got dismantled because people viewing the house were put off by it. The observatory was built in sections apart from the roof and it ended up being a posh chicken run for a guy in the village...

[fwm891]

Looking at the tracks/wheels from Brundle's I'm trying to decide on which wheel size to choose. I'm thinking the 200Kg per wheel is way OTT but that's the loading option I'm looking at with a 20mm round top galvanised track. The wheel options are either 60 or 80mm diameter.

https://www.fhbrundle.co.uk/groups/13SWR200__200_kgs_Weighthttps://www.fhbrundle.co.uk/groups/13SWR200__200_kgs_Weight

Any thoughts welcome

[JamesF]

I think pretty much anything you buy is going to be more than capable of handling the load so there just aren't any worries in that respect.  However, larger wheels are supposed to be easier to start turning, aren't they?  If you have more than one section of track per side then I think the larger wheels might well roll over the joins more easily too.

I went for 80mm wheels (though mine are for V shaped track rather than round):

https://www.fhbrundle.co.uk/products/0586604000__80mm_Dia_V_Groove_Wheel_One_Ball_Bearing_Internal_Support

Four are quite enough to carry my roof (probably about 150kg) and roll sufficiently easily that my fourteen year old daughter can open and close it without struggling.  In fact once it's moving it requires very little effort at all.  Definitely worth getting input from someone who has round track though, as I assume the round groove wheels will contact more of the track than the V groove ones (which only have a very small area of contact) and may need a bit more effort to turn as a result?

James

[Astrokev]

Agree with James’ comments. I too went for V profile track and wheels and have no complaints. 

I’m not sure what the functional difference is between V and round section, but I agree that round may suffer a little more friction due to extra area of contact. Is there a reason you’ve gone for round?

[Gina]

I went for 120mm diameter wheels and round profile - four of them.  The roof rolls with one finger.  I think there is more area of contact with V groove than round.  My round section shows two line contacts on the track.

[JamesF]

Same for the V track Gina, so it looks like it doesn't make a whole lot of difference.

James

[fwm891]

Thanks All for the track input.

Looking at the wall/bearer cross sections hopefully self explanatory. Not a great deal of loading as the obsy will be quite small. Footings: scalping's with a very liquid cement binding. Paving slabs over the footings with treated sleepers spreading the loading across the slabs. Waterproof membrane comes next with the floor joist bearer's pinning the membrane to the sleepers. Joists to support the T&G flooring. Walls sit on a weather board to take water away from the structure, Treated shiplap cladding over a CLS frame - internal cladding in 12mm OSB...

[Rusted]

Difficult to see from the drawing, but shouldn't the moisture barrier at the foot of the wall rise up inside it?
Just to ensure rain running down the outside face of the wall is eventually ejected.
You would seem to allow such moisture access to the underfloor from below the weather board level.
I'm just going by the weight of the lines in your drawing.

[fwm891]

Quote

Thanks @Rusted - There are two barriers (in green) one to stop moisture rising up from ground level this one wraps itself around the sleeper. Second is a vapour barrier behind the shiplap cladding. I've now knocked off the front edge of the sleeper to provide a slope for excess water to run off.

 

Edited April 24, 2019 by fwm891

[Rusted]

I still think water will run under [or be wind driven under] the weather board unless you lift it on a batten and provide a [nasal] drip.

A flashing over the weather board from under the cladding would be better but expensive in ally profiles.

[fwm891]

That's essentially what I did with my previous obsy. I used a plastic DPC as a skirt running from under the lower shiplap and down over the sleeper.

[Astrokev]

16 hours ago, JamesF said:

Same for the V track Gina, so it looks like it doesn't make a whole lot of difference.

James

Yep, same with mine. 

[Astrokev]

3 hours ago, Rusted said:

I still think water will run under [or be wind driven under] the weather board unless you lift it on a batten and provide a [nasal] drip.

A flashing over the weather board from under the cladding would be better but expensive in ally profiles.

I am tending to agree. With time I think water will soak into the weatherboard, or seep underneath it by capillary action, and have an unimpeded route to both the wall linings and the floor. 

In my build, I essentially positioned the wall to lie above the edge of the foundation concrete (resting on joists running around the edge of the structure. I used EPDM rubber as a barrier between joists and foundations). The wall membrane covering wall and joists then terminates below the top of the foundation concrete. Water running down the cladding simply drips off onto the floor. 

Your final design with the DPC looks more water tight, but the sleeper will still be sitting in a pool of water. 

Edited April 24, 2019 by Astrokev

[Astrokev]

Here are a few pics from my build thread which show more clearly what I was trying to describe above. All joists around the edges rest on EPDM acting as a DPC.

Edited April 24, 2019 by Astrokev

[JamesF]

48 minutes ago, Astrokev said:

Your final design with the DPC looks more water tight, but the sleeper will still be sitting in a pool of water. 

The slab could be moved further inwards perhaps, leaving the sleeper overhanging by a little?  Probably wouldn't need to be very much.

I have to admit that old sleepers from an actual rail line soaked in years worth diesel and oil (and probably a lot of other stuff I'd prefer no to think about) seem pretty much indestructable and I'd not be surprised if they lasted decades sitting on the slab as Francis has drawn.  I'm not sure it's possible to get those any more though, probably because they're soaked in years worth of diesel and oil and other stuff I'd prefer not to think about.  I've no idea how tolerant brand new ones are of abuse.

Were you planning on having the moisture barrier completely cover all of the ground under the observatory, Francis?

James

[fwm891]

21 minutes ago, JamesF said:

Were you planning on having the moisture barrier completely cover all of the ground under the observatory, Francis?

Yes. I ran a bead of bitumen sealer around the edge of the ground board (read sleeper) / slabs before and could find no evidence of water ingress when I had to dismantle the thing.

New sleepers have an expectancy of 10-15 yrs, I'm just about 68 now so if they rot in 15 yrs time I'm not sure I'll be too worried...

[JamesF]

13 minutes ago, fwm891 said:

New sleepers have an expectancy of 10-15 yrs, I'm just about 68 now so if they rot in 15 yrs time I'm not sure I'll be too worried...

I had something like that in the back of my mind :)

It doesn't have to stand forever.  Just for as long as you're going to want it...

James

[Astrokev]

2 hours ago, fwm891 said:

 

New sleepers have an expectancy of 10-15 yrs, I'm just about 68 now so if they rot in 15 yrs time I'm not sure I'll be too worried...

I guess that makes sense ??

[Gina]

I used DPC between the main beams and six concrete foundation blocks.

[fwm891]

Decided to try building a model at 10th scale - nowhere near finished, braces to add, sleepers, cladding, etc., etc...

[Gina]

I did my model in SketchUp!

[fwm891]

31 minutes ago, Gina said:

I did my model in SketchUp!

I have to say I hate Sketch-up. Never got on with it even the basics...

[JamesF]

But where are you going to get the 11.5mm apo to go inside the model? :)

James

[Gina]

Maybe he'll model that...

[fwm891]

14 hours ago, JamesF said:

But where are you going to get the 11.5mm apo to go inside the model?

I have a lathe and some small lenses...