Advice needed for new Obsy build

[blinky]

So Ive now sold my skyshed and am ready to embark on my own build of a roll off roof obsy:-)  Some info to get started before the questions!

• Im planning a pent roof, I figure this is easier to construct - pretty much thinking that one side, I will add an extra length of wood to raise that side up
• At this stage im not planning on insulating or having a warm room 
• Im planning to motorise the roof with a garage door opener and having it sliding on gate track with rollers/wheels

My first question is around insulation, do I ned damp proof membranes or vapour barriers?  I think Im going to have either shiplap/tounge&Groove or buy some plastic cladding.  If I do need membrane, do I secure this to the outside of the wall batons, then secure the cladding directly over the top of the membrane?  Does this cause problems as there is no air gap between the membrane and the cladding?

Cladding - what do people recommend?  I want it to look nice, be watertight but dont want to spend a fortune (hence building it myself).  My last obsy was tongue & groove and after a few months is all started to come apart at the joints and water started to come in but that was maybe the joiner I hired used crap wood!  Is it easy to install/cut etc plastic cladding?

I think this might take a few months to build but I will endeavour to keep this thread up to date - FYI here is the existing SkyShed and base that the new obsy will be going on:

[blinky]

Just measured - the obsy will be 2.6 x 2m - the decking is 3.3m long by 3m wide.  So 2m wide should give me space to get round it and 2.6m seems a standard length of cladding - edit, 3.6m is the standard length!  I assume I can reuse the 1m offcuts

Edited July 11, 2023 by blinky

[Carbon Brush]

On the exterior wood protection. My 2007 build shiplap shed based observatory still has good walls.
Tanalised (treated) wood was used. Since then I have been out with the cuprinol a few times.

When assembling, be generous with the cuprinol (or whatever) on areas you can't get to afterwards.
For example shiplap that is fastened to a batten. Or timber that is at the bottom.

The pent roof needed quite a bit of additional timber. If starting again I would make a frame non-flat roof for rigidity.

The original floor joists rotted about 10 years in. They were sitting on the concrete base.
I replaced them by pressure treated 3" fence posts. Jacking the shed to avoid having to remove the contents & dismantle.
Ask me in a few years how they have lasted. But I can jack it again.

Like you I used a garage door opener. Excellent choice😁.
The roof covering is pond liner - not roofing felt. Still good 2007 - 2023.

While building consider putting thin vertical wires in the walls. Eventually linked to your alarm.
When Burglar Bill tries to pry off planks to gain entry a wire breaks and you get lights and bells.
Other security arrangements can be made later in the build.

Following with interest.

David.

[Naughty Neal]

Butyl pondliner makes for a good roof membrane.

As for any timber ground bearers make use of dampcourse between the ground and the bottom face  of any bearers.

[iapa]

6 hours ago, blinky said:

Just measured - the obsy will be 2.6 x 2m - the decking is 3.3m long by 3m wide.  So 2m wide should give me space to get round it and 2.6m seems a standard length of cladding - edit, 3.6m is the standard length!  I assume I can reuse the 1m offcuts

I’m thinking that the gap between fence and obs could be minimise by using that space for pollinator friendly wild flowers - minimal effort required.

That’s my position for my dome - between fence and base is wild flowers

[blinky]

1 hour ago, iapa said:

I’m thinking that the gap between fence and obs could be minimise by using that space for pollinator friendly wild flowers - minimal effort required.

That’s my position for my dome - between fence and base is wild flowers

The base is a decking area so no room to plant anything

[blinky]

8 hours ago, Carbon Brush said:

On the exterior wood protection. My 2007 build shiplap shed based observatory still has good walls.
Tanalised (treated) wood was used. Since then I have been out with the cuprinol a few times.

When assembling, be generous with the cuprinol (or whatever) on areas you can't get to afterwards.
For example shiplap that is fastened to a batten. Or timber that is at the bottom.

The pent roof needed quite a bit of additional timber. If starting again I would make a frame non-flat roof for rigidity.

The original floor joists rotted about 10 years in. They were sitting on the concrete base.
I replaced them by pressure treated 3" fence posts. Jacking the shed to avoid having to remove the contents & dismantle.
Ask me in a few years how they have lasted. But I can jack it again.

Like you I used a garage door opener. Excellent choice😁.
The roof covering is pond liner - not roofing felt. Still good 2007 - 2023.

While building consider putting thin vertical wires in the walls. Eventually linked to your alarm.
When Burglar Bill tries to pry off planks to gain entry a wire breaks and you get lights and bells.
Other security arrangements can be made later in the build.

Following with interest.

David.

I would have thought a pent roof needed way less timber?

[bwj]

Look up shed plans for sheds with rafters of a size similar to the size you want. There are also joist and span tables you can use. That can give you a good basis to compare costs. I'm in the U. S, so dimensions are probably a little different. 

2m is about 6.5 ft. (rounded off) for a pent roof (what we call a shed style roof), you could probably get by with 2" x 4" rafters on 12 or 16 inch centers.

Good luck!

Edited July 12, 2023 by bwj
typo

[blinky]

Just discovered tonight that I need to relocate or rather remove and build a new pier 😞 i want to make the obs half or as near to as I can, the size of the deck.  When I looked tonight, the current pier is going to be pretty much on the back wall.....

[George Gearless]

I've just finished building my observatory. I used a pent roof, roll off design.

I had some trouble with the roof bending downwards in the middle. This was due to four factors:

1. The roof is 3x3m as is the observatory it covers. It's quite a stretch using wooden beams. Either use VERY sturdy and thick ones, or use many. 

2. The wooden boards (that make the actual roof) onto which I've nailed the bitumen shingles, were extraordinarily heavy. The aforementioned beams can carry them, yes. But the strain is far greater than I had anticipated. Add to that, the bitumen shingles. Or whatever you choose to finish the roof off with.

3. I was (too) worried about the roof being to heavy and that I wouldn't be able to move it easily. So I deliberately chose some slimmer beams to support the roof, than I might otherwise ideally have chosen. 

4. The inclination was initially too small. Because of the low inclination, the middle of the roof sagged down below the lowest part of the roof where the water was supposed to run off. Instead it ran down the first row of shingles, and settled in the middle of the roof, where it proceeded to run under the second row and into the observatory. I've managed to remedy the situation. But I've re-laid my roof 2 times now, before the problem was solved.

Good luck with your build.

[malc-c]

I went all in and built mine close to building standards... DPM in a dwarf wall from which 6" x 2" softwood but treated joists were laid, with 50mm insulation under the warm room.  Everything above the floor was made from studwork, keeping to 16" centers.  The frame work was clad in a quality T&G shiplap, and is treated to an annual application of a decent fence / shed preserve.  I dismantled the scope as I was intending to move this summer and I inspected the underside whilst pulling cables back and the joists are as good as they were the day they were installed over 12 years ago.

 

[blinky]

16" centre and T&G Shiplap - right, thats what I was wondering, will do mine the same

[malc-c]

1 hour ago, blinky said:

16" centre and T&G Shiplap - right, thats what I was wondering, will do mine the same

Here's an image of the floor supported by hangers off the dwarf wall

 

Then the framing was started

 

Edited July 20, 2023 by malc-c
hit post before adding the second photo

[blinky]

So progress report......  Removed the old decking boards to discover that when building the original frame, we took a shortcut and just dug trenches in the grass and now its all just a big waterlogged mess!  The old grass/soil is up against the wood and it will start to rot.  So today Ive dug out 20 rubble sacks of the old mud/grass/clay mix to give an air gap, thats the first half done, need to do the other side at the weekend 😞