Obs Main structure framework

[kirkster501]

I am at the planning stage of my obs before I start buying the timberwork.

I want to build the main frame of the obs with 4" x 4" fenceposts in a 9 x 9 foot footprint and about six feet high and this will form a "cube" of 4"x4" timbers that will be 9x9x6 - similar to the way laser-jock did his.  I may tinker with these dimensions but that's the general idea.  With these dimensions not being that large do you guys see the need for a central 4"x4" upright in the middle of each of the walls between the 4"x4" corner posts for additional support?  I was thinking that using 3"x2" with three or four verticals per wall would be more than enough between those 4x4's?

Laser-jock you used the metposts for the vertical corner timbers.  How do the the horizontal 4x4 timbers at the base of the wall then attach to the upright?  Are there holes in the Metpost to do this?

How do you guys get a 4x4 to extend backwards away from the side walls and rear wall to support the roof when it is rolled off?  How can you "join" two 4x4's since I imagine that obtaining two 4x4's that are 16 feet long is going to be quite tricky (to say nothing of being heavy).  Whatever is used to join the 4x4's cannot have anything on its top surface because that would inhibit the track the roof wheels would run in?  Also do you do this join on the top of the two rear corner posts?

[Mick J]

We used 3x2 carcasing timber just like an internal stud wall,  piece along the bottom, piece along the top, uprights at ends and every 620mm ish to suit the sheet ply we clad the inside with (we clad the outside with ply as well, over clad with shiplap in places).

Once 4 of these are fixed together (before internal ply) it's quite solid,  4x4 posts in the corners may be better but seems overkill to me.

On top of two of the walls 3x2's run and are supported away from the obs on 2x2 uprights in metposts, the roof rolls on these, its all quite light and won't take swinging on.

5.1 meter is a common length in most timberyards, longer is possible.   The 18mm ply screwed to the studwork  is where the strength is.

Hope this is helpful.

[Tinker1947]

Check with a timber merchant on supplied timber sizes buy at a supplied size means there's no waste 2.4m is the short end going up to 4.8m with other sizes in-between, as for the length sterling board comes in 8' X 4' sheet  these boards i used to cover the internal walls, the intermediate posts will make the walls more rigid and add to the floor joist if you are raising the floor a little Keeps the feet warmer and your not on the ground to make the pier vibrate...4" X 4" post come in 10' or 12' lengths

Something like this.....

The Sterling board is held in place with 4" X 1" treated timber with a rebate this will allow the entire board to be held in place with a few screws to stop it bowing, it also allow the entire wall to be opened up easily should you want to add wiring ect

[Gina]

I used 3"x3" corner posts (75mm square) and 3x2 framing like stud walls (75mm x 47mm).  I got nearly all my timber from the local timber yard at something like half the price of the DIY stores and much butter quality to boot - tanalised too.  The corner posts were recycled mahogany.

[JamesF]

The plan is to build an obsy with a suspended floor?  The description reads as though it probably is, but I thought it sensible to check.

James

[Mick J]

.  The corner posts were recycled mahogany.

Like that bit, well done 

[kirkster501]

The plan is to build an obsy with a suspended floor?  The description reads as though it probably is, but I thought it sensible to check.

James

Yes that's the plan.  Supported by the edging 4x4's and also some joists that will be supported mid span by blue bricks concreted into the ground.  At all points where the floor joists touch a brick or paving I will bitumen the point of contact.  I plan to use decking to create the floor.

I have a wood yard near me as well Gina.  

When you add up the costs of all this wood of 4x4, 3x2 ( about 20 x 4.8m lengths), all the metal work and bracketry to hold it all together, the cladding both outside and inside, the tilework and runners for the roof, it starts getting to be a big number, I'm looking at the thick end of £2000 I reckon for the materials.  A big enough number that some commercial offerings are not that much more expensive.  I can get a 9x9 from homeobservatoryuk.co.uk for £3200 including fitting and that's job done.  Would it be as substantial as I can build it?  There's a question!!!!     I am questioning what I should do.  I love a good 'ol DIT project.  But I worry if this is going to take months of work and it may be worth the £1200 cost delta to just get the job done!

[JamesF]

If you're going to support some of it on brick piers I'd be tempted to support the entire lot on brick piers and not worry about corner posts.  I'd be tempted to put a layer of DPC material between the bricks and the timber too.

If you made the floor structure and fix it on brick piers, then fix studding walls to the floor structure and screw them together at the corners and include a few diagonal ties along the way I think that would work.  Once the cladding is on it should stiffen the entire structure up nicely.  Even more so if you have an inner skin too.

Though it has a concrete base and a single block dwarf wall, my recently-built "beer shack" is of similar design from there up, though I did use 4x2 for the wall structure because the shed closer to 8'x20' and has a cut pitched roof on top as well as openings for doors and windows.  There are some pictures here: http://stargazerslounge.com/topic/232534-the-beer-shack/

For my obsy I shall take the same approach as I've suggested here, but rather than brick piers I shall be using gabions made of old tyres full of gravel to support the floor structure.

James

[Gina]

Yes, building your own is a long and hard job but very rewarding.  I haven't added up how much I spent on mine.  It was initially a bit over £600 on new timber but that was only the start.  I got that delivered in two lots as they gave free delivery on orders over £300.  But we went back and bought more odds and ends with the pickup truck, including 10 sheets of 8x4 ft 6mm outdoor grade plywood.  I also used a fair amount of recycled timber we bought at local auctions.  Farm shed roof beams 8"x5" came in very handy for the floor main supports that took the joists.  The hardware cost a fair bit too.  And all the fittings add up.  OTOH you can get exactly what you want if you build it yourself.  If you have the time and energy I recommend it

I used concrete pads 18" square by 10-12" deep to support the main floor beams - six of them with three beams, with DPP between concrete and timber.  Loops of stainless steel - two per block - were embedded in the concrete pads and bolted to the beams to stop the whole "shed" taking off in a storm!!  The main corner posts were bolted to the main beams.

[laser_jock99]

Laser-jock you used the metposts for the vertical corner timbers.  How do the the horizontal 4x4 timbers at the base of the wall then attach to the upright?  Are there holes in the Metpost to do this?I am at the planning stage of my obs before I start buying the timberwork.

I want to build the main frame of the obs with 4" x 4" fenceposts in a 9 x 9 foot footprint and about six feet high and this will form a "cube" of 4"x4" timbers that will be 9x9x6 - similar to the way laser-jock did his. I may tinker with these dimensions but that's the general idea. With these dimensions not being that large do you guys see the need for a central 4"x4" upright in the middle of each of the walls between the 4"x4" corner posts for additional support? I was thinking that using 3"x2" with three or four verticals per wall would be more than enough between those 4x4's?

 

How do you guys get a 4x4 to extend backwards away from the side walls and rear wall to support the roof when it is rolled off?  How can you "join" two 4x4's since I imagine that obtaining two 4x4's that are 16 feet long is going to be quite tricky (to say nothing of being heavy).  Whatever is used to join the 4x4's cannot have anything on its top surface because that would inhibit the track the roof wheels would run in?  Also do you do this join on the top of the two rear corner posts?

The horizontal 4"x4" timbers in my build were 'resting' on the Metpost flanges and then secured to one another using some heavy duty brackets.

The intermediate uprights I used were 4"x2"

The 'roll off' section is joined with even more heavy duty brackets. From the photo it seems I only used 2x4 for the upper part of the frame.

EDIT- and a flat joining plate on the outside!

If you find the raised floor areas a bit 'springy'- shove some breeze blocks under the joists before you lay flooring boards!

[SnakeyJ]

Glad to see you've kicked this off Steve - I'll keep an eye in with interest, but there are some excellent suggestions in here already to get you on the right road.   Do you have a pic of the intended site?

You've got to love those views over at LaserJock's