Outdoor Oak Frame Seating Area

[AdamW85]

Hi, I hope this is in the right forum location.  Not strictly house construction, but is timber! 

 

Looking to build an outdoor seating area, with a oak frame construction and flat roof.  Being an engineer, i'm have a high (an sometimes annoying) attention to detail.  I have worked with wood quite a bit, but never anything of this scale, or in oak.

 

I would like to keep it traditional looking, with knee braces and ideally pegs to hold the structure together.  

 

Attached is a plan view of the area.  Made a little more complicated by the shape, but not too bad.  I am thinking 4 main posts (ideally 8" square - shown red).  Timber attached to the wall (orange), a main lateral beam (green) with rafters coming out to meet the posts/main lateral beam (blue).  Spacing of beams is not accurate, just to show principle.

 

A couple of key points I am unsure of:

• The timber size to use for the wall beam, rafters and main lateral (assuming 8" square posts)
• The best joint design to use at the point the upright posts will meet the main lateral beam and the rafters from the wall
• Is it better to use wooden pegs to hold the structure together, or counterbored bolts with a peg purely for aesthetics

 

Can anyone direct me to some literature regarding these points, and also any general construction best practice would also be useful.

 

I'm confident in my ability to physically manufacture the parts, but its the detail design that I am unsure of!

 

Any help or advice would be much appreciated.

[Temp]

What's the roof covering going to be?

[Alan Ambrose]

This guy is good:

 

 

 

 

[Alan Ambrose]

Re beam size - theoretically depends on roof loading of course (if there is a roof). In actual fact, you’ll find it is all so oversized that you can use whatever works aesthetically / economically / practically given the joints you want to use.

 

Re joints - standard would be mortice and tenon with the tenon on the end of the upright post. You could tenon the rafters into the beam(s) also if you want, or birdsmouth them onto the top of the beam. Pegs are plenty strong - they’re only in shear. You might want padstones under the posts to reduce water damage.

 

There’s a bunch of oak frame books and videos. There can be a bit of subtlety re forming the joints etc but by and large go for it, green oak is fun. As Robin says - we’re not making a clock here.

 

BTW if you use any fixings, you’ll want a4 stainless - the acid in oak destroys standard steel fixings v fast.

[AdamW85]

Afternoon All.  Apologies for my delayed replies.  I thought I had notifications set to tell me when someone replied.  It seems I did not!

 

@Temp I would like to keep the garden side roof height as high as possible, so I don't bang my head and also restrict light into the property.  It is quite deep at its deepest, ~4.4m, so any pitch has a big impact on this height.  Height of the roof at the back wall of the house will be ~ 2.9m (topside)  I am not keen on a flat roof, as the coverings are never pretty.  So I was thinking as shallow as possible to get away with a pantile style tile.  Something in the region of 5deg.  Less than the minimum prescribed pitch, but given its an outside seating area (i.e. not a weatherproof habitable space), it doesn't need to be watertight as such, and building control might allow it.  If it does need to be watertight, was thinking the same, but with some EPDM (or similar) beneath the tile to act as the watertight layer, and the tile on top for cosmetic.  

Open to suggestions though.  Just want it to look nice and fit with the traditional style of the structure/house.


@Alan Ambrose Yes there will be a roof.  The only reason to build it is to have somewhere to sit in the glaring sun/rain.  I was thinking mortice and tenon for the main joints.  Is there a standard size for the mortice for a given beam size?  Would the same go for the knee braces into the upright and beams?  If I do put a shallow pitch on the roof, then birdsmouth would probably be the way to go for the rafters I think.  And yes, the plan is to have small brick pillars ~5/6 courses high with a chamfered pillar on top, for the main upright posts to sit on.

Any suggestions on how to finish the structure on the LH and RH property boundary?  If there are 4 upright posts with a main lateral beam, would you just run the rafters from the back wall of the house to the lateral full width?  Or have something different on the outer most edges?