Wood selection for outdoor garden room thingy?

[13eightyfour]

Ive been offered a few double glazed panels, they're quite large and have decided to construct a garden room thing, The picture below should explain what im going for, (My sketchup skills are average at best)

It will have a roof although i have left that out of the model.

Basically the main structure will be from 4x4 oak, with the window frames fixed to it, This is where im having trouble deciding on the wood. Is the main 4x4 frame best made from dried oak or green, Ive had conflicting answers from whome ive already spoken to.

And seeing as im making the frames for the glass myself the same question applies, Although im thinking dried would be better for that purpose due to hopefully moving less.

Can anyone give me guidance, ive never really done anything on this scale and want it to look good (and last)

 

[Richard Findley]

Hi 13eightyfour,

Not sure if this will be any help or not but this is what my timber merchant told me when I was enquiring about Oak of different kinds:

The American White Oak they stock is of a lower moisture content so is more suitable for indoor joinery/furniture etc. The European Oak they stock has a higher MC and so is usually used for external work or window frames such as yours.

My timber merchant is James Latham in Wigston (Leicester) but they have branches throughout the UK.

HTH,

Richard

 

[matthewwh]

Green would be cheaper, but it has a tendancy to twist as it dries out. If you use chunky M&T joinery pinned with dry oak dowels, the movement of the timber can be harnessed to lock everything together. This was how traditional timber frame houses have been built for centuries, so it works well and lasts a long time. Timber framing is a profession in its own right, so it will pay dividends to gen up on it before you start.

If you are thinking of something you can use coachbolts, pocket screws etc to join together, then dry would be a better way to go. Dry timber will still move a little with the seasonal changes in humidity but in a much more predictable way, so you can account for it in your design.

 

[13eightyfour]

Thanks for the speedy replies, I was thinking of going the doweled M&T route, i think it just looks nicer and shows off how its built.

Im trying to read up as much as i can on oak frame construction before i get stuck in, Ive been checking prices of both types and there doesnt seem to be as great difference as i thought there would be, going by prices at uk oak anyways

 

[wizer]

I'd try to get some quotes on timber prices ASAP. Sounds pricey to do it in HW. Would look really nice tho IMO

 

[MikeG.]

1384,

This is like my day job.....only without getting paid for it!!!

This would be a great project in green oak, but it is fraught with dangers. Exposed oak has to be designed carefully, and if you have no experience with the material or a project of this size I suggest that this might be starting at the more difficult end of the spectrum!

The biggest problem is allowing for movement between the frame and the glass. I can't really tell whether you are planning to fix double glazed units directly to the green oak, or whether they are built into a seasoned timber sub-frame. If the former, then I would just forget it! If the latter, you can't just screw the window frames to the oak frame, because the oak will pull the window frames to pieces as it shrinks and twists.

The fundamental difficulty you would have in design terms is that the inside of a conservatory can get extremely hot indeed (mine has been up to 45 celcius), and this will lead to differential drying between the inside and outside of an oak frame. This can be allowed for........but you really do need very careful detailing to make this work. Furthermore, it would need to be on a brick plinth.

You mention a 4"x4" section for the frame. Green oak framing would be much chunkier than this......probably 6x6 at least, and the plates wouldn't normally meet at the corners at the same level.

Designing an extension in isolation from the house is just not on.....so I can't begin to comment on how I might tackle this room. Unfortunately, I think that you really do need professional advice before you start this project. Don't forget that you may need planning permission, and that you musn't remove the house door or open up the wall of your house to make it open into the conservatory.

I don't mean to sound too cautious.....but don't just rush into this project!!

Mike

 

[13eightyfour]

Thanks mike plenty to think about there, it shouldnt need planning ive checked my council website aswell as the planning portal and it doesnt breach any of the conditions, Ill get someone from the council out to check before/if i go ahead.

I realise that im jumping in at the deep end, but i willing to give it a proper go. The sketch isnt very clear but the actual windows would be seperate framed units "fixed" to the chunky frame. its also going to be 20+ feet from the house (think gloryfied shed) so no worries about opening the house up into it

Its nice to get some balanced views, it makes you more aware of the problems that could happen

One thing is for sure i wont be rushing in, i might see if i can find someone in my area that does this kind of thing, and see if there willing to share some secrets.

I could just get someone into to do it but that wouldnt be any fun and i think im capable asl ong as i plan it well.

 

[wizer]

don't forget that it'll essentially be a greenhouse. i.e to hot in the summer and too cold in the winter.

What exactly are you going to use it for? Personally I like to be outside in the sunshine and inside when it's cold!

 

[13eightyfour]

Once the roof is on i rekon it will be more like a summerhouse, Im thinking somewhere to sit in late afternoon when its a bit cooler, after a bbq say.

quick sketch to show what i mean, its not quite right but should explain where its going to be (forgot to put the roof on again!! the roof will be solid not glass or perspex.)

thats a raised deck at the back that its sat on, the decking isnt there in reality yet but was planned before this crazy scheme came up. The brickwork however is there already.

 

[dennis]

Will the lawnmower go under the end, or have you got a rabbit.

Dennis

 

[13eightyfour]

Will the lawnmower go under the end, or have you got a rabbit.

Dennis

Hmmm i never thought of that, perhaps i could get a rabbit and mesh the it off

 

[MikeG.]

OK, that's a whole lot clearer!

Firstly, I hope those aren't boundaries adjacent to your building, because you will probably struggle with Building Regs if you are hard up against a boundary.

Secondly, I re-iterate.....you will need a plinth.

Thirdly, if you are going to use green oak you will struggle to make a modern sleek looking structure. You will need chunky members, big traditional joints (unless you are into stainless steel fabrication), and this will generate a very traditional look. I can picture this with a pitched roof with shingles, for instance.

The relationship of the glazing in its frames to the oak framing is critical to the look and the functionality of this building. I suggest that you sit the windows into rebates in the framing, such that the face of the window frame is 10 or 15mm or so back from the face of the frames....and that you have a tradtional oversaling cill to the window frame to throw all the rain clear of the sole plate.

With a plinth, you won't have a continuous sole plate either, because it will need to be broken at your doorway.

What are you proposing to make the back and end walls out of? What sort of roof do you have in mind?

Mike

 

[13eightyfour]

Thanks mike, Im undecided on the cladding for the back and side, as with the roof i would like the roof to be metal but am still looking into suitable products for both the walls and roof.

I get what your saying about the potential boudary issues, ill get an official to look at it.

The big problem is that i would like it to look fairly modern but in a traditional way, i dont even know it thats possible. Maybe im looking at it all in the wrong way and theres a better idea than the oak frame i ve suggested? would treated softwood do the job just aswell?

I like the idea for the windows,and m going to spend alot more time over the weekend thinking and designing to try and work out all the ideas youve all given.

 

[enecosse]

I am looking to build a glass veranda type structure on the back of the house, but I am thinking of using steel and cladding it in wood, still looking
into the material possibly cedar, I would like to use a stainless wood mix but what a price, one thing to note was the stainless teak gate I built the teak cost more than the stainless.
Don't know if you would consider this option, steel clad in oak.
How about a zinc roof, look the business with oak.

 

[MikeG.]

1384,

the reason I asked about the back and end of your design is that you have an inherently unstable structure at the moment, as drawn. There is nothing to prevent racking.

Now, you can get over this in so many ways and a stiff rear and end wall will help. However, you will still need to brace the two glazed walls, and the roof. My instinct would be to consider diagonal stainless steel wire, with a turnbuckle, from bottom plate to top plate. This you could re-tension easily as the timber shrank.

Whilst there are lots of options, you can't just rely on the mortice & tenons. Old buildings have wind-braces and/ or knees to do this job for them......and they often failed........which is why the characterestic of old historic timber frame buildings is that they are wonky.

Mike