Green Oak conservatory

[Nimster]

Hi
We have planning permission to build a conservatory-type room at the back of our grade II listed house, to link the Victorian and Georgian parts in a more usable manner than the existing passage/corridor. We've agreed with Planning that we will build in glass/timber to make the structure as "see-through" as possible, so that the true grade II listed bit (the Georgian cottages) can be clearly seen through the new section.

I've contacted a couple of companies, and have had an eye-watering quote of £48k plus VAT to build in kiln-dried oak. I'm waiting for a quote for the same build in green oak, but wondered if anyone could offer advice on the sanity of this? I'm aware green oak moves/shrinks, but is it going to warp to the point that the glazed roof panels fall out :shock: ?

If anyone has any experience of green oak builds, I would be very grateful for your opinions/advice. If anyone can recommend any good companies around Sheffield, that would be equally useful
Thanks
Nim

 

[middi]

The simple answer to green oak conservatory is a very big NO.

Extremely well seasoned/ air dried or kiln dried ( English or European ) oak is the correct way to build a conservatory.
Do not use kiln dried American oak.

Also, you may not find anyone in Sheffield to build your conservatory, but for that price there may be supply and fit companies that will install it over a prepared base from any part of the Country.
Middi

 

[Nimster]

Thanks Middi. Can you elaborate at all on why it's a big no? There seem to be loads of companies doing green oak builds - surely if they were such a problem they wouldn't be working (or is it just that insufficient time has passed for the problems to manifest.....).

The quote is from a Sheffield joinery company who seem extremely helpful and are keen to direct me to their clients for references. While I would love to sign on the dotted line with them, £48k is a lot more than we budgeted for that part of the build, so if there's a more cost effective way of doing it, we need to find it. What are you thoughts on other hardwood substitutes? We have had a quote for ?Utily that comes in at £40k plus VAT, and another company mentioned Idigbo ("the poor man's oak"), the latter apparently can be treated like oak (ie no maintenance required) and will silver down in a similar manner.

I'm starting to think this may be more trouble than it's worth. Maybe we'll just stick with our foundation-less, insulation-free, "I may fall down if you bang the back door too hard" plastic-roofed passageway

 

[Zebra]

I imagine it would be the labour and the glazing panels which would make up the bulk of the cost of building. Oak is expensive, but I imagine that unless your conservatory is huge (you describe it as more of a passage than a room), then the difference in cost of the raw materials between green and kiln-dried would be less significant, relatively speaking. So in view of the fact that green oak does move, I think that economising on the timber would be rather a false economy.
Once I was involved in the building of a green oak building, which was constructed off-site by a carpenter experienced in traditional timber framing. Then it was taken apart, and rebuilt piece by piece on site by a less experienced carpenter. Windows, roofing, electrics etc all came later, and lord knows how much it all cost.
I also know someone who built exactly what you are talking about - a green oak and glass link between two very old listed buildings. He had the frame built by one company, and it was glazed by another, over a period of quite some time.
So perhaps there are ways of economising on the labour, or in other ways, rather than on the timber.

 

[middi]

Green oak, albeit a very strong building wood, is very unstable and will distort, shrink ,warp and shake ( crack) at an alarming rate from the time a tree is felled to the time it can be used for " joinery " work .
The rate at which all these problems happen is dependent on rate of exposure to heat, humidity, ventilation until all 85% ( or so) of the water content has evaporated from the wood, Oak is a very dense wood and when green approx.half of its weight is water. It is due to it's density why oak takes a long times to dry for joinery purposes. For example, when the doors a Westminster abbey had to be replaced many years ago the oak trunks were selected for straight grain ( ie- knot free ) and kept ventilated in shade for eight years before is was used to make the new doors.

Joinery oak needs to be selected for straight grain and moisture content tested before it can be used for joinery ( ie-- staircases, furniture or, as in your case, conservatory, which, ( let us face it ) all a GOOD conservatory is --an oversize glass cabinet-- where there is not much room for shrinkages, distortions, shakes etc..
Because of " kiln drying" the speed of " seasoning" is speeded up and it is very useful for Indoor oak furnishings and finishes where the oak is dried to about 7 to 10 % humidity and unlikely to get wet. This is why American oak is used in such situation . Unfortunately, American oak is very straight grained and when exposed to ( semi)-outside conditions it will have the opposite effect of correctly dried English ( or European oak), it will expand and create even bigger problems than shrinking oak.
The best Oak for Conservatories, windows or other external joinery work where glass has to be used, would be correctly selected English or European oak with a moisture content of about 15%, The grain of this oak is more " interlocking" than American.

Perhaps now you understand why it is very expensive for you to build an English oak conservatory, especially if you may insist on some sort of warranty ( as you should !!!!!).
The better option wood for a conservatory ( if your conscience is clear) is Indigbo, Sapele, Iroko and obviously teak ( if you are lucky), Also western red cedar ( an excellernt but weaker wood) . All these woods are excellent rot resistant woods, all they need is a coat of oil and all of these are more stable than oak. The choise is yours

Middi

 

[middi]

Green oak, albeit a very strong building wood, is very unstable and will distort, shrink ,warp and shake ( crack) at an alarming rate from the time a tree is felled to the time it can be used for " joinery " work .
The rate at which all these problems happen is dependent on rate of exposure to heat, humidity, ventilation until all 85% ( or so) of the water content has evaporated from the wood, Oak is a very dense wood and when green approx.half of its weight is water. It is due to it's density why oak takes a long times to dry for joinery purposes. For example, when the doors a Westminster abbey had to be replaced many years ago the oak trunks were selected for straight grain ( ie- knot free ) and kept ventilated in shade for eight years before is was used to make the new doors.

Joinery oak needs to be selected for straight grain and moisture content tested before it can be used for joinery ( ie-- staircases, furniture or, as in your case, conservatory, which, ( let us face it ) all a GOOD conservatory is --an oversize glass cabinet-- where there is not much room for shrinkages, distortions, shakes etc..
Because of " kiln drying" the speed of " seasoning" is speeded up and it is very useful for Indoor oak furnishings and finishes where the oak is dried to about 7 to 10 % humidity and unlikely to get wet. This is why American oak is used in such situation . Unfortunately, American oak is very straight grained and when exposed to ( semi)-outside conditions it will have the opposite effect of correctly dried English ( or European oak), it will expand and create even bigger problems than shrinking oak.
The best Oak for Conservatories, windows or other external joinery work where glass has to be used, would be correctly selected English or European oak with a moisture content of about 15%, The grain of this oak is more " interlocking" than American.

Perhaps now you understand why it is very expensive for you to build an English oak conservatory, especially if you may insist on some sort of warranty ( as you should !!!!!).
The better option wood for a conservatory ( if your conscience is clear) is Indigbo, Sapele, Iroko and obviously teak ( if you are lucky), Also western red cedar ( an excellernt but weaker wood) . All these woods are excellent rot resistant woods, all they need is a coat of oil and all of these are more stable than oak. The choise is yours

Middi

 

[middi]

Sorry, I must have developed a st .st. st.tutter

Middi

 

[dans]

Great explanation Middi, very informative.

I am also looking to build an oak conservatory (or orangery) and have experienced a very wide range of price differences! I am yet to make a decision on wether I opt for a local joinery or a national kit supplier, but will post here when I decide.

I used Border Oak for my garage and porch kits, which I highly recommend. Of course, these were both green oak builds, which I agree with Middi that I wouldn't use with Glass. Especially seeing how much my green oak repairs have shrunk and twisted in my house!!

 

[Nimster]

Thanks Middi, that's really clear and helpful advice. I've just spoken to a guy from a company based near York who told me pretty much the same thing about using kiln-dried oak in external sections. He talked about building in air-dried oak (sides and internal sections) with the roof in kiln-dried, and that it would need to be treated regularly using an oil/wax (which I'm fine with, I just don't want to have to paint it every year). He reckons his quote will be in the £20k's, which is much more what we expected. I'm expecting a quote from another local company for Idigbo, so I'll see how it compares.
I have now scrapped the idea of a green oak build, despite the pretty photos on the internet

Zebra - just to clarify - our house is in two parts (victorian front/ georgian cottages to the rear). They are linked by a corridor/passage about 1.5m wide. This is being replaced with the glass box/room/conservatory which will provide us with a proper link and make the property feel like one house, rather than two. Having to negotiate the chicane of the corridor makes it feel like a separate unit entirely! The glass room will be (overall) 6m x 4m, so not a small structure.
While it would be good to try and reduce the costs by having the frame and glazing done separately, we (2 adults, 2 kids under 6) will be squeezed into half the house for the duration of the build, so I want it over with as quickly as possible. Unless I buy a caravan and go all Grand Designs on the family....... :twisted:

Thanks again
Nim

 

[MatthewC]

We have planning permission to build a conservatory-type room at the back of our grade II listed house ... I've contacted a couple of companies, and have had an eye-watering quote of £48k plus VAT to build in kiln-dried oak

Seeing that price I'm almost glad that we were refused permission to do a similar sort of conservatory on our grade II listed house!

 

[88v8]

Iroko.
£12,000 twenty years ago.
Plus 600 hours of my own work.

Ivor

 

[Keithj]

Curious! We had our Grade II Tudor house repaired (lots of oak needed) and a "Garden Room" added (think "conservatory with a tiled roof") in 2011.

The CO and the builders both insisted on green oak - I don't know why. The oak has shrunk, twisted and split as predicted, and I've had to fill gaps each summer to stop the water blowing through them on windy wet winter days. It's settling down a bit now (coming up for 3 years later). It would have been so much easier with dried oak, but ours was not to reason why...

 

[LadyArowana]

Curious! We had our Grade II Tudor house repaired (lots of oak needed) and a "Garden Room" added (think "conservatory with a tiled roof") in 2011.

The CO and the builders both insisted on green oak - I don't know why. The oak has shrunk, twisted and split as predicted, and I've had to fill gaps each summer to stop the water blowing through them on windy wet winter days. It's settling down a bit now (coming up for 3 years later). It would have been so much easier with dried oak, but ours was not to reason why...

Maybe the builder thought it would be a nice little earner to keep being called back to fix the gaps. Not sure what motivation the CO might have had, granted it would probably look a bit more in keeping with the original parts of the house if it all went a bit wonky looking, but that seems contrary to the idea of new parts being clearly identifiable as new parts.

 

[Nimster]

Very nice Ivor - if only we had the know-how and 600 hours free!

Ours will have a fully glazed roof, so green oak is definitely out of the question - I don't want the panels falling out and potentially killing someone when the oak twists and loosens the glazed panels :shock:

The quote for air-dried oak (sides and internal) and kiln-dried roof has come in around £28k + vat, though another company has said we don't want oak given the location (where the timber/glass will join onto the cottages it's very sheltered, north facing cottage wall, with no direct sun and a tendency to moss) and is pricing for idigbo.

Stress, stress........... what to doooooo?! Middi - any advice?

 

[dandrew]

Nimster,

if you are near Sheffield and you haven't done so already, contact Hector & Cedric who are timber framers who operate out of Ecclesall Woods sawmill (you'll find them with Google). Having seen some of their work it looks top class, but of course that may come with a top class price to match.

Good luck,

David

 

[Nimster]

Thanks David - their work looks good, I'll give them a call as well.

 

[middi]

Very nice Ivor - if only we had the know-how and 600 hours free!

Ours will have a fully glazed roof, so green oak is definitely out of the question - I don't want the panels falling out and potentially killing someone when the oak twists and loosens the glazed panels :shock:

The quote for air-dried oak (sides and internal) and kiln-dried roof has come in around £28k + vat, though another company has said we don't want oak given the location (where the timber/glass will join onto the cottages it's very sheltered, north facing cottage wall, with no direct sun and a tendency to moss) and is pricing for idigbo.

Stress, stress........... what to doooooo?! Middi - any advice?

maybe a couple of points need further clarification here before you decide.
As far as building with green oak, this only applies to repairs of and new oak frame builds, (although the green oak is, or should be, at least 2 years old). The reason for using "green" oak is that:A, it is cheaper, B, as green oak twists and bends will automatically lock itself into the newly constructed mortices and tenons therefore no need to be extremely accurate when cutting etc..C, the gaps and shrinkage that occurs with green oak can easily be Refilled and redecorated as necessary. Now, this kind of oak construction is a NO NO with glass panels inserts.
Also, whilst oak is an extremely pleasing to look at wood, especially when newly oiled, waxed etc, because of it,s tannic acid content will tend to "reject" all sorts of coatings applied to it,s surface be it new, seasoned or kiln dried oak. The tendency of oak is to always to assume it,s natural silvery grey coating .
Regular oiling etc. Will only delay the inevitable greying.
Let us face it oak is a lovely material to build with and so traditional material for traditional buildings and with great selection intuition, little worry about cost and less worry about silvery grey traditional oak look or leaks from distorted glazing sections , oak would make for a very strong conservatory . For practicality reasons the Victorians (the age of the mass production conservatory) hated using the stuff due to it,s unstable characteristics. They prefered scots pine, redwood, douglas fir, for cheapness and stability but cedar for longevity and teak for best of all.
Nowdays teak has been superseded by equivalents (or nearly as good) as other tropical hardwoods which are usually much cheaper than oak and a more stable wood.
the choise is still yours

Middi

 

[dans]

Having looked into this in more detail, whilst I agree that Green Oak is not good for glazing, it seems that a number of the reputable firms choose green oak for the structure, but then the large glazing is housed in kiln dried casements. This seems sensible and the company who is quoting me using this method, I would entirely trust.

 

[Penners]

As you'll have recognised, Nimster, Middi knows what he's talking about.

I would never risk building a conservatory in green oak, for all the reasons that he has given. The trouble is that you have no way of knowing how the oak is going to behave. You might just be lucky and have it behave itself acceptably, but you equally might find that it will shrink and move in such a way as allow panes of glass to fall out or crack.

It's just too risky.

 

[88v8]

When our conservatory was made in 91, I wanted oak, but could find no one prepared to use it in conjunction with dg. The Iroko we ended up using is a form of teak, and over 20 years proved totally stable and free from splits and shakes.
Like oak, it rejects coatings.
It's also a threatened species and nowadays is or should be a non-no from that pov.

Another point to consider with oak is that all fixings must be brass or stainless, as oak rusts all ironwork that is put into it. This includes any pins used to fix glazing beads. You have to watch the contractors like a hawk to ensure they really are using brass, and not brass-plated, otherwise when the glazing units need replacing, as they will, it won't be possible to get the beads off without destroying them. In fact, I would get them to run you an extra 40ft or so of beading and keep it for future need, as matching non-standard mouldings can be expensive.

To an extent I got my oak, I put down an antique oak floor... a mistake as leakage and spillage from various plant watering rather spoilt it despite the two-pack coating. If I were doing the job again, and it was really to be a conservatory - ie a place in which to keep plants - I would have a solid floor.

Ivor