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The Nightmare Begins

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Oh no not another one! I hear you cry, but I’m afraid it is.

I started planning my new bigger and better greenhouse project a couple of years ago now and like all best laid plans of mice and men, my intentions never quite seemed to come together, first I had not enough money, then that changed for the better, but I had no time and then all of a sudden I found myself with neither!

Over the winter, more time and a bit of dosh was coming back to me so I started to make noises as to my intentions again.

My original plan was to have an aluminium portal frame made from 4x2 box section with a clear span of 6m x 6m long all clad in 25mm multiwall polycarb, giving me 400sq feet which is almost twice what I have now, this would allow me to keep about the same space for my lowlanders, whilst doubling the highland section, space badly needed as many plants are maturing and just need more room.

Going all polycarb would also bring down the lowland running costs considerably, and I reckoned that the fuel saving would pay for the build in a few years……my bills have been horrific !! Last year keeping over 20c whilst it was -14c outside nearly got me a divorce!

This however, was, I argued, a very “good reason” for wanting to build a new BIGGER greenhouse as the fuel savings would be impressive.

Well the wife was finally coming round to the idea and then she saw the plans and said @#]]% that!

I should explain that we live in a barn conversion, set in a fairly traditional looking setting, and a hi-tech grow house would look out of place to a certain extent.

My argument was that it would be prettier than the current one and I could maybe screen it a bit better from the barn. Also, it would be very quick and easy to erect with some precision timing and cause least disruption to the plants……………...

So I lost that argument as is the norm and the idea was,or rather the plans, were shelved.

A new tack was required.

Now my wife loves to see good things happen, especially when they are ”her idea", and coupled with her complete inability to resist a bargain, I pointed out a few alternatives on ebay, and when we missed one item that I cried “ would have been perfect and so, so cheap too, and we will never see another like that” (all true) she was hooked on the idea, and it was now just a matter of finding something appropriate……….and pleasing to her eye.

Low and behold 2 weeks later, a massive Victorian style greenhouse (450sq ft)came up with no reserve.

“Wow this thing would cost a fortune new” I suggested, and it was not very old “but we will never get it within budget, what a shame! it will likely make a few grand” “similar things of a quarter the size cost loads” I sobbed. “but how beautiful it would look and there could even be space for you to grow a few chillis?” I said choking back the tears!

I suggested my guide budget, bearing in mind the extra work involved in building and converting this thing to my requirements, and was told I had no chance, “be realistic” she said and added 50% to my price…….. Game On!

Well amazingly it came down at under my estimate, so a real bargain could be attributed to the boss!! No going back now……………. Get in!!

Now the nightmare truly begins!

How to build a dwarf walled greenhouse with twice the footprint in a position 3ft offset from the existing (therefor dissecting the existing footprint) in super quick time?

Not possible! So I now have to plan the timing perfectly so that the plants can be temporarily housed in a polythene tent, erected inside the garage, for as short a time as possible, as they will surely suffer with reduced light levels, etc.

I also have to move the shed, dismantle and sell the old Hartley Botanic greenhouse (by auction to get rid quickly) demolish the old dwarf wall and rebuild the new in double quick time!!

I hope I can get the plants out and back within 2 weeks, but I suspect it will take longer.

Anyway, here are a couple of pics to get things going.

Here is the existing GH



And a couple of shots of the plants that need to be moved.





(sorry for quality of last 2 pics)

I will update as and when things get properly moving!

One saving grace is that the base, in form of a concrete slab, already exists.

Edited by Dicon
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Hi Dicon,

Really exciting project - best of luck.

I'd be very interested to know whether you change any of your equipment for the bigger space, in case I ever get the chance (and courage) to upgrade.

Please keep us posted!


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Well done on securing the greenhouse you wanted! When it comes to discussions of expenses with the girlfriend, I just point at her collection of dress making fabric (£240 FOR ONE METRE!!!!!!) and my arguments are won.

Really looking forward to seeing pics of the new greenhouse...?

Good luck with it!

I'm trying to save thousands of pounds on a Victorian-style greenhouse by building it myself from bits of wood, which is good for costs, but extraordinarily time-consuming... although I put my greenhouse construction thread in the Neps section of the forum. I thought mine was a good size, but it's going to look like a terrarium compared to yours.

The insulation is the big issue in my mind at the moment... I'm convinced polycarbonate is the way forward..... but I haven't got any facts yet.... experimentation is needed.

Presumably you're going to adapt the old structure to polycarbonate?

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Hi Gareth,

I just logged on to ask you (in your thread) if you had yet chosen your polycarb (and found you here!)

I have been following your thread too and think you are doing really well.

As I mentioned above, I had originally intended to clad with polycarb, and I still intend to do so. There are many thicknesses to choose from, as I am sure you know, however, it is a matter of choosing a happy medium between insulation and Light Transmittance.

I personally feel that 25mm is about the best compromise, LT is about 73%, but if you go to 32 or 35mm LT drops to 50% or worse.

50% is fine for summer (I use 50% shade cloth under glass) but in the winter months the low light levels are what stop the plants pitchering (or even growing)

The difference in U value from 25mm to 32 or 35mm is not very significant compared with higher price and the large loss of light transmittance.

What do you think?

I intend to insulate the floor in the lowland section with a screed over. This will provide good thermal resistance and also provide thermal mass.

I have not yet decided on the inner skin of the dwarf wall yet, either cheaper dense conc with more money spent in the cavity (high thermal mass) or to go for the aerated blocks (with the lower u values)

Are they Durox blocks you have chosen?

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With two of us building dedicated Nep greenhouses, I hope that all these discussions and experimentation will inspire others to do the same.

Neither of us have any real idea what we need, so I hope that when we both have our structure up and full of plants we can pass on some hard-won experience to others. It seems to me that there's not many people who build greenhouses for their hobby of tropical plants, so the information just isn't out there.

Here's my thoughts at the moment...

I'm not so fussed on insulation the floor. Heat goes into the ground or into a concrete floor... whatever, it's largely stored and not lost... it's not like the walls and roof where it's lost into the atmosphere. (In many houses, like my 1930s semi, the floors are floorboards over a ventiliated air gap, so no wonder these old houses are cold and draughty... the floorboards are all that's separating room temperature from the outside temperature. Modern houses with solid floors are much warmer.)

Light transmission... I'm not sure on this... I'll offer my opinion now and come back to you in a couple of years with some experimental evidence!

At the moment, all my Neps grow in a greenhouse that's shaded by trees. They get a couple of hours of sun first thing in the morning, then more sun from 4pm until sunset. It's really very shady indeed, and they grow well- and pitcher well. In addition, I get great pitcher colours... initially, I was worried that shady conditions would give poor pitcher colour, but it seems the reverse is true.

Some others have found the same:

Low light levels thread

I think we get poor growth and few pitchers in winter not because of the poor quality of light, but because of the short day length. If this is true, then the best way for us to go is with maximum thickness of polycarbonate, giving maximum insulation, even though that would reduce light transmission 50%. There's not a lot we can do about daylength without adding lights- and I don't want to go down that route.

I was going to use 35mm polycarb, but instead, for a little more money, I'm going for TWO thicknesses of 16mm. The whole structure is going to be double-glazed with triple glazing, with a 32mm air gap between the two layers. This turned out to be an easy option because of the way the greenhouse is made.

Light transmission should be comparable to 35mm polycarb.

Dwarf wall... I have no idea which would be best, dense concrete for thermal mass (useful to store heat in case of heating failure)? Or the Durox blocks that I've used. One thing I have found is that the Durox aerated blocks are a pleasure to work with- it makes building the thing a quick and easy project. The ability of cut the blocks with a saw makes all the difference (also being incredibly light, it makes building a breeze.) Also each block is 2 feet long which means you can crack through the wall-building stage.

I'm going to pop over to my greenhouse blog on the Nep pages now to do an update on my week's progress.

Edited by Gareth Davies
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Quote, Modern houses with solid floors are much warmer.

But this is because building regs insist upon min 50mm (may be more now?) insulation under the slab and cold bridging insulation at perimeters.

Heat transfer occurrs from a warm object into a colder contact, so if your air temp in the greenhouse is 30c, the floor is say 20c, and the ground temp is 10, then the 20 will transfer away into the 10 and not add back into the 30, this in turn pulls heat out of the 30.(radiators are hotter than the air temp)

Thermal mass creates a heat sink that will emit some wattage but it is only a background retention and certainly cannot be relied upon to provide emergency heat in the event of heater failure, not at these levels, the thermal store would have to be huge and built up to a higher temperature than the growspace ambient.

Victorian garden walls helped to keep glasshouses frost free, but anything higher required fire powered chimney walls.

Personally I would recommend a gas heater with mechanical stat, and use electric fans as backup. or vice versa, but gas is cheaper

LPG provides 100% efficiency and you just get CO2 and H2O both required by the plants. they rarely fail and are not beholdant to the utility supplier.

Unless you run a generator to back you up, you can have ten backup heaters all turned off by someone else.

Gas is cheaper too, get one that can at least keep your chosen minimum temp when it is minus 14 outside. Gareth please take this one piece of advice, you will thank me one day.


PS Gareths blog

Edited by Dicon
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Yes, I have an old thermostatically controlled gas heater that's going to be brought out of retirement for the "belt and braces" approach.

I have no idea about magnitudes of heat transfer and what's important and what isn't, I can't offer any sensible comment.

But heat transfer through the floor- the heat goes down... how good is soil at heat transfer, and how deeply does the heat go? How far does it vanish?

In a greenhouse at 30 degrees, once the floor is at 20, it'll keep heating up until it's at 30 with a gradient of temperature down through the soil... but how much is actually lost to lower depths? What's soil like as an insulator compared to polystyrene?

One point about the inevitable heating failure is that all we need to do is keep our Neps from freezing and they'll recover from disasters. For complicated reasons, I've dumped raffs and bicals in the post in winter where they've been kept in the dark and cold for a couple of weeks, and they've recovered just fine. I have a feeling- but no real evidence- that a tonne of water at 25 degrees would keep a greenhouse frost free for a few hours in the case of a heating failure on a cold night.

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A tonne of water at 25C does store a decent amount of heat. About 4-5 times more than a tonne of stone. The only problem is moving the heat from the water to the air (and back) a tonne of water takes a long long time to either heat up or cool down if its just sat in a tank for example, you need to pump it around a radiator or two.

Soil, particularly wet soil is quite a reasonable heat conductor, so you will lose heat through the floor, not a huge amount comared to glass windows but its still something.

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Oh boy, what have I let myself in for?!

Well I went to collect the new structure at the weekend……….oooh what a polava!

I had to hire a Luton to get the thing in as there were sections that were 14 foot by 4 and piles of components to pick up,

When I arrived, it soon became apparent that the information supplied to me was not exactly accurate, whilst there was nothing wrong with what I had bought, I was lead to believe that it had been mostly de-glazed ……….er.. nope!

It was one of those Chief Brody moments!!

80 quid in fuel and 95 for the Luton, and there was no way on earth I could get this lot on board without breaking the backs of the large sections. (unglazed they would have been ok balanced on top)

As luck would have it, there were a couple of local farm hands helping out with the loading, nice lads, and one of them suggested using their 20ft trailer to take the larger sections.

A deal was struck to deliver in convoy and we loaded everything up and set off for home.

Time was really pressing now, and there was no way I was going to get the Luton back off hire by 5pm, I rang the guy and asked if he could help me with a bit more time, and he gave me half an hour.

Well after a 110mile mad dash and a very rapid offload I got the van back by 5:15 phew!

I surveyed the mass of parts, strewn about my garden, piled up in the carport and leant against the wall where I usually park the car.

The enormity of this build has now fully hit me.............help!!

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......this is going to be a great side show to follow . Gareth yours has taken shape nicely, great job, as youve already commented I also feel like Im growing my plants in a terrarium (no offence to terrrarium growers) now Ive seen the scale of Matts plans. However if you want to grow neps properly and produce large plants you do need space and lots of it, eventually terrariums or other confined indoor growing areas are not going to be fit for purpose for some nep species.

Matt I agree entirely about gas heating for neps in winter 100% beneficial waste products.

A conclusion of I've come to is that I need to start saving if I ever want to expand my growing space theres no way I could undertake a job like this.

Edited by Simon Lumb
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But heat transfer through the floor- the heat goes down... how good is soil at heat transfer, and how deeply does the heat go? How far does it vanish?

Soil is full of water and is a reasonably good conductor. Put your hand in damp soil and your hand will chill quite quickly

The heat will go from warm to cooler however far that is until it is balanced whether thats down across or up. ie until temp in your greenhouse is the same as the outside (soil and air). There is nothing you can do to stop this just reduce the heat transfer with an insulator.

In a greenhouse at 30 degrees, once the floor is at 20, it'll keep heating up until it's at 30 with a gradient of temperature down through the soil... but how much is actually lost to lower depths?

Yes the soil will keep heating up until its 30 but that will never happen as the upper part of the earths crust in our temperate zone is far larger than your floor and will always be cooler and therefore a constant heat sink regardless how much heat is pumped into the greenhouse. If you have a unheated greenhouse this can work both ways as in the winter when the air in your green house is less that the soil temp it will loose heat to your green house. This wont be the case with you as you are keeping your greenhouse always above the soil temp so you need to reduce heat loss to the soil all year round.

What's soil like as an insulator compared to polystyrene?

C**p, A simple school boy experiment can show this easily. Just hold some soil in one hand and polystyrene in the other. The soil will feel cool (its actually warming up) as it is taking the heat out of your hand, but the polystyrene feels warm as less heat is lost from your hand. Why does it feel warm then if heat is being lost to the polystyrene I here you ask. Its because your blood is bringing heat to your hand and your living cells in your hand's muscles (mostly) are also making heat. These two sources of heat are greater than the loss so your hand starts to get warmer.

Edited by mantrid
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Hi All

Well what a dingy week!

Everything has had to be wrapped up to protect it from this continuous rain.

Well I am finally getting to the bottom of what is here.

The problem is that I have bought a huge jigsaw puzzle with no picture or instructions!

I know roughly what it should look like, and I know roughly how big it is, some of the parts are even numbered………….though that is not helping much without a guide.

It has been a process of elimination to decide exactly how it all goes together and I am finally getting on top of it, I now have precise dimensions for the dwarf wall.

The steel straining rods that brace the roof are mostly worked out, and rather than spend too much time and effort refurbishing them, I may just replace with stainless steel cables………we will see later.

Here are a few pictures rather hurriedly taken between downpours today.

Shed moved about as out of the way as possible, parts strewn about all over the place, the two piles of timber wrapped up and supported on ladders contain 12ft roof spars x 36, end spars, 2 part ridge and a few other bits.


4 x half gable triangle sections 6ft x 6ft and 2 huge single doors


wrapped up, 2 door frames with glazed lights above, total height 14ft to ridge


Wrapped up long side sections


these are four quarters of the long sides, one 7ft wide opening light has been removed, there is a similar opener in each quarter. Constructed length 28ft per side


Taking up most of the car port (MGB now under a cover for the duration)

4x opening rooflights on left, the frames by the brown bin are coldframe lids, there are 6 of those!

The 3 (of 4) glazed sections by the toolbox are the gable end sections for either side of the door frames 6ft x 4ft that support the triangle sections. Total constructed width of gable ends 16ft.


Aluminium roof glazing cappings.


Steel straining rods to support spread of roof and the cast aluminium ogee gutters.


OK much of this looks a bit of a mess, but it is only a matter of rubbing down an repainting the outside, the inside needs a quick rub and treatment with a clear water repellant.

The timber is Red Cedar (I had hoped it would be) and is actually in very good order with no rot, I have only found about 4 knots in the whole thing! I could never in a million years have afforded a new cedar greenhouse of this magnitude, so the effort involved in bringing it together will be well worth it.

The plan is to glaze the roof in 25mm polycarbonate and then use the same internally to double glaze the vertical sections. I will probably make up removable internal panels so I can maximise light levels and to aid cleaning..............well that's the plan for the moment!

If only the weather would improve, I could then make some actual progress.

More later

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My god, that's a project.

I'm just in awe of the whole thing... my little project is distinctly unambitious by comparison.

A proper cedar greenhouse bought new would be tens of thousands of pounds! Talk about a bargain.

One thought, at 14 feet tall, it's 2 feet taller than planning restrictions would allow? While our uk legal system doesn't seem too fussed about getting to grips with burglars, thugs, thieves and muggers, they law comes down hard on people who inadvertently deviate slightly from planning regulations.

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Yes that was my only concern, however it is a temporary structure so may be ok?

I might just see if I can reduce the wall height by enough to squeeze it under, depends a bit on the strainers but may be possible. (It is 9 in over the 4m limit)

Edited by Dicon
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I thought my greenhouse was a monster at just under 3m... 4m would be amazing.

It's hard to know what to do with the planning rules... that 4m limit tends to get strictly enforced. At least it does round here.

The law just seems insane. You can turn up at someone's door and threaten to kill them, in which case the police will ask you nicely not to do it again; you can break into someone's house, smash it up, steal a car using the keys you steal and go joy riding, in which case you might get fined £100 and told not to be so naughty in the future; if you're a tenant, you can refuse to pay any rent, smash the house up and steal all the furniture- in which case the law can't touch you and you'll also be put straight to the top of the council housing list and be given a £500 bonus...... but god forbid you fall foul of planning laws.

Near me, a guy spent over a million building his dream home. For whatever reason, it ended up two feet too big. Leeds city council spent years using huge amounts of taxpayers' money fighting him through the courts- and ultimately forced him to demolish the whole thing. Not just the two feet extra, the entire thing.

You couldn't see it from the road or any footpath, no-one complained about it, it wasn't harming anyone, but the city council had its priorities.

I guess the worst that could happen to your greenhouse is that they could land you with a huge fine, ask you to take it down and rebuild it nine inches lower?!

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I guess the worst that could happen to your greenhouse is that they could land you with a huge fine, ask you to take it down and rebuild it nine inches lower?!

If you dig down far enough it would be frost free, like some of the victorian glasshouses.

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Matt Im in the process of having a log cabin/summer house built its 4m x 4m and 2.5m high and the planning laws are something to think about as are the boundry laws as my neighbour 'kindly' pointed out. My project is not for plants but maybe one day something will find a way its way in there even it its only a few incubators with lights for seedlings, but I darent even mention this to the reichfuhrer or I'm a dead man.


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  • 3 months later...

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

All work and no play makes jack a dull boy

Ok time for an update,

What a shocking couple of months of weather we have had!

I have spent week after week sanding down, and preparing the timber sections, treating and priming ready for erection.

Smaller sections were worked on under the lean-to and in the garage.

Larger sections have had to wait for dry days, which have been very scarce!

So too jobs like treating the prepared timbers and laying them out to dry, I just don’t have enough space under cover and every day has been wet or promising rain, a real headache!

Every job seems so endless, it is very hard to keep the enthusiasm going, for example, each roof spar whilst only 12ft long, has 6 flat faces to be sanded (as they are tapered in section) each has 2 rebates with a rubber seal to remove, clean (scrape, sand, scrape again) and replace. x by 38 and that amounts to 2600ft of timber to pass my little orbital sander alone! Plus nearly 900ft of EDPM seal to replace.

This job really feels like the “Forth Bridge”, ‘though without the bonus of being able to throw myself from it when totally fed up!!

I have tried to get fairly advanced with the refurb before decanting the plants to their temporary home and taking down the old greenhouse.

Temporary enclosure ready to take the highlanders and a few lowlanders


Plants moved in


Orchids in the conservatory.


Old electrics and water filtration system


Old GH takedown


Demolished and skipped the old blockwork base during a massive thunderstorm, the only job that wasn’t hindered by the rain! The wife even had a go with the sledgehammer (likes destroying things) but when it comes to the laborious stuff like sanding and painting, ”you’re on your own mate”

Called in the brickie to do a 5 day job, and then it pissed down for 7 out of the next 11 days!, the yard flooded and the rain just kept coming. Fortunately the house has never been in danger, but it is still worrying and so I put the pump into the soakaway sump and pumped away 7000L/hr for 2 whole days…………what a crap summer!

I bought almost enough bricks from a neighbour, they are a tumbled and sand-faced brick and look like old reclaimed bricks but are hard and to class B spec, I made up the shortfall with class B’s for the first course and quoined corners. I have used a 100mm thermal block for the inner leaf with a 50mm insulated cavity.

I also built in a cool passage within the cavity that will draw fresh air in through air bricks, along the cool, damp passage and into the Highland section, this should aid summer cooling by 1 or 2 deg C. I have also set a raised insulated slab under the Lowland section and a duct to feed the gas heater.

Finally the brickwork was done

Progress has been much slower than I had anticipated, mostly due to the weather, however, the poor weather has also provided a milder climate for the plants whilst in their temporary homes, so I am not so unhappy, I guess the storm clouds have had a silver lining.

Finally I decided to replace the rusty old steel brackets (invent some missing ones) and strainers with stainless steel plate and wire cables with turnbuckle strainers. Making up the cables is fairly simple but hard on the hands.

The whole job has needed a lot of planning and investigation to ensure all components are there to complete the build, it has been like a giant 4D jigsaw with no picture.

Few shots of progress







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