Hi,

Looking for advice on a greenhouse I am looking to build in the sunniest (relative) spot in my London garden.

My garden is West facing, the patch is South facing and gets sun from 12:30 to 18:00 (5.5 hours). Last summer I grew cherry tomatoes and courgettes with fair success in this patch (birds got most of the cherry toms tbh). I got a bunch or large tomatoes which didn't ripen in time before the plants died at the end of the season (I didn't realise you could ripen them indoors).

I want to build a greenhouse on this spot to increase my success rate with tomatoes and other sun-lovers like peppers, cucumbers, squash and pumpkin.

Originally I was going to buy a 4 x 6 foot aluminium greenhouse as the space is awkwardly shaped and this is all I could find that would fit, but then I thought if I design and build my own I could make better use of the space and have a bigger greenhouse for the same money.

It's going to consist of a brick foundation (neighbours old driveway), wooden frame (scrap liberated from skips), kitchen flooring for floor (have this lying around) and a polycarbonate surface which I will need to source. The whole structure will be covered in polycarbonate as I don't want any wood exposed to the elements. See CAD drawing attached (dimensions in mm). I've got my brother visiting in Sept and he has some carpentry skills so planning to start work when he's over.

What I couldn't figure out how to get across in the drawing with my limited CAD skills is the panels A and B, I want the poly carbonate sheet at B to be fixed in place, and A to open upwards on hinges, like a grow box, except a 1.6 meter high grow box = ). This should give me good access to all the plants as the space behind B will be quite large for me to be able to duck under.

So questions:

1. What thickness polycarbonate and how many chambers is usual for greenhouses?
2. Does the pitch of the roof look OK? Is this important?
3. Will leaving the door open (A) occasionally be enough for ventilation purposes?
4. Does the design look practical?
5. Is it worth the effort considering limited access to sunlight?

BTW I will growing plants in self watering containers as used by this guy: How Self-Watering Containers Work |

Any thoughts/comments appreciated.

Oh yes, imagine the frame in the CAD drawing covered in polycarbonate sheets.

I am going to cross post this on a DIY forum for the construction nitty gritty but wanted to hear from the gardeners first if this is a good idea or not.

"Howzit_China" wrote

Looking for advice on a greenhouse I am looking to build in the sunniest
(relative) spot in my London garden.

My garden is West facing, the patch is South facing and gets sun from
12:30 to 18:00 (5.5 hours). Last summer I grew cherry tomatoes and
courgettes with fair success in this patch (birds got most of the cherry
toms tbh). I got a bunch or large tomatoes which didn't ripen in time
before the plants died at the end of the season (I didn't realise you
could ripen them indoors).

I want to build a greenhouse on this spot to increase my success rate
with tomatoes and other sun-lovers like peppers, cucumbers, squash and
pumpkin.

Originally I was going to buy a 4 x 6 foot aluminium greenhouse as the
space is awkwardly shaped and this is all I could find that would fit,
but then I thought if I design and build my own I could make better use
of the space and have a bigger greenhouse for the same money.

It's going to consist of a brick foundation (neighbours old driveway),
wooden frame (scrap liberated from skips), kitchen flooring for floor
(have this lying around) and a polycarbonate surface which I will need
to source. The whole structure will be covered in polycarbonate as I
don't want any wood exposed to the elements. See CAD drawing attached
(dimensions in mm). I've got my brother visiting in Sept and he has some
carpentry skills so planning to start work when he's over.

What I couldn't figure out how to get across in the drawing with my
limited CAD skills is the panels A and B, I want the poly carbonate
sheet at B to be fixed in place, and A to open upwards on hinges, like a
grow box, except a 1.6 meter high grow box = ). This should give me good
access to all the plants as the space behind B will be quite large for
me to be able to duck under.

So questions:

1. What thickness polycarbonate and how many chambers is usual for
greenhouses?
2. Does the pitch of the roof look OK? Is this important?
3. Will leaving the door open (A) occasionally be enough for ventilation
purposes?
4. Does the design look practical?
5. Is it worth the effort considering limited access to sunlight?

BTW I will growing plants in self watering containers as used by this
guy: 'How Self-Watering Containers Work |' (http://tinyurl.com/km9fpqb)

Any thoughts/comments appreciated.


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|Filename: GreenHouseDesign2.jpg |
|Download: http://www.gardenbanter.co.uk/attachment.php?attachmentid=15649|
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I built my own greenhouse glazed with twin walled polycarbonate roof and
acrylic glazed sides. What I have found is that some plants seem to elongate
as if fighting for light (eg. tomatoes) whilst others don't seem to have any
problems (eg. cacti & orchids).
The main problem is the dampness and humidity of the greenhouse rotting the
wood as the condensation always drips down towards the ground rotting the
wood from the bottom. Also a problem where any sloping roof meets wood
inside the house.
--
Regards. Bob Hobden.
Posted to this Newsgroup from the W of London, UK

On 22/06/2013 21:06, Howzit_China wrote:
Hi,

Looking for advice on a greenhouse I am looking to build in the sunniest
(relative) spot in my London garden.

My garden is West facing, the patch is South facing and gets sun from
12:30 to 18:00 (5.5 hours). Last summer I grew cherry tomatoes and
courgettes with fair success in this patch (birds got most of the cherry
toms tbh). I got a bunch or large tomatoes which didn't ripen in time
before the plants died at the end of the season (I didn't realise you
could ripen them indoors).

I want to build a greenhouse on this spot to increase my success rate
with tomatoes and other sun-lovers like peppers, cucumbers, squash and
pumpkin.

Originally I was going to buy a 4 x 6 foot aluminium greenhouse as the
space is awkwardly shaped and this is all I could find that would fit,
but then I thought if I design and build my own I could make better use
of the space and have a bigger greenhouse for the same money.

It's going to consist of a brick foundation (neighbours old driveway),
wooden frame (scrap liberated from skips), kitchen flooring for floor
(have this lying around) and a polycarbonate surface which I will need
to source. The whole structure will be covered in polycarbonate as I
don't want any wood exposed to the elements. See CAD drawing attached
(dimensions in mm). I've got my brother visiting in Sept and he has some
carpentry skills so planning to start work when he's over.

What I couldn't figure out how to get across in the drawing with my
limited CAD skills is the panels A and B, I want the poly carbonate
sheet at B to be fixed in place, and A to open upwards on hinges, like a
grow box, except a 1.6 meter high grow box = ). This should give me good
access to all the plants as the space behind B will be quite large for
me to be able to duck under.

So questions:

1. What thickness polycarbonate and how many chambers is usual for
greenhouses?
2. Does the pitch of the roof look OK? Is this important?
3. Will leaving the door open (A) occasionally be enough for ventilation
purposes?
4. Does the design look practical?
5. Is it worth the effort considering limited access to sunlight?

BTW I will growing plants in self watering containers as used by this
guy: 'How Self-Watering Containers Work |' (http://tinyurl.com/km9fpqb)

Any thoughts/comments appreciated.


+-------------------------------------------------------------------+
|Filename: GreenHouseDesign2.jpg |
|Download: http://www.gardenbanter.co.uk/attachment.php?attachmentid=15649|
+-------------------------------------------------------------------+

Firstly I'd make the front a lot taller, Min of 1.25m I'd make the back
2m, and slope the roof in one piece not 2 sections,
I can't see where you intend to have a door,
What are the ground measurements, I have no idea what 3477 0677 is.
What is the back wall? part of the house or what.
David @ a damp and windy part of Swansea Bay

3477 0677 is 3.48 meters. The base is 1m (left) x 3.2m (back) x 1.5

Thanks for the responses

Yes rotting is a big concern. The best I can do is give the wood a couple of layers treatment. I am thinking of coating the base in tar (don't know where I got that idea but sounds like a good one). Not sure what else I can do.

Are you saying where sloping roof meets wood is prone to rotting? I was thinking maybe it would be a good idea to have rubber spacers at intervals so the poly never actually touches the wood.

3477 0677 is 3.48 meters. The base is 1m (left) x 3.2m (back) x 1.5 (right) x 3.48m (front). The space narrows as you move right to left.

I had difficulty getting across my idea for the door but what I had in mind was for poly sheet A to be on hinges and open like a growbox.

The back wall is the garden fence, there will be a small gap between the greenhouse and the fence. The back will be poly too as I don't want any wood exposed to the elements. The fence is 1.5m which is why I made the height 1.6m, didn't want to upset my neighbour but I will speak to her. Maybe a traditional pitched roof would be better.

I will take your comments onboard re the height and roof and do another drawing, I am curious why you would have the rook in one piece?

Can we not edit posts?

Roof....not rook, obviously.

Forgot to ask, would you not use polycarbonate for the sides?

Here's a quick drawing with the back adjusted to 2m.

The reason for the elaborate roof on my original drawing was to get around what is happening in this drawing, which is that the roof angles of the sides are different due to the different side widths so the polycarbonate will need to twist slightly to fit the frame, but maybe this will not be a problem.

Is polycarbonate strong enough that I could use one sheet for the entire roof and one for the front without any supports in the middle?

On 23/06/2013 07:22, Howzit_China wrote:
Thanks for the responses

Bob Hobden;985645 Wrote:

I built my own greenhouse glazed with twin walled polycarbonate roof and

acrylic glazed sides. What I have found is that some plants seem to
elongate
as if fighting for light (eg. tomatoes) whilst others don't seem to have
any
problems (eg. cacti & orchids).
The main problem is the dampness and humidity of the greenhouse rotting
the
wood as the condensation always drips down towards the ground rotting
the
wood from the bottom. Also a problem where any sloping roof meets wood
inside the house.

Yes rotting is a big concern. The best I can do is give the wood a
couple of layers treatment. I am thinking of coating the base in tar
(don't know where I got that idea but sounds like a good one). Not sure
what else I can do.

Are you saying where sloping roof meets wood is prone to rotting? I was
thinking maybe it would be a good idea to have rubber spacers at
intervals so the poly never actually touches the wood.

David Hill;985647 Wrote:

Firstly I'd make the front a lot taller, Min of 1.25m I'd make the back

2m, and slope the roof in one piece not 2 ,
I can't see where youu intend to have a door,
What are the ground measurements, I have no idea what 3477 0677 is.
What is the back wall? part of the house or what.

3477 0677 is 3.48 meters. The base is 1m (left) x 3.2m (back) x 1.5
(right) x 3.48m (front). The space narrows as you move right to left.

I had difficulty getting across my idea for the door but what I had in
mind was for poly sheet A to be on hinges and open like a growbox.

The back wall is the garden fence, there will be a small gap between the
greenhouse and the fence. The back will be poly too as I don't want any
wood exposed to the elements. The fence is 1.5m which is why I made the
height 1.6m, didn't want to upset my neighbour but I will speak to her.
Maybe a traditional pitched roof would be better.

I will take your comments onboard re the height and roof and do another
drawing, I am curious why you would have the rook in one piece?


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A picture of the plot would be a big help.
So you have a wooden fence behind, what's in front?

"Howzit_China" wrote
Bob Hobden;985645 Wrote:

I built my own greenhouse glazed with twin walled polycarbonate roof and

acrylic glazed sides. What I have found is that some plants seem to
elongate
as if fighting for light (eg. tomatoes) whilst others don't seem to have
any
problems (eg. cacti & orchids).
The main problem is the dampness and humidity of the greenhouse rotting
the
wood as the condensation always drips down towards the ground rotting
the
wood from the bottom. Also a problem where any sloping roof meets wood
inside the house.

Yes rotting is a big concern. The best I can do is give the wood a
couple of layers treatment. I am thinking of coating the base in tar
(don't know where I got that idea but sounds like a good one). Not sure
what else I can do.

Are you saying where sloping roof meets wood is prone to rotting? I was
thinking maybe it would be a good idea to have rubber spacers at
intervals so the poly never actually touches the wood.


What happens when it's cold is that condensation slides down the sloping
roof inside onto the wood where it sits and rots the wood. Probably only a
problem if you intend to heat your greenhouse in the winter as I do. I gave
my wood three coats of Sadlin but still in places it rotted after time
requiring a refurb. The glazing at the bottom now sits on plastic embedded
in cement and the legs are held by metal brackets also embedded in the
cement capping. If I made it again I would be even more careful to ensure it
could be taken apart again and mended, wood replaced, as required.
--
Regards. Bob Hobden.
Posted to this Newsgroup from the W of London, UK

On 22/06/2013 21:06, Howzit_China wrote:
Hi,

Looking for advice on a greenhouse I am looking to build in the sunniest
(relative) spot in my London garden.

My garden is West facing, the patch is South facing and gets sun from
12:30 to 18:00 (5.5 hours). Last summer I grew cherry tomatoes and
courgettes with fair success in this patch (birds got most of the cherry
toms tbh). I got a bunch or large tomatoes which didn't ripen in time
before the plants died at the end of the season (I didn't realise you
could ripen them indoors).

I want to build a greenhouse on this spot to increase my success rate
with tomatoes and other sun-lovers like peppers, cucumbers, squash and
pumpkin.

Originally I was going to buy a 4 x 6 foot aluminium greenhouse as the
space is awkwardly shaped and this is all I could find that would fit,
but then I thought if I design and build my own I could make better use
of the space and have a bigger greenhouse for the same money.

It's going to consist of a brick foundation (neighbours old driveway),
wooden frame (scrap liberated from skips), kitchen flooring for floor
(have this lying around) and a polycarbonate surface which I will need
to source. The whole structure will be covered in polycarbonate as I
don't want any wood exposed to the elements. See CAD drawing attached
(dimensions in mm). I've got my brother visiting in Sept and he has some
carpentry skills so planning to start work when he's over.

What I couldn't figure out how to get across in the drawing with my
limited CAD skills is the panels A and B, I want the poly carbonate
sheet at B to be fixed in place, and A to open upwards on hinges, like a
grow box, except a 1.6 meter high grow box = ). This should give me good
access to all the plants as the space behind B will be quite large for
me to be able to duck under.

So questions:

1. What thickness polycarbonate and how many chambers is usual for
greenhouses?

Depends on your budget, but twin-walled is sufficient for a greenhouse.
Probably 6mm would be best.

2. Does the pitch of the roof look OK? Is this important?

Can't tell from the diagram. Why does it need to be pitched anyway?

3. Will leaving the door open (A) occasionally be enough for ventilation
purposes?

No. You will need a vent near the ground on the right-hand side (near
where the "B" is on the diagram). That will give you airflow through the
greenhouse. Without it the RHS will get really hot in full sun.

4. Does the design look practical?

Is there no way you can increase the height? I think you'll find that
1500mm will leave you a bit cramped and hot, especially if it is a very
sunny day

5. Is it worth the effort considering limited access to sunlight?

Only you can really decide that, but as you've grown things successfully
before, it should be ok. But you might find that it's cheaper in the
long run to buy one of those polythene/PVC-covered greenhouses and
replace the sheeting every couple of years. I mean the sort of things
shown he
http://www.robertdyas.co.uk/?attribu...E%20DESCENDING

That might also give you a relatively cheap idea of whether or not it's
worth bothering constructing the polycarbonate-covered greenhouse you
are thinking about.

--

Jeff

On 22/06/13 21:29, Howzit_China wrote:
Oh yes, imagine the frame in the CAD drawing covered in polycarbonate
sheets.

I am going to cross post this on a DIY forum for the construction nitty
gritty but wanted to hear from the gardeners first if this is a good
idea or not.

Be careful to understand the difference between a newsgroup and a forum
- newsgroups have grandfather rights and members can get rather testy if
they are confused with the rather crude arrangements for continuety in
a forum.

--
Rusty Hinge

On 23/06/13 07:22, Howzit_China wrote:

Yes rotting is a big concern. The best I can do is give the wood a
couple of layers treatment. I am thinking of coating the base in tar
(don't know where I got that idea but sounds like a good one). Not sure
what else I can do.

Old sump oil is probably your best option. Kills rot, kills woodworm.
Diseasel oil is if anything, better.

--
Rusty Hinge

3: No, you need more and better controlled ventilation. If you google, you should come across recommended ventilation:floor area ratios. It may be that with such a small greenhouse, the area of the door theoretically adequate for ventilation, but unless you have another vent elsewhere, it will be difficult to get a through-flow of air.

You will also find yourself using the greenhouse in winter (even though you may have no intention at the moment of so doing), so think about whetehr you want to be opening the door in winter - there will still be sunny days raising the temperature inside, or you may need some airflow to stop the inside being both damp and cold and thus encouraging mould.

Think also about whetehr an automatic vent opener would be useful.

4) yes, it's worth the effort. The protection from wind provides a microclimate which will extend your growing season, growing tomatoes in the greenhouse will help protect them from blight, and it's good for the soul to have somewhere to potter with plants when its raining outside ;-)

For what it's worth has all its sides shaded to a greater or lesser extent. Even the roof is partially shaded by nearby trees. But it's still very worthwhile.