Greenhouse FAQs

Whether you are new to Alitex, or a loyal customer, our expert team will answer any queries you have regarding your Alitex greenhouse design. 

We pride ourselves in our engineering and structural expertise, especially when it comes to bespoke solutions and flexibility of design. Whatever the size, shapes and global location, we are confident we can design the most durable and effective greenhouse for you, and the needs of your plants. With available variants for door furniture, spandrel style and of course colour, you can be assured your Alitex greenhouse will be built specifically for you.

Our Alitex greenhouse and conservatories will provide you with a lifetime of pleasure and satisfaction. Making your mind up can sometimes be daunting with so many options to choose from – we hope you will find our guides and FAQs useful in your decision-making process. However, if you would rather talk through your questions, we are more than happy to discuss these with you contact us on 01730 826900.

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Arranging an Alitex visit

Help, I’m not sure what I need!

Don’t worry this is where our years of experience can help. Contact us and we will chat through your growing requirements and advise you on your various options. Often, a no obligation visit is a good starting point. If you would like to arrange a visit contact us on 01730 826900 or email us on

How do I arrange a no obligation visit?

Simply contact the office on 01730 826900 or email us on and arrange a convenient time. Distance is not an issue - our team is constantly travelling around the country. 

Why is a site visit useful?

Past Alitex clients have always found a home visit to be worthwhile as it helps shape thoughts and provides a solid understanding of possibilities (and limitations). To see the house and garden of a customer and to discuss their requirements allows us to give useful advice. If you would like to arrange a visit contact us on 01730 826900 or

Aluminium and paint

What is the greenhouse made of?

Polyester powder coated aluminium. Before being painted, the aluminium sections undergo three pre-treatment stages:

  1. The cut aluminium sections get a hot soapy wash, then rinsed, and prepared with primer.
  2. The paint is then applied in powder form with a spray-gun which carries an electro-static charge so the paint adheres to the aluminium in a smooth, even layer.
  3. The painted sections are then passed through an oven, bonding the paint to the aluminium.

In order to control the quality, all our painting is done in house. Our quality is also monitored by an independent company every 6 months.

How accurately are the doors, the glazing bars and corner joints finished?

We are the only greenhouse manufacturer to use CNC (computer numerically controlled) machinery to ensure the precision and accuracy of the profiles and sections we use. The latest technology, combined with an eye for traditional craftsmanship, produces an unrivalled level of finish.

Does an Alitex greenhouse ever need re-painting?

No. Neither does it chip, fade or flake.

How long is the paint finish guaranteed for?

We pass on the manufacturer’s guarantee of 10 years, but the science behind it predicts a lifetime in excess of 60 years. We have been coating our structures with polyester powder coating our structures since the late 1980s with no reports of the paint failing.

Can I have any colour I like? My windows are a Farrow & Ball colour and I want it to match.

Yes. We have the whole range of the international RAL colour chart available to us and can do specific matches for which there would be an additional charge.

Wood and restoration

Conservatory or greenhouse? I’m not sure if I need a double-glazed or single-glazed structure

As a rule of thumb, if you want to actively grow in the structure (i.e. start plants off from seed, have work benches etc), you will need a single-glazed greenhouse. This will maximise light levels to encourage healthy growth. A single-glazed structure will provide a warm environment from spring through to autumn which will also be ideal to sit in and use as a summerhouse. However, there is no insulation, so in the colder months the structure is prone to condensation and will be too chilly to sit inside. Even when heated, the atmosphere will remain moist, which is ideal for plants but not so ideal for people, or soft furnishings.

If the structure is to be used as an additional room, it will need to be warm and condensation-free, even in winter. In this case we would recommend a double-glazed conservatory.

Some older houses have original Victorian or Edwardian conservatories which will be single-glazed. The same rules above apply. To replace it in single-glazing, a high-quality external door must be installed between the structure and the dwelling. However, with single-glazing, it is liable to be damp and chilly in winter.

Do you make timber greenhouses?

No. Timber greenhouses have too many drawbacks. Typically they will need rubbing down and repainting every 2 years. Every 5 years, the putty holding the glass in dries out and will need replacing. Doors tend to absorb moisture and shrink and/or swell as the seasons change. Greenhouses are humid places in any case, so timber will quickly rot if left unpainted or untreated. Although cedar greenhouses don’t need painting, they will need treating.

How well do the proportions of your greenhouse follow the design principles of a traditional timber greenhouse?

An eaves height lower than the top of the door combined with a steep pitch of roof not only provides a truly authentic appearance, but also optimises air circulation and light penetration to give the perfect growing environment. Cresting and finials on the roof are made of solid aluminium, die cast from their original timber counterparts to ensure both the shape and size are authentic and pleasing to the eye.

I’ve got an old original Victorian greenhouse. Can you restore it?

No, but we can replace it in aluminium. Before embarking on restoration, consider all the maintenance associated with wooden greenhouses (See above).

NB: We don’t replace individual glazing bars or sections of timber greenhouses. All our sections are designed solely for use as an integral structure. A combination of wood and metal is not recommended, as the aluminium will remain sound, while timber section will continue to decay over time.


What kind of glass do you use and what happens if it breaks?

We glaze with 4mm toughened glass. We cannot guarantee against breakage, but we can replace any broken panes for a small charge.

Polycarbonate gives better insulation do you ever use it instead of glass?

No. The aluminium glazing sections are not deep enough to accept sheets of polycarbonate. Also, polycarbonate scratches and dulls over time and detracts from the look of the greenhouse.

Do you build greenhouses with glass to ground or do they all need to go on brick walls?

It is sometimes assumed the plinth wall will reduce light levels that plants and particularly tomatoes need. However, most light will enter the greenhouse through the long slope of the roof rather than the vertical sides. Plants on the rear of the greenhouse will get plenty of light at ground level as a result. Plants at the front will typically be on top of a bench above the height of the plinth wall.

We recommend a brick plinth 675mm high as this provides protection against frost and is typical of the style of Victorian greenhouses. It also means items stored under the benching are hidden from view on the outside, so the greenhouse looks neat and tidy.

However, we can design a greenhouse to have a lower glass side, but it will still need to sit on 3 courses of brick and have foundations. This is because the attaching bolts are 150mm long and need to be anchored into solid material.

Size and shape

What size greenhouses are available?

Clearly this depends on the space you have. As a starting point, we recommend a width of around 2.5m or 3.0m (about 8’ - 9’6”). This provides a good internal layout of a central path wide enough to access with a wheelbarrow, with room for benching or soil beds on either side of the path. Benching and beds are typically about 0.7m (2’6”) - 0.9m (3’) wide. This happens to be about as long as your arm so gives a comfortable working distance.

A length of 3.5m (approx 12’) will be needed if the greenhouse is going to be used for larger scale production of fruit and vegetables, overwintering of large pots (e.g. citrus) and, of course, sitting down with a cup of tea!

Hmm… I think I need something a little bit bigger

A 3.0m wide greenhouse can take a length of up to 10.0m and still look in proportion.

If wider than 3.0m is needed and the greenhouse is not going to be used as sitting area, we suggest increasing the width to 4.50m (approx 14’). This gives a typical layout of a central bench or soil bed with a path either side, and benching or beds either side of the path.

The minimum length for a 4.50m wide greenhouse (to maintain proportion of width to length) is 7.60m.

Building a greenhouse more than 3.0m and less than 4.50m wide is only advisable if it is floor space that is needed, as benching will remain 0.9m wide - which is the average length of your arm. If the bench is any wider, you end up with an unused area along the back of the bench that can’t be reached easily.

Can I have a lobby?

A lobby is a lovely feature that really captures the Victorian greenhouse look, but the dimensions have to be carefully assessed to achieve the right result. The minimum length to fit an extended lobby in a greenhouse is 5.10m. The minimum length for a flat fronted lobby is about 4.0m.

Can I have double doors?

Yes. Generally the greenhouse will need to be at least 3.50m wide if they are to go in a gable end or about 8.0m long if they are for a lobby.

What is a mono-pitch greenhouse?

This is best explained visually:

Monopitch diagram

Rear walls and lean-tos

Do you only build freestanding greenhouses?

Not at all. We design many greenhouses to be built against walls.

NB: All greenhouses against walls are bespoke and are priced to take into account the additional design time needed. Our National Trust greenhouses are all freestanding only. They cannot be adapted to fit against walls on any side. However, we can design a bespoke greenhouse of a similar size to fit against a wall.

To build a mono-pitch lean-to greenhouse around 3.0m wide, the wall will need to be about 3.50m high.

If the wall is not high enough for a mono-pitch lean-to, we can design the greenhouse as a ¾ span or even a “full span to wall”. A ¾ span will need a rear wall about 2.50m high.

The lowest height for a rear wall is 1.80m. The greenhouse will then be a “full span to wall”, i.e. the front and back roof slopes will be the same length, so the greenhouse will look more like a freestanding greenhouse pushed against a wall.

Bespoke greenhouses can also be designed to attach to a wall on the gable end(s) as well as on the rear.


Will your greenhouse have the correct ventilation?

Ventilation is a critical part of growing under glass. Our combination of roof and side vents creates a 'chimney effect' inside the greenhouse that encourages air circulation and prevents unhelpful through drafts. The number of opening vents is designed according to the needs of each individual greenhouse to give the optimum level of ventilation. On larger greenhouses, vent depth can be increased accordingly and electric motors added for precision control.

Do you put in ventilation as standard?

Yes. Ventilation is such a critical part of growing under glass that we refuse to skimp on it!

Vents are positioned in one vertical side in a bank (or banks, depending on the size and shape of the greenhouse). They are 0.90m deep (3’) and operated manually using a traditionally styled solid cast aluminium lever and link system. The length of the bank(s) of side vents will depend on the length of the greenhouse.

Vents in the roof are also set in bank(s) and 0.610m (2’) deep. On greenhouses up to 3.50m wide they are operated by temperature sensitive openers. These consist of a piston filled with synthetic wax which expands, as the external temperature heats up, to open the vent. As the external temperature cools, the wax contracts and the vents close. Once set they can be left to operate automatically. The openers are often referred to by the manufacturer’s name “Bayliss”.

Greenhouses 4.50m wide will have roof vents 1.20m (4’) deep. Due to the increased weight of the vent, they will need to be operated by an electric motor.

Why do you only put vents in one vertical side and in one slope of the roof?

This is to create a “chimney effect”. Air comes into the greenhouse via the side vents and heats up under the glass and begins to rise. Some air will exit through the roof vents and a proportion will cool and sink down on the opposite side to where it came in. It will then heat up and rise again, creating good air circulation within the greenhouse.

Putting vents in both vertical sides and in both sides of the ridge would create a through draught which is not beneficial to plants. The exceptions are greenhouses for alpines, which need as cool an environment as possible.

Can you put Bayliss openers on the side vents so they open automatically?

No. Bayliss are designed to remain closed in colder weather and start to open at around 15°C (60°F). But, even in winter, you will need some ventilation in the greenhouse; hence the need for some manually operated vents.

What happens when I am away?

We suggest the side vents are left slightly open. The roof vents will open and close throughout the day, so the greenhouse will remain vented.


Can you fit your shades onto my greenhouse/conservatory?

Only if it is an Alitex greenhouse. We do not fit them to other structures as the roller brackets are designed specifically to suit our aluminium sections.

A further complication is that drilling into another manufacturer’s structure to fit brackets/pulleys will breach their guarantee. Drilling into UPVC will also risk splitting the UPVC.

We do not do “supply only” shades for clients to fit themselves at their own risk, even if they measure up what material is needed. The mounting of the brackets and routing of the cord and pulleys still need consideration when designing the shade for manufacture. Fitting shades to non-Alitex structures causes difficulties.

My greenhouse is not Alitex. Can I buy some cresting to go on it?

No. The cresting is welded onto the ridge during manufacture. Since it does not get drilled or bolted, there is no means of attaching it. Also, it is likely to be too big and heavy to sit on the ridge of a non-Alitex greenhouse.

What material do you use on top of the bench?

It’s Hydroleca (pronounced “high-droll-ica” or “Hydro-leaka”). This is expanded clay granules which retain moisture, as well as providing a stable place to put pots.

Do you supply collapsible/folding benching?

No. But if required, you can remove the Hydroleca and corrugated metal sheet and grow plants up through the bench top.

What are the grids for?

On larger greenhouses, heating pipes are located in a duct under the grid which allows hot air to rise through the greenhouse, as well as acting as a walkway. In smaller greenhouses they are used mainly for decorative purposes.


Do I need Planning Permission for a Greenhouse?

We are increasingly finding Planning Permission is becoming an essential requirement for building a new greenhouse. Under permitted development rights, in some cases, planning permission will not be required; this will depend on the size and location of the proposed greenhouse.

As the greenhouse is a significant and long term development we also think that gaining planning approval is prudent and good practice. Part of our service is to undertake all planning negotiations for you. Having completed countless applications over the years we can anticipate most eventualities. (Our success rate is over 95%!)

You are however, free to submit your own planning application, particularly if you have a good ongoing relationship with your local planning office.

We are well versed in understanding the needs of conservation officers and the nuances of the planning process. And we have nurtured strong links with the National Trust, English Heritage and the Royal Horticultural Society.

As a general guide, planning permission will be required if any of the conditions listed below apply:

  1. The greenhouse is located on land at the front of the property
  2. The height of the greenhouse would exceed 4.0m for a dual pitch roof, 3.0m for any other roof. The height of the greenhouse would exceed 2.5m if located within 2.0m of a boundary
  3. The height of the eaves would exceed 2.5m
  4. More than 50% the area of land around the ‘original house’ would be covered by additions or other buildings
  5. In general if you live in a Conservation Area, Areas of Outstanding Natural Beauty, National Parks or the Broads, planning permission will be required. In these areas the maximum area to be covered by all outbuildings more than 20.0m from the house to be limited to 10msq. Greenhouses in these areas located at the side of the property will require planning permission
  6. Within the curtilage of a listed building, a greenhouse will require planning permission and, if built against a listed wall - listed building consent.

It should be noted that other consents may be required such as Party Wall agreements which we can advise and provide assistance with.


What guarantee do you offer?

The structural integrity of the greenhouse is guaranteed for 25 years or the lifetime of the purchaser, whichever is the longer.

  • Paint finish is guaranteed for 10 years
  • Accessories, electrical items and moving parts are guaranteed for 1 year
  • Bayliss are guaranteed for 2 years
  • Building work (by Alitex) is guaranteed for 10 years.
Will your greenhouse have undergone rigorous structural testing to ensure its legacy for generations to come?

The expertise of our team of in-house structural engineers informs all aspects of the design of our greenhouses to ensure their integrity, especially at frame joints and structural interfaces. It may surprise you to learn that to ensure they contain no imperfections, load-bearing members in our greenhouses undergo X-ray testing too, a procedure used in the aeronautical industry.

Does the warranty apply to the paint finish on your greenhouse?

We carry out all our polyester powder coating in-house to standards that exceed current regulations. This ensures your bespoke Victorian greenhouse will look as good as new long after the greenhouse paint manufacturer's 10 year guarantee ends. Every 6 months at the factory, samples of our paint finishes undergo stringent external testing for salt spray and scratch erosion - they pass every time.

Does the guarantee that comes with your greenhouse stand up to scrutiny?

In over 50 years we have never had a greenhouse fail, which means we can confidently provide a lifetime guarantee. Our trained staff are on hand to offer a comprehensive Clean & Care service to keep Alitex greenhouses in tip-top condition, whether 10 months or 10 years after installation.

Building Works

Will Alitex build the base for my greenhouse?

Yes, we offer a building works service for all our National Trust Greenhouses within 100 miles of our head office, Torberry Farm (on the Hampshire - Sussex border). And for those further afield we can provide a turnkey service to source and project manage a builder local to you. Bespoke greenhouses are assessed on a case by case basis. Please ask if you would like us to quote for building works. 

Can I use my own builder for the greenhouse base?

Yes, we will provide you and your builder with a detailed ground plan and the building notes to ensure the base is constructed to the correct specification. 

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