Frequently Asked Questions

Aluminium and paint

Do Aluminium windows cause condensation?

Our system is fully thermally broken (i.e. the inside face of the aluminium is separated from the outside face of the aluminium with a polyamide, plastic thermal break). It is not 100% condensation free (the correct balance between heating and ventilation will be needed to keep condensation at bay), but the system reduces condensation. In most conditions, aluminium will be as condensation free as timber. However, in very humid conditions (with cold conditions outside) aluminium is more likely to condensate than timber (as will the glass). But it is important to remember that if you do get condensation, an Alitex structure will not rot, whereas timber will.

What are the advantages of aluminium over timber?

Aluminium doors and windows have weather test ratings as timber products do. The main advantage is that aluminium will maintain its initial weather integrity over the entire course of its lifetime whereas timber will not. Our windows and doors meet BS6375:pt1 severe exposure category 2000. You can see all the British Standards that we build to here. You will obviously also benefit from the reduced maintenance. A regular wash down is all that is needed – no re-paints. Finally, it provides reduced expansion and contraction, which with timber leads to warping that will affect weather tightness in the long term.

Can you paint a greenhouse any colour? My windows are a Farrow & Ball colour and I want 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.

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.

Does an Alitex greenhouse ever need re-painting?

Unlike timber, it does not need regular painting and treating. We do recommend regular cleaning and prompt repair of any paint damage to maximise the longevity of the coating. We provide a 10-year warranty on our standard finishes.

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.

What material 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.

Wood and restoration

How to restore a greenhouse? I’ve got an old Victorian greenhouse, can this be restored?

Unfortunately not, but we can replace it in aluminium. Before embarking on restoration, consider all the maintenance associated with a timber greenhouse.

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.

How well are the design principles of a traditional timber greenhouse followed when building a 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.

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.

Size and shape

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.

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.

What size greenhouse do I need?

We have a variety of sizes available in our National Trust collection, starting with the Hidcote from 2.6m x 3m. We do also offer a bespoke greenhouse service where the size can be tailored to your growing needs.


How to secure a greenhouse for when I’m 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 I fit a Bayliss automatic greenhouse window opener?

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.

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.

How much ventilation does a greenhouse need?

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.

Rear walls and lean-tos

Do you only build freestanding greenhouses?

No, 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 greenhouses in the National Trust Collection 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.


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, such as 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 Victorian greenhouse style. 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.

What is the best greenhouse insulation, is polycarbonate used?

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.

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

Our greenhouses are single-glazed with “low-e” (short for “low-emissivity”) 4mm toughened glass. We cannot guarantee against breakage, but we can replace any broken panes for a small charge.


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 Alitex greenhouse will look as good as new long after our 10 year guarantee. Every 6 months at the factory, samples of our paint finishes undergo stringent external testing for salt spray and scratch erosion, passing with flying colours every time.

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.


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

Unfortunately not. 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 are the grids for?

On larger greenhouses, heating pipes are located in a channel under the grid which allows hot air to rise through the greenhouse, as well as acting as a walkway. In addition, you can spray the heating pipes to create humidity, or add water to the channel for the same reason. They are also an attractive walkway that adds to the period feel inside the greenhouse.

In smaller greenhouses they are used mainly for decorative purposes.

Do you supply a folding greenhouse bench?

Not right now, but we are looking into it. If required, you can remove the Hydroleca and corrugated metal sheet and grow plants up through the bench top.

What material do you use on top of the bench?

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

Can you fit your shades onto my greenhouse?

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.


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. When it comes to planning, Alitex can certainly advise on the best route forward. Our team of experts are continuously working with various planning authorities across the UK and will work with you or your chosen architect to try and satisfy the various criteria. Please contact us here to find out more about any potential planning permissions you may need for your greenhouse.

Costs and timings

What is your lead time?

Our lead times depend of a few factors such as the size and type of your chosen greenhouse. If you'd like to find out what our lead times are for your chosen greenhouse, please give us a call on 01730 826900 or get in touch with us and we would be more than happy to go through this with you. 

How much does a greenhouse cost?

This very much depends on the nature of the design. Prices for our National Trust Greenhouse collection can be found here. For a bespoke structure, please contact us here.

Examples of work

Where can I see examples of your work?

Over the years, we have created some beautiful Victorian greenhouses. On our case studies page, you will find a range of projects from our National Trust Collection and bespoke greenhouses. These case studies are a fraction of what we have built, we hope that you will find inspiration for your project. 

We also have a number of display structures at our premises in Hampshire and have also built several in Hampshire, Surrey and Sussex as well as the Channel Isles. We have customers nationwide so may well have a structure nearer to you. Please get in touch and we will let you know.

Arranging an Alitex visit

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

How do I arrange a no obligation visit?

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

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

Can I arrange for Alitex to visit me?

Of course. Give us a call - 01730 826900.

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. 

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.