Greenhouse frequently asked questions

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.

No. Neither does it chip, fade or flake.

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 polyester powder coating our structures since the late 1980s with no reports of the paint failing.

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.

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.

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.

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 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.

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.

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 (eg citrus) and, of course, sitting down with a cup of tea!

3.0 m 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.

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 4.00m.

Yes. Generally the greenhouse will need to be at least 3.50m wide if they are to go in a gable end or about 8.00m long if they are for a lobby.

This is best explained visually:

Yes. Ventilation is such a critical part of growing under glass, 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.

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.

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

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.

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 free-standing 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 monopitch 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 monopitch 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 free-standing 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.

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

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.

It is sometimes assumed the plinth wall will reduce light levels that the plants and particularly for tomatoes. 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.

• The structural integrity of the greenhouse is guaranteed for 25 years or 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.

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 etc will breach their guarantee. Drilling into UPVC will 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.

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.

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

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.

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.