Key takeaways
- Check the roof vents first; aim for about a fifth of the floor area
- Fit an automatic vent opener to every roof vent
- Budget for a level base, delivery, assembly, staging and guttering, not just the greenhouse
- Pick a sunny, sheltered spot clear of overhanging trees, with water nearby
- Most garden greenhouses need no planning permission, but check if you live in a listed building or conservation area
- Toughened glass is the safer choice where children or pets play
The best way to choose a greenhouse is to check the things that are hard to change later: the roof vents, the frame, the base and where it will stand. Get those right and almost any sensible greenhouse will serve you well.
This checklist takes you through each one before you order. If you’re still deciding which size, frame or budget to go for, start with our guide to the best greenhouse for UK gardens, then come back here before you buy.
Check 1: Are there enough roof vents?
This is the most important check, and the one cheap greenhouses most often get wrong. Aim for roof vents adding up to about a fifth of the floor area.
Hot air rises, so roof vents do most of the cooling. Side vents and louvres help by letting cool air in low down, but they only work well alongside roof vents. A small greenhouse with one little roof vent gets very hot on a sunny summer day, and tomatoes and seedlings suffer.
- Count the roof vents on the model you like, and ask whether more can be added.
- Order extra vents with the greenhouse. Fitting them later is fiddly.
- Fit an automatic vent opener to each roof vent. A wax cylinder inside expands as it warms and pushes the vent open, even when you’re out.
A guide to greenhouse ventilation and humidity explains how to keep the air moving through the seasons.
An automatic opener lifts the roof vent as the greenhouse warms up, so a sunny day while you’re at work doesn’t cook your plants.
Check 2: Is the frame strong enough?
A sturdy frame matters more than looks, especially in a windy spot. Look for a frame that feels rigid when assembled, with proper bracing in the roof and sides.
Check the bracing and glazing clips before you buy. They’re what keep the panes in when a gale blows through.
Aluminium is the low-upkeep choice and comes in silver or powder-coated colours such as green and black. Wooden frames, such as cedar or thermowood (heat-treated timber), look lovely and hold a little more warmth, but need occasional treatment.
Questions worth asking:
- Does it come with diagonal bracing and a base frame?
- How do the glazing clips work? Spring wire clips can pop in high winds. Some greenhouses use stronger clips or glazing strips.
- Is the door a smooth sliding one, and is it wide enough for a wheelbarrow?
- Is guttering included? It feeds a water butt and stops drips along the sides.
If you like the look of wood, Greenhouse Stores stocks Swallow thermowood greenhouses alongside aluminium ranges.
Check 3: Is the glazing right for your garden?
Toughened safety glass is the usual choice for a permanent greenhouse. It lets in plenty of light and, if it breaks, crumbles into small blunt pieces.
Polycarbonate shrugs off a stray football, which makes it a good choice where children and pets play.
Horticultural glass is cheaper but breaks into sharp shards, so it’s best kept away from play areas. Polycarbonate is light, cheap and almost unbreakable, which suits family gardens and exposed sites. It can scratch and discolour over the years.
Our guide to polycarbonate vs glass greenhouses compares them in more detail.
Check 4: Have you planned the base?
Every greenhouse needs a firm, level base at least as big as its footprint. A wonky base twists the frame, so doors stick and panes slip.
There are three good options:
- Paving slabs laid level on a compacted sub-base. Ideal for most small and medium greenhouses.
- A low brick or block plinth on a concrete footing. It adds headroom and keeps the glass clear of soil splashes.
- A concrete slab. Very solid, but plan for drainage so water doesn’t pool inside.
Avoid bare soil, loose gravel, lawn or decking. They settle unevenly over time. Before you build the greenhouse, measure both diagonals of the base. If they match, it’s square.
Our step-by-step greenhouse base guide shows how to lay each one.
Check the base with a spirit level before the frame goes on. A few minutes here saves sticking doors and slipping panes later.
Check 5: Have you picked the right spot?
Choose the sunniest, most sheltered level spot you have, clear of overhanging trees.
- Sun. A spot that gets sun for most of the day is best. Running the ridge east to west gives the most light in winter.
- Shelter. A wall, fence or hedge on the north or east side keeps off cold winds without shading the glass.
- Trees. Keep clear of overhanging branches. Falling leaves block vents, and branches can break glass in storms.
- Water and power. Being near a tap or water butt makes summer watering much easier. Plan any electrics with a qualified electrician.
- Access. Leave room to walk round at least two sides, for cleaning the glass and fixing panes.
- Drainage. Avoid spots where water sits after rain.
A sunny spot near the house, with a fence for shelter, makes it easy to pop out and check on things.
If your spot is windy, our guide on how to secure a greenhouse in wind shows how to anchor it.
Check 6: Do you need planning permission?
Usually not. In England, most garden greenhouses count as permitted development, as long as they meet a few rules:
- It stands behind the front of the house, not between the house and the road.
- It is no more than 2.5m tall if within 2m of a boundary.
- The eaves are no higher than 2.5m.
- Outbuildings together cover no more than half the garden around the original house.
The rules are tighter for listed buildings, and in conservation areas, National Parks and National Landscapes. Wales, Scotland and Northern Ireland have their own rules. If you’re unsure, check the Planning Portal outbuildings guidance or ask your council.
Check 7: Have you added up the extras?
The price of the greenhouse isn’t the whole bill. Before you order, add up:
- The base, whether slabs, bricks or concrete
- Delivery, and whether it reaches your back garden
- Assembly, if you won’t build it yourself
- Extra roof vents and automatic openers
- Staging and shelving
- Guttering and a water butt, if not included
- Shading for summer, and insulation if you’ll use it in winter
Order in winter if you can, so it’s built and ready for spring sowing. Greenhouse Stores has a greenhouse buyer’s guide comparing the main brands they sell.
Staging, guttering and a water butt turn a greenhouse into a working space. Remember to budget for them.
Greenhouse buying calendar
| Month | What to do |
|---|---|
| November to January | Choose your spot, measure up and compare models |
| January to February | Order, so delivery comes before the spring rush |
| February to March | Lay the base on a dry spell |
| March to April | Build the greenhouse and fit vents, openers and staging |
| April to May | Start sowing and move in tender plants |
| June to August | Add shading and keep vents open on hot days |
| September to October | Clean the glass and check clips and seals |
Common mistakes when buying a greenhouse
Too few roof vents. The most common regret. A greenhouse that overheats is hard to grow in. Add vents and openers at the start.
Skipping the base. Building straight on soil or gravel leads to twisted frames and stuck doors. Lay a proper level base first.
Buying on price alone. A cheap greenhouse with flimsy clips and bracing may not survive a winter gale. Compare the total cost, including extras.
The wrong spot. Shade from trees or buildings and a long walk from the tap both mean it gets used less.
Forgetting to check planning rules. Usually fine, but listed buildings and protected areas are different. Check before you buy.
Not sure a greenhouse is right for you? Our polytunnel vs greenhouse guide weighs up the alternative. You’ll find more practical guides in the how-to section.
Once your greenhouse is up, read our guide on how to insulate a greenhouse for winter to keep it working all year.
Frequently asked questions
What should I look for when buying a greenhouse?
Check the roof vents, frame, glazing, door and base first. Plenty of roof vents matters most, followed by a sturdy frame and secure glazing clips. Then add up the extras, such as base, staging and guttering.
How many roof vents does a greenhouse need?
Aim for roof vents equal to about a fifth of the floor area. Many small greenhouses come with just one, which isn’t enough on a hot day. Order extra vents with the greenhouse rather than adding them later.
Do I need planning permission for a greenhouse?
Usually not, if it sits behind the house and stays within height limits. In England it must be under 2.5m tall if within 2m of a boundary. Listed buildings and some protected areas have stricter rules, so check the Planning Portal or your council.
What is the best base for a greenhouse?
A level base of paving slabs, a brick plinth or a concrete slab. Slabs suit most small greenhouses. A low brick plinth adds headroom and keeps the glass clear of soil splashes.
Where is the best place to put a greenhouse?
Somewhere sunny, sheltered and level, away from overhanging trees. Shelter from cold north and east winds helps. Being close to the house and a water supply makes it much easier to look after.
Glass or polycarbonate for a greenhouse?
Toughened glass suits most permanent greenhouses. It lets in lots of light and breaks into small blunt pieces. Polycarbonate is lighter, cheaper and safe around children, but it can scratch and discolour over time.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
