How to Insulate a Conservatory Properly
Conservatory insulation starts with the roof, because that is where most of the heat leaves and most of the summer heat arrives. After the roof comes the glazing in the walls, then the draughts around doors and frames, and finally the floor. Done in that order, the improvements compound. Done in the wrong order, you can spend a great deal on a floor that sits under a roof still leaking warmth into the sky.
The options, ranked by how much difference they make:
Replace the roof glazing with high-performance glass (or a solid or hybrid roof): the biggest improvement; medium to high cost.
Upgrade the wall glazing: a large improvement where units are single glazed or old; medium cost.
Seal the draughts: a noticeable improvement; low cost.
Insulate the floor: a real improvement when the floor is being replaced anyway; medium cost.
Thermal blinds, lined curtains and window film: a modest improvement, mainly after dark; low cost.
Internal insulated ceiling: warm in winter but dark and prone to condensation; a last resort.
We build luxury conservatories that are insulated from the outset, so the same list also shows what a new room should get right.
Why is a conservatory so hard to keep warm?
Glass conducts heat many times faster than an insulated wall, and older conservatories add a polycarbonate roof, early double glazing, an uninsulated base and doors that no longer seal. The room loses heat from every surface at once, so no single fix solves it; the aim is to bring every surface up to a standard where modest heating keeps it comfortable.
Where does the roof fit in?
The roof is where most of the heat leaves, and there are three routes: an internal insulated ceiling, high-performance replacement glazing, or a full solid or hybrid roof. They differ sharply in light, weight and building regulations, so we cover them separately in our guide to conservatory roof insulation, including what drives the cost of each. Where the frame is sound we recommend high-performance glass, because it keeps the light; an internal ceiling is the last resort.
Everything below is about the rest of the room: the walls, the draughts and the floor, which is where an insulated roof either pays off or is undone.
What about the glazing in the walls?
Wall glazing loses less than the roof but there is a lot of it. If the units are single glazed, replacing them is the most effective step after the roof. If they are double glazed but old, look at the spacer bars: early units with aluminium spacers lose heat around the edge of every pane and are prone to misting. Modern warm-edge units with a low-emissivity coating and an argon fill perform far better in the same frame, provided the frame will accept the unit thickness.
Where the frames themselves are the problem, because they are thin, un-broken aluminium or a system that no longer seals, upgrading the glass alone will disappoint. A thermally broken aluminium frame or a hardwood frame is what separates a room that holds heat from one that does not.
How do you stop draughts in a conservatory?
Draughts are the cheapest thing to fix and the most often ignored. Check the seals on every door and opening window and replace any that are flattened or split. Look at the junction between the conservatory and the house wall, where the flashing or sealant often fails after a few years. Check where the frame meets the base for gaps. A smoke pencil on a windy day finds them quickly.
Doors between the conservatory and the house matter too. A conservatory that is exempt from building regulations relies on those doors being of external quality and kept closed in winter; a room open to the house pulls heat out of the whole ground floor.
Can you insulate a conservatory floor?
Yes, and it is worth doing when the floor is being replaced anyway. A layer of rigid insulation under a new screed or a floating floor cuts the cold radiating up from an uninsulated slab and makes underfloor heating far more efficient. Lifting a sound tiled floor purely to insulate underneath is rarely justified on its own; it makes sense when the room is being refitted or when underfloor heating is going in.
For a room that is otherwise well insulated, a thick underlay and a good carpet or rug over a cold floor is a modest but real improvement.
When is replacing the conservatory the better answer?
There is a point at which the cost of insulating an old conservatory, roof, glazing, seals and floor, approaches the cost of a new room built to modern standards, and the old frame is still the old frame. If the structure is more than twenty years old, the frame is not thermally broken and the base is suspect, we would rather have the honest conversation about replacement than sell a sequence of upgrades. A new winter garden or hardwood conservatory arrives insulated, with a roof designed for the room and glazing chosen for its orientation. The heating side of that decision is covered in our post on how to heat a conservatory.
Conservatory insulation questions, answered
What is the cheapest way to insulate a conservatory?
Fixing draughts, adding thermal blinds or lined curtains, and applying a low-emissivity window film to the glass. All are inexpensive and make a noticeable difference, though none addresses the roof, which is where the real loss is.
Does insulating a conservatory need building regulations?
In an exempt conservatory, replacing glazing does not need approval, though it must meet the safety glazing rules; where the room is part of the house, replacement glazing must meet building regulations, normally through a FENSA or CERTASS-registered installer. Adding a solid roof or an internal insulated ceiling usually needs approval, because the room stops meeting the exemption criteria and the structure is being altered.
Will insulation stop a conservatory overheating in summer?
Roof insulation and solar control glass both help, because they block heat coming in as well as going out. Ventilation at high level is the other half of the summer answer.
How warm can an insulated conservatory get in winter?
A room with a well-specified roof, modern glazing and proper heating can be kept at the same temperature as the rest of the house. Insulation makes that affordable rather than merely possible.
Talk to our design team
If your conservatory is cold in winter and you are weighing upgrades against a new room, we are happy to look at it with you and say plainly which route makes sense.
