Winter
Windows lose heat fastest on cold, still nights. A closed shutter traps a layer of air between the curtain and the glass and adds the insulation of the foam-filled laths, which reduces heat loss while it is closed. Good guide seals and a bottom seal make a noticeable difference.
Summer
External shading stops solar heat before it reaches the glass, which is why shutters are common in hotter countries and increasingly used on south and west-facing rooms and glazed extensions in the UK. Internal blinds stop glare but let much of the heat into the room.
Getting the most from shutters
- Close shutters at dusk in winter and open them in the morning to let the sun in.
- Close sun-facing shutters on hot afternoons, part-closed so slotted laths still let some light through.
- Use timers or sun-based automation so it happens even when you are out.
Setting expectations
Shutters complement good windows, insulation and draught-proofing rather than replacing them, and they only help while they are closed. If energy saving is your main goal, sort out draughts and loft insulation first, then add shutters for comfort, privacy and security as well.
Which shutters help most?
Insulated foam-filled laths with brush seals in the guides and a seal on the bottom rail do more than single-skin laths, and a shutter that closes snugly in its guides traps a stiller layer of air in front of the glass.
South and west-facing glazing, roof-lit extensions and bedrooms that overheat see the clearest summer benefit, because that is where solar gain is highest.
For garages under bedrooms or attached to the house, an insulated roller garage door with seals cuts draughts and noise as well as heat loss.
Ventilation still matters
Shutters do not replace ventilation. Keep trickle vents open and ventilate kitchens and bathrooms as normal, and in summer leave slotted laths part-open so air can move while the glass stays shaded.
This guide is general information, not legal advice. Rules can change; check with the relevant authority for your property.