One thermostat can be trying to control parts of a home that were built decades apart.
The original house may have one wall construction, one floor type and a conventional pitched roof.
A later extension or conservatory can introduce different glazing, a different roof, a different floor and much more exposed external surface area.
So it is entirely possible for the main house to feel comfortable while the newer addition still feels noticeably colder.
Quick answer: Conservatories and extensions can feel colder than the rest of the house because they may use different walls, floors, roofs and glazing from the original property. The heating may serve both spaces, but the rate at which they gain and lose heat can be very different.
The house may look like one space but behave like several
Once an extension is opened into the original property, the two areas can feel visually connected.
Thermally, though, they may still be quite different.
The original part of the home may have:
- a traditional loft
- older cavity or solid walls
- a suspended timber floor
while the extension may use:
- a solid floor
- a flat or pitched roof
- larger glazing
- a different cavity-wall build-up
Key point: A thermostat measures temperature. It does not know whether the room beside it was built in 1935 or added in 2005.
Extensions change the shape of the thermal envelope
Adding a room does more than increase floor area.
It can introduce new:
- external walls
- roof surfaces
- corners
- glazed openings
- junctions with the original building
This is why extensions can change the way a house loses heat even when the heating system itself has not changed.
Why can conservatories feel especially different?
A conservatory usually contains much more glazing than the rest of the house.
That can create a very different internal environment.
Even where the air is heated, the large glazed surfaces can remain relatively cool in colder weather.
That can affect comfort in the same way that sitting close to a cold window can.
Large openings can connect two very different spaces
Many extensions and conservatories are opened into kitchens or living rooms.
This creates one large usable space, but it can also connect areas with very different construction.
The thermostat may respond to the combined room temperature even though one end of the space consistently feels cooler.
The roof is often one of the biggest differences
The original house may have a conventional cold loft insulated at ceiling level.
A newer addition might have:
- a flat roof
- a pitched vaulted roof
- a warm roof build-up
- a glazed conservatory roof
Those constructions cannot all be approached in the same way.
Where might HYBRIS be relevant?
Where an extension has a suitable roof construction with restricted depth, HYBRIS roof insulation may be one option within an appropriate roof build-up.
That does not mean every extension needs HYBRIS. The roof structure and existing insulation need to be understood first.
What about a traditional loft over the original house?
The original section may still have a completely conventional cold loft.
In that case, suitable traditional loft insulation can remain the straightforward approach above that part of the house.
There is no reason the original roof and the extension roof need to use the same insulation system if their constructions are different.
The walls can differ too
An older home and later extension may both have cavities, but that does not automatically mean the cavities are identical or suitable for the same treatment.
Where appropriate, cavity wall insulation can improve a suitable wall construction.
The actual build-up should always be established rather than assumed from appearance.
And the floor may have changed completely
This is another common contrast.
The original house may have a suspended timber floor while a later extension uses a solid slab.
If the colder sensation is strongest underfoot in the older part, underfloor insulation beneath suspended sections may be relevant there.
The extension would need to be considered separately.
Why can the junction between old and new feel colder?
The point where an extension meets the original house can include several changes in construction at once.
There may be:
- former external walls
- steel beams
- changes in ceiling height
- different floor levels
- different insulation systems
This can create a more complicated thermal junction than the middle of either room.
Modern does not automatically mean warm
A newer extension may have been built to a different standard from the original house, but comfort still depends on the whole design.
Large areas of glazing, room orientation, roof shape and how the extension connects to the older building can all affect how the space feels.
Likewise, an older part of the house may have been upgraded over time and now perform very differently from when it was first built.
Why turning the thermostat up may not even things out
Increasing the set temperature can put more heat into both spaces.
It does not make their construction identical.
If one area loses heat faster or has colder internal surfaces, it may still feel different even when more energy is being supplied.
| Part of the home | Possible reason it behaves differently |
|---|---|
| Original house | Older roof, wall and floor construction |
| Extension | Different floor, roof and wall build-up |
| Conservatory | Large proportion of glazed surfaces |
| Open-plan junction | Old and new construction meeting in one space |
| Vaulted extension | Roof insulation follows the slope rather than an open loft floor |
| Original suspended-floor room | Cold ventilated void beneath the floor |
What should you notice before simply turning the heating higher?
Compare:
- The original house with the extension
- Floor temperature in each area
- Roof types above each space
- Amount of glazing
- External wall exposure
- Whether one space warms more slowly
- Whether one space cools more quickly
- Where the old and new parts of the property meet
Different parts of the same home can need different solutions
The useful lesson from the first cold days of the heating season is not that one construction is automatically better than another.
It is that a house can contain several completely different thermal zones.
A 1930s original building, a 1990s extension and a later conservatory may all be connected to the same heating system while needing very different insulation approaches.
Before assuming the answer is simply a higher thermostat setting, look at which part of the property is actually struggling.
Frequently asked questions
Why is my extension colder than the main house?
The extension may use different walls, flooring, glazing and roof construction, so it can gain and lose heat differently from the original property.
Why is my conservatory cold even with the heating on?
Conservatories often contain a much larger proportion of glazing than normal rooms, which can create colder surrounding surfaces in winter.
Can an extension need different insulation from the main house?
Yes. Different roof, wall and floor constructions can require different insulation systems within the same property.
Can cavity wall insulation help an extension?
Where the wall construction and cavity are suitable, it may be relevant, but suitability should be confirmed before work is recommended.
Should I just turn the thermostat up if the extension is cold?
That may increase the room temperature, but if the extension consistently behaves differently from the rest of the house, it can be useful to understand the construction and heat-loss routes first.
Explore the full series: From draughts and cold floors to windows, localised cold patches and extensions, this series looks at what your home may be telling you when the colder weather finally makes you reach for the thermostat.
Start the series: Before You Touch The Thermostat, Can You Feel A Draught?
