The heat-loss element homeowners forget
Roofs and walls get most of the attention, but the ground floor is a large surface that can lose a surprising amount of heat — especially in older homes where floors were built with no insulation at all. On a suspended timber floor, heat escapes downwards and cold air rises up through the gaps; on a solid floor, warmth is drawn away by conduction into the ground. Either way, an uninsulated floor undermines comfort and adds to your bills.
Because floor insulation is less visible and less talked about, it is often left undone even after walls and lofts have been improved. A floor heat loss investigation measures how much your floor is actually costing you and whether insulation is worthwhile.
Suspended timber floors
Suspended timber ground floors are common in London's period housing. The ventilated void beneath keeps the timber dry but also allows cold air to move up into the room. Insulating between the joists — while maintaining under-floor ventilation and sealing the draughts at the skirting — can transform how a downstairs room feels. The detail matters: done poorly, floor insulation can trap moisture and rot the joists, which is why measured, moisture-aware design is essential.
Solid floors
Solid concrete floors rarely leak air but lose heat by conduction if uninsulated. Insulating a solid floor is more involved and usually considered when a floor is being replaced or a room refurbished. The investigation tells you whether the heat loss justifies it, and how to detail it so damp-proofing and insulation work together.
How Retrofit IQ investigates floor heat loss
Thermal imaging maps heat loss across the floor. Where accessible, we inspect the floor void, joists, existing insulation and construction. Blower door testing and smoke tracing quantify and locate cold air rising through the floor. Where relevant we assess moisture, because floor insulation must keep the structure dry. You receive a measured picture and a prioritised, moisture-safe insulation strategy.
Part of a full Building Performance Investigation
Floor heat loss sits alongside walls, roof and air leakage in the overall picture. A floor investigation is most valuable as part of a full Building Performance Investigation, which prioritises floor works against every other element so your spending is sequenced correctly.
Ground moisture and the under-floor void
A suspended timber floor sits over a void that is deliberately ventilated to keep ground moisture away from the joists. This is why the detail of any floor insulation matters so much: it must keep the timber dry while making the floor warmer and less draughty. Blocking the under-floor ventilation, or fitting insulation that traps moisture against the joists, can lead to rot over time. Our investigation checks the condition of the void, the joists and any existing insulation, so that recommendations protect the structure rather than putting it at risk.
Insulation methods for suspended floors
There are several ways to insulate a suspended timber floor, and the best choice depends on access, the condition of the timbers and how the room is used. Insulation can be fitted between the joists from below where there is a cellar or crawl space, or from above when the floorboards are lifted during other works. The draughts at the perimeter and between the boards must be sealed as part of the job, while maintaining the void ventilation. We set out the option that suits your home, so the work is done once and done correctly.
Solid floors during refurbishment
Insulating a solid concrete floor is a larger undertaking, usually only sensible when the floor is being dug out or a room comprehensively refurbished. When that opportunity arises, it is worth taking: an uninsulated slab loses heat continuously and stays cold underfoot. The detail must coordinate insulation with damp-proofing and floor build-up so the finished floor is warm, dry and at a workable level. Our report tells you whether your floor heat loss justifies this and how to detail it if you are already planning works.
Comfort, bills and how the home feels
Because cold air pools at floor level, an uninsulated, draughty ground floor has an outsized effect on how a room feels — it is the reason a room can read 21 degrees on the thermostat yet still feel chilly around your feet. Warming the floor and sealing the draughts raises the perceived comfort of the whole room, often allowing a slightly lower thermostat setting and lower bills. For a downstairs living space in constant use, it is one of the improvements homeowners notice most immediately.
Insulation, build-up and the finished floor level
One practical consideration with floor insulation is the finished level. Insulating between joists on a suspended floor usually keeps the floor at the same height, but insulating over a solid floor adds a build-up that can raise the level, affecting doors, skirtings and thresholds. Where a floor is being dug out and re-laid, insulation can be incorporated within the new construction without a level change. Our report flags these practicalities so there are no surprises, and so floor works can be planned to suit how the room is used.
Coordinating with heating and pipework
Floors are also where much of a home's pipework runs, and where underfloor heating might be considered. If you are planning to upgrade heating, add underfloor heating or re-run pipework, that is the ideal moment to insulate the floor, because the boards are already up and the two can be detailed together. Insulating beneath underfloor heating, in particular, ensures the warmth goes up into the room rather than down into the ground. We help you coordinate floor insulation with any heating work so it is done once and done efficiently.
Sealing the perimeter and the skirting line
Insulating a floor without sealing its edges leaves much of the benefit on the table, because cold air continues to leak in at the perimeter and behind the skirting. Effective floor works therefore address both the thermal insulation and the airtightness at the junction with the walls — while preserving the ventilation the under-floor void needs. Getting this detail right is a large part of why a professionally investigated and specified floor upgrade outperforms a well-meaning but partial DIY attempt.
Period floors and keeping character
Many London homes have attractive original floorboards that owners rightly want to keep. The good news is that insulating and sealing a suspended timber floor can usually be done from below where there is access, or carefully from above, without sacrificing the character of the boards. Where boards must be lifted, they can be numbered and relaid. Our investigation takes account of what you want to preserve, so improved warmth and comfort do not come at the cost of the features that give the home its character.
What you receive
- A measured picture of how your floor loses heat
- Thermal images and a floor-void inspection where accessible
- Identified draughts rising through the floor
- A moisture-safe, prioritised insulation strategy
- Clear next steps any competent contractor can follow
A real-world investigation example
A homeowner planning a ground-floor renovation wanted to know whether the existing solid floor was worth insulating and how the suspended timber floor in the older part of the house performed. Thermal imaging and moisture readings showed the suspended floor losing heat downwards and leaking cold air up through the boards, while the solid floor was cold but dry. This distinction shaped the design: the timber floor justified insulation and perimeter sealing with careful attention to keeping the void ventilated, while the solid floor could be insulated as part of the new build-up without moisture risk. Measuring first meant each floor type got the right, moisture-safe treatment.
Common homeowner mistakes
A frequent mistake is treating all floors the same, when a suspended timber floor and a solid concrete floor lose heat and handle moisture very differently and need different solutions. Sealing a suspended floor's ventilation to stop draughts, without providing an alternative, risks rot. Insulating a floor without addressing the perimeter and skirting gaps leaves cold air still tracking up around the edges. And overlooking the floor entirely — because attention usually goes to walls and lofts — leaves one of the more uncomfortable heat-loss paths unaddressed.