Loft joists were usually sized for a cold roof space and a few boxes of decorations, not a bedroom, a bathroom and a wall of fitted wardrobes. A habitable floor is normally designed for an imposed load of about 1.5 kN per square metre, and that allowance often has very little room to spare once you add furniture, people and the weight of the floor finish itself.
The differences are greater than most people expect. Natural stone can weigh 50 to 80 kg per square metre before adhesive and backer board. Porcelain tile lands around 20 to 30, engineered wood roughly 12 to 15, luxury vinyl with a plywood overlay about 10 to 12, and carpet with underlay a mere 3 to 5. Point loads matter too: a freestanding bath, a chimney breast or a packed bookcase can test a floor far more than an even layer of planks.
Two other measurements deserve a mention early. Floor build-up steals headroom, which is precious under sloping ceilings and above the stair head. And anything heavy has to travel up a staircase that may be narrow and winding.
Heat rises, and a well-insulated loft under current Building Regulations holds it well. That does not make underfloor heating a waste of money, but it does change how you use it: a gentle background warmth is usually enough, and the system needs to be low-profile so it does not eat into your headroom.
Thin electric mats, or hydronic systems laid in routed boards, add far less height than a traditional screed. The covering you put on top then decides how well it performs. Insulating layers trap heat, so look at the combined tog rating of carpet and underlay rather than each separately. Most manufacturers suggest keeping the total below 2.5 tog for underfloor heating, and ideally nearer 1.5.
This is the issue that turns a beautiful conversion into a source of household friction. Footfall, dropped phones and the rumble of a chair all travel through the joists into the room below, which is very often someone's bedroom. There is no legal acoustic requirement between floors within one dwelling, but the practical need is real.
You cannot solve impact noise from above alone. If the ceiling below is being replaced or opened up as part of the work, that is the moment to add mineral wool between the joists and resilient bars beneath. From above, a carpet with a dense crumb rubber or felt underlay is comfortably the most effective covering. Hard floors reflect and amplify; a floating floor on acoustic underlay helps, but it will never match carpet.
Carpet is warm, quiet and forgiving over a subfloor that is not perfectly flat. Its weakness is fading near roof windows and its thickness where underfloor heating is involved.
Engineered wood gives you a genuine timber surface with a stable plywood core, typically 14 to 20 mm thick with a 3 to 6 mm wear layer. Acclimatise it in the room for 48 to 72 hours, and expect to re-oil an oiled finish periodically.
Luxury vinyl tile or plank is tough, waterproof and well suited to an en-suite. Look for a wear layer of at least 0.3 mm for domestic use, and 0.55 mm in a busy room. It demands a genuinely flat subfloor, generally no more than 3 mm of deviation over 2 metres. Glue-down is quieter and more stable; click systems need a suitable acoustic underlay beneath them.
Most loft conversion floors are boarded with 18 mm plywood or 22 mm tongue-and-groove flooring grade chipboard, screwed down at around 150 mm centres with staggered joints. Fixing it properly now is what stops the squeaks you will otherwise live with forever.
A loft en-suite is best served by glue-down luxury vinyl over underfloor heating, or tile if the structure allows it. A main bedroom suits a good carpet with acoustic underlay. A study, landing or dressing area takes engineered wood or vinyl plank beautifully, and eaves storage does well with a hard floor so boxes slide in and out.
Ask three questions before you buy: how much weight can the floor take, how much headroom can I afford to lose, and how much noise will reach the room below? Answer those honestly and the right finish usually chooses itself. Spend your money on a flat, well-fixed subfloor and a careful fitter, because on a loft floor, preparation matters more than the price of the planks.
Garret Ridge shares practical, down-to-earth guidance on loft conversions and attic renovations for readers across the UK.
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