A room in the roof is hot because of the slope above you, and awkward because the full-height wall is small. The decision is whether a gable, a knee wall or a dormer cheek can take an indoor unit, and whether the pipe drop to a lawful outdoor spot stays inside the height limit. Survey the slopes before you buy a standard bedroom package. Condensate must not drip into the loft. An F-gas certified company commissions the pair if that geometry works.
The gable, the dormer cheek and the knee wall
High-wall units want a vertical face and clear ceiling above the casing. A slope that starts at the door head often leaves only the gable end or a strip beside a dormer. Measure that strip. If it is shorter than the unit plus the service gap, that wall is finished as an idea. A knee wall is frequently too low, so the air blows at the mattress rather than along the ceiling. A floor console on the knee wall is sometimes the fit, and it is still a visible box. A ducted unit in the eaves only works if the eaves are a real void you can service, not a wedge of insulation. Many roof rooms have nowhere to hide the machine. The survey should say so. Say the room is in the roof, and attach photos of the slopes, the gable, any dormer, the bed position and the outdoor elevation below. Note which floor it is on. Gable or dormer cheek comes before the slope. Service clearance above the casing still applies. Knee-wall units must not blow straight at the bed. Do not promise a hidden unit the eaves cannot hold.
The drop to the yard, and water above a ceiling
From a second-floor slope down to a rear yard is a long drop. That height difference, plus any loft travel to reach the gable, has to sit inside the manufacturer's limit. If it does not, this room cannot join a multi-split parked at the back. It may still take its own outdoor unit on a gable wall, if that wall is lawful under Planning Portal conditions in England and the neighbour can live with it. The cooling load is the roof as much as the floor area. Poor insulation and a south-facing dormer will outrun a tiny unit. The survey sizes that. Improving the loft insulation is still worth doing. It does not replace the unit in a room you use on a hot afternoon, and a unit will not rescue an uninsulated felt roof on its own.
Condensate in a roof room is above someone else's plaster. The pipe has to fall to a soil stack or be pumped on a route that is visible enough to maintain. A drip onto loft insulation becomes a ceiling stain. Specify the route on the quote, including insulation so the pipe does not sweat. Electrics in loft conversions are often a spur that was tight when it was fitted. A dedicated circuit from the consumer unit is the usual ask. As a 2026 illustration, a roof room that already has a gable and a sensible drop is often in the low thousands including VAT, and a failed height limit or a pumped drain across the loft is what changes the job into a different design. Ask whether a stated model fits the full-height wall with service clearance, what the height difference is, and how condensate leaves the loft. If the height limit fails, ask for that in writing rather than a longer pipe. The job is the roof room itself, sized for the slope and the glass.
Frequently asked questions
Can you fit a normal wall unit in a sloped bedroom?
Only on a vertical piece of wall tall enough for the unit and the clearance above it. If the slopes leave no such face, the survey should look at a floor console or say the room cannot take a high-wall unit.
Why do roof rooms need a height check?
The outdoor unit is often two storeys below. Manufacturers cap that difference. Past the cap, this room should not be added to a system sitting in the yard.
Will cooling the roof room cool the landing?
Only with the door open, and only a little. The job is the roof room itself, sized for the slope and the glass.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.