Underfloor Heating Upstairs in a Renovation

Why upstairs is a different job

Ground-floor renovations often sit on solid slabs. First floors and many extensions sit on timber joists with a deck above and a ceiling below. Weight, deflection, access and fire/acoustic details all change.

A system that is perfect in a new screed can be the wrong product upstairs. Start with construction, not with a favourite board from the ground-floor quote.

Main upstairs options

System families overview: systems explained · renovation framing: best system for renovations.

Between-joist plates — detail that decides performance

Plates only work if heat reaches the room. That means:

• •Contact between plate and underside of the deck (or correct detail for the product)
• •Insulation below the heated plane so you are not heating the room underneath
• •Pipe spacing and loop lengths that match room heat loss
• •Clear route to a manifold without crushing or kinking pipe

Poor plate contact and missing void insulation are classic “upstairs feels weak” causes — not a mystery of first-floor physics.

Floor height upstairs

Overlay on the deck raises finished floor level. That hits:

• •Door clearances and ironmongery
• •Stair nosings and top step
• •Built-in cupboards and skirtings

Between-joist systems keep the deck level if the void is used — often the reason they win when height is tight. Measure before you order boards.

Access: above vs below

From below (ceiling down): plates and insulation can be fitted if the room underneath can be opened. Messy but sometimes the only path in a finished bedroom.

From above (deck up): more control, structural boards become realistic, and you can fix joist issues while you are there.

Programme and decoration cost often decide this more than pipe preference.

Same heat source, same design rules

Upstairs zones still need design output at the flow temperature you will run. On a heat pump that usually means low flow temperatures and steady controls — not cranking the manifold because “bedrooms always feel cold.”

• •Room heat loss still drives pipe spacing and flow
• •Manifold balancing still prevents starved loops
• •Mixed ground-floor overlay + upstairs plates is normal — commission both

If upstairs never gets there: cold spots · not warming fast enough.

Acoustics, fire and neighbours

Opening ceilings between flats or party floors raises acoustic and fire detailing. Even in a single house, think about:

• •Pipe noise / expansion at night in quiet bedrooms
• •Maintaining required separation where regulations apply
• •Not drilling chaos through joists without knowing what you are cutting

This is where a competent installer earns the fee — not only clipping pipe.

Devon & Cornwall upstairs patterns

• •Low ceiling heights and tight staircases — height is often the binding constraint
• •Older joists, uneven decks, mixed repairs over decades
• •Bedrooms over unheated or partially heated spaces — insulation in the void is non-negotiable
• •Whole-house heat pump projects that only upgrade the ground floor leave upstairs on tired radiators — plan both if budget allows

Decision sequence (upstairs)

1. Confirm joist direction, centres and deck type
2. Decide access: ceiling down, deck up, or both
3. Measure finished height limits at doors and stairs
4. Choose plates vs overlay vs structural boards
5. Detail insulation below the heated plane
6. Design loops for room heat loss at target flow temperature
7. Plan manifold position and pipe routes
8. Commission and balance with the rest of the house

Honest bottom line

Frequently asked questions