Communal heating or triple glazing: which costs a developer less?
Updated: 3 days ago
A planning authority told our client that individual heat pumps would only be acceptable with triple glazing. We were asked to work out which of the two compliant routes was cheaper. Communal heating added £1.56m. Triple glazing added £0.54m. The saving from the glazing route was £1.02m, about 2% of the scheme cost.
London Plan policy pushes new residential schemes towards communal and district heating. In practice, the first thing a developer sees when a communal system is proposed is the energy centre, and the first question is what it adds to the build cost. The second is the sales area lost to the network. Coupled with the recent requirement for a second staircase, that is a significant loss of value and a further pressure on the viability of a scheme. The question has become more pointed as individual air source heat pumps have improved, because an all-electric scheme can now meet carbon targets without a heat network at all.
We were recently asked to look at this for a client on a two-block residential scheme in south London consisting of 179 apartments over 12 and 16 storeys. Our cost plan assumed an individual air source heat pump in each apartment, serving underfloor heating and hot water, with double-glazed aluminium windows. The Greater London Authority then indicated that it may accept individual heating only if the scheme goes to triple glazing. That left two routes to a compliant scheme:
Option A: communal heating with double glazing.
Option B: individual heat pumps with triple glazing.
Both are additions to the same base cost plan, so the comparison is straightforward. Here is how we built it up, from limited design information.
Option A: what communal heating really adds
The M&E engineer set out what a communal air source heat pump system would need: an 80m² plantroom at ground floor with 4m clear height, 100m² of roof plant with a 1.5m screening zone around it, two new 800mm x 800mm heating risers in each block and a further riser linking the plantroom to the roof. That list is the useful starting point, because the cost of a communal system is as much about the building work it requires as the plant itself.
The roof-mounted heat pumps, thermal stores, pumps, heat exchangers, controls, primary pipework to every apartment and heat metering came to between £1.4m and £1.7m before the M&E subcontractor’s own preliminaries. Against that we could omit the 179 individual heat pumps, worth just under £1m, and trim the electrical supply to each apartment. The hot water cylinder in each flat becomes a heat interface unit at broadly the same cost, so that line was a straight swap. The net system delta was £390,000 to £770,000.
The knock-on builders work is the part that is easy to miss. The plantroom needs a fire-rated, acoustically lined, bunded enclosure with louvres and drainage. The roof deck needs structural strengthening, plinths and a louvred acoustic screen. The risers need shaft walls, fire-stopping at every floor and access doors, across 72 riser floors. The plant deck also displaces around 40% of the roof-mounted PV the base scheme relied on. Those works came to £500,000 to £730,000.
With main contractor preliminaries, overheads and profit and contingency applied at the same percentages as the base cost plan, the communal option added between £1.16m and £1.96m, or 2.3% to 3.9% of the scheme cost.
Option B: what triple glazing really adds
On a tower the windows are aluminium framed, and on an aluminium system the move from double to triple glazing is mostly a change of glass unit and hardware rather than a new window. The triple-glazed unit is thicker and roughly 50% heavier, so the glazing pocket is deeper, and the friction stays and locking gear on opening lights are heavier. We priced that at £90 to £140 per m² on top of a £700 per m² double-glazed allowance, across 2,529m² of windows.
The balcony doors needed separate treatment. They are 1.8m by 2.1m sliding screens, one per apartment, and at that size a triple-glazed leaf is heavy enough to push most systems from a standard roller onto lift-and-slide hardware with a heavier track and threshold. The uplift there is proportionately larger, £150 to £250 per m², or roughly £570 to £950 per door.
With the same on-costs applied, triple glazing added between £430,000 and £680,000, or 0.9% to 1.4% of the scheme cost.
The comparison
Additional cost over the base cost plan, including preliminaries, overheads and profit and contingency. Indicative figures at Q4 2026 prices.
Option | Low | Mid | High |
A: communal heating with double glazing | £1,163,000 | £1,564,000 | £1,965,000 |
B: individual heat pumps with triple glazing | £431,000 | £541,000 | £685,000 |
Saving from Option B | £732,000 | £1,023,000 | £1,280,000 |
Saving per apartment | £4,100 | £5,700 | £7,200 |
Individual heat pumps with triple glazing were cheaper at every point in the range. Even in the least favourable case, with communal heating priced at the low end and triple glazing at the high end, Option B was still around £480,000 ahead. The result is not sensitive to the rates: a communal system carries a fixed energy centre and distribution cost that a glazing uplift does not approach.
What the construction cost does not show
The communal option also removed around 33m² of saleable floor area to the new risers, roughly one studio apartment. The 80m² plantroom was larger than the residents’ lounge it would have displaced, or it would have cost car parking instead. The roof plant took 170m² of amenity and PV area. And a heat network brings the scheme into the Ofgem regulatory regime, with an operator to appoint, metering and billing to run and a long-term heat tariff for residents.
Triple glazing, by contrast, added 40 to 50 tonnes of dead load for the structural engineer to check, a slightly longer lead time on the sliding screens and a Part O overheating assessment to re-run. None of it was material.
Three things to take from this
Price the building work, not just the plant. On this scheme the knock-on builders work was as large as the net system cost. An M&E cost alone would have understated the communal option by half.
Treat the balcony doors separately from the windows. The hardware change on a large sliding leaf makes the triple glazing uplift on doors nearly twice that on windows per square metre.
Check what the glazing is for. If the authority’s concern is overheating rather than heat loss, solar control glass on a double-glazed unit is a cheaper route. If it is acoustics, an asymmetric acoustic double-glazed unit will usually outperform standard triple glazing. The specification should be aligned with the reason for the request.
None of this argues against heat networks in principle. Where a scheme can connect to an existing or planned network, the developer’s capital cost falls to the secondary side and a connection charge, and the picture changes. But where the choice is between building a standalone communal system and upgrading the envelope, the envelope is usually the cheaper way to a compliant scheme, and the numbers are worth running before the planning position hardens.
Facing the same question?
We can run this comparison on your scheme from a cost plan and an M&E brief, normally within a week. Contact mark@qsetc.uk.
About these figures. The figures in this article are indicative, drawn from a specific scheme at Q4 2026 prices, and have been rounded. They should not be applied to another project without a scheme-specific assessment.
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