CareHomeDeskCareHomeDeskExtensive sedum systems are lighter than most people assume, but 'lighter' is not 'light enough without checking' -- the structural assessment a retrofit needs before anything else.
A lightweight extensive sedum system typically adds in the region of 40-60 kg/m2 for the lightest build-ups, with standard extensive sedum systems more commonly in the 60-100 kg/m2 range once saturated after rainfall (the wet weight, not the dry weight, is the figure that matters for structural loading). An intensive green roof -- one supporting shrubs, grasses or a genuinely landscaped area rather than a shallow sedum mat -- typically exceeds 100 kg/m2 and is a materially larger structural undertaking. For a care home retrofit, an extensive sedum system is almost always the realistic option; intensive systems are generally new-build decisions, not retrofits onto an existing flat roof.
General guidance figures suggest a minimum load-bearing capacity in the region of 75 kg/m2 as a rough threshold for a standard extensive sedum system, but this is not a substitute for an actual structural assessment of the specific building -- roof construction (timber, concrete or steel deck), span, age and current condition all affect what a given roof can actually carry, and general figures from a supplier marketing sheet should never be treated as a design calculation. Commission an assessment from a structural engineer before committing to a green roof retrofit on any existing building; this is a genuine go/no-go gate, not a formality, since retrofitting additional dead load onto a roof that cannot bear it is a serious structural safety issue, not a maintenance one.
A green roof system sits on top of, and must be compatible with, the existing waterproofing membrane -- installing a green roof over a membrane that is already near the end of its service life simply buries a roof that will need to be stripped out again in a few years, at far greater cost and disruption than replacing the membrane first would have been. Commission a proper condition survey of the existing membrane (see the flat roof condition survey guidance elsewhere in this topic) before specifying a green roof retrofit, and budget for membrane replacement first if the survey shows it is needed, rather than treating the green roof as a way to avoid that cost.
Beyond the general sustainability and biodiversity case, a green roof retrofit on a care home has some specific practical advantages worth weighing against the cost and structural constraints: it protects the waterproofing membrane beneath from UV degradation and thermal cycling, which can genuinely extend the service life of the membrane; it provides a measure of additional thermal buffering against summer overheating in the room below, relevant given the vulnerability of an elderly resident population to heat; and where a green roof is visible from upper-floor windows (rather than only accessible for maintenance), it can provide a genuinely calming outlook for residents. None of these benefits removes the requirement for the structural assessment above -- they are the reason to commission one, not a reason to skip it.
CareHomeDesk gives you compliance checklists, maintenance logs, and contractor management tools built around exactly this kind of knowledge.