DB-HS: health and hygiene in the Spanish building code

Section	Requirement	What it translates into
HS 1	Protection against moisture	Waterproofing grade of walls, floors, façades and roofs
HS 2	Waste collection and disposal	Storage and handling spaces for waste
HS 3	Indoor air quality	Ventilation flow rates and the systems to achieve them
HS 4	Water supply	Sizing and conditions of the plumbing network
HS 5	Wastewater drainage	Foul and rainwater drainage networks
HS 6	Protection against radon	Barriers and systems in priority action municipalities

Three sections concentrate the application questions and the design impact, and have their own article: moisture protection under HS 1, ventilation under HS 3 and radon protection under HS 6. The other three are settled with the usual services documentation.

HS 1 works by waterproofing grade: each element in contact with water or the ground is assigned a grade according to exposure, and that grade determines the admissible construction solutions. It is a section where the cost of error is deferred: insufficient waterproofing is not noticed at handover, it is noticed at the first pathology.

HS 3 works by flow rate: it sets the required air flow rates per room and type of use, and leaves the choice of system to the design, from hybrid ventilation to mechanical double-flow with heat recovery. It is the section with the strongest interaction with the DB-HE, because ventilating costs energy and that energy counts in the energy verification.

HS 6 works by territory: the requirement is triggered when the municipality appears in the appendix of priority action municipalities, classified by zones, and is satisfied with protection barriers, ventilated cavities or depressurisation systems depending on the zone and the building type. It is the most recent requirement of the document and the one that generates the most budget surprises for developers who discover it late.

DB-HS items concentrate in four packages. Waterproofing and drainage in the buried envelope, façades and roofs, where section HS 1 sets the performance level. Ventilation, with ducts, grilles, extract units or treatment units depending on the chosen system, a block that in residential can sit between 1.5 and 4 % of the PEM (presupuesto de ejecución material, the direct construction cost). Plumbing and drainage, whose regulatory sizing HS 4 and HS 5 govern. And, in affected municipalities, the radon solutions, a modest item in well-planned new construction and an expensive one as a retrofit.

The document's general budget rule is that these are low-visibility, hard-to-skip items: almost none appears in a development's sales pitch, almost all appear in the pathologies when missing. Cutting them in the budget moves the cost to the warranty period.

The first is treating waterproofing as a brand name rather than a performance grade: section HS 1 requires justifying the waterproofing grade, and the chosen solution must demonstrate it. The grade required depends on the presence of water and on the type of wall or floor.

The second is sizing ventilation by habit instead of by flow rates: systems inherited from previous projects rarely match the required flow rates and the energy verification of the specific building. Flow rates are calculated for the specific building and condition its energy demand.

The third is not checking the municipality against the radon appendix at project kick-off: a minutes-long check that avoids a change order. The check belongs to the appointment, not to the detailed design.

The fourth is forgetting coordination with the rest of the code: HS 3 ventilation counts in the DB-HE, and the HS 4 and HS 5 service penetrations cross DB-SI fire compartments and must be sealed accordingly. All three documents are verified against the same construction solutions.