HS 1: moisture protection

The section does not prescribe universal waterproofing: it grades. For each type of element at risk, walls in contact with the ground, floors, façades and roofs, it defines a minimum waterproofing grade depending on the specific element's exposure conditions, and associates with each grade a repertoire of accepted construction solutions, described through coded combinations of conditions.

The exposure variables are specific to each element. In walls and floors in contact with the ground, the grade depends on the presence of water, low, medium or high according to the position of the lower face relative to the water table, and on the ground's permeability coefficient. In façades, on the area's rain exposure grade, a combination of the rainfall zone and the wind exposure grade according to the building's height and surroundings. Roofs receive in practice the most demanding treatment, with detailed conditions of build-up, slopes and singular points.

This architecture has a methodological consequence: the waterproofing grade is not chosen, it is determined. The design that starts by choosing the commercial solution and then seeks its justification inverts the document's order and usually ends up justifying the unjustifiable.

In the buried envelope, the accepted solutions combine, according to grade, external or internal waterproofing, drainage, membranes and moderate-shrinkage concretes, with additional conditions at junctions, joints and service penetrations, which is where water finds its real path. The economic golden rule of this front is brutal in its asymmetry: waterproofing the outer face of a buried wall costs a membrane and its careful execution; repairing it afterwards means excavating or giving up the external solution. Few budget items buy so much peace of mind for so little.

The section's boundary with buried networks is worth keeping in mind: HS 1 protects the construction element against ground water; the organised removal of water belongs to section HS 5 and the drainage networks. Both are designed together even though they are justified separately.

In façades, the required waterproofing grade translates into combinations of conditions on the external finish, the composition of the main leaf, the presence of an air cavity and additional barriers. The market's real repertoire, rendered masonry façades, external insulation systems, ventilated façades, fits those combinations naturally, and the designer's vigilance must concentrate where the section insists: the singular points. Ground-level starts, junctions with joinery, sills, movement joints and copings concentrate real façade pathology, and their construction conditions are defined in the document with a level of detail that surprises whoever has only read the tables.

The roof is the most punished and most regulated element. The section sets its complete functional build-up, from deck to protection, with the waterproofing system as the critical layer, its admissible slopes by type, and the treatment of the constellation of singular points that decides a roof's real life: junctions with walls, outlets, joints, anchors and penetrating elements. Flat or pitched, trafficable or not, conventional or inverted, green, each variant has its regime, and the quantities must reflect that complexity: a well-budgeted roof is measured by layers and with its singular points counted, not as an area times a price.

As an indicative order of magnitude, moisture protection as a whole sits between 1.5 and 3.5 percent of the PEM (presupuesto de ejecución material, the direct construction cost) in ordinary residential, with the roof as the dominant block. In the method of the article on the cost of CTE compliance, it is the canonical example of deferred regulatory cost: cheap to comply with, extremely expensive not to, because moisture is the first cause of pathology and claims in building, and its repairs are paid at finished-building prices.

The section also dialogues with its neighbours: the ventilation of cavities and rooms, covered in the article on HS 3, participates in condensation control, and the radon barriers of the article on HS 6 share a working plane, the building's base, with this section's membranes, an evident invitation to resolve both requirements with a joint design. A joint design of the building's base saves layers and avoids incompatibilities.

The first is inverting the method: choosing the solution before determining the grade, with forced justifications and protection inadequate by excess or default. The grade is determined before any catalogue is opened.

The second is measuring waterproofing by square metres of surface and forgetting the singular points, which concentrate the cost of careful execution and the pathology when missing. Junctions and corners are measured as items in their own right.

The third is accepting on site substitutions of membrane or system for commercial equivalents without verifying that the substitute demonstrates the same grade. Equivalence is demonstrated with documentation rather than the supplier's word.

The fourth is neglecting the junctions between elements of different sections, the façade's start on the buried wall, the roof parapet against the façade, no man's land between trades where water thrives. Those details are drawn and assigned to a specific trade.

The fifth is treating condensation as the user's problem: the insulation and ventilation pairing that controls it is design matter, and the mould stains of the first winters are almost always design pathology, not usage pathology. The pairing is resolved in the design and checked during execution.