How Loads Travel Through a Building Before You Open an Opening

Before opening up a wall, you need to know how loads move through the building and what role that wall has in the chain. In a Lisbon renovation, the same wall may be a simple partition, support an old floor structure or contribute to the building’s stability under horizontal forces. Thickness, a hollow sound when tapped, or a similar doorway on another floor are not enough to decide: the work starts with a technical reading of the building, its existing elements and the proposed alteration.

Contents

1. The load path: from everyday use to the ground
2. Why an apparently light wall may still need attention
3. What changes when you create a passage
4. What to record without trying to diagnose it yourself
5. Before appointing a contractor: a sequence that prevents costly decisions
6. Where DIY ends and technical responsibility begins

The load path: from everyday use to the ground

A home is constantly transferring forces. The self-weight of floors, walls, finishes and equipment is added to people, furniture and everyday use. In many buildings, loads pass from the slab to beams, then to columns or load-bearing walls and finally to foundations and ground. In older masonry buildings, the route can be less obvious: timber joists may bear directly into walls, while connections between floors, walls and roof are central to the behaviour of the whole building.

There are also horizontal forces, such as wind and earthquakes. They do not necessarily follow the same route as vertical loads. Walls, floors and connections help the building act as one system, so removing a partition without understanding its role can change how forces are redistributed. The Lisbon municipal guide on removing walls explains that even non-load-bearing walls can contribute to bracing and force redistribution.

Why an apparently light wall may still need attention

Lisbon’s building stock includes very different systems: reinforced concrete, load-bearing masonry, timber floors, mixed construction and buildings altered repeatedly over decades. A thin wall may be a lightweight partition, but a plastered wall may conceal masonry, an embedded beam, services or earlier alterations. Greater care is needed near staircases, façades, party walls and walls that line up from one floor to another.

Lisbon City Council notes that it is not always straightforward to distinguish a structural wall from a non-structural one. Its list of potentially relevant elements includes columns, beams, structural walls, floors, foundations, stairs and roofs. Read the municipal seismic-strengthening FAQs before accepting the idea that the answer is simply to “open it and add a beam”.

Visual comparisons are unreliable too. An opening in a neighbouring flat does not prove that the same cut is appropriate in yours. It may sit below a different beam, result from an undocumented earlier intervention, or conceal a defect that has not yet become visible.

What changes when you create a passage

When a wall is removed, any load that used to pass through that location needs another route. If the wall has a structural role, the solution may require a beam, new side supports, foundation work or a different layout altogether. A beam is not an automatic fix: it has its own weight, needs supports with sufficient capacity and can concentrate forces that were previously more spread out.

In a timber-floor building, opening a wall can also interfere with joist bearings or with floor bracing. In masonry buildings, cutting walls and Pombaline cage elements without proper assessment can reduce seismic performance. The Council specifically warns that the so-called “miracle beam” must be assessed by a specialist because it can reduce earthquake resistance.

If the aim is to connect rooms or two separate flats, also read what to check before joining two Lisbon apartments. The structural decision comes before selecting sliding doors, finishes or the final shape of the opening.

What to record without trying to diagnose it yourself

Cracks, doors that no longer close, sagging floors, repeated patches or walls out of plumb cannot, on their own, identify a cause. They can still guide a technical survey. Photograph them with dates, mark their position on a simple plan and note whether they appeared after building work, water ingress or a change in loading.

Also gather useful information for the person carrying out the assessment: approximate construction date, available plans, previous works, pipe-stack locations, position of the staircase and whether walls line up on floors above and below. Do not cut exploratory chases into suspect walls, remove pieces of masonry “to see what is inside”, or treat one crack as proof that a wall is structural.

In older properties, cuts made for pipes or cables can have outsized consequences. Municipal repair guidance notes that cutting floor beams and removing structural walls can cause damage that is difficult or impossible to reverse through a simple repair.

Before appointing a contractor: a sequence that prevents costly decisions

1. Define the purpose. State the width, height and intended use of the opening; a small daylight connection does not necessarily call for the same solution as a wide kitchen-to-living-room opening.
2. Collect what exists. Plans, photographs of earlier work, condominium information and access to relevant spaces reduce uncertainty.
3. Commission the right assessment. Where stability is affected, specialist design documentation may include a structural project, as indicated in the municipal information on specialist projects.
4. Agree the construction method. Temporary propping, demolition sequence, protection of common areas, rubble removal and reinstatement should be set out.
5. Coordinate the site. The designer, contractor and subcontractors need to work to the same solution, without improvised changes on site.

For concrete structures, execution is framed by NP EN 13670, referred to in Decree-Law No. 90/2021. This shows why a structural solution is more than choosing a steel section: design, materials, execution and control form one connected task.

Where DIY ends and technical responsibility begins

Painting, replacing skirting or dismantling a loose cabinet are very different tasks from demolishing a wall, cutting a beam, making deep service chases or introducing a concentrated load. Stop the work and obtain technical advice if there are significant cracks, decayed timber, persistent moisture at bearing points, visible corrosion, floor deflection, uncertainty about the wall’s role or a need for temporary propping.

A useful kick-off meeting should also establish what cannot be changed without approval. See the decisions to set at the start of a renovation and confirm who approves changes, who monitors the structural sequence and how unexpected issues are recorded. A wall is only “simple” once a competent assessment has shown that it is.

Key takeaways

• Do not infer a wall’s role from its thickness, sound or an opening seen in another flat.
• Creating an opening changes the load path; a beam needs properly designed supports and execution.
• Photos, plans and existing warning signs help the specialist but do not replace a structural assessment.
• Set out propping, demolition sequence and approvals before work begins.

If your Lisbon renovation involves opening or altering a passage, speak to Obra Lisboa before appointing the work so the scope, site sequence and technical requirements can be set out in the proposal.

Sources and further reading

• Lisbon municipal guide on removing walls
• municipal seismic-strengthening FAQs
• municipal information on specialist projects
• Decree-Law No. 90/2021

Editorial image; it does not depict an Obra Lisboa project.