Renovating a house near Tibidabo and Vallvidrera: forest, fire risk and the natural park

What limits apply to houses next to the Collserola park?

The park plan does not admit new buildings, existing heritage is kept and improved, and illegally built structures are to be removed progressively. So the first thing to check is the house's legal status and where it stands: inside the park, in the adjoining functional zone, or in the city's built-up land.

The Special Plan for the Protection of the Natural Environment and Landscape of the park (PEPNat) was approved by decision of the Catalan government on 6 April 2021 and published on 9 April 2021. It covers the natural park of 8,156 ha across nine municipalities and a functional area around it of 3,676 ha. Tibidabo and Vallvidrera are part of Barcelona, but the rules for a given plot depend on the zone it lies in. The plan is not paraphrased from memory: it is read in full together with the plot's planning certificate from the city.

You invest cautiously in a house by Collserola bought with an undocumented extension. Check the building licence, the cédula de habitabilidad and that the cadastre matches the real house. A mismatch is a reason to stop and show the papers to a lawyer, not a reason to haggle.

Can you extend a house on a slope?

Inside the park the plan does not admit new buildings, so any increase in volume must be checked against the plan for the specific plot. Count on what already exists: a basement, an attic, extensions within the legal volume. In built-up land outside the park the usual rules apply.

Any extension starts with a request to the city about the plot's planning regime and with a written reply. How to check a building's protection and regime is in the article on the planning certificate. Until then, the design and estimate for an extension are guesswork.

The slope adds engineering. Before foundations and retaining walls a geotechnical study (estudio geotécnico) is carried out, and drainage is calculated together with the plot's drainage. In practice the retaining wall, drainage and earthworks take a notable share of the budget, often more than the extension itself. More on retaining walls, drainage and access on slopes in the article on a house on a slope in the Garraf: the engineering problems are the same.

Does a house in a forest need fire-protection measures?

Yes. Around buildings that border forest, a strip of at least 25 metres is maintained, cleared of dry vegetation, with thinned trees and no undergrowth. The house owner is responsible for the strip, and neighbours must allow the work on their land.

The same requirements apply to unbuilt plots. Access roads are kept clear. For urbanisations the Catalan Interior Department recommends, where possible, two separate roads at least 3 m wide or one at least 5 m wide with verges, and trees along streets are trimmed to 3.5 m so a fire engine can pass. Urbanisations in forest need a self-protection plan.

Beyond the strip, owners usually add measures on the house itself. These are recommendations of practice, not a legal requirement: a non-combustible roof, fine metal mesh on vents against embers, toughened glass and shutters, no timber decking or pergola at the forest edge, clean gutters, the gas cylinder away from walls, and a water reserve with a pump. How this applies to your house and how it is checked is cleared with the city.

How do you bring materials up narrow mountain roads?

With small vehicles on a schedule, transfer before the hard stretch and lifting by lorry crane. A concrete mixer or an articulated lorry often cannot pass a mountain road, and delivery times are planned with a margin.

Before the estimate the route is driven and measured: width and bends, the load limits of bridges and retaining walls on the road, the height of branches. Materials come in batches, and large pieces (stone, glass, kitchen) are planned so they arrive intact. If concrete is needed, you check whether the pump reaches and, if not, pour with skips.

In the high fire-risk season, work that gives sparks or flame near forest (angle grinders, welding, torches) is restricted, and conditions are clarified with the Agents Rurals and the city. It is built into the schedule from the start. If the road is private and belongs to the urbanisation, heavy traffic is agreed with the community, because damaged paving often leads to a claim for compensation.

What about water, drainage and electricity in a house by the forest?

Check the connections before the design: sewer, water pressure, electrical capacity, communications. Mountain houses can differ from those in the city: a septic tank instead of a sewer, low pressure, limited capacity. This shapes the estimate more than the finishes.

If the house is not connected to the public sewer, you look at connecting it or at local treatment under the rules that apply on the plot. Water pressure is tested at peak hours, and a water reserve for fires can be combined with a tank for rainwater and irrigation (see the article on the rainwater tank). Electrical capacity is raised by an application to the distributor, and where there are limits, solar panels with a battery are considered.

A slope takes a lot of water in a downpour. Rainwater from the roof and paths is collected and led away from the house so it does not undermine the foundation or the retaining wall. A storm drain costs less than repairing an undermined plinth.

What about trees, the garden and wild boar?

Trees in the forest and the park are felled and thinned by the rules: a permit is normally needed, and its conditions are clarified with the city and the park's managers. Thinning the strip around the house does not cancel this rule.

A garden by the forest is designed to withstand fire and drought: plants of low flammability, spacing between crowns and no conifer thickets next to the house wall. How to make a Mediterranean garden with minimal irrigation is in the article on that kind of garden. Protecting trees on the plot and felling licences have a separate article.

Wild boar live in Collserola and they come into gardens. The fence is solid at the bottom and has a gate that closes, rubbish bins are locked and no animal food is left outside. This is not about convenience but about damage to the lawn and the irrigation system and about the safety of dogs.

How do you check a house by Collserola before buying and renovating?

Commission an inspection of the house and the plot, request the planning data and documents, and only then work out the estimate. A house by the forest cannot be judged by its interior: the slope, the park zone, the fire strip and the access decide.

BCN YARD runs projects in Russian and Spanish: one person is responsible for the project and payment is by stages under a contract. We have run the full cycle on a private house with a pool and solar panels (2022–2024), but a house by Collserola needs its own calculation. As a price guide: Premium from 1,000 €/m², Luxury from 2,000 €/m² and Signature from 3,000 €/m², excluding VAT; the exact price comes in the estimate after a visit and measurements. We reply to an enquiry within an hour.