Enclosing a penthousewithout building work.

Yes, you can: glass curtains, retractable roofs and pergolas fix to the floor, the parapet or the existing structure, with no new walls. No building work does not mean no paperwork, because the town hall and the community still have a say. On a penthouse the deciding factor is wind, which pushes harder the higher the terrace is.

Without building work means without masonry: no new partitions, no demolition and no changes to the building’s structure. The system arrives made to measure and is bolted to what is already there. On a penthouse terrace that is usually the floor, the perimeter parapet or the slab above, if there is one. Installation takes days rather than weeks, and you can live in the flat throughout.

What does change on a penthouse is the demand placed on the system. The terrace is more exposed to wind and sun than one on the ground floor, often has no roof and comes with views nobody wants to block. So the decision starts with two questions: what happens overhead, and how much wind the facade takes. The usual combinations are on our page about penthouse enclosures.

In everyday terms, no building work means no rubble and no bricklayer. Light enclosure systems are made in the workshop from aluminium profiles and toughened glass, and on the terrace they are only assembled. The bottom track is screwed to the floor or the parapet, the top one to a beam, a ceiling or the system’s own frame. No wall goes up and none comes down.

No masonry does not mean nothing is touched. The fixings drill into the floor finish or the parapet, and every hole passes through layers that keep water out of the home. A good installation seals each fixing and keeps the fall of the floor so that rain still runs to the drain. That detail is settled at the survey, not on installation day.

• No building work: bolted tracks, glass panels, aluminium profiles, sealed fixings.
• Building work: opening or filling a wall, putting up partitions, moving drains, strengthening the slab.
• Grey area: replacing the floor finish or raising the parapet for a higher balustrade.

The Basic Document SE-AE of the Spanish Technical Building Code (CTE) works out wind pressure on a facade as the product of three factors: the dynamic pressure of the location, an exposure coefficient and a shape coefficient. For the dynamic pressure it allows a simplified value of 0.5 kN/m² anywhere in Spain.

The exposure coefficient is the one that penalises penthouses. It rises with height and with how open the surroundings are. According to table 3.4 of the same document, at 30 metres on the seafront it is 3.7, while at 3 metres it is 2.4. In a built up urban area it goes from 1.3 to 2.6, which is double. With the same formula, the pressure on the glass rises in the same proportion.

All LUNEKS systems mount onto what is already there, and they combine: some close the sides, others deal with the roof. On a penthouse the usual starting point is the perimeter, because the wind comes in from the side. Then you decide whether a roof is needed, and what kind, depending on how you want to use the terrace in winter and in summer.

Glass thickness, the type of fittings and the spacing of the fixings are worked out for the exposure of each facade, with the Technical Building Code table as the starting point. Two penthouses in the same building can need different solutions if one faces the sea and the other a narrow street. Systems LUNEKS fits on penthouses and their size and wind limits

• Glass curtains: panels with no vertical profiles that stack to one side; they block the wind and keep the view.
• Frameless sliding glass: panes that glide on tracks, for openings with no room for a stack.
• Retractable roofs: a glass roof that opens on good days and keeps the rain off.
• Bioclimatic pergola: adjustable louvres that control sun and airflow.
• Insulated glass curtains: to use the penthouse as a room in winter too.

Not always. The AEMET climate averages for Alicante for 1981 to 2010 give 311 mm of rain a year, spread over about 37 days with more than 1 mm. With so few wet days, many penthouse terraces are enclosed only at the sides with glass curtains and left open to the sky. The wind stops being a nuisance and the view stays.

The sun is a different matter. The same station records 2,851 hours of sunshine a year and an average August high of 30.8 °C. On a penthouse with no shade the floor and the glass heat up, and a side enclosure with no roof does not fix that. If the terrace is used at midday in summer, a bioclimatic pergola or a retractable roof with solar protection usually matters more than the rain.

A penthouse terrace is often the roof of the flat below as well. That double role means looking closely at where each fixing goes and where the water runs. Most problems that appear after enclosing a penthouse do not come from the glass but from a badly sealed fixing, or from a drain left inside the enclosure with no way out.

• Waterproofing: where the membrane is and how each hole will be sealed.
• The parapet: solid masonry, block or a metal balustrade, and whether it is level.
• Drains and floor fall: water has to keep running away with the enclosure in place.
• Access for installation: lift, stairs and the size of panel that will fit.
• The community and the town hall: an enclosure up high can be seen from the street.

No. Under the Horizontal Property Act, enclosing a terrace alters the building even without masonry: Article 10.3.b names it explicitly, and Article 17.4 requires a vote of three fifths of owners and shares. When the penthouse can be seen from the street, the owners meeting tends to look at the design more closely.

At the town hall a light system usually goes through a responsible declaration or a minor works licence, depending on the municipality. We cover the rules of Alicante, Valencia and Murcia in the article do I need a permit to enclose my terrace, and more briefly on the page about enclosure permits.