Penthouse Design: Space, Light, Terraces and Structure

Good penthouse design makes the most of what only the top of a building can offer: sky, views, daylight from above, outdoor space and a sense of separation from the floors below. It also has to deal with what the top of a building imposes: exposure to sun, wind and rain, a roof to keep watertight, and a structure that was designed for the loads of the floors beneath it.

This article covers the architectural opportunities of a penthouse, the planning of terraces and double-height spaces, and the technical issues that are most often underestimated, particularly structure and waterproofing. It closes with what owners in Singapore need to know before altering a condominium penthouse.

What makes a penthouse

The word comes from the Middle English pentis, a lean-to or annex attached to a larger building, later reshaped by association with “house”. For centuries it meant a modest structure, often a shed or roof enclosure. In the early twentieth century, in New York in particular, the rooftops of apartment buildings were reconceived as the most desirable homes in the building, and the modern luxury penthouse was born.

Today the term covers a range of homes: a single top-floor apartment, a duplex across the top two floors with its own roof terrace, or a set-back pavilion on the roof. What they share is position. A penthouse typically has views on several sides, access to outdoor space, and the possibility of daylight through the roof, which no other apartment in the building has.

Planning the plan: space, light and views

The architectural strengths of a penthouse are worth organising the whole plan around.

Views: living spaces belong where views are best, usually at the corners or along the longest open side. Bedrooms can take more private orientations.
Daylight from above: rooflights and clerestories can light the centre of a deep plan, something not possible lower in the building. They need careful shading and glazing to admit light without excessive heat.
Height: a duplex penthouse often includes a double-volume space, a living room open through two floors, connected by a feature stair and a gallery.
Threshold to outside: wide sliding or folding doors can join interior and terrace so they read as one space.

In a tropical climate these advantages come with a cost: the roof and extensive glazing expose a penthouse to more solar heat than any other unit. Deep overhangs, shaded terraces, high-performance glass and generous roof insulation are essential, not optional. Without them, a penthouse can be the hottest and most expensive home in the building to cool.

Terraces, pools and gardens

Outdoor space is what most buyers value in a penthouse. Penthouse design for terraces involves:

Shade and shelter: pergolas, canopies or deep roof overhangs to make the terrace usable in sun and rain.
Wind: at height, wind is stronger and gustier. Glass balustrades, screens and planting help, and loose furniture and planters must be designed or fixed to resist being blown over.
Planting: roof gardens need adequate soil depth, drainage layers, root barriers and irrigation, all of which add weight. Our article on sky gardens discusses them at a larger scale.
Water: plunge pools, spas and water features are popular and are the heaviest additions a penthouse can receive.

Every one of these has structural consequences, which is why they should be planned with an engineer from the start rather than added later.

The structural side of penthouse design

A roof slab is usually designed for lighter loads than a floor slab. Converting part of a roof into a terrace, adding planters, or installing a pool places loads on it that may far exceed its original design. The figures are straightforward: water weighs about one tonne per cubic metre, so a pool one metre deep imposes roughly ten kilonewtons per square metre of water alone, before the structure, finishes and equipment. Saturated soil in planters is similarly heavy.

Key structural questions include:

Was the roof or terrace slab designed for the intended use, and what does the original structural design allow?
Where are the beams and columns beneath, and can heavy items be positioned over them?
Will removing walls between rooms, or opening a slab for a new stair or double-volume space, affect the structure? Our guide to load-bearing walls explains how to tell.
Can the structure support a private lift, its shaft and machinery, if one is planned?
Are large glazed walls and their frames designed for the higher wind pressures at the top of the building?

In many cases the answer is yes, with care: positioning loads over beams, using lightweight soil and planters, choosing a shallower pool, or adding local strengthening. But the answer should come from calculation, not assumption.

Waterproofing and the roof

A penthouse sits directly below, or on, the roof, and it often has large terraces over habitable space below. Waterproofing is therefore critical. A leak from a terrace or pool can damage the penthouse itself and the units below, and is expensive and disruptive to trace and repair.

Sound practice includes continuous membranes with proper upturns at walls and doors, adequate falls to drains with overflow outlets, protection layers over membranes beneath planters and paving, flood testing before finishes are laid, and access to drains for maintenance. Our guide to waterproofing in construction covers the main systems.

Altering a condo penthouse in Singapore

Most penthouses in Singapore are in strata-titled condominiums. Changes are governed by several sets of rules at once:

The MCST: the management corporation’s by-laws and approval process apply to renovation works, and changes affecting common property or the external appearance of the building usually need the management corporation’s approval, sometimes by resolution at a general meeting.
Planning: enclosing terraces, adding roofs or structures over them, or converting open space to enclosed floor area can affect gross floor area and require URA planning permission.
Building and structural control: structural changes such as new openings in slabs, removing structural walls, pools and heavy planters need a Professional Engineer’s design and, typically, BCA approval.
Fire safety: changes to compartments, escape routes or roof access may need SCDF approval.

Our article on condo renovation rules in Singapore explains the process in detail. Bringing in an architect and engineer early avoids designing a penthouse that cannot be approved or built.

Frequently asked questions

What is a penthouse?

A penthouse is an apartment on the top floor or floors of a building, typically with views on several sides, private outdoor terraces and, often, double-height spaces or rooflights. The term derives from a word for a lean-to annex and took its modern luxury meaning in early twentieth-century New York.

Can I add a pool to my penthouse terrace?

Possibly, but only after a structural engineer has confirmed that the slab can carry it. Water is very heavy, and a pool may exceed the terrace’s design load. Approvals from the management corporation and, for structural works, BCA are usually required in Singapore.

What are the key elements of good penthouse design?

A plan organised around views and daylight, well-shaded and sheltered terraces, sound thermal and solar control, careful waterproofing, and a structure checked for any terraces, planters, pools or openings. In a tropical climate, shade and heat control are especially important.

Can I enclose a penthouse terrace in Singapore?

Enclosing or roofing a terrace may count as additional floor area and require URA planning permission, as well as MCST approval and, where structural works are involved, BCA approval. Check the rules for your development before designing it.

Planning a penthouse renovation with terraces, pools or structural changes? Talk to our consultancy or get in touch for a structural assessment.