Furniture and plant pots on a walk-on rooflight: what the glass will carry

A walk-on rooflight is designed around a stated load, and everything you put on it is measured against that number.

The glass in a walk-on panel is a stack of laminated layers, thick enough to take a person's weight without flexing much. The manufacturer publishes a rated loading for each build, and our page on walk-on glass load ratings explains how to read it. That rating is written for foot traffic. A chair with a person in it is still foot traffic, more or less. A stone planter holding wet compost is a different kind of load altogether.

Two things matter about any object. One is its total weight. The other is how that weight reaches the glass. A sofa weighs a great deal but rests on four feet, each of which is a small patch of contact. A rating for foot traffic assumes a load spread over roughly the area of a shoe. Narrow feet press harder on each square centimetre than the same weight on a wide base.

When we survey a terrace, we ask what you expect to put on the glass, and we write the answer into the specification. If a dining set is part of the plan, the glass build is chosen for it from the start. That costs far less than discovering afterwards that the panel was sized for occasional footsteps.

Lightweight, wide-footed pieces are the safe end of the range, and a few habits keep them that way.

Think of a pair of folding chairs, a small bistro table or a slatted bench. They are light, and the feet can be fitted with soft pads. Soft feet do two jobs. They stop hard plastic or metal edges from scratching the surface, and they spread each point of contact over a wider area. Felt or rubber pads are cheap, and worth replacing once they wear through. Our page on whether walk-on glass scratches covers the marks that grit can leave, which is the reason for the pads.

Some things that seem harmless deserve a second look:

• Metal chairs with bare feet. Dragged across the pane, they carry grit with them. Lift them instead of sliding them.
• Loungers with small wheels. Each wheel is a tiny contact patch under a heavy person. Choose a model with flat feet.
• Parasol bases. These are often heavy and stand on a small plate. Put the base on the roof surface beside the glass.
• Barbecues. Heat, hot fat and a heavy frame on legs are a poor match for any glazing. Keep them on the terrace deck.

Sliding is the habit to drop. Glass tolerates a steady load well. It resents grit being ground across its face, and a scratch on the top surface is permanent. A quick sweep before you set anything down costs nothing.

Pots are awkward because they are heavy when watered, they leak, and people leave them in one place for months.

A small terracotta pot of herbs is a modest load and a modest risk. A large glazed pot of shrub and soil is another matter. Wet compost weighs far more than it looks, and the base of the pot is a hard ring pressing on a small area. Stone and cast troughs are heavier still. Keep anything like that on the surrounding roof surface, where the decking or pavers sit on a proper support system.

Water is the second concern. A pot left on glass drains onto it, and standing water leaves a ring of lime scale as it dries. That ring is cosmetic, but it is easy to avoid with a saucer and a little airflow underneath. Plant feed and leaf litter also stain, and a pot pressed against the glass edge can trap damp against the sealant line. Our advice on cleaning and caring for walk-on glass shows what to use on those marks.

Then there is light. A rooflight exists to bring daylight into the room below, and a pot sitting on the pane shades it. A row of planters along one edge can darken the room more than you would expect. If you want green on the terrace, arrange the pots so the glass stays clear and the room below keeps its daylight. That matters most over a kitchen or a loft bedroom, where the glass is often the brightest thing in the space.

Heavy items belong on the structure, and the simplest way to give them somewhere to sit is to plan the terrace around the glass.

The table below sets out the usual placement for common terrace items.

A well-designed terrace often leaves a band of solid surface around the glass for exactly this reason. You walk across the pane for the light, and you stand furniture on the deck. Our page on walk-on rooflights for roof terraces shows how the glass and the decking are usually laid out together, and the page on sizing a walk-on rooflight covers how big the panel needs to be for the room below.

If you already own a heavy planter and want it on the terrace, tell us before the survey. We can place the glass away from where it will stand, or confirm a build that was chosen for that loading.

Because we specify for quiet as well as light, there is a noise side to this, and it is mostly about hard feet.

A chair dragged across the terrace makes a noise in the room below, and on glass the sound travels straight down. Heavy glass and a laminated build damp that a good deal, but bare metal feet still scrape. Soft pads quieten it at the source. The upstand and the support around the panel also affect how much footfall reaches the ceiling below, which is covered in our page on keeping the room below a walk-on rooflight quiet.

The quiet spec we write with every quote names the glass build, the seals and the upstand, so the room below is considered alongside the terrace above. If furniture is part of how you will use the space, say so at the survey and it goes into the note. You can get a quote for the glass and we will include the loading we specified it for.

Can I put a rug or mat on the glass?

A breathable mat is fine for a short time, but a rug left down traps damp and grit under it. Anything that holds moisture against the glass and sealant is best lifted regularly, and an outdoor rug should never be pinned at its edges to the frame.

Is it safe to host a party on the terrace?

The loading rating is for people standing and walking. A crowd in one spot is a greater load than one person, so check the rating for your build. Our page on whether a walk-on rooflight is safe to stand on explains what the rating covers.

Will furniture void the guarantee?

Our 10-year workmanship guarantee covers our installation work. Using the glass within the loading it was specified for keeps you inside the terms, which is another reason we write the intended use down. Details are on our guarantee page.

What about a planter box built into the terrace?

A fixed planter is best built on the structure beside the glass, with its own drainage. That keeps soil, water and weight away from the pane. The full service is described on our walk-on rooflight installation page.