Patio Extensions in Perth

Nothing gets designed until the existing structure is checked. Post sizes, beam depth, footing type, sheet profile, fall and the condition of the fixings all go on the list.

The critical question is whether the existing frame can carry more. Extending outward changes the load path, and a beam sized for a three metre roof does not automatically suit a five metre one.

Original approval documents help enormously. If the patio was permitted, the engineering that goes with it tells us exactly what we are working with instead of having to assume the worst.

Where there is no paperwork, we assess on site and design conservatively. That sometimes means the extension gets its own posts rather than leaning on the old frame.

Extending depth, away from the house, is the more involved of the two. The existing fall continues into the new section, which means the front beam ends up lower and head height at the outer edge drops.

That is the constraint people underestimate. Adding three metres of depth at 1:30 takes another hundred millimetres out of the beam height, and on a low patio that can be the difference between comfortable and cramped.

Extending sideways is usually easier. The new section runs at the same fall on the same plane, so the roof simply gets wider and head height is unchanged.

Where depth is wanted but height will not allow it, the answer is often a separate stepped plane rather than a continuation of the existing one.

Colorbond colours are consistent across the range, so a new sheet in the same colour will match a new sheet. Matching a fifteen year old roof is different.

Weathered Colorbond fades, particularly in strong WA sun and particularly in the darker colours. A perfect colour code match can still look slightly different for the first year or two.

There are ways to hide it. Running the new sheets as a distinct plane with a flashed step, or extending sideways so the join falls on a natural line, both work better than trying to butt new sheet against old.

Profile matching is the other issue. Discontinued profiles do exist, and where an exact match is unavailable a deliberate change with a clean junction beats a near-miss.

The join has to be watertight and it has to look intentional. Where the extension continues the same plane, sheets are lapped in the direction of fall with the lap sized for the pitch.

Where the planes step, a flashed upstand carries water from the upper roof onto the lower one. That detail is more forgiving of a colour or profile mismatch and often looks better.

Structural continuity matters too. The purlin that was the end of the old roof usually becomes an intermediate support, and it needs checking for its new role rather than being assumed adequate.

The honest answer is usually no, at least not for the new area. The old footings were sized for the old tributary area, and a larger roof puts more uplift and more load on the same pads.

The old posts often stay where they are, becoming intermediate supports within the enlarged roof. That is a good outcome, because it avoids disturbing paving that has been down for years.

New posts then take the new perimeter, with their own engineered footings. The engineer checks the whole assembly rather than only the new part.

Where the old footings are genuinely inadequate for the new loads, they get supplemented. Digging beside an existing post is not glamorous work, and it is cheaper than the alternative.

This is the part most people forget. A roof that grows by fifty per cent produces fifty per cent more water in the same downpour, arriving at the same gutter.

So the gutter gets reassessed. A quad gutter with one downpipe that handled the old roof may need a deeper profile, a second downpipe, or both.

The soakwell has to grow too. Councils require on-site stormwater disposal sized to the catchment, so an extension almost always means additional soakwell capacity rather than plumbing into the existing one and hoping.

Overflowing gutters undermine footings and soak the wall of the house. It is a slow, expensive failure that starts with a decision to save a few hundred dollars.