Free tool
Deck roof calculator
A deck roof keeps the summer sun off your deck and windows, but set too low it can block the winter sun the house needs. Put in your address, the size of your wall and the deck roof, and see where the sun lands in summer, spring and winter, at midday or any time of day.
1. Where is the window?
Type your NSW address, then tap the boundary your wall runs along on the lot plan.
Until you pick an address, the drawing shows a north facing window on the Central Coast.
2. Set the wall up like yours
Drag the round points, or type a size into any grey box on the drawing. All sizes are in millimetres.
NSW clock time, with daylight saving in December.
Or type the sizes here
3. What the midday sun does
Summer, 21 December
Sun 80° above the horizon at midday (12:52 pm).
Window in shade: 100%
No sun on the floor inside.
Spring, 21 September
Sun 56° above the horizon at midday (11:48 am).
Window in shade: 100%
No sun on the floor inside.
Winter, 21 June
Sun 33° above the horizon at midday (11:56 am).
Window in shade: 31%
Sun reaches 2.3 m across the floor.
The sun angles are worked out for your address on each date, at solar noon when the sun is highest, or at the time of day you pick. They allow for how far your wall turns away from north. The back of the deck roof sits on roof extenders, steel brackets bolted to the timber frame in the wall, and a ray only reaches the room if it gets past the brick reveal (the depth of brickwork around the window opening) and the window frame to the glass. Clear or translucent roofing lets some light through, which the drawing does not show.
More ways to keep your home comfortable
- Awning calculator: size an eave or awning over a window so it keeps the summer sun off the glass and still lets the winter sun in.
- What is a north facing home?: why the north side of the house is where your living areas and big windows belong.
- Passive solar design principles: the guide to orientation, shading and thermal mass on the Central Coast.
- NSW Planning Portal: shading design principles: the guidance on shading windows for BASIX, the NSW sustainability rules for homes.
If you would like me to look at your deck roof with you, book a free chat.
Questions people ask
How high should a deck roof be to let the winter sun in?
High enough that the 21 June sun passes under its outer edge and still reaches your windows. Set your deck roof in the calculator and look at the winter line: if it stops on the deck roof, raise the outer edge, tilt the roof up away from the house, or make it shorter.
Should a deck roof slope up away from the house?
Tilting it up lifts the outer edge, so more low winter sun gets under it while the high summer sun is still kept off the windows at midday. The water then runs back toward the house, so plan where it drains.
What is a roof extender?
A steel bracket that lifts the back of the deck roof above the house roof. It comes up through the house roof and is fixed to the timber frame in the wall, so the deck roof clears the gutter and lets light in under it. The calculator starts the deck roof 300 mm above the house roof, and you can change that.
Can I use clear or translucent roofing instead?
You can, but it lets light and heat through all year, including in summer, which the calculator does not show. A solid roof set at the right height usually keeps the summer sun out better and still lets the winter sun in.