Energy ratings, weather seals and condensation

A door is a hole you intend to close. Energy ratings try to say how well it closes against heat, solar gain and air. Weather seals are the cheap, replaceable part of that promise. Condensation is what happens when the promise meets an Australian winter, a steamy bathroom, and an aluminium stile with no thermal break.

The Window Energy Rating Scheme — WERS — covers doors as well as sashes. The National Construction Code’s energy provisions cover the building. Climate zones 1 to 8 decide which problem you are actually solving. This is a compliance and physics note for people who have been sold “double glazing” as a personality.

The coastal half of the aluminium problem is in aluminium doors for coastal Australia. Here the same extrusion is asked about heat, not salt.

What WERS is telling you

WERS gives a product a set of numbers: U-value (how readily heat moves through the unit), solar heat gain coefficient (how much sun becomes indoor heat), air infiltration, and often a star rating aimed at heating or cooling. The identifier matters because two sliders that look identical in a showroom can be different glass, different frames and different seals.

Read the numbers for your climate, not the biggest star on the card. In Melbourne or Canberra (zones 6 and 7), a lower U-value and a tight air-leakage figure earn their keep through winter nights. In Brisbane or Mackay (zone 2), a lower SHGC on a west stacker, plus shade, will do more for summer comfort than an imported triple-glazed slab that never sees a frost. In Darwin (zone 1), you are in a humidity and solar argument; heating stars are a curiosity.

The NCC energy pathway — NatHERS, a deemed-to-satisfy elemental path, or a Verification Method — will ask for whole-building performance. A beautiful WERS door in a wall of uninsulated brick and a garage that leaks like a flyscreen is a feature, not a strategy. Put the door in the model as the door you will actually install, including the glazed area.

Air leakage is the forgotten rating

Heat through glass is visible. Air under a door is audible. A worn wool pile on a slider, a warped timber leaf, a letter slot, and a garage that shares air with the hallway can move more energy than a modest difference in U-value. They also move dust, ash, mosquitoes and the smell of the bins.

Weather seals are a system:

• Compression seals on hinged doors at the stiles and head.
• A threshold seal that meets the leaf without becoming a trip — the access and threshold rules now police this on new houses.
• Pile or fin seals in sliding interlocks and at the sill.
• A latch that holds the leaf against the seals. A door that only seals when you lean on it is leaking.
• Continuity at corners. A perfect sill and a missing head seal is a whistle.

Seals die. Ultraviolet, grit, salt, paint overspray and the family dog all shorten a pile. Budget replacement the way you budget a recoat. A ten-year-old slider with original pile is a common Australian energy fault, sitting right there in the living room.

Garage doors are the large print. Even when the house is sealed, an attached garage with a tired roller seal will wash the inner door with cold or hot air every time someone comes through with groceries. If bushfire overlay applies, those same gaps are ember paths; see BAL ratings and door specification.

Thermal breaks, glass and the cold aluminium problem

Aluminium is a heat fin. Without a thermal break, the indoor stile tracks the outdoor temperature. In a Hobart southerly or a Canberra July night, that stile is a condensation rail. Indoor moisture — showers, cooking, unflued gas, too many people in a tight unit — hits the cold metal and becomes water. The water becomes mould on the reveal, swollen MDF architraves, and a household argument about who left the door “wrong”.

A polyamide break between inner and outer extrusions interrupts the fin. Warm-edge spacers in an insulating glass unit help the pane’s edge. Low-e coatings change the glass temperature and the SHGC. None of these repeal a house that makes too much moisture and exhausts too little of it.

Timber and composite doors are kinder on this particular physics. They can still leak at the perimeter. They can still host condensation on the glass. They are less likely to present a continuous metal refrigerator in the hallway.

Steel doors conduct too. A painted steel entry in a cold climate wants an insulating core and a frame detail that does not sweat behind the plaster. The look can stay civil; the section needs to be a sandwich.

Condensation is a moisture budget

The NCC and the plumbing and ventilation standards expect wet rooms to exhaust. A door cannot fix a bathroom fan that vents into the roof space, a laundry that steams with the door shut, or a household that dries clothes on a rack beside a cold slider.

Practical diagnostics, before you buy a new leaf:

• Which surface is wet — glass, aluminium, timber, or the floor? That tells you the cold element.
• What time of day? Overnight bedroom doors that sweat are often a heating-and-closed-room story.
• Is the wet on the inside face only? Then you have indoor dew point, not a rain leak. Rain leaks leave dirt tracks from the outside in.
• Does the problem vanish when you run the exhaust and crack a window? Then the door is a witness, not the accused.

In climate zone 2, summer condensation on air-conditioned aluminium is the reverse story: cold indoor metal, humid balcony air when the door opens, a puddle that looks like a leak. Seals and a break still help. So does not blasting the split system at 18 degrees with the stacker half open.

Mould on a reveal is a health problem dressed as joinery. Clean it, fix the moisture, then recode the paint. Replacing a door into the same wet air is how you get a new door with old mould.

A WERS star is a product score. Condensation is a building conversation. If you only buy the star, the stile will still weep when the shower and the southerly agree.

Climate zones, without the brochure

A short, usable map for door energy:

• Zones 1 and 2 (Darwin, Cairns, Brisbane, coastal northern New South Wales): prioritise solar control, shade, insect and security screens you will actually close, and air leakage that keeps humidity management in your hands. Heating U-values are secondary.
• Zones 3 and 4 (hot dry inland): brutal solar on west walls, cold nights in winter. Shade plus a decent U-value. Dark unshaded plastic doors suffer here; so do unsealed aluminium sliders that sandblast themselves.
• Zone 5 (Sydney, Perth, Adelaide and much of the populated coast): mixed. You want both a reasonable U-value and a civil SHGC, plus seals that handle a southerly change.
• Zones 6 and 7 (Melbourne, much of the tablelands, Hobart’s kinder bits): heat loss and condensation dominate. Thermal breaks, insulating glass, tight seals, and a threshold that does not leak night air.
• Zone 8 (alpine): the full winter argument. Doors become part of a snow and meltwater detail as well as an energy one.

A verandah is an energy product. So is a tree, until it is a BAL problem. Specify the door for the wall you have, including the shade you actually keep.

Specifying a quieter envelope

Write, on the door schedule:

• WERS identifier or the U-value, SHGC and air infiltration for the exact glass and frame.
• Thermal break or insulating core, named, not implied.
• Seal types and a replacement note.
• Glass to AS 1288 where human impact applies — energy glass is still safety glass when it is in a door.
• How the unit meets the NCC access threshold if the opening is on an accessible path.
• Exhaust and moisture notes for any door that sits on a wet room or a laundry.

Then stand at the door on a windy night and on a still, cold one. If you can feel air at the sill, the rating on the sticker is a rumour. If you can write your name in condensation on the stile, the frame is telling you about a break and a bathroom fan. Believe the door. It is the most honest instrument in the wall.