Summer overheating (without shrinking the windows)
Three building‑science moves that stop summer overheating in compact family homes (without shrinking the windows).
You know this dance.
Client: “We want big glass. Light, views, that indoor–outdoor feel… you know.”
Also client: “Oh, and we don’t want it to be hot in summer. Or cold in winter. Or expensive to run.”
Meanwhile, the code is quietly pushing you toward more performance, the budget is trying to drag you backwards, and every second “advice” article is basically: “Install a fan and manifest cooler air.”
My favourite recent gem: BRANZ recommending putting wet towels over your fans to cool your house, while also saying “don’t add humidity if you’re worried about moisture.” So… add water / don’t add water. Got it. (Erm…)
Let’s sidestep the towel origami and talk about the three moves that actually work in compact family homes – and don’t wreck your elevations.
After 15+ years staring at temperature logs in “perfectly fine” houses that turn into saunas every January, I can tell you: most projects don’t need magic technology. They just need concept‑stage decisions that line up with physics.
Move 1: Shade outside the glass (on purpose, not as decoration)
The standard pattern on small homes is: big sliders, minimal eaves, lightweight blinds, fingers crossed.
Result: lovely photos at 8am, thermal regret by 4pm.
External shading is still the single most effective, most boringly reliable way to stop glazing turning into a radiant heater. That’s deep eaves, fins, screens, pergolas with something real on them – all tuned to where the summer sun actually is.
A few blunt truths most people won’t say:
A 300 mm eave over a 2.2 m high slider in the wrong orientation is basically a hat on a giraffe. It looks like “shading” and does almost nothing mid‑afternoon in summer.
Tinted glass is not a strategy. It’s usually an apology.
If the shading doesn’t line up with the glass on the drawing, it won’t line up with the sun in real life either.
From a client’s point of view, external shading means:
Cooler rooms on the worst days
Less glare on screens
Windows they can actually use without pulling blinds down all day
From your point of view, it’s cheap insurance: fewer callbacks about “we can’t sit in the living room after lunch.”
When not to go nuts? If the house is severely orientation‑compromised (e.g. suburban site, west view is non‑negotiable), you won’t “shade your way” entirely out of trouble. Do what you can, but manage expectations. Don’t let anyone pretend a tiny fin equals a high‑performance facade.
Move 2: Put the big glass where it earns its keep
Architects are visual, so we fall into a trap: we spread glass around like it’s parsley. A little hero moment on every elevation.
The problem is that the sun doesn’t care about symmetry, and neither does overheating risk.
In compact homes, I’d rather see strategic extravagance than uniform glazing:
Big, glorious openings in living / kitchen / dining where the family actually spends time
Tighter, better‑shaded glass in bedrooms, especially west‑facing ones
Circulation and secondary spaces that are “light enough,” not over‑glazed
On a recent small two‑storey project, the original sketch had full‑height sliders to a west deck off two bedrooms “for resale.” The overheating modelling said: those rooms were about to become sleep‑deprivation chambers.
We kept the deck, shrunk the bedroom glass, added proper external shading, and gave the living space the hero glazing to the nicer orientation. Same facade rhythm. Completely different internal comfort.
Here’s the trade‑off conversation I usually have with clients:
“We can afford some big glass. If we put it where you live – not where you sleep – you’ll feel like the house is lighter and the bedrooms will actually be usable in summer. If we spread it evenly, we get a brochure that looks balanced and a home that feels average.”
If they still want full‑height west sliders in every room, that’s fine – but you’ve made the trade‑off explicit.
Move 3: Design for night‑purge ventilation like you actually mean it
Summer comfort isn’t just about stopping heat from coming in. It’s also about giving it a way out.
This is where night‑purge ventilation comes in: using cool night air to flush stored heat out of the building fabric.
Done well, it looks like:
High‑level openings or clerestories that can be left safely open at night
A clear cross‑flow path through the plan (not just isolated windows)
Hardware that lets people lock windows partially open without feeling like they’ve invited burglars in for a tour
Done badly, it looks like:
Token awning windows hidden behind curtains
Security grilles that everyone hates and never uses
“We’ll just open opposite windows” in rooms that don’t actually have them
On small family homes, a good night‑purge design can easily drop bedroom temperatures by several degrees after hot days. That can be the difference between 29°C and 24°C at bedtime – which is the difference between melatonin and meltdown.
But here’s the awkward bit: it needs to be designed at concept stage, not during hardware selections. If there’s no safe, cross‑connected pathway, no handle or trick frame will suddenly create one.
What this looks like on a real job
Picture a tight urban site, two‑storey, compact three‑bedroom home. North isn’t perfect; you’ve got a bit of west on one side, a neighbour breathing down your neck on the other.
What we did:
Living level:
Pulled the big sliders toward the better orientation
Deepened the eave and added vertical fins where the sun angle demanded it
Checked actual sun paths instead of guessing
Bedrooms:
Reduced full‑height west sliders to more modest openings
Added external shading and considered light‑coloured external finishes near those rooms
Designed high‑level windows for safe night opening
Ventilation:
Ensured a night‑purge path from cool side to hot side
Added secure window hardware so parents actually feel comfortable leaving them partially open
Cost impact? Some extra thought, some additional shading elements, minor joinery reshuffle. No exotic systems, no post‑rationalised “smart home cooling package.”
Performance impact? Summer peaks down, nighttime recovery up, significantly fewer “we just sleep in the living room now” stories.
When not to hire a building‑science nerd (aka: me)
If your client:
Refuses to consider shading
Insists on all‑glass west elevations for “the look”
Will not move a single window 300 mm even on paper
…you probably don’t need me to tell you what’s going to happen.
In those cases, don’t waste their money pretending we can engineer our way out of reality. Give them basic comfort advice (fans, blinds, maybe even the occasional wet towel if you like living dangerously), and be honest that they’ve prioritised aesthetics over peak comfort.
They’re allowed to – but they shouldn’t be surprised later.
How to “sell” this without selling
You don’t have to pitch any of this as premium magic. Just frame it as:
Fewer callbacks for you
Cooler bedrooms and lower bills for them
A house that still looks like your design, not a code workaround
That’s it. No hype. Just aligning the drawings with the physics.
A builder told me last week, “Clients never complain that you over‑designed the shading, but they complain for years if you under‑do it.” That’s the real resale metric.
And no, the solution is not a wet towel over a fan.
