Why We Tell Customers Not to Put Light Strips in an Insulated Patio

Cutting polycarbonate light strips into an insulated patio roof defeats the entire reason you bought an insulated roof. The strips have about a tenth of the insulation value of the foam panel, you can't clean them, and every penetration is a future leak. We don't fit them - and a year on, the customer who originally asked for three of them is glad we didn't.

The kitchen-table conversation that started this

A nice couple in Erina rang up wanting an insulated patio - 6m x 4m, off the back of the house, west-facing. Standard job, the kind we do every other week. Then on the design call they said it: "Can you put three light strips in? We're worried the inside of the house might get too dark."

They'd seen them on a neighbour's patio. They liked the idea of "a bit of light coming through". And honestly, three polycarbonate strips spread across a 6m x 4m insulated roof is a job most outfits would happily build. Easier money, makes the customer happy on quote day, and the problems don't show up for two summers.

We drove out the next morning, sat at the kitchen table, and told them straight - we weren't going to do it.

This is the story of why, what we suggested instead, and where they ended up a year later.

What the customer actually wanted (vs what they asked for)

The first thing we do when someone asks for something we think is wrong is shut up and listen. Because nine times out of ten, the thing they're asking for isn't the thing they actually want.

In this case, what they were asking for was light strips. What they actually wanted was for their kitchen not to feel like a cave once the new roof was up. Two completely different problems with two completely different solutions.

The kitchen window faced the back deck. The patio was going to sit two metres above the window line. They'd seen friends put in a patio and lose half the natural light through the kitchen window, and they didn't want that to happen to them. Fair concern. Real problem.

But here's the thing - light strips in the patio roof don't fix that. The kitchen window doesn't see the patio roof. The kitchen window sees the back of the patio, and whatever light comes in is whatever light reflects off the deck and back through the window. Three holes in the patio roof, four metres away from the window, do almost nothing for the kitchen.

The thermal physics nobody talks about on quote day

Let's talk numbers for a second, because this is the bit that gets glossed over.

A standard 75mm insulated foam panel has an R-value somewhere around 1.0 - roughly. That's not amazing by house-roof standards, but for an outdoor patio it's the difference between sitting under a frypan and sitting under shade. It's the entire reason insulated patios cost what they cost.

Polycarbonate, by comparison, sits at about R-0.1. One tenth. It's a window, basically. In summer, sun hits the strip, the strip transmits and re-radiates heat into the air directly underneath, and you get a column of hot air sitting in your "cool" patio. In winter, it works the other way - the cold leaks in.

Now do the maths on three strips. A 6m x 4m roof is 24sqm. Three 300mm-wide strips running the full 4m length is 3.6sqm of polycarbonate. That's 15% of the roof working against the other 85% - and because the strips are spread across the area, the hot zones turn up exactly where your outdoor table tends to live.

If you put four strips in, like one company has been known to suggest on bigger jobs, you're at 20%+. At that point you're paying insulated patio money for what's effectively a single-skin roof with extra steps.

The cleaning problem you only realise five years later

Here's the bit that doesn't show up in the brochure.

When we install a polycarbonate strip into an insulated roof, the strip sits between two foam panels and gets capped with flashings on either side. From below, it looks tidy - clean line, ceiling sealed up underneath. From above, the flashings cover the edges of the strip so water doesn't get in.

What that means in practice is that dust, leaf litter, pollen, bird droppings and roof-borne grime all settle on top of the polycarbonate. Over a year, that becomes a brown-green film. Over five years, it's a layer thick enough to actually block the very light you cut the hole for.

And you can't get to it. You can't clean the underside through the strip, because it's sealed up. You can't get on the roof and clean the top, because the strip is the weak point of the roof - you'll crack it. The dust just sits there, getting darker every year, until you eventually wonder why the "light strips" don't let any light through.

We've been on jobs where we've gone to repair a leak and pulled the flashings off a five-year-old strip. The state of the polycarbonate underneath is something else.

Every penetration is a future leak

The third reason - and the one we care most about as the crew whose licence and name is on the warranty - is leaks.

An insulated roof, done properly, is a sealed system. Panels lock together with concealed-fix joins, the perimeter is flashed and sealed, and water has nowhere to go except down the gutter. No penetrations. No edges. No future trouble.

The moment you cut a polycarbonate strip into that roof, you've created two longitudinal seams - one each side of the strip - that have to be flashed, sealed, and trusted to stay sealed for the life of the patio. Every flashing is a join. Every join is a future maintenance job. Every silicone bead has a clock on it.

We've seen too many "light strip" patios with brown drip stains on the ceiling lining around the strips after seven or eight summers. The roof was fine. The strip flashings let go. Now you've got water inside the foam panel, which is a bigger problem than a wet patio - because foam panels don't dry out properly once water gets in.

We're not putting our licence number on a build that we know is going to do that.

“

The roof's only as good as its weakest point. The moment you put a hole in it, the weakest point is the hole. We'd rather build you something simple that lasts twenty years than something fancy that gives you grief in five.

”

The actual fix: skylights in the house roof

Here's what we suggested in Erina, and what we suggest pretty much every time this comes up.

If you're worried about losing natural light to the kitchen, living room, or any other room behind the patio, the right fix is a skylight in the existing house roof - directly above the room you're worried about. Not in the patio.

A house-roof skylight has a few enormous advantages over a patio light strip:

• It's directly above the room that needs the light, so you actually get light into the room
• It's installed by a roofer or skylight specialist with the right flashings for an existing house roof
• It doesn't compromise the thermal performance of the new patio you just paid for
• It's in a roof you can clean (or pay someone to clean) without the strip-flashing problem
• Velux and similar units come with proper integrated flashings designed for tile or Colorbond roofs

We don't fit skylights - it's not our trade - but we'll happily point you at someone who does it well. In Erina, we put them onto a roofer we've worked with for years, who came out, fitted two skylights above the kitchen and the dining area, and the room went from "a bit dark in the afternoon" to genuinely bright. The patio stayed cool. Everyone won.

How we handle this kind of disagreement

Inside the crew, we don't always agree on the spot. The project manager is the one who's been talking to the customer for two weeks, building rapport, working through what they want. The licensed builder is the one who turns up on quote day with a different opinion.

The way we run it is simple - we'd never undercut each other in front of the customer, and we'd never let the customer feel like they're being lectured. If we think a build is wrong, the rest of the crew already knows about it before the conversation, because we've talked it through the night before.

On the kitchen-table day, the project manager set it up by saying, "We've got a strong view on the light strips - it's worth hearing us out before we lock anything in." Then we explained the three things you've just read. The couple asked good questions. We talked it through for maybe twenty minutes. They went away to think.

They rang back two days later and said go ahead - no light strips, plain insulated roof, and they'd organise a roofer separately for the skylights.

A year on

We drove past the Erina job a few weeks ago - dropped in to say hello and check the gutters were clear. The patio is one of their favourite spaces in the house. The kitchen, with the two skylights, is bright. The under-roof temperature in summer is, in their words, "miles cooler than the old deck ever was".

No light strips. No leaks. No regrets.

That's what doing it properly looks like. Sometimes the right answer is not building the thing the customer first asked for - and having the conversation early enough that everyone agrees on what we're actually trying to fix.

The short version

If somebody quotes you an insulated patio with polycarbonate light strips, ask them three questions:

1. What's the R-value of the strip vs the panel?
2. How will I clean the top of the strip in five years' time?
3. What's the warranty on the strip flashings, and what's the path if they leak?

If they can't answer those without hand-waving, you've got your answer. If they can answer them properly and still recommend the strips, fair enough - get a second opinion from someone who's prepared to disagree with you on quote day.

We'll always be that second opinion. Even when it costs us the job.