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How to insulate existing patio roof?

Hey all,

Full disclosure — I’ve got very little DIY experience. Apart from painting, I haven’t really done much else around the house.

We want to insulate our existing patio — do it properly, but keep costs down. We looked at replacing the whole thing, but it was just too pricey. Plus, we actually love the current structure with the timber beams, so we’d like to keep it and just give it a bit of a refresh. The plan is to eventually semi-enclose the space with retractable clear vinyl blinds so it can be used as an indoor/outdoor dining area for entertaining.

After doing a bit of research (mostly from this forum — super helpful!), I’ve landed on Foilboard insulation (15 x 2400 x 1200 Foilboard Green) with fibre-cement sheeting (6 x 2400 x 1200 Duralux Fibre Cement Sheets) as probably the best option. Seems doable for someone with limited experience.

A few details and questions:

Roof: Zinc-alum with two Laserlite sheets for natural light. The roof sits on timber purlins running horizontally, supported by timber beams running lengthways.
Plan:
- Cut 15 mm Foilboard to fit between the purlins, resting it on the beams and gluing it to the sides of the purlins/tops of beams.
- Then cut 6 mm fibre-cement sheets to fit between the beams and fix them to the purlins.
Questions:
1. Is that method sound? Any tips for fixing the Foilboard — what’s the best adhesive to use?
2. Can I just glue and screw the fibre-cement sheets, or do they need a different fixing method?
3. Is there a lighter product than the Duralux I mentioned — maybe something that gives a VJ-panel look without the weight (something lighter than Hardie Groove Lining)
4. How should I finish the joins where the insulation meets the Laserlite — some kind of flashing (really struggling for a solution to this)?
5. Lastly, at the end of the roof where there’s a gap between the horizontal beam and the sheets — what’s the best way to seal that? Just timber infills or something else?

Appreciate any advice or lessons learned if anyone’s done something similar.

Cheers

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Comments

EricL

Hello @medivh_sun

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about insulating your patio roof.

I would probably suggest using Foilboard Spacer Blocks - 100 Pack to create an air gap between the foil board and the roof. I propose looking at Parfix 300g Clear All Purpose Silicone, it is a neutral cure silicone and will not corrode the surface its put on. Yes, the cement sheets can be glued and screwed but it will have to be on the surface of the beams as the purlins might not be strong enough to hold the weight of the panels.

The only lighter panel that comes to mind is the James Hardie 2400 x 1200 x 4.5mm 2.88m² HardieFlex™ Cladding. If you are keeping the Laserlite section open a square tunnel will need to be built to seal the gap between the roof and the cladding. I suggest using the same HardieFlex cladding to seal the ends of the beams and roof.

Let me call on our experienced members @Nailbag, @Dave-1, @AlanM52 and @Noyade for their recommendations.

If you need further assistance, please let us know.

Eric

Just a friendly reminder to our New Zealand readers: The use of foil board is prohibited.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/59473#Comment_59473

Good Morning @medivh_sun

I do like the idea of insulating the roof, always a bit hessitant about adding extra weight to an existings tructure. The post we can see in the back right that has the join with two bolts on it will end up carring a larger load on half the width of the post. If you could add an extra piece of timber there to span the join and distribute the weight it would go a long way aboutremoving weight concens.

There is no stays I can see? Is the existing structure attached to the house?

I was thinking of using timber beeding to hold the cement sheeting in place between the beams but think it would sag with time and the purlins as @EricL has mentioned are too small to support the sheeting.

An extra beam installed beside the laserlite would allow you to install the sheeting up to it but again you are adding more overall weight to a roof.

I like the exposed beams as well 🙂 I had a nice set in my garage roof (for the loungeroom that is above the garage) but and to forgo the old layout as the beams were starting to cup badly. I think the sheeting will have to end up being attached to the base of the beams to give it enough of a bond/fixing to stop any sagging. I am trying to think of a material that is light then the concrete sheeting, either yours or @EricL's suggestion but wont flex as easily. If I can think of something I will come abck and add it.

Dave

Nailbag

Hi @medivh_sun

My first concern is using cement sheeting to line the ceiling for two reasons; 1. it's going to add considerable weight to a structure not designed for it. 2. It will be very challenging to install overhead. And though you need an effective heat insulation solution, you would also want to avoid something to substantial considering its a temporary project.

You could consider first stapling silver wrap length ways to the roof joists. Then the foil board also screwed directly to the roof joists There is already going to be a 35mm air gap running left to right between each joist.

Then consider using lightweight Corflute sheets as the lining fixed lengthways to the underside of the large beams with button screws. The Corflute could be spray painted if there wasn't a suitable colour available. You would then also achieve another air gap with end to end air flow providing yet another layer of insulation.

I would class this as a relatively easy DIY project for someone with limited skillsets and tools.

Nailbag

AlanM52

Hi @medivh_sun,

I am thinking of the upside down roof insulation thing.

Batts held in place with stapled foil board, coreflute or flute board with minimal weight.

Cheers

medivh_sun

Thanks for your advice @EricL , @Dave-1 and @Nailbag — really appreciate the insight. I hadn’t even considered the weight issue. We definitely want this to be a one-and-done solution. I don’t want to be coming back in a year or two to fix sagging sheets or 'redo it properly'. Ideally, we’d like whatever we do to be good for 15–20 years.

Saying that, it’s sounding like insulating the existing roof might not be the best option. What about replacing the zinc-alum altogether?
I was looking at the Suntuf Twinwall polycarbonate panels. Still need to dig into what’s required for installation, but do you reckon there’d be any issues using that as a replacement for the current zinc-alum / Laserlite?

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/59568#Comment_59568

Good Evening @medivh_sun

I dont see a reason why not, Tho I would possibly start with just replacing the alsonite first and see how you feel with the twin wall panels. No reason in particular other then outlaying money 🙂 I will point out that tin roofs survive hail far better then plastic and depending on where you are there does seem to be more instances of hail about..

One old school way of reducing temperture is to have a material on top of the roof and wet it down. Not sure if shadecloth would work as it dosnt absorb the water to dissipate the heat but it may help stop the heat level getting so high? You could try with a section and check out the temp imediatly bellow the tin? Id weight down the shadecloth with bricks tho 🙂

Dave

EricL

https://www.workshop.bunnings.com.au/discussion/comment/92207#Comment_92207

Hello @medivh_sun

I agree with @Dave-1's recommendation. Replacing even just a few sheets should tell you immediately if the Suntuff Twinwall provides better insulation. You could also do a combination of the Foilboard and use shade cloth as a cover underneath to cover up patio roof beams. Since shade cloth is very light it will not present a weight problem to the patio frame.

Eric

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/59568#Comment_59568

Hi @medivh_sun

Why not consider then the Suntuf Twin wall polycarbonate panels as the ceiling rather than replacing the actual roof? This would then provide a couple of air-gap layers. Add a layer in-between of the silver wrap and get another layer. All super lightweight and very easy to instal without modifying the existing structure.

Nailbag

Harro0599

https://www.workshop.bunnings.com.au/discussion/comment/59484#Comment_59484

Hi Nailbag, love the idea of this. I have a similar situation (photo attached), where it’s getting way too hot during summer and having a lot of condensation as well. Do you think this method would work?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/92311#Comment_92311

Hello @Harro0599

Welcome to the Bunnings Workshop community. It's sensational to have you join us.

Let me tag @Nailbag to make them aware of your query. I believe it will work, but it might be necessary to add extra timber battens for support as the beams you have appear to have large gaps between them.

If you need further assistance, please let us know.

Eric

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/92311#Comment_92311

Yes definitely @Harro0599 You will just need to add few additional supporting 70mm x 45mm joists to accommodate the sheet sizes to give you something to fix to.

Nailbag

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