How to fix solar reflective foil

[eyecatcher]

Looking for a practical way of fixing solar reflective foil to the underside of roof tiles.

New roof construction from scratch so sounds easy. With a timber roof and timber battens doesn’t even need thinking about.

So as with all roofs here, we have steel rafters and purlins; then we have the 25mm steel “tiling laths” then the tile.

As I see it the ideal is to give a 25-50mm air space between the foil and the underside of the tile. Yep, common sense, it’s the same with fibreglass/rockwool and the like though in the west the purpose of the gap is to prevent condensation and rotting of the timber.

Foil cannot be laid on the steel rafter because the tile lath cannot be welded to them.

Roof tile cannot be wired because it has no holes in.(mine are the white concrete diamond style)

Wiring from the underside around the rafter is awkward and the foil will be ripped to shreds.

With blinkered vision I am looking at nailgunning the foil to the underside of the steel rafter which seems a bit overkill.

Is there a technique like wiring through a plastic disc (similar to the discs holding cavity wall insulation batts on the wall tie)

With most westerners incorporating this upgrade in their house has it been a problem?

[IMHO]

For flat tiles, the foil should be installed under the battens - the secret is, don't use regular box section steel welded onto the trusses - use proper roofing battens which are screwed onto the trusses:

For tiles with a profile (rain channels) the foil can be installed either below the battens, or on top, as this style of tile permits airflow either way.

[CGW]

Like this :-

[eyecatcher]

I like it and now i can see a diy job coming along.

Looks like regular c line top hat profile.

[pb1936]

The method of using the top-hat section battens is a good one, but i have never seen it used here. The usual technique seems to be for the foil to be loose laid over the top of the rafters and welded battens and held down by the tiles - which is a very poor method and subjects the flimsy foil to movement during tile laying and to mechanical damage by the tile lugs.

Almost invariably, the foil is damaged anyway by men climbing over the roof structure. The foil is little more than baking foil. There are more robust alternatives.

[Gandtee]

Perhaps the easiest solution but maybe not the cheapest way is to have the underside of the roof sprayed with urethane foam. It seals and waterproofs at the same time.

[Gandtee]

I have a wooden old style veranda. Over the years I have replaced boards which have shown the signs of rot. Now I find that the cross timber supports are also showing these signs. Is there any treatment that I can apply without scrapping these supports? Timber is expensive now and I don't want to fork out for new heavy supports.

[IMHO]

The foil is little more than baking foil. There are more robust alternatives.

Not sure what brand of foil you've been looking at, but the good stuff is nothing like baking foil, except for color. A good roofing contractor who uses scaffolding won't leave you with damage to it either - roof tiles go on from the bottom up, so there's no need to be walking on the foil.

There is no questioning it's effectiveness either - any heat you radiate back through the tiles is heat that didn't need to be insulated against.

[cracker1]

Perhaps an adhesive like "No more Nails" on the underside of the rafters ?

[Greenside]

IMHO's picture is the best way to do it I believe. SCG has a bolt together system that allows for the same fixing, but it's probably very pricey so if you can find someone to fit the purlins to a "normal" steel structure it would be very good.

[eyecatcher]

Certainly agree that mechanical fixing of the tile battens is the answer. Tek screws self tappers donkey work but the way to go.

With due respect to thr above poster suggesting NMN. Its a non starter for several reasons. Mastics dont llast 10minutes here. They simply break down in the heat and will not hold anything.

Use them as gap fillers and maybe fix skirtings but leave it at that.

But thanks for the suggestions its not an easy one to resolve technically or practically is it?

[Daffy D]

You could screw wooden batons to the underside of the roof joists then using heavy duty staple gun to staple the reflective foil to the batons.

The foil is not heavy so not may screw fixings would be needed to hold the batons.

Just make sure the wood batons have a good soaking in preservative first.

[cooked]

I was initially planning on removing the roof, laying the foil over the steel joists, screwing wooden joists on top of that and then relaying the roof. I thought that this was doable but the fact that I was raising the roof by a few centimetres would have led to all kinds of details to fix.

I decided finally to get adequate insulation, aluminium foil on both sides, above the ceiling and ensure that the roof space is ventilated. This of course means that any heat that has accumulated in the room during the day time cannot rise into the roof space, but a quick burst of A/C should look after that.