Adding insulation under a tile roof?

[spbookie]

Hi,
I have an existing tile roof over my workshop, with no ceiling, and I want to add insulation. I have planned to push rockwool batts between the trusses up against the tiles and then nail sheets of hardboard to hold the batts in position and give me a good surface to paint.

After a bit of research it seems I may have to provide a waterproof membrane between the tiles and the insulation. Can anyone please tell me if this is true? And if so what should I use as the membrane?

Are there better ways to directly insulate an existing tile roof?

Any assistence would be muchly appreciated.

Charles

[Harry72]

You only need a small space between the roof and the insulation, got to allow room for the condensation to evaporate otherwise mould will take hold during winter. Also insulation starts loosing its effectivness if its compressed.
Use sisalation for a water proof membrane, needs to be about 20mm away from the roof.
How wide is the wood used on the trusses?

The price you pay for hardboard it would be cheaper to gyprock it, unless there are wide spans to cover.

[spbookie]

Thanks Harry72 for the informative and useful reply.

How wide is the wood used on the trusses?

I'm not exactly sure what measurement you want here. The trusses are roughly 700mm apart. The rafter timber is 35x90 hardwood.

The price you pay for hardboard it would be cheaper to gyprock it, unless there are wide spans to cover.

I was planning to use 4mm MDF as the cheapest sheet material I could find. I just want to have a smooth surface I can paint white to help brighten up the workshops. It has to have a little impact resistence as I may well occasionally poke it with a piece of timber when I get over enthusistastic.

The battens under the tiles look like they would hold the batts 20mm away from the roof, especially if I use sisalation. Err Just checking sisalation is the foil like material I can buy in harware shops?:confused:

Charles

[echnidna]

4mm mdf is too thin it will sag. go for 9 or 10 mm

[Harry72]

"Err Just checking sisalation is the foil like material I can buy in harware shops?"

Yes.

[echnidna]

An alternative to all the above would be to fit rigid blue foam as the ceiling. Its insulation and its waterproof so eliminating the membrane and the rockwool. Takes acrylic house paint ok. The blue stuff won't support a flame.
Would be the easiest way but maybe a bit dearer.

[spbookie]

The blue foam insulation sounds interesting. I don't mind paying a bit more for the work it would save. I would much prefer to spend my time making sawdust rather than hanging off a ladder with a nail gun.

Do you think it would hold between the rafters or should I glue it in with a no-more-nails or equivilent.

Can you tell me a generic plastic name or a trade name for the "blue foam"? I worry that if I go to an insulation place and request it by that name I could end up buying 3 cases of the latest shaving cream.

Charles

[adrian]

I'm with Harry, I don't know about using MDF in that situation. It's a very humid environment up there near those tiles and MDF is another word for sponge.
Gyprock was made for the job.
This link shows the work involved in retrofitting sarking.
http://www.roofcover.com/sisalation.htm

[echnidna]

The blue foam is a standard building product so you should be able to get it from major building suppliers. But I've forgotten the proper name for it and the brands.
Its available in several thicknesses up to about 19mm and has tongue and groove edges. I think its about 600 wide and 2400 long. It should span 700 easily.
I'd just hang it underneath the rafters like a normal ceiling sheet rather than cut it in.

[Wildman]

I would use (and I have) foilboard insulation. It is foil backed polystyrene, is easy to install in sheets, easy to cut to size, is rigid and water and rodent proof and gives much better summer performance than any bulk insulation while still giving good winter performance. Just nail or glue to to the tile battens between the joistsor stick up whole sheets if you can to the underside of the joists.

www.foilboard.com.au
10mm is about $21/sheet (2440x1200) and 15mm is about $24/sheet

You nail it on with special staple type nails that the foilboard people cann sell you as well. 10mm is sometimes available at larger Bunnings.

Cheers
Ben

[Jacksin]

A question if I may Wildman.

Looking at your foilboard link, how does the bricky nail his wire ties to the timber wall framing? Here in SA, unless I am mistaken, the wire ties are clouted to the sides of the studs.

Do you then cut holes in the foilboard to allow this? Just interested
Jack

[echnidna]

Should leave this for Al.
They use a shaped sheetmetal one that justs holds the tie onto the stud with a clout.

[ozwinner]

I thought the nail to the side of a stud type were banned???:confused:

Normaly we use face of frame type, which are held on with a clout banged into the wait for it,..........................face of frame.
Rant on............
Although I doubt that they hold very well, the clouts are usually only 25mm long, and dont seem to hold much, but hey, Im not an engineer so what would I know.
And what about timber shrinkadge, what happens then??
I doubt modern houses will last 50 years.................
Rant off..........

Al

[spbookie]

While watching this thread go wayyyy thata way. I thought I would summarise my choices.

Thanks for the suggestions.


1) Strip the tiles, add sisalation, use batts between the rafters, finish with gyprock or 10+mm MDF but not recommended because MDF is a better sponge than roof ceiling.

2) Use blue foam straight across the rafters, paint with acrylic paint. Remember that blue foam is not a new deodorant.

3) Use foilboard in a similar way to blue foam.

4) Use bricks nailed to a faceframe with a 25mm clout. :confused:

5) Wait 50 years and it wont matter anyhow. :eek:

Have I got it right?


To use sisilation effectively it seems I would have to lift the tiles and that probably more effort than the job is worth.

I will follow up on the rigid foam and foilboard and report back when I have completed the job.

Charles (the smartar*e)

[micko]

At my old house which has a colorbond roof, I nailed wire at right angles to the roof to hold foil backed bats insulation blanket in place.I cut the foil bats as I went and taped accesible joins with duct tape.Then I gyprocked over them.
No problems in 15 years.

micko