# Forum Home Renovation Roofing  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

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## 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.

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## spbookie

Thanks Harry72 for the informative and useful reply.  :Biggrin:    

> 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

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## echnidna

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

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## Harry72

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

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## 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.

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## 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

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## 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

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## 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.

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## 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

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## 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  :Wink:

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## echnidna

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

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## 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  :Biggrin:

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## 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. :Wink:  
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)  :Biggrin:

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## 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

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## Harry72

Sp, you wont need to lift your tiles to install the sisalation, if your trusses are 700mm apart buy the 1500mm wide sarking(proper name) cut it in half accurately and run it long ways between the trusses. 
You should have 25mm overlap on each side too staple it in place with. Work along the trusses putting in just enough staples to hold it inplace then come back over it with staples every 10-20mm to tighten it up and seal it against the trusses.
To hold the bats inplace until its covered use cheap fishing line just string it accross the trusses and staple it in place on the lower face(the staple height of less than 1mm wont affect the ceiling you put up...) 
Hints, dont unroll the sarking to cut it in half... cut the whole roll in half, last time I used it we cut it with a sharp bow saw!
electric or air driven staplers will help save your sanity, if not dont try and do it in one day... your shoulders will kill you unless your used to working in overhead situations!

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## echnidna

an electric kitchen knife is great for cutting rockwool or f/g insulation

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## Rosethorn

Charles, I have used concentina foil batts to do exactly the job you want.  Easy to put up-just staple them to the rafters up to 50mm away from the tiles.  They insulate brillliantly and stop moisture at the same time.  Cost effective as well. 
Look at www.concertinafoilbatts.com  - tim renouf is the guy I dealt with- couldnt be nicer.
regards rosethorn

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## spbookie

So this thread can make the uBueat best-of, my summary now is: 
Otions for insulating a tiled workshop cathedral roof (new term I just learnt from references in this topic) are: Use sarking (nother new term) and standard insulation batts, and finish with gyprock and paint. See Harry72's post above for detailsUse rigid blue foam horizontally and finish with acrilic paints directly on the insulation. See Wildman's post for details. Use foil-backed-batts,tape joints with duct tape, finish with gyprock. See micko's post above. and Rosethorn suggested concentina foil batts, stapled to the trusses, which in a workshop could be left unfinished, see her post for details. 
So many good suggestions, thanks guys my life just got harder  :Wink: . 
On a slightly serious note, once again I have seen the power of this board and its members. I now have several interesting new options to follow up and a exceptionally good answer to my orginal question. 
Thanks to all that responded, your answers and willingness to give are what makes this board be what it is. 
Charles

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## MrFixIt

> 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?

  I don't know if that is true or not. My guess is it's dependant on the local council building regulations. 
When I built my second storey addtion (25 years ago) I used sisalation as insulation, as I had a solid Jarrah timber (cathedral) ceiling with exposed (dressed) rafters and laminated Jarrah beams. (Loved that ceiling). 
After installing the timber ceiling I then installed 25mm battens on to which the sisalation was attached (reflecting side UP) then the tile battens were placed over these battens and sisalation, then the tiles were placed on the tile battens. 
This method provided a 25mm air gap between the tiles and the sisalation and a 25mm gap between the sisalation and the (inside) timber ceiling. This proved to be quite effective in keeping the upper storey cooler. 
I know that the supposedly proper way of installing sisalation is blue side up but I could not see the benefit of having the reflective side down??? Besides, the builders of my (then) home did it with the reflective side up. To me that is more logical  :Biggrin:  
A combination of sisalation and f/g batts anfd then a 10mm thick mdf liner should keep the workshop nice and cool. It could be a good idea to seal (oil based) the tile side of the mdf.

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## MrFixIt

Hi  

> Sp, you wont need to lift your tiles to install the sisalation, if your trusses are 700mm apart buy the 1500mm wide sarking(proper name) cut it in half accurately and run it long ways between the trusses.

  *DON'T* do this if you have to have a moisture barrier! 
Sisalation is supposed to overlap HORIZINTALLY (IIRC at least 200mm) so that ANY moisture runs off. If you lay the sisalation VERTICALLY you effectively destroy the moisture barrier properties! It can *leak* out of the "sides".

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## MrFixIt

Hi  

> Sp, you wont need to lift your tiles to install the sisalation, if your trusses are 700mm apart buy the 1500mm wide sarking(proper name) cut it in half accurately and run it long ways between the trusses.

  *DON'T* do this if you have to have a moisture barrier! 
Sisalation is supposed to overlap HORIZINTALLY (IIRC at least 200mm) so that ANY moisture runs off. If you lay the sisalation VERTICALLY you effectively destroy the moisture barrier properties! It can *leak* out of the "sides". 
Sisalation is *really* supposed to be installed under the roofing material NOT UNDER THE RAFTERS!

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## Harry72

How can you install it directly under the roofing material if it needs a gap of 20mm and dont want to remove every tile and the batton the whole roof structure!
Laying it verticaly does not destroy its moisture barrier effectivness at all. 
If you read what I've written its installed 20mm from the roofing material... just like the manufacturer advises too do, not cover the rafters/trusses they are still exposed!

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