From what I've read (here, mostly), some sort of mechanical fixing is a must as with glue alone there's the risk of the plasterboard falling off the insulation in a fire.

The hammer fixings sound OK. Getting the boards level seems like the difficult part.

Yeah i know pur isn't the best plan but its the best I think I have given that external insulation requires extending the roof and rafters and the walls are already 1m thick. Making it thicker on the outside again would look awful recessed around the front of the windows

Quick question for you reefray, all of the tutorials on drylining (onto battens) I saw on youtube were American, and they all use the boards horizontally. It never occurred to me to do that, I have always seen boards being placed long-way-up.
Why is that, are there any advantages or differences?

evan

To be honest I'm not sure why. Sometimes I see joiners fitting sheets in the same manner so maybe it's a throwback from the past.

To get the desired fire rating for stud walls will involve the vertical fixing of plasterboard sheets so for us it's second nature.


Ray

Posted By: evanI saw on youtube were American, and they all use the boards horizontally. It never occurred to me to do that, I have always seen boards being placed long-way-up.
Why is that, are there any advantages or differences?

Posted By: reefrayTo be honest I'm not sure why. Sometimes I see joiners fitting sheets in the same manner so maybe it's a throwback from the past.

First thing to remember is that North American homes are generally "stick built" timber frame rather than the blockwork that's typical in the UK. Hence "dot and dab" is never used. Ever. Since the framing members are usually vertical, you want to run the drywall perpendicular to these, hence the horizontal orientation. Secondly, drywall comes in sizes other than 8'x4'. Since it's easier to tape and fill joints that are at chest height rather than running from floor to ceiling, this gives another advantage to running the sheets horizontally. For a room that's the standard 8' high, that's two sheets horizontally of 4' width - and since you can get sheets up to 12' or longer, then you can finish the installation much quicker (and with fewer joints) if you run the boards horizontally. Tape-and-fill is the usually finishing method here, skim coating is very rarely used.

Posted By: reefrayTo get the desired fire rating for stud walls will involve the vertical fixing of plasterboard sheets so for us it's second nature.

Surely the fire rating is based on the thickness of the drywall, not the orientation.

I've personally used both horizontal and vertical installation, depending on the walls. In some places, I had horizontal strapping (holding the insulation in place as discussed in other threads) and so I affixed the boards vertically (for an 8' high ceiling height and this gave me only 'factory edge' joints, rather than butt joints) but in other places I used horizontal - where I had ceiling heights greater than 8' and didn't want the hassle of having to handle larger (and heavier) sheets. In our new house, with 9' ceilings, they used boards that were 12' long and 54" wide so they could do the two horizontal sheet installation method.

Paul in Montreal.

Horizontal boards have a joint that is much easier to hide when dealing with an oblique light source. And as Paul points out, often much easier to work with. I don't skim so my taping has to be pefect.

PS over a stone wall such as yours the same fire rating will not be required

I am begining to get confused here. Just to confirm (cos I also have thick stone walls and need to internally insulated as discussed).....
1. Are people agreeing that there should be NO air gap between the stone wall and the insulation / plasterboard? (I have been advised that an air gap / ventallation is important - thus dab / dot seems a sensible idea, and follows advise elsewhere on this site regarding increased moisture levels in old walls if inetrnally insulated)
2. If so - is it OK to screw PIR / PUR insulation to a thick stone wall? Or is it better to use a fabric (sheeps wool etc?)
3. Would dab / dot breech fire / building regs with stone walls behind?
4. Is a VCL required?
5. Is it worth skimming over the plasterboard if it can be tapped / filled - then painted?

Sorry - but I am not clear on this at all. Many thanks

RR

Roserambler,

The last (similar to yours) job we did was a stone/rubble wall construction, drylined with Kingspan insulated p/b.
The stone wall was left alone, but a metal furring system built about 50mm off the wall, floor to ceiling, tied back to the wall. The stone wall was uneven, so we could not use it to attach the p/b to directly. The Kingspan was screwed through to the metal C studs, as well as being sealed to the top and bottom rails.
The joints between the p/b sheets, and around the edges where the boards met the wall and floor, were caulked, and then the whole lot was painted with two coats of board sealer, and a vinyl undercoat. This gave us the vapour impermeable layer required to stop condensation problems. The cavity between the back of the p/b and the stone was ventilated to the outside.

I am not sure if this helps, but feel free to whisper me if you want any more info.

Cheers

Yes, you make holes right through the wall!

As far as I can tell:

1) No air gap: mould shouldn't grow but you now have a wall which is basically waterproof on one side and possibly both sides if it's rendered. It might fill up with water and disintegrate. Also it might leak through to the drylining.

2) Unventilated air gap: mould might grow in it. Is it a concern to the occupants, providing the room is properly sealed? Not sure. Also no good way for moisture to get out if it gets in, but at least it shouldn't reach the room interior.

3) Ventilated air gap: should eliminate moisture and mould problems but also removes the insulation value of the outside wall, and you have to make holes in the wall.

How lucky do you feel?

(PS anyone please correct any of the above if it looks wrong)