Insulated plasterboard advice

amsbam1 wrote: »

I am putting insulated plasterboard on an extension I am building. Wondering what people thought was the best choice for me.

Trying to juggle building slimmest walls that I can with getting best insulation I can. Space is at quite a premium here, so don't want to make my rooms to small with super thick board.

The extension being built is hollow block.

Currently i'm planning to do option 1:

Option 1: Stick High End 50mm Insulated Plasterboard straight to the Hollow block wall.

However I could do option 2:

Option 2: Create a small cavity between the plasterboard and the wall with a dry lining system. Use thinner boards (maybe 38mm to make up for the space lost.

What do you think?

I have an extension, which is built fairly similarly to your Option 1. Perhaps my expectations were just low, but I've had no issues with the place being cold or not holding heat well.

We struggled to get insulation when we were doing the extension (I think there was some kind of shortage), and as a result 50mm is smaller than we'd have wanted. But it's been great, and it does hold heat well, in my opinion.

I also haven't really had any issues with the cavity-block build either. The builder I used only really seems to use cavity block, and he gave me details of a few extensions he did in my area. I called one or two of them and they were all happy enough with the end result.


I have no knowledge of building regulations or anything, though. So I'm not sure about that kind of thing, but for the day-to-day practicalities of living here, i am happy with the extension and it's heat-holding abilities.

amsbam1 wrote: »

Thanks for the reply, and great to hear it turned out well.

Do you know if your 50mm was stuck directly to your hollow block wall or if you put a slight cavity in between?

Straight to the wall, if I recall correctly.

listermint wrote: »

OP has no way of knowing the size of your room., The orientation, the window size and or spec, the roof type, the make up of the rest of your house in context with this extension.

It's really not apples for apples tbh.

All fair points. My extension is made up of a kitchen extension to the rear of the house, approximately 30sq/m. It also consists of a 'hallway' to the side that houses a bathroom and a 'utility' room.


I'll ignore the side part for the sake of this thread, as it adds no value to this conversation.


We have only one 'opening', in the form of a 3m/10ft wide sliding door, which faces west into the back garden (a window/door this size, I presumed would immediately hinder any attempts to keep the place comfortably warm, but it hasn't impacted much/at all. I thought the glass might always make the place too cold, or too hot, in the case of a sunny day, but it seems to have balanced out just fine).




The roof is a flat felt roof, with a fairly typical 'cold roof' design.


My extension is a fairly 'budget' extension, in the construction sense, but in the process of wanting to build it, and during the building stage, I was constantly on Google and running around to people who had extensions built.


Perhaps it's just me, or maybe it's that my house was just well built in the first place (or perhaps not - an 80's council build concrete house, cavity wall with sheets of insulation in the cavity) I've always found our house to be very warm. Adding the extension, despite using cavity blocks, less insulation than I wanted, a 'cold' roof, large pane of glass, etc. I still find the place to be as warm as it ever was before.


Despite me taking lots of 'budget' approaches, my extension turned out really well, and I'm genuinely happy with it. I find it comfortably warm long after the heating has been turned off, and I wouldn't recommend it to anyone if I didn't feel it was justified. I wouldn't deliberately bother writing up a message saying "50mm is grand" if i had 50mm and was constantly frozen.




One thing I am glad of (now that I know 50mm is sufficient for my personal use), is when I think that if i wanted to double the performance of 50mm, I'd need to go to 100mm. To double that, I'd be at 200mm, (etc. etc.). I don't think the extra 'efficiency' is worth it if you're in a space that's not massive in the first place. In a small space, a lesser effective 50mm is still probably a better option than a much more efficient 200mm, as the chunky walls can become a much bigger annoyance, in and of themselves.


(Again, though, me getting 50mm wasn't by choice - i couldn't get thicker for love nor money at the time. I can't recall how thick the floor insulation is, but i know that's not as thick as I wanted at the time either, for the same reason, but still we've had no noticeable or major heat loss issues in the 3-4 years we've had it built).




It is worth noting though, that the chap putting up the sheets of plasterboard was very much on the ball. He acknowledged that there's no point putting a meter of insulation on the wall if theres gaps between each sheet and they're put up ass-ways. He made sure it was tight and closed up and spent ages getting it right, so perhaps that helped a lot in the long run.


Also, and I am aware this point will annoy you in particular listermint, but we also didn't install any vents in the extension room itself (the hallway part to the side, has some, though). I presume this helps with holding heat, albeit I do 'air' the place regularly.