30mm Vs 70mm Insulated Plasterboard on External Wall

FrankN1

Hi there,

Currently hallway is very cold. Semi D house and external wall bring in cold. Can't pump the wall with insulation as it's cavity brick.

But there is 30mm insulated plasterboard. I'm wondering if I dryline it to 70mm would it make a big difference or should I just do external wrap insulation?

Cost for internal maybe 4k Vs 10-12k external.

10-10-20

Internal insulation is a sticking plaster when a full wrap is what the doctor ordered. 👍️

FrankN1

https://www.boards.ie/discussion/comment/122511134#Comment_122511134

A lot of people say that but if the plaster does 75 percent of the job for a third of the cost then that's perfect for me

We dry lined all external walls on our semi with 120mm foil backed insulated plasterboard. It's worked remarkably well with very stable temps without any heating since early April.

Do it right and pay attention to board sealing and opening sealing with airtightness tape and it can be highly effective.

Can also be an entirely DIY job that will cost a quarter of what external insulation will cost. It's not as good as external - but can you afford the extra cost for the relatively small overall gain.

FrankN1

Unfortunately I think there is only space for me to do 70mm but still wondering if I should do it or not..the cost is about 4k.

https://www.boards.ie/discussion/comment/122511219#Comment_122511219

I heard people say that there's not much gain after 60mm since the various leakage paths would start to dominate, but I cannot say if that is so.

Airtightness is half the job and if you externally insulated and don't go and seal all air pathways you are wasting a lot of the effort - at least you get to do it in one pass with dry lining.

DC999

https://www.boards.ie/discussion/comment/122511528#Comment_122511528

@Shoog, I'm just about to do this myself. Could you pls let me know how you fixed to the wall? As in batons, or direct to wall using adhesive (what type) and what type of mechanical fixings? And what air tape did you use? Am a little paralysed trying to find the info before I can other it. Or could u let me know if there is another decent thread on this on boards? Search feature isn't great. Cheers

https://www.boards.ie/discussion/comment/122520252#Comment_122520252

I used foam glue adhesive to glue mine to the walls. Get a glue gun for this and also a tin of glue gun cleaner to use between glue cans.

In order to be fire safe you also need to add at least 4 mushrooms to each board. These are 150mm long (different lengths for different boards) and hollow, they are pressed out of galvanised metal and the spike has a slot down its side which should be hammered in with the slot downwards. This allows any condensation to drain out of the shaft. In the case of a fire these will hold the board even if the foam glue melts.

Procedure is;

• spray a permimeter bead of foam on the back of the board and at least two more from top to bottom. Make this continuous to create a closed aircell on the back of the board.
• Lightly wet the wall with a hand spray bottle (aids adhesion).
• get a second person to lift the board into place and hold it there, you will want a board lifter for this.

• drill your mushroom holes and hammer in your mushroom plugs until they are just below the surface of the board. Try to judge your hole depths so they don't punch through your block and create a air pathway to the cavity, failing this will significantly compromise the end result.
• spray a dab of foam down the shaft of the mushroom. Spray foam into any large uneven gaps between the boards.
• air-tightness tap over the heads of each of the mushrooms and down the seams between boards and at least along the top where it meets the ceiling.

This is the cheapest airtightness tape available in the country and very good. Its more of a cloth and very sticky. You will want special window tape for sealing round windows

https://www.ecologicalbuildingsystems.com/product/tescon-vana

Hope that helps.

10-10-20

The mushrooms don't need to be angled-in, they aren't a pathway for moisture. Keeping them horizontal makes it easier to bed them in below the surface of the boards anyway. These are the end-caps which prevent stains on the paint finish.

https://grange.ie/product-detail/small-38mm-wide-nylon-cap-for-mushroom-plugs-100-pack

Thread on it all here, if it helps:

https://www.boards.ie/discussion/2055278598/insulated-plasterboard-and-mushrooms

DC999

Thanks @10-10-20 and @Shoog - appreciate the steer!

Calahonda52

Couple of things to consider here:

Heat loss through walls helps to dry out the wall.

IWI will mitigate against that process.

30mm vs 70 mm

70 will drag the dew point in closer to the interior face of the wall.

EWI will do the reverse, as well as keep the wall dry, assuming you get a proper rain shield.

Teson tape is world class but its one way, it wont come off if the substrate is providing sufficient adhesion, it will actually delaminate rather than peel off

https://www.boards.ie/discussion/comment/122520456#Comment_122520456

Just to be clear, I never suggested sending the mushrooms in at an angle - the slot in the mushroom should be on the bottom when they are hammered in horizontally.

https://www.boards.ie/discussion/comment/122520566#Comment_122520566

If you use the correct boards there are effectively two foil vapour barriers between the house inside and the inner wall surface. Additionally the cavity is still there to allow moist air to escape at the top of the wall.

Gusser09

I have a semi d that was wrapped. Cant beat it.

I got an extension on the side with 92mm insulated plaster board which is grand but nothing compared to the wrap. Im getting the extension wrapped asap.

10-10-20

https://www.boards.ie/discussion/comment/122520621#Comment_122520621

Ok, misunderstood you there.

FrankN1

Would anyone know companies that do this? Don't want to try it myself as it's too big of a job

https://www.boards.ie/discussion/comment/122521158#Comment_122521158

Any plasterer should be well up for it.

FrankN1

https://www.boards.ie/discussion/comment/122521173#Comment_122521173

Just don't want to get someone who will half ass it and do it as fast as possible and not make it airtight or to fire regs.

https://www.boards.ie/discussion/comment/122521209#Comment_122521209

Yep that's all an issue. There is quite a bit more work than many plasterers are used to or familiar with. I would stear well clear of old blokes as they can be very set in their ways and fail to grasp what you are trying to achieve.

Also something to note is that you need to document all the details with photos and receipts as proof for your BER.

FrankN1

https://www.boards.ie/discussion/comment/122521318#Comment_122521318

Can I ask what insulation did you have before and after it?

10-10-20

https://www.boards.ie/discussion/comment/122521318#Comment_122521318

My point about insulated plasterboard is that it doesn't resolve the cold bridges within the boundaries of the room, where EWI would normally do that. So when comparing EWI to insulated plasterboard as the original poster did, you can't really compare the two as they are chasms apart. But to improve the heat-loss overall in a single room, it's a very good solution as long as the overall heatloss has been assessed and the walls are found to be the most significant contributor to heatloss.

Calahonda52

https://www.boards.ie/discussion/comment/122520627#Comment_122520627

You are assuming g that the cavity is open.

In any event, with 70 mm IWI, it wont be moist air, it will be water, from outside and inside as unless you go with a proper A/T layer and a service cavity, there are always holes in the foil layers.