I insulated my outer bedroom walls BUT . . . . .

Atlantic1

I've posted about this already in an itsy bitsy fashion but I'm pulling everything together here.

My house is cavity (hollow) block build. I recently put insulated plasterboards on all the external bedroom walls.

The walls were already drylined. I thought it was with 12.mm plasterboard on wooden battens but, I recently discovered it's 15mm plasterboard put on with dot and dab.

Instead of taking this plasterboard down, I put insulated plasterboard on against it and fixed it to the cavity block with 140mm metal fixings.

I went with 62.5mm of Kingspan TW52 which was the only insulated plasterboard the builders providers had in stock.

I realised, too late, that TW52 isn't foil backed and only has a thermal conductivity of 0.026. I now realise that I should have used Kingspan TW56 which is foil backed and has a thermal conductivity of 0.22, or some similar product.

I had originally hoped for a fairly decent U Value. I contacted Kingspan and got in touch with a very helpful guy there. He did a full U Value calculation on the walls and calculated their U Value at 0.41, which I am disappointed with.

He also told me that condensation between the original plasterboard and the cavity block may lead to problems as the TW52 isn't foil backed and doesn't act as a vapour barrier.

I was more concerned about this but, having spoken to him again, it appears that mould on the walls may not be a major issue going forward as I never had any on the original plasterboard and the outer walls are in good condition.

I know that, if I had contacted him before I'd started the job, things would have worked out much better, e.g., by using TW56 I'd have a lower U Value and little or no risk of condensation or mould problems. And if I had removed the original plasterboard, I could have used thicker insulation.


I've been beating myself up over it since doing the job a few weeks ago. I know that I can't change things now and I won't be taking it down to replace it with better insulation as it would be too big a job and too expensive. It's just that, for little or no extra cost, I could have had a much better result.

I'm just interested in getting people's obversations and views on it . . . . . .

Thanks in advance.

Atlantic1

I forgot to mention that the gentleman at Kingspan calculated that if I'd used 62.5mm of Kingspan K18 instead, I'd have a U Value of 0.34, which I'd obviously be much happier with.

And he also informed me that they're now making their TW52 insulated plasterboards with a foil backing. I obviously got ones that were made just before they started making them this way.

BryanF

Atlantic1 wrote: »

I
He also told me that condensation between the original plasterboard and the cavity block may lead to problems as the TW52 isn't foil backed and doesn't act as a vapour barrier.

I was more concerned about this but, having spoken to him again, it appears that mould on the walls may not be a major issue going forward as I never had any on the original plasterboard and the outer walls are in good condition.

isnt it wonderful how much comfort you can get for a company rep over the phone - first he's concerned, then he isnt... :pac:

you've altered the due point location by adding internal insulation. I'd be happy with the .41 w/m2k - with fingers crossed on the mould.

Atlantic1

BryanF wrote: »

isnt it wonderful how much comfort you can get for a company rep over the phone - first he's concerned, then he isnt... :pac:

you've altered the due point location by adding internal insulation. I'd be happy with the .41 w/m2k - with fingers crossed on the mould.

Hi Bryan. In fairness to the rep, it was he laid out the condensation/mould risks first and did say for a finish that it was a fingers crossed situation also. He was concerned, to be fair to him.

Like I said, I'm just going mad because I could easily have done much better in hindsight.

You think 0.41 is reasonably ok? That cheers me up a bit!

I have a few more rooms to do still. I'm thinking of taking down the existing plasterboard and scraping off the dab and putting 60mm of rigid insulation board directly onto the wall, taping it and putting 12.5mm plasterboard over it, mechanically fixing them to the wall. That would give me a U Value of around 0.28.

What do you think?

BryanF

Atlantic1 wrote: »

Hi Bryan. In fairness to the rep, it was he laid out the condensation/mould risks first and did say for a finish that it was a fingers crossed situation also. He was concerned, to be fair to him.

Like I said, I'm just going mad because I could easily have done much better in hindsight.

You think 0.41 is reasonably ok? That cheers me up a bit!

I have a few more rooms to do still. I'm thinking of taking down the existing plasterboard and scraping off the dab and putting 60mm of rigid insulation board directly onto the wall, taping it and putting 12.5mm plasterboard over it, mechanically fixing them to the wall. That would give me a U Value of around 0.28.

What do you think?

Google/See 'breaking the mould' series of documents - it all depends on your existing construction and your certifiers confidence in due point assessment. I don't have it to hand but 0.45wm2k rings a bell as max dry-lining for non-insulated existing block walls. Read the conclusions of the series mentioned above.

rickmoister

You could try sealing the wall with a liquid type vapour barrier google it and I am sure there is a product available.

Atlantic1

Could someone please tell me where the dew point was before I insulated the wall.

(Standard cavity block drylined with 15mm plasterboard using dot and dab).

I removed a small section of the plasterboard in another room to have a look. The air space between the board and the wall is minimal. Only a few mm.

Thanks.

rickmoister

As there was no insulation dew point was probably on the surface of the plasterboard.

Atlantic1

Thanks, Rick.

Because there's such a small air space (only a few mm) between the original plasterboard and the cavity block where there isn't any dot and dab, will this reduce the chance of dampness and mould?

MicktheMan

Atlantic1 wrote: »

Could someone please tell me where the dew point was before I insulated the wall.

(Standard cavity block drylined with 15mm plasterboard using dot and dab).

Towards the centre of the wall.

MicktheMan

rickmoister wrote: »

As there was no insulation dew point was probably on the surface of the plasterboard.

incorrect