Spray foam into cavity blocks?

MontgomeryClift

I have a situation where I need to build on cavity blocks so I'll be using more cavity blocks, but I need to insulate them. Could anyone please tell me: Would it work to spray insulating foam into each block and allow it to harden and expand before laying the blocks?

Viking House

Sorry! That would not work! there would be too many cold bridges.

MontgomeryClift

Oh. I thought they filled cavity blocks after construction. Thanks for letting me know. Any other ideas? The wall could be insulated inside afterwards but wouldn't it be better to insulate the wall itself somehow?

I was looking at these, but apparently they're hard to lay right:
http://www.roadstone.ie/products/Blocks/SafeWarm.htm

fatchance

My wifes old family house was built back in the 50's with cavity blocks, recently we did it up and the option we decided upon was to use insulated plasterboard on all the external walls. It's made a huge difference, fitted them myself and got plasterer to skim them.

Viking House does not agree with using insulated plasterboard, because it brings the dew point to the inside of the house (condensation). I'm still confused about this?????????????????

The insulated plasterboard we used was kingspan and it had a vapour barrier incorporated in it (what exactly this does I'm not sure). I can't see any condensation if any being caused, the heat is kept in the room and does not make it throught the insulation to the outter wall to cause condensation. And even if it did, the amout would be minimal. However, if someone explained it properly then I might change my opinion, all I know is that the rooms are alot warmer and we have encountered no problems at all.

MontgomeryClift

OK. Thanks. That's an option then.

It's been suggested to me that instead of putting cavity blocks on cavity blocks I could have the carpenter build a timber frame inside the gables. Then I could use 4 inch cavity blocks on the outside and insulate the frame inside. This would presumably provide for about 5 inches of insulation.

Could anybody please tell me if this would be worse than the insulated board or if it would be a bad idea generally? Would it be a problem that parts of the timber frame would be uninsulated because they'd be 5 inch timber? What would the situation be regarding dampness?

fatchance

Viking House wrote:

When you dryline you only insulate 90% of the wall because you are not insulating the parts where the middle walls and floors meet the outside. Drylining with polyeurethene backed plasterboard causes fungus and mould growth.

I am a little confused about this fungal growth/mould issue? I intend using kingspan's wt52 insulated plasterboard on all my external walls and will have the cavity pumped with Warmfill beads (Co.Down company). The cost of using kingspan in the cavity was dearer than pumping it and pumping is a much better option. Mould and fungus occur where there is a consistent moisture level present. This is not an issue generally with new builds. The cavity insulation prevents the temp of the inner cavity wall from getting cold, and the insulated plasterboard keeps the heat in the room so and temp conflict does not occur which might cause condensation. Even if it did cause a small degree of condensation, which I doubt, it would be minimal and not a issue.
For arguments sake, say there was condensation and this eventually caused slight mould which was behind the skimmed plasterboard, the vapor barrier and the insulation, why would this be a problem? It's not going to be a mushroom field in there, there just isn't enough of moisture to cause a problem.
Just my 0.02$ worth!

As for fixtures, total thickness of insulated plasterboard is 42mm and then you are into concrete, so all you need is longer screws, no problem.