Insulated plasterboard/slab is it worth it.

grimeire

Hey,

So currently renovating a house with 6" cavity and no insulation in the cavity. Just had fitted triple glazed windows and doors with u-value of 0.07 as it was working out less than 10% for triple glazed vs double glazed with u-value of 1.2

Going to pump the wall with insulation and wondering what u-value I could expect in an ideal world for with this? Currently its smooth plaster finish < standard block < 6"/150mm cavity < standard block.

Wondering is it worth my while now with the price of insulation of putting a 50mm(38mm insualtion + 12.5mm) slab around all the external walls on top of pumping the walls. The internal walls need to be plastered so really the only cost here is going to be the plasterboards slabs as i can fit them myself.

Thanks

Tefral

When you say the walls need plastering are they bare block currently?

If so you have a great chance to increase your airtightness here which would be a big help. You would need to parge coat the walls or spraying blowerproof membrane on the block before slabbing them as standard block is very porus to air.

Id get someone to do U-Value calcs first. I would always advocate keeping your insulation in one place to reduce the likelyhood of condensation issues. Slabbing the walls reduces your thermal mass also - your house will cool quicker when the heating is off as it doesnt have the concrete walls as a thermal battery.

Furze99

I thought a standard cavity in times past was 100mm or 4" - so total wall width of 300mm or 12". Building regs 20 years ago stated 60mm insulation against the inside leaf and 40mm gap for moisture/ ventilation of cavity. Wall ties were supplied to suit with a drip kink cavity side of the insulation.

6" or 150mm cavity seems fairly wide, why built like this with no insulation slabs placed at same time? Regardless I'd have thought that if you can fully pump a 6"cavity and happy about loss of air gap, then that's pretty good. The interior leaf should be well insulated and absorb/ retain heat.

grimeire

the place is only a few years old. Was built for other purposes hence why the inside was not done but put in larger cavity for future proofing. 6" cavity not is that wild was working in a lot of houses before that had 8"+ cavity and got them pumped.

Not sure is it worth doing with airtightess and it would not be cheap. The tape around 2 windows alone would be like the best part of €80 and then would probably need heat recovery or ventilate each room which would add additional costs that probably are not going to be worth it in the end. Im going to have to buy plasterboard for the walls anyway so from my estimates it would be around an extra grand to get the insulated slabs.

any ideas what 350mm cavit walls U-value is with a 150mm cavity thats pumped?

MicktheMan

Not sure is it worth doing with airtightess and it would not be cheap. The tape around 2 windows alone would be like the best part of €80 and then would probably need heat recovery or ventilate each room which would add additional costs that probably are not going to be worth it in the end. Im going to have to buy plasterboard for the walls anyway so from my estimates it would be around an extra grand to get the insulated slabs.

You may very well regret this decision. Do you realise that, in our climate, generally more heat is lost through lack of air tightness that lack of insulation.

0ph0rce0

Whatever about u values and ber's I have a gable wall to the side garden, just cavity blocks and dabbed plasterboard.

Gaff was freezing, threw a few 50mm insulated boards on the gable wall and haven't had to turn the upstairs heating on in 2 years.

Best 600 quid on materials I've ever spent.

grimeire

https://www.boards.ie/discussion/comment/120380792#Comment_120380792

you could be correct but going the full wack with airtightess i dont think is nessacary as the place i live in at the moment is not air tight and only has a stove for heating.

We stopped burning coal as it gives off too much heat so only burn timber and rarely refill the stove as it gets too hot. Only air tightness that was done in this place was around windows. This place just has a 50mm slab around all external walls, no cavity insulation and 100mm solid insulation in attic and double glazed windows.

Back when that was being built insulation was half the price it was now hence why the question is it worth the cost in this case.