U values for wall insulation

[rreanor]

I've been using various online calculators for calculating u values for wall insulation, however they seem to vary considerably and make massive assumptions.

I need to decide how thick insulated plasterboard i install into some bedrooms - my property is a victorian semi detached, 2x brick skin without a cavity. The ceilings are higher than usual - 2.7m and there are large (sometimes bay) windows of at least 1.5m square, there is enough insulation in the loft above.

Is 62mm celotex/kingspan sufficient? I will be fixing it via batons, as there is no render externally and i dont want to remove all the plaster as its in good nic.

 

[Dereekoo]

Is 62mm celotex/kingspan sufficient? I will be fixing it via batons, as there is no render externally and i dont want to remove all the plaster as its in good nic.

Depends what U value for the wall you are aiming for

 

[rreanor]

Why would you be given a choice? Is the objective not just to retain as much heat as possible?

 

[Dereekoo]

Why would you be given a choice? Is the objective not just to retain as much heat as possible?

If that was the case you would put 1000mm thick insulation on your walls, more a case of having having an adequate amount to be cost effective in saving heat/money

Generally minimum requirement is based on building regs but people can improve on this if they so wish.

Current BR U value for new builds I believe is 0.18 at the moment.

In your case your achieved U value is 0.3

 

[rreanor]

If that was the case you would put 1000mm thick insulation on your walls, more a case of having having an adequate amount to be cost effective in saving heat/money

Generally minimum requirement is based on building regs but people can improve on this if they so wish.

Current BR U value for new builds I believe is 0.18 at the moment.

In your case your achieved U value is 0.3


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Thanks, do you mean the u value i've achieved without any wall insulation, or that would be the achieved value if i were to put 62mm PIR board on?

If the latter, would 0.3 be considered decent?

One thing i would say is that most new builds are unbearably hot during the summer, does this indicate that the target u value for new builds is basically too high?

 

[cdbe]

I suspect what you want to know, and something that interests me, is at what point do you start chasing marginal returns. As above, you could fit a metre of celotex and heat your home with a candle but a line has to be drawn somewhere. My extension is to the now old regs bug I'm wondering whether to insulate internally to beef it up - selfishly I probably won't as I don't want to lose the space and I doubt I'll see much payback in the 5-10 years we'll stay in the house.

 

[rreanor]

I suspect what you want to know, and something that interests me, is at what point do you start chasing marginal returns. As above, you could fit a metre of celotex and heat your home with a candle but a line has to be drawn somewhere. My extension is to the now old regs bug I'm wondering whether to insulate internally to beef it up - selfishly I probably won't as I don't want to lose the space and I doubt I'll see much payback in the 5-10 years we'll stay in the house.

Yes sort of, but i'm happy to put in 62mm insulation, but any thicker than that and it starts to become an issue. I guess what i want to know is will 62mm insulation make a big difference, or marginal? The 'real feel' of my house is that as soon as the heating goes off, you notice it starting to cool down immediately, whereas i compare it to more modern properties (even my parents 80s house which has insulated cavity) and it retains the heat for a lot longer.

 

[Dereekoo]

Thanks, do you mean the u value i've achieved without any wall insulation, or that would be the achieved value if i were to put 62mm PIR board on?

If the latter, would 0.3 be considered decent?

One thing i would say is that most new builds are unbearably hot during the summer, does this indicate that the target u value for new builds is basically too high?

0.3 achieved with insulation. Without it your U value is 2.12 so you would make the wall about 7 times more effective in retaining the heat

Building regs state that if a thermal element (e.g. a wall) is upgraded it should not have a U value of greater than 0.7 and suggests an improved value of at least 0.3 so your proposal can be considered to be within normal parameters.

 

[rreanor]

0.3 achieved with insulation. Without it your U value is 2.12 so you would make the wall about 7 times more effective in retaining the heat

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Building regs state that if a thermal element (e.g. a wall) is upgraded it should not have a U value of greater than 0.7 and suggests an improved value of at least 0.3 so your proposal can be considered to be within normal parameters.


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tHANK YOU VERY MUCH