Insulation, when is more not better

[IMM]

There is no problem of overheating. Where do they come from?

[Ian Stirling]

No, it's not. If you end up living in a 2m*2m*1m box, and having to constantly actively cool, then you've probably put too much on.

[IMM]

You can fit a duct that is built into the wall that fans this hot air back to ground level.

It is not a matter of robbing Peter to pay Paul. You insulate properly,

0.1ish for the walls. Buy the book, The Whole House Book, all is there, all the figures. Don't rely on the advise of inexperienced people making it up.

Spend more on insulation and eliminate a full hearting system.

[Ian Stirling]

Unless you are insane, there is no point in insulating better than where the minimum solar gain plus energy emitted by the house equipment and householders causes a temperature rise high enough over ambient that it'll be warm enough even on the coldest blizzard.

Adding more just reduces habitable volume, and adds cost. You've also got to consider on whether you want to hit this level.

At what point does the income of just sticking the money in the bank of a portion of your insulation at base-rate exceed the savings on possibly rising energy costs.

[IMM]

overheating

It is obvious you don't know enough about this subject. Do a Google on "superinsulation" and a raft of information comes up. Read it all.

[Dave Stanton]

Surely the rule of diminishing returns applies here.

Dave

[Tom]

Except around a pipe!!

[IMM]

???

[Tom]

Sorry, I was just making the point that whereas increasing the insulation on a plane surface is always additive hence your supposition "more is better", on a pipe it is not so. Sorry to butt in. Cheers Tom

[Ian Stirling]

Even around a pipe, but to a much, much lower degree.

[G&M]

Not in a conservation area you don't. I would love to as my windows are under 12% of the wall area.

[G&M]

This can happen in some very modern highly insulated houses but for most of us doing up existing houses it ain't going to happen. There will always be thermal bridges and so on leaking heat.

And if it does happen all one has to do is use low energy lighting and so on.

[G&M]

Yes

Nope. 50mm of Celotex has a U value of 0.46

[Ian Stirling]

For large values of slightly :)

I think I meant to type 10mm, but got confused.

[IMM]

or open a window

[Tony Bryer]

^^^^^^^^^^^^

Given that more than a few buildings are constrained by having to be x from the boundary or some other limitation, increasing the wall insulation thickness reduces the internal floor area. This is more than just 'incidental' IMO.

[IMM]

Well move and get a proper house.

[Tom]

On a pipe, I assume the surface area of the insulation increases by a factor of approx 6.3 times the thickness of the insulation, I'm afraid my maths is not good enough to work out at which point it starts to be non effective. Perhaps there are some mathematicians out there that can help on this one.? Tom

[Ian Stirling]

It never starts to be non-effective, it's always better than air. It rapidly starts to have a vanishingly small effect. Consider the heat flow.

The heat flow from the surface of the pipe is the same as the heat flow from the surface of the insulation. (once it's all reached steady temps) This means that the temperature difference across the last little bit of insulation depends on its area. So, at ten times the pipe diameter, the insulation is only doing

1/10th as good a job as that just next to the pipe. If you need a very well insulated pipe (or worse, tank that's small compared to the insulation) then it usually pays to buy some really expensive insulation to put next to the pipe,

For example, considering the insulation at various numbers of times the pipe diameter from the surface of the pipe. (1 is next to the pipe)

Distance from pipe Relative insulation

1 1 2 1/2 3 1/3 4 1/4 5 1/5

Total=2.28 (this is inaccurate, finer and finer graduations would give a more accurate idea, but this is ballpark)

So the last fifth has contributed about a tenth. But it's a third of the total volume.

[The Natural Philosopher]

I went with 2x rockwool purely on cost. It was good enough.

Despite IMM's blatherings, once you meet building regs U values, you are already into the law of diminshing returns as unless you put in heat recovery ventilation, and have no windows, the majority of the heat loss will be via the windows and ventilation - which you need to avoid steamy damp atmospheres in winter anyway.