Loft Insulation

[Andy Hall]

Supawrap from BuilderCenter is £12.66 exc. for 4sqm and 150mm thick.

So for 70sqm coverage you would need 35 rolls to achieve a thickness of 300mm at a total cost of £520. This appears to be the cheapest they have on a volume basis. You could probably get 20% discount, so say £400.

On your assumed U value of 0.5, which is worse than it probably is, you are saving 588W worst case.

If the temperatures were worst case all year all day then at 1.4p a unit for gas you would save £72 per annum.

If you work on the 10 degree average which is closer to reality, then the loss is going to be 8/21 x the figure - i.e. 220W and £27 per annum.

In reality, the insulation you have is probably better than 0.5 and the saving perhaps £20 per year.

A 20 year payback or 10 years if energy costs double today....

Doesn't seem interesting to me.

I'd think about using even a thin Celotex layer on a few outside walls during redecoration first, if that's practicable. This is about £5/sqm for 50mm, 25mm is about £3.50.

.andy

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[Andy Hall]

Exactly. See my other post. Slightly different prices, but the principle is the same.

.andy

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[Neil Jones]

Exactly, although I'm looking at Kingspan rather than Celotex.

[IMM]

You have to look at individual upper rooms.

Not in that room it isn't.

It is NOT! It is looking at the house realistically, instead of one blob of a box.

If these wo rk then I will. Do you have a URL?

Figures? For what type of house? Do they all one bedroom wall top to toe built-in cupboards? Etc, etc.

The devil is in the detail. Your detail was not fine enough. It is worth having high levels of insulation in my house just to keep the bedrooms warm and cool. For those who have an upper room as an office the benefits are even greater. Keeping bedrooms cool is good in preventing cots deaths too. I'm sure the lower rooms didn't benefit too much.

Even in the depths of winter, once the bedrooms are up to temperature, the TRVs virtually stay off all day. I have the bedroom doors always closed, so no heat is rising from downstairs into them.

[IMM]

You did? Do you laugh at the Vicar of Dibley too?

[IMM]

Because you haven't looked at it properly.

[IMM]

Do both. Loft and walls.

[Neil Jones]

insulation

Of course I'm looking at the whole house. I pay the whole gas bill, which covers the heating for the whole house. If I only paid for my study, and my wife paid for the rest, then I'd turn the radiator off in that room and buy a few jumpers.

That's right - the extra 300mm required to take it up to the 400mm you requested. Well spotted.

You have to

I did, actually, because the costs I have been quoted for the Kingspan alone are less than I mentioned, but I allowed extra for battening etc.

Loft

As I have shown, the loft insulation is the same cost and has a much smaller benefit, so it is lower priority.

Also do downstairs too with

Do you think I am made of money? If my budget is (lets say) £400, it's either/or, not both. Insulating the downstairs wins hands down because it has a much bigger effect for the same outlay.

Regards

Neil

[Neil Jones]

thickness

discount,

Do you live in the real world? Money is finite, and so we prioritise.

[timegoesby]

Just to add my 2p. I insulated my loft to 150mm. I had lots of insulation over so doubled up over the main bedroom where I sleep. This bedroom is warmer in winter, and thankfully last summer a lot cooler. I could always sleep while neighbours complained they were too hot to sleep in similar houses to mine. When I have time I will do the whole loft to at least 300mm. If I can get a decent deal maybe thicker. To me it will be worth it. I don't know about economics as I haven't kept a watch on the gas bills. To me that is not the real issue during a hot summer.

[Andy Hall]

OK. So present a worked example of a typical house of today, yours if you like, and show figures for why you believe this is significant in the context of this discussion.

Obviously this is important in terms of heat emitter sizing but that is not the discussion here

OK, so why don't you present some real figures and workings to demonstrate your point.

On that argument you would insulate different rooms to different degrees.

If there were a real issue here, rooms would be insulated from one another in addition to anything related to external surfaces. Unless one wants to deliberately maintain a temperature of one room at a significantly different temperature from the others, insulation between them is not used, simply because the overall differences are

6-8 degrees.

Just provide a typical example with worked figures to demonstrate your point if you believe there is one.

So please provide the detailed data and worked examples to justify these assertions. Yes I know that cooler bedrooms impact SIDS so you don't need to search Google for those numbers. Stick to the point of providing the detailed data on the extent to which insulation at your recommended 350-600mm makes the large difference that you claim relative to 100-150mm, stated in the context of the house in total.

.andy

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[Andy Hall]

No, just at your notion that 2.5% is meaningful when compared to a context of over 30% for the solid walls.

.andy

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[Andy Hall]

OK so present the hard data with numbers to justify that assertion. A complete example as I did and as Neil did separately.

.andy

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[Andy Hall]

As compared with having nothing? It would be. That is certainly worth doing but was not the point.

With how much insulation?

That's fine if you want to do it, but there is nothing to support that just doubling the insulation like this is going to make any significant difference to what you have now.

.andy

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[IMM]

NO need, common sense prevails.

Could be. You could do all the bedrooms to 400mm and 200mm the rest.

Most walls have some sort of built-in insulation.

Just use some common sense. Bedrooms have a large loft ceiling area with a very cold or hot loft above. Insulating these to high degrees pays dividends in the particular rooms below.

before> >> >> makes a significant difference to the overall effect in the house, I

Just use some common sense, instead of just looking at a Myson heatless programme.

[IMM]

Apply some common sense and don't keep relying on a Myson program.

[IMM]

Can't you read? he said that he doubled the insulation over his bedroom and it was better comfort conditions than the neighbours.

[Andy Hall]

Not with you it doesn't. If you can't produce figures, that's OK but makes further discussion rather pointless.

If you do heat transfer calculations between internal rooms, the numbers are usually fairly small. Sometimes, heat gain from a lower floor room to an upper floor room can result in reducing radiator size a little, but that's about all.

More of the same waffle.

I look at a variety of sources, all of which provide hard data.

.andy

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[Andy Hall]

You don't need a Myson program or any other to determine heat transfer through a surface. A pocket calculator is perfectly adequate and the methods of calculation well charted.

.andy

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[Andy Hall]

That isn't what he said at all. He said that he insulated it to

150mm, but did not say what was there before. If it was nothing, then of course there was an effect because the U value is reduced from about 2 down to less than 0.4

Do you know about how to calculate thermal conductivity and use U values?

.andy

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