So, about 5 to 6 years payback at current fuel prices. As fuel prices rise the payback drops as well, so maybe 3 to 4 years. After that you are saving probably £30 plus per ann as fuel would have risen in price. Also it keeps you cooler in summer and increases comfort conditions. A win, win situation.
This one can't focus. He is going on about choices, when the point is insulating the loft.
NO. On a house built to current building regs standards the heating and DHW costs are not much more than £100p.a. and the saving from increasing the loft insulation from 200mm to 400mm will be about 4-5%, £4-5p.a.
If the house is built to a much lower standard with said costs being £500p.a the saving will still be £4-5 - insulating the roof will do nothing to stop all the heat losses elsewhere. Payback time - longer than you are likely to stay in the house, and that's disregarding the interest the money spent on this excess insulation would earn in a savings account.
That is the point in question.
Which is irrelevant.
Around £120 worth. Are you kidding?
200mm doesn't meet the current building regs. I was referring to a 70s house.
Agreed. But it will reduce heat loss through the roof by the amount quoted - about £20-25pa if heating bill is £500pa.
Increasing the insulation from 200mm to 400mm will save £5 or so regardless of what the rest of the house is made of. If it's a 70's house with 50mm insulation going to 200mm will save you about £17p.a. so is worth doing; going to 400mm will save you an extra £4p.a. and patently isn't.
Anyone with the least understanding of these matters sees that whilst each additional 25mm of insulation costs the same (more or less) the saving diminishes. There's an ODPM study on polyurethane insulation boards in cavities that shows that beyond a certain point you will almost certainly never recover the energy used to make the board, and even for 'normal' thicknesses there isn't an overall net energy saving for a number of years.
That is most definitely NOT what it says. It concludes that for all normal situations the energy in making the board can be disregarded. Of course if one was to consider using several feet thick of it the time to recover the energy would be long but there are few situations where the energy is never regained. Please go and read it again.
I'd agree with all this, subject to the type of heating, ceiling area and heating needs...
Not so sure this is a good way of looking at things, as energy price rises are likely to outpace interest rates in the long term.
Also against a backdrop of high energy prices and a flat housing market, a well insulated house with efficient heating is more saleable than the opposite.
cheers, Pete.
Never said anything else. But okay - let's calculate the saving.
Assumptions (from ODPM figures) :
200mm of insulation has a U value of 0.2 400mm of insulation has a U value of 0.1 There is no effect of the walls on the heat loss though the ceiling - the owner turns the heating up if it's too cold Insulation to be placed flat on top of ceiling Reduction of insulation due to joists is roughly cancelled out by insulation of plasterboard, tiles, etc so will be ignored. Typical detached house has 50 sq m of upstairs ceiling Typical house is heated to 18 deg C Average outside temperature is 11 deg C for the nine months heating is active. Energy costs 3p/kWhSo with 200mm of insulation : Heat loss per annum = 50 m^2 * 0.0002kW/m^2K * 9 degK * 24 hours * 270 days
Increase of cost of 400mm insulation over 200mm = 50 * £2.25 = £113
Therefore ROI = 7.75%.
This is about halfway between our finger in the air estimates and to my mind is worth doing. Of course there are numerous other things which are worth doing as well but the problem is many of these cannot be done to existing properties either for constructional or conservation reasons. Loft insulation is one which can easily be applied to most properties.
The ODPM have a list of the gains to be had somewhere on their site (or used to) and the one thing it really showed was double glazing is the one where payback is marginal at best yet this is the one most people go for.
That's a very small detached house--- = 600 sq ft 20@ x 30'
Bloody freezing, comfortable sitting temperature = 75F = 24C
Can't quite reconcile 11C =52F as average temperature, depends on where you are and other conditions. Seems too high.
Bear in mind that a floored loft has only minor air currents, so the insulation values of the glass fibre--etc-- approach the theoretical values. Unfloored, the local draughts, totally destroy the insulation value of fibre layers, so flooring is essential if fibre alone is used. Also, a floored loft is normally covered in a thick layer of junk, which adds considerably to the insulation values for no additional costs!
Regarding ROI, many stock market investments will give returns in excess of 10% when capital gains are taken into account (IIRC LLoyds TSB is currently yielding around 7-8% in dividends alone). Quite a good case for using the money elsewhere can be made.
Just a few comments. Regards Capitol
times 2 - I was assuming an upstairs as well. And I think if one just counted this year's new builds it's even smaller but that's
Not in the bedrooms surely. I'd be suffocating at that. But then again that's probably why a mate of mine spends nearly £3k pa on oil whereas I spend £300.
I thought that as well but it's from the official numbers. I suspect it's the average temperature in the centre of London, anything north of Watford not counting of course.
But there's then tax to pay. And I seem to recall most stock market investments took a 33% jump downwards a few years ago.
I agree with you it's an inverse law (iirc) ie. law of diminishin returns, so that just piling it high doesn't help.
have you tried the calculations for just air ;-) (having done thes sorts of calcs for some very harsh conditions a number of years back)
not so amazingly air is a better insulator than any solid (think doubl glazing) the trick is in stopping the air moving (natural to force convection heat transfer) which is what the insulation material i doing at best (thinks I).
reasonable amount of insulation material sounds good; boards on top although probably not in themselves having a significant insulatin property will provide a barrier against any drafts which yield force convection conditions so sounds good possibly the silicongun to sea big holes, thinks however, I would suspect that some ventilation i needed to stop condensation/damp etc. so some thought required here t let the air change/circulate a little
regards, newboy (theoretician
-- newboy
Actually it does. Read the thread. Lord Hall says chipboard improves thermal insulation. In fact the insulation value is so low it is not worth considering. His calcs are flawed.
Yep. Not as good as the results when using insulation material.
Yep it is. That is why insulation has very small air pockets to prevent air circulating. But insulation material is better than air.
No. Water vapour will rise up through insulation and through the chipboard. You can lay a vapour barrier on the ceiling to prevent/reduce water vapour.
I did not say that chipboard improves insulation.
Go and check the threading and you will find that the OP did.
You may also wish to study the meaning of the terms "law of diminishing returns", "context", "3rd order effect" and "why black is white".
Read above: "Adding an extra board layer in this way must logically be a way to improve thermal insulation."
It improves it so little it is not worth taking into account.
And 400mm is well within diminishing returns. Read the thread and what others who this better than you have said.
Not so. You go around the loft with a silicon gun and seal up all holes and cable and pipe penetrations. You can also lay a plastic vapour barrier that is good practice to prevent warm water vapour entering the loft in winter and then condensing in the loft. Ifthe ceiling is ait-tight, no open water tank to evaporate, and has a vapour barrier, realistically the vents in the eves can be reduces by about half..
Until oil prices rise again the frequency they do. If you want to save money and make in the long run, add 400mm of insulation, making the ceiling air-tight and boarding, is great investment all around. Then there is the super cooling and comfort conditions it adds.
I have. Go and check back in the thread and you will see that it was not me who said that. Once again you have been cutting and pasting and have fitted the pieces together wrongly.
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