Loft Insulation

These are quite typical numbers, Neil.

I guess that this is an older house with a new extension?

It's interesting to note that the losses are close to being the same upstairs and downstairs.

.andy

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Thermal conductivity of mineral wool = 0.038

U val = 1/9.9 ~ 0.10

Losses through ceiling reduced to 70 * 0.10 * 21 = 147W

Saving 588W, 5% of the total loss previously. How much does it cost to buy 70 m2 loft insulation, at a depth of 300mm?

Also what

What about it?

Yes. The old part is 500 year old, or so. The extension was bulit in

Quite.

The U value for 100mm of mineral fibre in a pitched roof construction is 0.36 according to BS 5449.

So in fact Neil's heat loss via this route is less than suggested and more like

This is about 4% of his total 12.3kW

Increasing the insulation to your suggested level might achieve a U value of 0.15 taking the heatloss down to 220W.

This represents a difference of 2.4%

Not very interesting in the context of 20% going out through the solid walls.

The only effect that can happen there is to assume that the hallway downstairs is at downstairs temperature and that the landing above will achieve the same temperature via convection.

In most houses the upstairs landing might be 15-20% of the total upstairs area, so in essence the landing becomes 3 degrees warmer than the bedrooms. the impact is demonstrably marginal. Another corner case.

They look remarkably similar, even accounting for convection from downstairs.

If you think that that is a win, win then you are missing out on much bigger prizes.

Somebody once related the following tale to me, which seems apropos.

There were too bulls standing on the top of a hill and below them a field of cows.

One was always enthusiastic about chasing the latest idea, so he said "Cor. Look at that lot. Let's run down and f*ck one of them"

The other one said

"Let's walk down and f*ck all of them"

.andy

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In fact I deliberately increased the U-value of the loft because I don't know exactly how much insulation there is throughout the whole thing - part of it is inaccessible at the moment - and some of it appears to be somewhat low quality.

Yes, and all the exterior walls and windows have an even larger area that is hot in the summer and cold in the winter.

Please provide the figures to demonstrate that assertion.

If you are saying that adding insulation where there was none before makes a significant difference to the overall effect in the house, I will accept it. I don't accept that insulating up to 300-400 mm rather than 100 or 150 makes a huge difference to the *total* for a house because the figures don't support that.

If you can demonstrate, for an existing property, (not an eco-special), with independently verifiable figures and quantitative references that doing what you propose makes a difference of more than a very few percent then there is something to discuss.

Otherwise you are just doing your normal arm waving with nothing substantial to back it up.

.andy

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U value of mineral wool of 100mm is 0.36 according to the British Standard, Neil, so I think you are probably better off than you think with respect to the roof, and the difference is not as substantial as this suggests. I reckoned that this would save about 2.5%.

.andy

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Must be regarded as a ground floor room.

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

The word you are thinking of is slightly. As has been repeatedly pointed out, we are currently insulating to levels where providing any more has a minimal effect.

On the typical 108m2 2-storey house file we supply with our SuperHeat program the structural heat loss with a roof UV of 0.18 is 111.92W/K which would fall to 105.15 if you could get the U-value down to 0.05. But at this point with a condensing boiler the energy split is roughly 33% fabric, 17% ventilation, 33% DHW and 17% system losses, and the cash saving shown on the SAP worksheet is £5.78p.a. Most people would rather have a usable loft.

You really haven't got it have you?

What was the answer to this?

They generally do not. Most it is about equal in area. My main bedroom has a very large ceiling area. More than the walls. And when you take into account much of the outside walls have build-in wardrobes across them, there is not much wall area at all compared to ceiling area. Most homes have built-in floor to ceiling wardrobes these days, with many of them against outside walls, which gives an extra level of insulation against the outside walls. Packing in loft insulation for the benefit of the upper rooms is a win, win, win situation, giving greater benefits to these rooms than others. It is worth alone just for these rooms.

As I have told you. Last August in a heat wave, the coolest roomin my house was the main bedroom. The insulatio above proteced it from the 55C in the loft above. A breeze runningthrough the uper windows, which are beter for breeze being higher up, and it was very comfortable.

Many selfbuilt homes have the living areas on the upper floors, which makes much more sense.

considerably,

Depends on the house in question. 90% plus will benefit and many others will greatly benefit.

You are a thicko! The upper rooms greatly benefit, of which there is usually 3 or 4 bed and one or two baths. You make the silly mistake of looking at the whole house and treating it as one with all rooms being equal. Big mistake.

So worth it.

You can have both. I do. Look at the benefits to the upper rooms only. You are looking at the house as one big blob.

I'll answer my own question. About £300, as far as I can tell.

For the same price I can get enough boards of 25mm Kingspan to dryline the solid walls downstairs, which would reduce the U-value to 0.6.

So the heat loss here would become

Walls = (27*2.1 - 5.9 - 3) * 0.6 * 24 = 688 W +( 8*2.1 - 2.2 - 3) * 0.6 * 24 = 167 W Walls Total = 855 W Previous Walls Total = 2462 W

Saving = 1607 W

So I can either spend £300 to save 588 W, (£1.96/W) or I can spend the same and save 1607 W. (£5.35/W)

If I go for 50mm Kingspan, the price goes up to £400, but the saving goes to 1870 W. (£2.63/W for the extra £100, which still gives a better return than more loft insulation).

Alternatively, I could spend another £300 on 25mm Kingspan for the upstairs and get another 1573 W saving, at £5.24/W.

Extra loft insulation comes well down the priority list for my house, because the cost/Watt saved is easily beaten elsewhere.

Whoops! These are all in Watts saved / £ spent, not the other way around.

Neil

Nonsense.

Detached House. 7m x 7m x 5m high Outside wall area 140 sq metres Ceiling area 49 sq metres

Semi detached house 7m x 5m frontage x 5m high outside wall area 85 sqm ceiling area 35 sqm

Bungalow 10m x 7m x 2.5m high outside wall area 85 sqm ceiling 70sqm

Terraced house 15m x 5m *5m high outside wall area 50sqm (assuming small front and back walls) ceiling area 75sqm.

This is the only case, and even then there is a question mark over the party walls which should probably be treated as a third to a half the heat loss of an outside wall.

By counting three walls as internal? That's a crock because for the house as a whole there will be 2,3 or 4 external walls overall.

This is just pulling things out of the air.

Maybe you should try mirrors on the ceiling as well......

Figures? Otherwise this is just armwaving again.

I've done heating calculations in fine detail for different properties, counting losses and gains through internal surfaces as well.

The temperature ranges for different rooms by recommendation range from 16 to 23 degrees and I suspect a lot of people run with less than that. If you plug in these factors for most properties, the heat flow internally is generally relatively small in comparison with flows through external surfaces.

.andy

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ROTFL.

.andy

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You are looking at the house as a whole again. Duh! The extra insulation benefits greatly the upper rooms.

The loft insulation is the depth over and above the 100mm. You have to take into account the fixing of the downstairs wall Kingspan. Loft insulation is cheap and easy, so do it. Also do downstairs too with Kingspan, but the installation cost is greater.