Calculating benefit of insulation

Calculating benefit of insulation

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AnotherUsername

Original Poster:

113 posts

28 months

Tuesday 2nd March
quotequote all
Bit of a maths question this, maybe!
Ok, live in a barn conversation and we noticed the insulation was poorly done. I’ve got myself a thermal imaging camera and improved some test areas. Now, the ceiling I re-insulated surface temperature has risen by 3 degrees compared to the surrounding surface.
If the room temp is 21 degrees and the normal surface temperature is 12, increasing the temp to 15 will obviously lower the losses. Based on our fuel consumption it must be possible to calculate the payback of insulating the entire roof.

Do I assume I’ve improved things by 25% (12 to 15). Calculations prove a new R (or was it U) of 3 x insulation improvement.

Help!

Equus

10,844 posts

65 months

Tuesday 2nd March
quotequote all
It's more complicated than that and will depend on the temperature profile through the thermal element (among other things).

If you were measuring things really and truly accurately, all the surface temperature would tell you would be the room temperature minus the surface resistance.

Theoretically, its the U-values before and after that should tell you the percentage reduction in heat loss at any given difference between internal and external temperature, but even those will be subject to a lot of 'ifs' and 'buts' (not least that they ignore the effects of thermal mass, and that the standard test for thermal resisitivity - hence calculated U-values - is flawed).

AnotherUsername

Original Poster:

113 posts

28 months

Tuesday 2nd March
quotequote all
Hmmm. Knew it wouldn't be easy....

Basically my 'problem' is that whoever insulated my property during renovations used a 'foil based multi layered' superquilt from YBS insulation. Now despite them attaching instructions to every roll - overlap and tape joints, the idiots who installed it forgot the tape, so wind basically blows all the warm air out, not that this was immediately obvious because the plasterboard covers everything up.

Now, rather than rip the house to pieces I've been drilling 8mm holes and filling the area between the plasterboard and the 'leaky quilt' with expanding foam.

This appears to massively improve things by stopping the draft behind the plasterboard and moving us from air gap insulation to 150mm of semi rigid foam.

Equus

10,844 posts

65 months

Tuesday 2nd March
quotequote all
AnotherUsername said:
Basically my 'problem' is that whoever insulated my property during renovations used a 'foil based multi layered' superquilt from YBS insulation.
The multifoils are snake oil, anyway.

AnotherUsername

Original Poster:

113 posts

28 months

Tuesday 2nd March
quotequote all
Equus said:
The multifoils are snake oil, anyway.
I’m not doubting that but the fact it’s not taped is just ridiculous.

dickymint

19,305 posts

222 months

Tuesday 2nd March
quotequote all
Equus said:
AnotherUsername said:
Basically my 'problem' is that whoever insulated my property during renovations used a 'foil based multi layered' superquilt from YBS insulation.
The multifoils are snake oil, anyway.
Worked for me in my flat roof extension (warm roof in conjunction with Kingspan to keep it having to be a stupid ugly thickness) despite Building Controls (indie) initial thoughts! As long as it's installed to manufacturers recommendations where's the problem?

Equus

10,844 posts

65 months

Tuesday 2nd March
quotequote all
dickymint said:
As long as it's installed to manufacturers recommendations where's the problem?
That they don't work to the manufacturer's claimed level of performance when tested.

How do you know yours worked, particularly if it was in conjunction with PIR?

How did you test it?

Equus

10,844 posts

65 months

Tuesday 2nd March
quotequote all
AnotherUsername said:
... the fact it’s not taped is just ridiculous.
It is, but the fact that method for establishing the thermal resistivity of insulation materials does not take account of wind wash and infiltration is one of the shortcomings of relying on U-values (in other words, even if you did all the comparative calculations in accordance with the standard methodologies, it still wouldn't account for that factor).

ETA: This LINK might interest you.

dickymint

19,305 posts

222 months

Tuesday 2nd March
quotequote all
Equus said:
dickymint said:
As long as it's installed to manufacturers recommendations where's the problem?
That they don't work to the manufacturer's claimed level of performance when tested.

How do you know yours worked, particularly if it was in conjunction with PIR?

How did you test it?
You said yourself earlier ..............

" It's more complicated than that and will depend on the temperature profile through the thermal element (among other things).

If you were measuring things really and truly accurately, all the surface temperature would tell you would be the room temperature minus the surface resistance.

Theoretically, its the U-values before and after that should tell you the percentage reduction in heat loss at any given difference between internal and external temperature, but even those will be subject to a lot of 'ifs' and 'buts' (not least that they ignore the effects of thermal mass, and that the standard test for thermal resisitivity - hence calculated U-values - is flawed)"

So you know how I "tested it" I didn't! How do you test yours other than people you may employ who in turn will rely (to a large extent) on manufacturers figures?

At the end of the day how do quilt manufacturers get away with selling "snake oil"?



Equus

10,844 posts

65 months

Tuesday 2nd March
quotequote all
dickymint said:
How do you test yours other than people you may employ who in turn will rely (to a large extent) on manufacturers figures?
I rely on informed assessment of the results of standard tests; the point being that most insulations are tested and certificated using a standard method (which has its shortcomings, but at least it's consistent and we understand where those shortcomings lie).

Multifoils are not tested using the standard method, because their manufacturers know that if they did, they'd fail. The reason I refer to them as snake oil is because the claims made for them are very similar in basis (ie. they have none) to most homeopathic medicines. Their manufacturers simply expect you to believe that they work because they say they do.

if you actually test a multifoil, it doesn't demonstrate the level of thermal resistance that the manufacturers claim for it (there are reasons the manufacturers incorrectly claim higher performance, but they're very boring).

dickymint said:
At the end of the day how do quilt manufacturers get away with selling "snake oil"?
Lack of effective regulation on the claims being made, and ill-informed customers.

Edited by Equus on Wednesday 3rd March 00:00

AnotherUsername

Original Poster:

113 posts

28 months

Wednesday 3rd March
quotequote all
Thanks everyone- it sounds like I should do whatever I can to improve things, even if it’s just psychological!

AnotherUsername

Original Poster:

113 posts

28 months

Wednesday 3rd March
quotequote all
I’ve also got loads of double glazing- none of which has any form of blind / curtains. Probably a big pay back on those too

Equus

10,844 posts

65 months

Wednesday 3rd March
quotequote all
Do you know your annual expenditure on space heating, yet?

If you do, then in terms of adding insulation to the roof, it's possible to do rough and fairly (fairly being a relative term!) quick and simple calculations on the energy saving and payback period just from the additional thermal resistance.

Beyond that, SAP calculations will give you a 'standardised' assessment of the heating costs; again not terribly accurate, but better than nothing for comparative figures, but to do two SAP calculations (before and after, for comparison), to a worthwhile level of accuracy, is going to cost you £several hundred via an Energy Consultant - it's not practical to do them yourself.

If you're adding insulation to an existing build-up on the roof, I would also suggest you seek professional advice to ensure that you won't create problems with dewpoint profile and interstitial condensation.

AnotherUsername

Original Poster:

113 posts

28 months

Wednesday 3rd March
quotequote all
The vaulted ceiling/ roof build is:

Plasterboard
Rafter creating 3-4 inch air gap
Plywood
Batten
Foil
Batten
Membrane
Batten
Tiles

The original problem was that the wall insulation wasn’t taken up (as plans show it should have been) to the plywood under the roof.
This error was causing wind to blow behind the plasterboard!
This has now been rectified by foaming the wall / roof joint.

Im either going to fill the air gap cavity with foam or use insulated plasterboard (much more expensive) and re board the ceiling/roof (it’s vaulted).

Equus

10,844 posts

65 months

Wednesday 3rd March
quotequote all
The existing multifoil is already a condensation risk if it's not properly lapped and taped to function properly as a vapour barrier, but certainly adding a layer of insulated plasterboard below the ceiling would be an additional risk.

Incidentally, one of the 'weasel words' marketing techniques used by mutifoil manufacturers is that you'll often find that on their agrement certificates/LABC accreditation, they're described as FOR EXAMPLE a 'thermal radiant vapour barrier'. In other words, it's a vapour barrier that happens to be good at resisting the passage of radiant heat... but then you knew that, didn't you? And you also knew the fact that most heat escaping from the house is transferred by conduction and convection (see the video I linked above) not by radiation? You weren't silly enough to think that it is intended to work as a primary insulation layer, or that our tested figures are for conductive heat loss, not (largely irrelevant) radiant heat loss, 'cos that's clearly not what we've said on our spec. sheet? wink

At risk of digression: these multifoil insulations were originally fallout from the NASA space programme. They were designed to stop astronauts being cooked by solar radiation, at which they are very effective indeed, because the only way that heat can be transferred in the vacuum of space is by radiation.

Is the roof membrane (immediately below the tiles) breathable (which would help, but still be far from ideal)?

It needs looking at properly, I think.

AnotherUsername

Original Poster:

113 posts

28 months

Wednesday 3rd March
quotequote all
Thanks for all of the helpful replies and info. fwiw we've never seen as much as a drop of condensation on any windows. House has underfloor heating and fully air conditioned / dehumidified as well as fresh air heat exchanger (during the installation of AC is when I discovered all of the issues)

Equus

10,844 posts

65 months

Wednesday 3rd March
quotequote all
AnotherUsername said:
fwiw we've never seen as much as a drop of condensation on any windows.
If condensation is occurring, the risk that it is happening out of sight within the roof structuire - most likely on the underside of the roofing membrane, in the gap between the multifoil and the membrane. Problem is, it will potentially be trapped there, so that it can't easily evaporate off, and in time will cause your roof timbers to rot.

It's called 'interstitial condensation'. See explanation HERE.

You will need an effective vapour barrier (VCL) on the warm side of the insulation. Multifoils can provide this (as can a simple sheet of polythene or, less effectively, taped, foil-backed plasterboard), but in all cases you need to lap and tape the joints so that they're absolutely airtight, otherwise you're wasting your time - the vapour pressure will find the path of least resistance through.

AnotherUsername

Original Poster:

113 posts

28 months

Wednesday 3rd March
quotequote all
The gap between the foil and the membrane does have airflow. If anything like the rest of the roof - lots of it!

Equus

10,844 posts

65 months

Wednesday 3rd March
quotequote all
AnotherUsername said:
The gap between the foil and the membrane does have airflow. If anything like the rest of the roof - lots of it!
You might be alright, then.

It's difficult to predict, until your roof collapses! biggrin

Little Lofty

2,778 posts

115 months

Wednesday 3rd March
quotequote all
I used Tri Iso multi foil on a few lofts around 12 years ago. One in particular was for a mate, he still raves about how warm the loft rooms are and that he virtually never heats them. I also remember revisiting one of the lofts on a very hot summers day (rare up here smile ) and was surprised at how cool the room was, my loft at home had been very warm. I stopped using it when building control lost confidence in it. It didn’t save a lot of money but did save time, it also didn’t really improve on headroom as the rafters always had to be beefed up anyway. It was much easier to handle and store though.