Help please on insulation options

[janedevon]

Hi and thanks for reading,

timber frame due to go up in a couple of weeks, our plans show overkill in our opinion on roof insulation,

It's a dormer so habitable roof space and our plans show tlx gold under rafters, then 150mm celotex and a further 38mm of kingspan, we have been told this is overkill and very pricey!!!

We need to achieve uv 0.16 in roof any better suggestions?

Many thanks

[Oz07]

Your opinion won't be validated here I can assure! 

[Crofter]

There's no magic bullet I'm afraid. To achieve the same U Value for less money you would need to have a different type of insulation, which would work out up to twice the thickness, and I'm guessing you don't have the headroom for that?

[ProDave]

I'm getting a better U value than that, with 100mm wood fibre board and 190mm of Frametherm 35 earthwool. That's a warm roof room in roof house (see my avatar)

More detail of your roof make up, thickness of rafters etc. What are you putting between the rafters etc.

[janedevon]

Thanks for your answers I'll get the spec listed tomorrow, basically it's the tlx gold in place of standard breather membrane, then 150mm celotex between rafters with kingspan over.

150m sq roof equals about £1500 for,the tlx gold alone several builders have said we wouldn't need that.

 

just looking at options.

 

thanks

[NSS]

Don't know how it would compare price wise but our 150mm Actis Hybris plus 45mm Actis H-Control gives a u-value of 0.14

Edited June 12, 2016 by NSS

[janedevon]

That was going to be my next question, I've had someone from Actis send me this:

 

Your SAPS assessment claims that you are required to achieve a 0.16 u-value within your pitched roof. This can be achieved with just two products of ours without the need for an insulated breather membrane as first thought. The build up that you require is:

 

 

Slate

Batten

Breather Membrane

120mm Hybris – Reflective Insulation stapled between the rafters

HControl Hybrid – Reflective Insulated Vapour Control Layer stapled/nailed under rafter

38mm Batten

Plasterboard

 

 

 

this would be cheaper on the membrane and less labour intensive at least fitting the hybris compared with cutting celotex, waiting on a price to see how they compare.

 

how did you find the actis did you self install?

[PeterW]

It's a marmite product !!! It's not a "true" insulation the way a lot of normal insulation works and tbh it's useless at stopping noise transfer which they don't tell you. 

You can easily hit 0.16 with standard insulation - have a look on the Kingspan website as they have a quick calculator that shows you how to do it. 

 

[NSS]

I love marmite. 

In the process of self-installing now. I'll post results pics when I get a moment.

[NSS]

Here we go again, bashing anything you haven't used yourself.

Edit: this was actually posted in response to JSH's post below, which he seems subsequently to have removed, edited and reposted. Sailing close to libel rules?

Edited June 13, 2016 by NSS

[Jeremy Harris]

The reflective multifoils are snake oil, pure and simple.  They are tested in a way that is atypical for use in a house and rely on the addition of real insulation to gain 99% of their insulating properties.  It's about time their mis-selling was picked up on as they've been sailing exceedingly close to the wind with their descriptions of the stuffs supposed performance for years.  They started out with what can only really be called an open lie years ago, around the time when Kevin McCloud infamously held up a thin bit of insulation and declared that it worked as well as a bit ten times or more thicker during a GD show.  It had those of us with a bit of a basic scientific background reaching for calculators and proving within seconds that it was total bunkum.  I wrote about it over on Ebuild last year, when the Hybris stuff came up in discussion:

 

Quote

The problem with multifoils is that they fiddle the tests and only get a BBA certificate with some very careful wording that says they have to be used with conventional insulation to get the claimed U value. When you work back from the BBA certificate to get the contribution from the multifoil (by subtracting the insulation effectiveness of the other insulation) you find that the multifoil itself isn't doing much at all.

Originally, the manufacturers argued that their hot plate test method (which seems to show better performance for long wavelength IR reflective materials) was valid in a domestic application, but it'isn't (except, perhaps, for one specific application), whereas the tried and tested hot box test method is. When you test multifoil using the hot box method it is an extremely poor insulator, particularly when used in thin layers (which is the selling point). The companies making the stuff even managed to get it on Grand Designs, where Kevin McCloud was famously taken in by the very false claims.

For every application in house insulation, except a reflective layer under a roof covering, where reflecting back long wavelength re-radiated IR from under the roof helps keep the roof cool, other types of insulation are better and cheaper. There are houses beng built with this stuff where the architects or designers have been fooled by the advertising claims and they almost certainly don't even meet building regs insulation levels, let alone something a bit better. The giveaway is that they do actually quote the lambda value, and leave it to you to work back to the U value. For example, 100mm of Hybris with it's stated lambda of 0.033 W/m.K has a U value of 0.33 W/m².K, way off building regs and a long, long way away from giving the sort of target insulation level a new build should have.

Here's a list of materials, including the Hybris multifoil stuff with the added insulation and air gap, listed in order of lambda.  The lower the lambda the better the insulation and so the thinner the layer needed.  You can see that the Hybris stuff is not great, even with added insulation and an air gap.  You need around a  50% thicker layer in order to achieve the same U value as you would using ordinary PIR foam:

Concrete (dense) =	1.2	W/m.K	Range is 0.6 to 1.8 from Kaye and Laby
Sandstone =	1.2	W/m.K
Plasterboard  =	0.22	W/m.K
Wood (12% moisture content) =	0.15	W/m.K
OSB/3 =	0.13	W/m.K
Glass fibre roll =	0.044	W/m.K
Warmcell =	0.04	W/m.K
Steico wood fibre =	0.038	W/m.K
Low density EPS	0.037	W/m.K	Kore SD
High density EPS =	0.034	W/m.K	Kore floor HD
Hybris (multifoil with insulation and air gap) =	0.033	W/m.K	λ value taken from BBA certificate
PU foam =	0.025	W/m.K
PIR board =	0.022	W/m.K
Silica aerogel =	0.017	W/m.K
Silica carbon aerogel =	0.0135	W/m.K

[Jeremy Harris]

39 minutes ago, NSS said:

Here we go again, bashing anything you haven't used yourself.

Edit: this was actually posted in response to JSH's post below, which he seems subsequently to have removed, edited and reposted. Sailing close to libel rules?

I'm just stating facts, facts taken from the certification for the product, not bashing anything.

The post change was pure accident, nothing more.  The table I inserted didn't format properly, so I tried several times to edit the post as soon as I'd written it.  In editing it the formatting of the table went really haywire, so I copied the text, deleted the post and then started again, just so I could get the table formatted properly.  I've no doubt I was struggling to edit the table formatting at the time you posted.

Nothing libellous there either - the data comes from their published data and BBA certificate, so is not my data, it's the manufacturers data.

If you check back to find some of the withdrawn adverts for other multifoils (and I honestly can't recall if Actis was one of those early multifoil manufacturers or not) you will find some ludicrous claims, which is why many of the adverts have been modified or withdrawn.  At the time they came out they were arguing that their stuff should be measured differently from all other types of insulation, because by using this different measurement technique the stuff appeared to be an insulator.

This was argued about by other insulation manufacturers and, I believe, the BRE, to the extent that there were a lot of changes made, and the BBA certificates are now clear as to what the make up is that gives the quoted insulation performance.  To give credit to Actis, they have been increasing the thickness of their product a great deal with added proper insulation, and they do make it clear what the lambda of the correctly installed system is, 0.033 W/m.K.  It's not that great, as to meet building regs you need about the same thickness overall as you would for EPS, and it does have a very short decrement delay, shorter than EPS, and much shorter than systems with a greater heat capacity.  I don't know the price of the stuff, so maybe it's so cheap as to make it worth fitting thick layers to get a decent insulation level.

 

[PeterW]

39 minutes ago, NSS said:

Here we go again, bashing anything you haven't used yourself.

Edit: this was actually posted in response to JSH's post below, which he seems subsequently to have removed, edited and reposted. Sailing close to libel rules?

So I've used it... Installed 7 years ago (Actis Tri-Iso 9) in a large extension.

And have the data to prove that it doesn't work as described hence my comments being what they are. It has low/nil sound insulation, is pretty poor at heat insulation in the summer and it works 'OK' in the winter however some of that is down to the detailing in how I installed it and ensured that there were no gaps at all at the edges and every joint was double taped.

The one I used was part of the legal / advertisement retraction and had the certificate revocation due to how it was calculated. The whole set of discussions (including all tests) is here

http://www.lifespacedesign.co.uk/msc/Foil.pdf 

In my experience I wouldn't reuse it due to the issues I've had and now that I've lived with it and also read a LOT more than the sketchy data that was originally available.

 

[Declan52]

I would stick with keeping it as simple as possible. Use standard non tenting  roof membrane for under the tiles. Costs approx £60+ a roll and for your roof you would need 3 rolls depending on the shape of it. 

Would fully fill the rafters with high density earth wool. Much easier to cut and fix in place and will save you money on the labour costs. 

Then you have your choice of either a warm roof or cold roof set up. If going for a warm roof then you can use 100mm of pir insulation or even the wood fibre board that Dave used on his. For a cold roof then the extra insulation and vcl will be below the rafters. 

First thing first is decide on either a warm or cold roof and then pick the best way to get you a roof with a low u value. 

[Jeremy Harris]

Just for completeness, I'm far from being the only one to look at, and question, the real performance of multifoil insulation.  It's been discussed to death elsewhere, with a range of opinions and facts being expressed:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125

and here are some facts about the stuff, from BRE and as guidance to LABC building inspectors:

multi-foil-insulation_july2005.pdf

MG0190512 Use of Multi-foil Insulation Products - Compliance with Regulation 7 and Requirement L1.pdf

just to show that I'm reporting facts, not making something up because I don't like it.  As it happens I've stated elsewhere, more than once, that there is a role for reflective insulation wherever there is a significant probability that it may reduce re-radiation.  The main use for it that I can see (there may be others) is as a reflective barrier immediately under a roof covering, where it may well act to reflect back re-radiated heat from the under surface of tiles, slates etc, and so be an aid in reducing solar gain.

[Nickfromwales]

1 hour ago, NSS said:

Here we go again, bashing anything you haven't used yourself.

Edit: this was actually posted in response to JSH's post below, which he seems subsequently to have removed, edited and reposted. Sailing close to libel rules?

Hmmm.

Unless you're aware of a specific and purposeful alteration in a post, and then it's deemed a misrepresentation, then could we please stick to facts. Are you aware of a change in the posted texts, or have you assumed the posts were altered for the purpose of disposing of a statement? If it's the latter then I'd politely invite you to edit your comment to be less abrasive please!

There are no members here who wish to "bash" anything . We give free impartial advice here, and in this case only the facts have been posted according to the manufacturer, warts and all, and it's always been the best way to provide real life info. The supporting comments about the multifoils' other shortcomings, like poor sound insulation, are vital components of any critique, and should be in no way stifled as that would be worse IMHO. 

Many thanks. 

[Jeremy Harris]

Nick,

You can check the edit history and see what I did.  It is exactly as I described - I had problems getting the table (cut and pasted from Excel) to format - it had a big gap between rows at the bottom that I couldn't find a way to edit out).  That is the only reason for the delete and repost, and the rest is pretty much identical, as I cut and pasted the first section (above the table) and stuck it straight back in the cleaned up repost.

As a tip to anyone posting tables, complete your post first, then paste in the table.  If you try and add text after the table you can mess up the formatting (this is what I found).

[janedevon]

Many thanks to all of you for comments thus far, I'm just waiting to confirm depth of rafters to work out the best options hopefully architect has never discussed warm or cold roof so I'm a bit confused there, will have to do some more research before I decide the final build up, it's a dormer so space is a premium hoping the rafters deep enough to provide room for decent insulation.

[Nickfromwales]

49 minutes ago, JSHarris said:

Nick,

You can check the edit history and see what I did.  It is exactly as I described - I had problems getting the table (cut and pasted from Excel) to format - it had a big gap between rows at the bottom that I couldn't find a way to edit out).  That is the only reason for the delete and repost, and the test is pretty much identical, as I cut and pasted the first section (above the table) and stuck it straight back in the cleaned up repost.

As a tip to anyone posting tables, complete your post first, then paste in the table.  If you try and add text after the table you can mess up the formatting (this is what I found).

I'm quite happy that you've stated the correct order of events Jeremy. Just a bit of moderation was, I felt, necessary to address a certain comment which I didn't feel met with out normal site etiquette.

Let's move on folks . 

[PeterW]

Jane - if the rafters are over a span of more than 3.5m then they will be 150x50 - to get 0.16 you can part fill with 140mm PIR and then overboard with 35mm PIR which is the same depth as using the foil plus the batten

Hope that helps

[Jeremy Harris]

Jane,

Something worth taking account of is the insulation decrement delay, especially in a roof that may well be exposed to hot sun.  There is a useful article here about it: http://www.greenspec.co.uk/building-design/decrement-delay/

It can sometimes be worth making a compromise on the insulation value in order to get a better balance between it and the decrement delay, in terms of overall comfort level.  Clearly you have to meet building regs insulation levels, and they are far from a high standard, IMHO, so I'd suggest going for better if you can manage it. 

I spent a long time looking at insulation materials before making a decision, as our first choice was SIPS, with foam insulation that has a short decrement delay, and in order to improve both the insulation value and increase the decrement delay I was looking at adding a layer of wood fibre to the outside.  The manufacturers found this a challenging idea, and in the end the cost of it ruled it out, so we accepted a compromise on interior space and accepted a system with thicker walls that used a longer decrement delay insulation.

It's all about compromise in any building project, and often getting hold of accurate information to make a decision as to what that compromise should be can be difficult.

[Ferdinand]

12 hours ago, janedevon said:

Hi and thanks for reading,

 

timber frame due to go up in a couple of weeks, our plans show overkill in our opinion on roof insulation,

It's a dormer so habitable roof space and our plans show tlx gold under rafters, then 150mm celotex and a further 38mm of kingspan, we have been told this is overkill and very pricey!!!

 

we need to acheive uv 0.16 in roof any better suggestions?

Many thanks

 

I'm not sure why that mentions both "Celotex" and "Kingspan", since as I understand it they are both almost the same thing - foil faced polyisocyanurate (PIR) insulation - which are offered with several minor differences.

I think you need to clarify when you post your full spec.

Ferdinand

Edited June 13, 2016 by Ferdinand

[Nickfromwales]

7 minutes ago, janedevon said:

Many thanks to all of you for comments thus far, im just waiting to confirm depth of rafters to work out the best options hopefully architect has never discussed warm or cold roof so im a bit confused there, will have to do some more research before i decide the final build up, its a dormer so space is a premium hoping the rafters deep enough to provide room for decent insulation.

Basically ( in rough terms ) a cold roof is your typical rock-wool / other insulated attic where the insulation layer is on top of the 1st floor ceilings. From the underside of the roof you just see the felt. 

A warm roof has the insulation layer directly under the breather membrane, so the attic 'space' is within the heated envelope, rather than cold and draughty . 

[Stones]

I used a multifoil insulation on one of my builds, because at the time, it was billed as the best thing since sliced bread.  The performance was worse (in terms of amount of energy used for heating) than a previous house which had 140mm of mineral wool in the coombs and loft. You may think this is subjective, but is our experience.  Of course there are many reasons why this could have been the case - poorly fitted, areas missed etc but the interesting thing was that when we sold that house and bought our next one (from a small developer) they had to change from proposed multifoil insulation back to mineral wool as NHBC withdrew their support for the product and said they wouldn't cover the house if it were installed.

[Declan52]

For your build a cold roof will have insulation between the rafters and on the underside. You will also have an airtightness membrane in there as well and maybe even a service cavity. 

A warm roof will have the insulation on top of the rafters. A lot of different methods to do this using sarking and pir insulation or you can use wood fibre board, read prodaves blog where he explains it in more detail. 

With a cold roof it's best to cross batten the roof so you can fully fill the rafters. Still do this on a warm roof as well but the battens will be on top of whatever material you choose to make up your warm roof. 

An advantage of a warm roof is that you wouldn't be making the rooms smaller by having no insulation on the underside of the rafters.