External Insulation of Timber Frame

[nozzaamazon]

Hi - I'm sure this has been answered here before but can find anything......

I have a timber frame with studs at just over a foot spacing. The wall is constructed with daub panels inside that finish 3 inches inside the inner surface of teh studs. Externally there is lath and and lime&Cement render. I plan on hacking off the render on the outside and would like to insulate without effecting breathability and then re-render with lime or possibly oak boarding.

Does anyone know of a good board material to use, or whether good results can be had with battening out and filling the new space created (with Hemp, wool, cellulose..........). Whats the best/most cost effective option?

Has been the first year with my wood gasification boiler running and although heat is free with the logs - I am kind of tired seeking out and preping 10m3.

Thanks

 

[middi]

Hi
If your building is listed obtain permission from your CO before you start hacking away at the building, the CO may require for new render to go back after you have insulated the wall . My educated guess is that to the CO will have to seriously consider if it is appropriate for the building to have the facade changed in favour of lap-boads.

If Lap-boards are allowed these would be the prefered choise as far as the building is concened, they do not crack like solid renders as normally is the case with perpetually moving oak framed buildings.

I suggest you use the multilayered flexible insulation, such as TRISO insulation, this can be fixed directly to the external beams and held in position with 50 or 75 x 25 treated battens screwed int the studs using stailess steel screws, these battens covered by breatheable membrane ( such as TYVEK) and then lap-boards ( or EML if you prefer to render the walls).

From a practical point of view, the advantages of using the multilayered insulation is that this material will compress only a few millimeters under the battens therefore not bulking the overall thikness of the existing wall as this is a major consideration in order not to destroy the details at eaves height.

I hope this will get you started, There are other option available to insulate exterior walls but sometime these are not suitable for traditional building due to the amount of space they require.

 

[Jon Maine]

Good advice from Middi, I would recommend you followed it.

 

[biffvernon]

I suggest you use the multilayered flexible insulation, such as TRISO insulation,

Oh no. That is so controversial. There are lots of folk who dispute the efficacy of this products, saying that the internal layers of foil can add very little to its insulating properties but add greatly to its cost. It has been the subject of testing at the National Physical Laboratory and has received accreditation from BBA only in the context of a part of other insulation. Adverts have been subject to ASA rejection and in the US a company was finned a fortune for making false claims. There is a 500+ post thread on the Green Building Forum, started by me, which has been rambling over and over the same ground for a couple of years. The product is still vigorously defended by a minority of people who, in my opinion, invoke some imaginative pseudoscience:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=18#Item_3

 

[middi]

Biff, I am sure that the product has been hyped as to it's insulation qualities and the quantities required to meet recommended U values and " creative" calculations have crept into the equation, nevertheless it has good insulation qualities and feel( in my view) that it is quite suitable as supplementary insulation to external of traditional timber framed buildings to aid and add to the already good insulating properties of the daub. This, combined with the 25mm air gap under a thermal breatheable membrane will create an extremely good insulation barrier.

I would prefer to use 75mm thick insulation where the external outline of the building is not an issue, ( if contemporary materials is not an issue)

All of the above mentioned is a deviation from the traditional methods ( as you very well know) but a quite economical way to improve heat retention, not too disruptive to the building, and quite easy to do.

Still I am sure there are better calculated scientific methods that would do the same job.

Packing a "created" external cavity with sheep's fleece would be a more traditional and very effective alternative.

 

[Lime]

I agree with biffvernon.
The claims made for the stuff always ignore it's obvious ability to stop draughts.

 

[Jon Maine]

I suggest you use the multilayered flexible insulation, such as TRISO insulation,

Oh no. That is so controversial. There are lots of folk who dispute the efficacy of this products, saying that the internal layers of foil can add very little to its insulating properties but add greatly to its cost. It has been the subject of testing at the National Physical Laboratory and has received accreditation from BBA only in the context of a part of other insulation. Adverts have been subject to ASA rejection and in the US a company was finned a fortune for making false claims. There is a 500+ post thread on the Green Building Forum, started by me, which has been rambling over and over the same ground for a couple of years. The product is still vigorously defended by a minority of people who, in my opinion, invoke some imaginative pseudoscience:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=18#Item_3

I thought you had tested it in a positive light Biff previously, although that was a long time ago.

However we have it on our roof here, it was installed before it was put in the naughty corner around 4.5 years ago, It seems to perform very well. It is very useful for the type of application where you do not have much depth to play with. Whilst I am all in favour to install the highest grade insulation we have to compromise with historic property due to other factors some places you simply do not have the room to. Certainly in this snow only the sunshine has melted the snow on the roof and there was no demand for heat from the thermostat top floor of the south wing half an hour ago.

What personal experience do you have with it?

I am just working out the energy efficiency for the building for an award we are entering and we are on sub 100kw per annum per m2 and a co2 footprint of around 35kg per m2 for all electrical use. Sadly I found out that defra will not allow for renewable energy generated off of site to be classed as zero carbon 08/09 onwards so we cant claim to be carbon neutral.

 

[Flyfisher]

I've recently used it to create a 'warm roof' to our GII* property where it was the key factor in minimising the 'lift' to the roof line, thus avoiding changing the roof appearance around the eaves, dormers and gables.

 

[nozzaamazon]

Hi - thanks for the information. Understand the arguments for performance.

So this multi layerd foil material is breatheable/ vapour permeable and not effect the health of the building?

 

[AMc]

When I looked at the great insulation debate I couldn't find a slim, effective, breathable solution - internal or external.

My understanding is that multifoil isn't breathable at all (but I could be wrong). It is expensive and subject to a great deal of debate which put me off specifying it. The one thing that would upset me more than paying top dollar for it would be it not doing its job.

Be aware that unless you are listed, major works on the walls can be classed as 'renewing the thermal element' at which point building control may expect you to meet 2006 Part L1B of the building regs for that element.

As far as breathable alternatives go - sheeps wool is effective and breathable but to meet 2006 building regulations you will need a lot of it, significantly increasing your wall thickness - window reveals, possibly requiring you to extend the roof at the eaves and move gutters...its a lot of work.

My usual advice would be to start by eliminating ventilation heat loss (daughts) and (over) insulating the roof space before you look at major changes to the walls.

 

[Jon Maine]

Multi layer is not breathable.

 

[nozzaamazon]

Not breatheable = not smart? Thats why I'm removing the cement. Am I missing something?

 

[Flyfisher]

Depends on the design and application. Breathability wasn't an issue for my warm roof whereas minimal change to the roof line was.

 

[Lime]

Not breatheable = not smart? Thats why I'm removing the cement. Am I missing something?

No, I don't think you are.

 

[MdB]

Not breatheable = not smart? Thats why I'm removing the cement. Am I missing something?

Only that insulation old houses is not easy and can end up with compromises..

 

[Jon Maine]

Not breatheable = not smart? Thats why I'm removing the cement. Am I missing something?

No, I don't think you are.

Lime I hope you mean he is not missing someting, not that he is not smart :lol:

In a situation like this a compromise is what is likely to be needed, you will have to weigh up for instance if you can construct a breathable structure maybe either side of a non breathable insulation barrier maybe. The theory goes that you should be able to do this, if the insulation keeps the moist air inside the building warmer then you should not get a dew point on the inside surface of it. Any moisture can still travel in and out of the internal structure as required but not right through the wall to outside. As long as the atmosphere does not get to humid you should be ok. If it starts to look like it will be a problem you may wish to consider an air change/heat recovery system which could dump the moist air out the building replacing it with fresh air from outside and transfering the heat content back into the fresh air.

I am fortunate that we have very breathable walls and a warm roof structure whilst it doesn't breathe right through it does either side of the insulation. Assuming the insulation is not cold on its inner surface you should not get a dew point.

I understand the concerns about the multifoil insulation however it is currently less than 1 degree outside here and the inner surface of the insulation is showing up the same temperature as the room below the loftspace I can see the insulation in, the single glazing is showing up at around half this temperature. No evidence of condensation on the multi foil. Whilst there may be arguments not to use it, it was a solution for us which seems to have worked well for us in the limited space we had to play with before we radically altered the structure and looks of the building.

I am slightly more concerned about recommending you wrap your whole house in it, although taking into account what I have suggested I think it is something that could be managed ok.

nb I would suggest to anyone however that if you are installing insulation to a high specification do not give it to just any old labourer to do, give it to an intelligent person who is fastidious and joins things to spec and cuts things tightly. Many problems can occur when high grade products are installed in a slapdash manner.

 

[CHRIS]

nb I would suggest to anyone however that if you are installing insulation to a high specification do not give it to just any old labourer to do, give it to an intelligent person who is fastidious and joins things to spec and cuts things tightly. Many problems can occur when high grade products are installed in a slapdash manner.

I second this - especially if you use Celotex type insulation between studs you may have to use expanding foam for a good fit as it is very difficult to get to fit exactly.

 

[biffvernon]

Some multifoils are punctured by pinpricks to make them 'breathable' (allegedly).

When I first encountered multifoils I was suitably bedazzled by the shiny space-agey look and thought this must be the best thing since sliced bread. But I couldn't work out in my head just how the interior foils foiled the heat flow, so sat down and attempted to write a simple iterative computer model that might clarify my thinking. I just couldn't see how it could work as advertised. So I set up a crude experiment with a cafetire full of hot water, a thermometer, a clock and various types of insulation. I found that the multifoil (Tri-iso9 is what I had at the time) did not perform significantly better than some other, much cheaper materials. This confirmed my theoretical understanding but disappointed my hopes.

The Green Building thread has rambled on through many arguements but I still hold to the narrow view that the internal layers of a multifoil contribute little to the insulation and much to the cost.

If you want to draught proof and improve airtightness then there are other materials designed for the job. Don't defend a poor insulator on the gounds that it is good for some other purpose.

The best (though it's not cheap) insulator for thin spaces is 'Spacetherm', an aerogel product supplied by Proctors. This actually does what it says on the packet.

(Multifoils do have a place - in cryogenics and deep space, where up to 30 foils are used, separated by paper, and in a vacuum - the physics is very different in that environment.)

 

[AMc]

I second this - especially if you use Celotex type insulation between studs you may have to use expanding foam for a good fit as it is very difficult to get to fit exactly.

And thirded, I had to keep an eye on the guys putting ecotherm between the rafters as they were quite happy to leave a 2" gap to avoid having to cut out a slot for a rafter. Once I'd made it clear how expensive the stuff is and how carefully I needed it to be cut they were much more careful (though also slower).
My builder only trusts doing the expanding foam to one of his guys, if you're over enthusiastic you can push the tiles off the roof.

 

[middi]

I think a lot of you are getting your knickers in a twist.

Let us start all over again. If contemporary insulation is used on a wattle and daub timber framed buildings to complement and improve the already good insulating qualities of the daub it is not a problem whatsoever. AS LONG AS, the building is able to breath from within and from without , it is not absolutely necessary for the breathing mechanism to travel back and forth through the walls.

Any moisture or water that reaches the insulating material will not reach the studs, therefore it is impotant that whatever type of external cladding is used above breathing paper and battens must be BREATHEABLE otherwise the battens will rot. CEment is totally useless due to the fact that it is extremely rigid and therefore will not follow the perpetually moving frame. Cracks will appear, water will penetrate, cannot escape faster than it goes in and will induce rot, BUT NOT TO THE OAK STUDS, because the isnsulated unbeatheable material will stop water getting that far. It is important that the breathing mechanism is correct within the building, any internal moisture that may reach the studs and the inner face of the insulation will be "SUCKED" in by the baub and as long as this can be reasonably ventilated it will work in the opposite direction and suck out any moisture that is likely to accumulate on the inner surface of the insulation or studs therefore extremely imporatant not to use any impermeable covering within the building inner walls or on top of the daub. It is a question of balance of materials.
I have adopted this method on G II listed buildings for a number of years and it works extremely fine, the CO's have had no objection to this approach. Different story on G I buildings.

I have suggested what has woked for me, and at least I made a suggestion which I know it works, there is not much science in this, or my approach, just observation and experience.

After all that is how these building were built in the fist place.

I am the last person on this forum which advocates indiscriminate use of modern materials on traditional buildings, BUT, if cleaverly adopted they can help save and prolong the life of these decaying buildings.

This is why I suggested lap boards work better on these buildings than ANY type of hard renders, this includes lime renders.