17th Century Timber framed house - breathability

[middi]

Middi - if there isn't enough roof overhang for Zebra to follow your original plan, wouldn't it be possible for the insulation to be inserted between the studs? A breathable membrane could then be applied to the outside of the studs, then battens, then stainless EML and lime render.

Would that work?

You have made a very good and valid point Penners, in order to minimise thickness" intrusion" on the existing elevations of the building and therefore avoid interference with roof eaves.
Another possible solution that would work quite well, although a little less efficient, is to insert the insulation between the wall studs, as you suggested. As long as there is an existing void and not all those wattle and daub panels. These could be sealed if loose within the studs by stuffing wool between studs and panel.
Once this has been done, be it with rigid insulation ( ie celotex or similar), sheeps wool, rockwool or one of those multilayered insulation blankets, it would be wise to add structural plywood ( or engineered stirling board) on the outside of the studs in order to strengthen and stabilise lateral movement os studs. Above this plywood I would fix the battens and then the breatheable membrane. The reason for this would be to create an air gap between the ply and paper and therefore freedom of air circulation eliminating the membrane to be in close contact with the ply as this would render the function of the breatheability factor useless.
One has to assume that water vapour will permeate to a certain extent through the paper/membrane and as long as there is a reasonable air gap beyond the entry point and behind the membrane then there will not a problem. This arrangement would work quite well and allows for provision of substantial insulation.
If wattle and daub panels are in situ then it would be wise to use those multilayered isulation blankets on the exterior of studs in order to preserve them. Ply panels, battens and membrane to be used as above.
Middi

 

[Penners]

Thanks for that view, Middi.

Judging from Zebra's original photo, there doesn't seem to be much evidence of wattle & daub infill. There seems to be a lot of controversy about the efficacy of foil insulation blanket, so assuming there are voids between the studs personally I would favour one of the thicker forms of insulation - rigid foam (Celotex, Kingspan, etc.) reportedly being the most efficient.

 

[middi]

Thanks for that view, Middi.

Judging from Zebra's original photo, there doesn't seem to be much evidence of wattle & daub infill. There seems to be a lot of controversy about the efficacy of foil insulation blanket, so assuming there are voids between the studs personally I would favour one of the thicker forms of insulation - rigid foam (Celotex, Kingspan, etc.) reportedly being the most efficient.

I would agree with the above.

Middi

 

[andrew gayton]

complete permeability is the only way to deal with this. with readily available permeable materials, there is no need to use ply and celotex etc. look into diffutherm/pavatherm etc and warmcell/thermafleece etc as a way of providing a structural diaphram and insulation prior to lime plastering. interstitial condensation - between building layers - is to be avoided at all costs.

 

[Zebra]

complete permeability is the only way to deal with this. with readily available permeable materials, there is no need to use ply and celotex etc. look into diffutherm/pavatherm etc and warmcell/thermafleece etc as a way of providing a structural diaphram and insulation prior to lime plastering. interstitial condensation - between building layers - is to be avoided at all costs.

Thanks, I will look into those products.

Middi, I'm afraid I still don't get it with your original idea of Celotex on the outside of the structural ply, followed by breathable membrane and lime render. If the celotex is sealed with aluminium foil, and a seal fails, then it's as bad as the cement render I'm taking off, in that it is not a breathable layer.
Also, if the celotex isn't breathable, what then is the point of using a breathable lap board/lime render outer layer at all?
Thanks for your help though people.

 

[Zebra]

There's no wattle and daub infill. I can insulate between the studs but there's only 50mm or depth, then possibly another 25mm over the top of the studs, before a finish of plaster/lime/whatever. Thinking of using a heavy plasterboard because of sound insulation. I can hear what hymn they're singing in the church from my bedroom. Which means they can hear me too!!

 

[middi]

complete permeability is the only way to deal with this. with readily available permeable materials, there is no need to use ply and celotex etc. look into diffutherm/pavatherm etc and warmcell/thermafleece etc as a way of providing a structural diaphram and insulation prior to lime plastering. interstitial condensation - between building layers - is to be avoided at all costs.

Thanks, I will look into those products.

I'm afraid I still don't get it on Middi's original idea of Celotex on the outside of the structural ply, followed by breathable membrane and lime render. If the celotex is sealed with aluminium foil, and a seal fails, then it's as bad as the cement render I'm taking off.
Also, if the celotex isn't breathable, what's the point of using a lime render at all?
Thanks for your help though people.

As the saying goes Zebra " there are many ways to crack a nut ". ( see Andrew Gayton Post).
The solution I put forward is an option when modern materials can be used in old buildings to obtain the most heat and sound insulation whilst protecting the building structure.
There are other ways to protect and insulate these buildings it depends on the type of materials used and how they are applied that will determine the degree of success.
The reason to use lime render ( externally) is to allow the wood battens that hold the celotex in position to breathe. the moisture will only go as far as the EXTERNAL celotex face and having done so the lime render will allow this to evaporate externally therefore avoiding premature rotting of battens. No moisture will travel past the celotex onto the bulding studs or to the interior of the building. In other words whatever permeates from the outside has to be dissipated to the outside. The same has to apply within the building, whatever moisture is present has to dissipate itself with the aid of judicious heat and/or ventilation as applicable, the internal fabric has to be breatheable to allow any moisture that has travelled as far as the shuttering play ( if used ) and the INNER face of the celotex to evaporate outwards within the building.
I wouldn't worry about about taped alluminium seals failing.
This system ( as reccomended to me by a respected and Nationally well known SPAB architect) has served me well over the years where it was possible to be applied with the CO approval.

Middi

 

[Zebra]

Thanks Middi...

 

[Zebra]

Worried about revealing my ignorance here, but exactly how involved does the Conservation Officer have to be in all this? Mine is not a listed building, although it is in a Conservation Area. So what permission does it need exactly?

My local Planning Dept are extremely uncommunicative. They've already missed the deadline on my planning application, and not communicated a new date. You can only call them on a Wednesday between 2=4pm, and then on a Wednesday between 2-4 pm they don't pick up the phone. I did see a Duty Planning Officer some months ago who told me I wouldn't need permission to replace like with like. On which basis I've replaced the roof (with new handmade clay tiles...). Trying to get hold of someone in the Planning Dept every time I want to change something will be a nightmare. So if I'm replacing one render finish with another, and I don't need planning permission, what's the problem?

Or is that not how it's supposed to work?....... :?

 

[Penners]

If you're replacing a failing render finish with a new (better) one, then that clearly constitutes a repair, doesn't it? You don't need consents to repair.

 

[middi]

I agree with Penners. If you intend to repair and improve the insulation of the building I don't see how the council can object to it if you go ahead without telling them. Especially as you do not intend to alter the facade of the building. Obviously if listed or in a conservation area I would inform them as a matter of courtesy as to the intended repairs.

Middi

 

[AMc]

I think some may have assumed your house would be listed because of it's age?
I'm not an expert on conservation areas or listing either but I would make a documented attempt to inform the planning dept. you were renewing the render on a visual like for like basis with a lime top coat, limewashed in the same colour (if applicable).
If would send a registered/recorded delivery letter which states your intention and a date when you will commence works (a couple of weeks to allow them to respond).

I was told informally that our renovation work didn't need planning permission but I sent drawings to the planning dept. anyway as we were replacing a large vinery with a similar stucture - I got an email that said the work didn't need permission. That set my mind at rest and had there been any dispute I think it would have been in my favour.

If the work affects more than 25% of the thermal element (a.k.a. the wall) then technically it should comply with PartL1B of the building regulations for thermal performance. If you're doing other work with Building Control consents may want you to demonstrate this - your building control officer (if you have one) should be able to advise.

If you're happy to proceed on your previous verbal confirmation - having already done the roof! - then I wouldn't worry.

 

[robgil]

Thats not the way it works here, my house (unlisted) would never comply with part l1b without major work and when the council were contacted about re-rendering the exterior they simply said sheeps wool between the batts would suffice.
If your house isnt listed you may be opening up a can of worms. I would say do the best you can without being unkind to the building, anything is an improvement and better than nothing.
Different councils and B.I's will take different views so if you can ask around and figure out their form first it may save you making a mistake.
A good place to start would be asking a builder who specialises in restoration work in your area what the local councils views are.

 

[AMc]

robgil - glad your Building control officer/inspector takes a pragmatic approach. Mine was unconcerned about demonstrating the chosen solution complied but I had to get a full SAP report done to get my plans approved by Building Control first!
What we installed exceeded the plans but he merely gave it a look and was satisfied we knew what we were doing. I was just trying to highlight that there is another set of regulation that may come into play if the work is deemed to be a "renewal" rather than a "repair".

Listed Building Consent
Planning Permission
Building Control permission
are all different but related to the process of renovating old houses.

Sometimes they may compete with one another with BC requiring improvements in thermal efficiency that are counter to the requirements of a listing to maintain the appearance and construction of the property.

 

[Zebra]

Thank you Penners, Middi, Robgil, and AMc. Am much relieved. Will write to Planning & Conservation as you recommend, and will give Building Control a ring on Monday - they do answer the phone!!

 

[Zebra]

Dear all,

Sorry to return to this thread, but without at all wishing to dismiss the solution offered by Middi, I am looking into alternatives also suggested i.e. fully breathable insulation, and find that I still have more questions than answers!

1. The only thing that worries me with the idea of taped Celotex (or equivalent) as an external insulator and barrier preventing water reaching the frame, is the possibility of failure - for how many years would you be really sure that the system was still watertight and that the tape was not coming away from the Celotex?

2. Diffutherm/Gutex/wood wool/other modern breathable external insulators and render carriers - they seem to say in their product literature that they require the sheathing board to be applied internally. This is not possible in my case because the frame is not flush internally. The beams are deeper than the studs. Is it then not possible to use these products? Anyone with more experience? I've found breathable sheathing boards available. Would this work?

3. The Building Control Officer has said that I need not put in a Building Notice unless I want a Completion Certificate as the works don't affect the whole building, but that I will need to achieve a U-value of 0.35w/m2k as it's an older building I won't have to meet the current Building Regs standard of 0.28w/M2K. The literature for various products gives values in W/mK or in m2/KW-1 or other ranges, and I'm quite frankly not capable of working it out by myself. How can I realistically compare systems, or where could I find someone who could calculate the U-values of the whole wall construction, taking into account different elements combined?

Help much appreciated.
Z

 

[andrew gayton]

You could use heraklith externally and plaster over. insulate between studs with thermafleece/warmcell/hemp etc. I have seen pavatherm/pavadentra/diffutherm used externally also. I recently revisited a house I had specified the repair of - wattle and daub infill panels with lath and plaster over frame externally and internally; according to the owner it is working well - thermally speaking - so old 'technology' remains applicable in works of restoration, even those with an emphasis on thermal performance. The main issue here has to be permeability and the avoidance of any forms of condensation. Saturation will of course have a massive impact on long term thermal dynamic. In my experience most 'modern' solutions will eventually cause a problem.

 

[middi]

You could use heraklith externally and plaster over. insulate between studs with thermafleece/warmcell/hemp etc. I have seen pavatherm/pavadentra/diffutherm used externally also. I recently revisited a house I had specified the repair of - wattle and daub infill panels with lath and plaster over frame externally and internally; according to the owner it is working well - thermally speaking - so old 'technology' remains applicable in works of restoration, even those with an emphasis on thermal performance. The main issue here has to be permeability and the avoidance of any forms of condensation. Saturation will of course have a massive impact on long term thermal dynamic. In my experience most 'modern' solutions will eventually cause a problem.

I agree with your point ,Andrew, regarding the avoidance of installing an impermeable barrier within the walls of these buildings. I must add that this will only hold true if a single film barrier is introduced where the film in question has no thermal insulation property in it's own right and therefore susceptible to rapid cooling and warming of it's surface layers. these surfaces will, therefore, immediately attract condensation/dew at small temperature flactuations, as the air flow in this area is not fast moving problems wil be encountered as the water droplets will not be able to disperse faster than tey can accumulate.
The reverse is true if an impermeable barrier/film is introduced where the barrier in question has good thermal properties, ie:- tightly packed with insulation therefore not prone to rapid cooling or temperature flactuations. As we all know that warm air condenses on cool/cold surfaces this arrangement eliminates the condensing problem that would be very evident and damaging as per our single film example.
The obvious thing to do would be revert to completely traditional construction by using wattle and daub, lath an plaster with a lick of "whitewash". We know that this works with reasonably well insulation properties .
As soon as we "stick our nose" into the use of modern insulation materials that may be used and adapted into these properties we are dictated by the latest available insulation on the market and an endless question as to what may be best for the buildings,ourselves and the environment.
Just observations that may help.
Middi

 

[AMc]

It seems to me that the numbers you have been quoted aren't for a wall from the 2010 revision but I'm not that current. nor am I a professional
If you really want professional help then have a look for energy assessors who are qualified to perform Standard Assessment Process (SAP) studies of thermal performance but I really don't think that you need to do that for a simple wall renovation.

You'll want to download, print, highlight and inwardly digest PartL1B of the 2010 regulations esp; Part 5.7

Everything
http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partl/approved#ApprovedDocumentL1B:ConservationoffuelandpowerExistingdwellings2010edition

Free PDF here
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1B_2010.pdf


U value is W/m2-K - R value is the inverse of that IIRC.

You should be able to get the U and R values of commercial products from their technical datasheets. This should also be acceptable to Building Control to prove compliance. I doubt you need to work out the composition of frame to infill separately providing you can show you've used a manufacturer approved construction for the bulk of the wall.

When discussing with BC pay particular attention to the phrases "technically, functionally and economically feasible" in paragraph 5.9 you are doing the right thing by insulating but there is flexibility in what you can reasonably achieve.

My experience of Building Control is that they are often out of their depth with this stuff so you need to be well briefed and confident and they'll often trust you're doing the right thing.

 

[biffvernon]

I think it is offering some structural support to the frame....I think is helping to hold the building in shape and keep it from warping...

That strikes me as pretty unlikely. It will be the timber that's holding the cement up, not t'other way about.

Be a purist, remove anything put there since the industrial revolution and repair with materials that were available 300 hundred years ago. As you say, it's only a small building, so you can afford to do a proper conservation job. It will be more satisfying and bring more joy.