External insulation and moisture

cerastes

I was thinking of a potential problem with external insulation (EI) being moisture existing in the walls at the time of insulation being fitted. Could this lead to moisture being trapped in a wall causing problems. Does it mean walls should only be insulated at certain times (of the year/weather conditions/relative humidity?).
I saw this thread below but as there is very little in it to read and as it's an older thread I thought Id just link to it rather than reply.

http://www.boards.ie/vbulletin/showthread.php?p=74273037

Other things that I think may be a concern are the surface of an existing wall, in my case I believe it is called a wet dash (pebble dashed?). Ive seen a few Irish and other demonstrations of fitting EI where it is just applied with dabs of a plaster like adhesive and fixed in place with mushroom headed bolts.
On one demo they showed options of using a plaster like substance and another a more synthetic glue like product (it was foreign, I think it was a german product, but it was in English and they seemed to be doing it on a building that didnt look like it was a UK/Irish build). They did show hardpoints for attaching and supporting external fixtures, in their example I believe they were suggesting drainage for toilets and possibly roof. I thought this was interesting as I was thinking also along the lines of how, drainage, satellite dishes and side gates would be accounted for in fitting? As the Irish demos didnt show these hardpoints which were drilled out portions fitted with a plastic support block, but which were larger than the mushroom supporting attachments, presumably larger to spread the load and weight of attached fittings.

Anyway, my original thinking was the cavity block could have moisture trapped under the EI, and then that the space under the EI between dabs being nearer the cold exterior might still suffer from moisture formation? so although sealed, might trap moisture, I began to wonder should the adhesive cover the entire EI slabs or even could the cavity block space be vented through vents in the EI that are either spring loaded flaps operating under negative pressure from an internal fan (potentially one used in heat recovery internally that might require cooler external air as part of its operation) and switched on the basis of an RH sensor in the blocks, periodically or on demand if part of another system (although the later may not be preferable).

Id also seen a wall design in an engineering book, it was like an entire large cavity between the outer and inner wall (I cant recal what the name of the book or the wall design was and I suspect its rare enough if non existant in the UK/Irl). It showed a wall design that avails of solar energy to heat and I believe create ventilation also or at least pulled heat through vents when the surface was heated by the sun, Id wonder could this design be incorporated into an EI scenario? where external panels that would warm in the sun could have ducts through and up under the EI into perforated plastic channels to create a cavity, then fed up the walls to another higher vent, where it aided heating when solar energy was available but limited heat loss and could be shut off in colder weather.

Previously Id considered potentially putting up some insulation internally myself to reduce heat loss, but not without investigating it first, after some reading, I now believe doing nothing is better than doing that, not at least without measuring the performance first.
I have still wondered might internal and external insulation complement each other though, where a small thickness of added internal insulation might reduce heat loss, but still allow sufficient heat escape to prevent moisture buildup in the structural walls while allowing the EI to do the larger portion of heat loss reduction, although Im still uncertain how existing moisture in the structure or any that may gain access is expelled.

sydthebeat

Typically the walls in an ewi house Will be 16 - 17 degrees average. More than enough to turn the water to vapour and remain so until it's exhausted internally.
I'm talking about properly installed systems.

cerastes

sydthebeat wrote: »

Typically the walls in an ewi house Will be 16 - 17 degrees average. More than enough to turn the water to vapour and remain so until it's exhausted internally.
I'm talking about properly installed systems.

The internal walls? doesnt it depend on the external temperature though? or what heat is being applied internally?
If that is so, Id have thought there is no typical surface temperature of the internal wall? just that its dependant on the temperature outside, I dont know for certain though, Im just trying to get it right in my head.

My wonder is what the temperature across the structure is, whats experienced in the cavity, that presumably would be colder? and the dew point anywhere is dependant on? the moisture content of that pocket of air and the temperature presumably.

Maybe moisture internally might be carried away as it cant penetrate the wall, but what of any moisture (edit in vapour or liquid form) in the structure? is it trapped, how does it escape? or not create a problem, assuming no extra moisture gets in, does an EI concrete structure just dry out and stay dry?

sydthebeat

im not quite sure exactly what you are asking because you seems to be inferring problems causes by bad installation practices.

perhaps this youd find more consise answers here

and if your very eager, you should read the whole series 1 - 5 here

cerastes

sydthebeat wrote: »

im not quite sure exactly what you are asking because you seems to be inferring problems causes by bad installation practices.

perhaps this youd find more consise answers here

and if your very eager, you should read the whole series 1 - 5 here

Ive read that before, If I recal correctly there were some parts which I didnt understand, I'll have to read it again to tell you which parts. No harm readin again or having a recent link to look back on it when I have some time.

Anyway, there was a bit in my first post,
so a summary is, mainly I was thinking about if EI is fitted, even done well, then do the atmospheric and weather conditions at the time affect moisture in the concrete structure that is now sealed in? can it be a problem? should EI only be done after drying out the structure by applying heat internally or relying on solar energy and dry weather or all.
Does a now sealed concrete wall which may have some moisture content present any problem from the perspective of forming moulds or anything that might damage the insulation (I think unlikely) or transmit damage to other aspects of the structure or create health problems?
OR
assuming normal heating is applied and the concrete structure is now sealed from the elements, does it just dry out and get and stay drier?

If so, could also some internal (complementary/supplementary) lower level of insulation help reduce heat loss but not allow the temp on the internal structure drop to a level moisture can form,

And how can any water vapour present in the now sealed structure escape?? regardless of internal insulation or not, given its likely between a vapour barrier and EI.

BryanF

This answers your question:

sydthebeat wrote: »

Typically the walls in an ewi house Will be 16 - 17 degrees average. More than enough to turn the water to vapour and remain so until it's exhausted internally.
I'm talking about properly installed systems.

cerastes

BryanF wrote: »

This answers your question:

I wasnt certain which walls that refers to though? the internal walls or the walls of the concrete structure, which is sealed between a vapour barrier to prevent moisture travel from the living space where people breathe and dry clothes etc and the EI?
If this refers to the temperature on the structural wall and not the plasterboard, how does the water vapour ever get expelled? through where? what opening/membrane? it seems like its sealed in there? if not then isnt heat exiting that way too?

sydthebeat

cerastes wrote: »

I wasnt certain which walls that refers to though? the internal walls or the walls of the concrete structure, which is sealed between a vapour barrier to prevent moisture travel from the living space where people breathe and dry clothes etc and the EI?
If this refers to the temperature on the structural wall and not the plasterboard, how does the water vapour ever get expelled? through where? what opening/membrane? it seems like its sealed in there? if not then isnt heat exiting that way too?

There should be no vapor barrier.
I think that's where you are getting worried. There's no need for one.

As the external walls are warm they will dry off pretty quickly and remain dry.

BryanF

cerastes wrote: »

I wasnt certain which walls that refers to though? the internal walls or the walls of the concrete structure, which is sealed between a vapour barrier to prevent moisture travel from the living space where people breathe and dry clothes etc and the EI?
If this refers to the temperature on the structural wall and not the plasterboard, how does the water vapour ever get expelled? through where? what opening/membrane? it seems like its sealed in there? if not then isnt heat exiting that way too?

Could we narrow this down to one question?

cerastes

sydthebeat wrote: »

There should be no vapor barrier.
I think that's where you are getting worried. There's no need for one.

As the external walls are warm they will dry off pretty quickly and remain dry.

I see, I thought there was a need to have a vapor barrier to prevent mositure moving around? ie exiting outwards and not instead going through vents or being drawn out by a air replacement/heat recovery system.
I asked this or it was answered (vapor barriers) in a question on boards recently about attic insulation and I believe it was suggested a vapour barrier should be put in place on the dry side to prevent moisture moving across from the habitated side towards the exterior colder part,

although this just throws up more questions for me? what if the barrier is in situ just outside the internal plasterboard, long before EI is fitted?

I'll definitely have a read of those Joseph Little documents again, interesting stuff, of what I could understand.

cerastes

BryanF wrote: »

Could we narrow this done to one question?

At the time it was assuming a vapor control layer existed just under the internal plasterboard,
so as one question,

If moisture exists in the structural wall at the time EI is fitted, is the moisture now trapped and how does it get out?

Id supplement that with,
If it doesnt get out can it cause harm or damage?
and
If it can escape, how?

3 questions is the leasdt I can reduce it to

BryanF

sydthebeat wrote: »

Typically the walls in an ewi house Will be 16 - 17 degrees average. More than enough to turn the water to vapour and remain so until it's exhausted internally.
I'm talking about properly installed systems.

The above answers your question

cerastes wrote: »

At the time it was assuming a vapor control layer existed just under the internal plasterboard,
so as one question,

If moisture exists in the structural wall at the time EI is fitted, is the moisture now trapped and how does it get out?

Id supplement that with,
If it doesnt get out can it cause harm or damage?
and
If it can escape, how?

3 questions is the leasdt I can reduce it to

cerastes

BryanF wrote: »

The above answers your question

ok, its all hypothetical anyway, in this case there will hypothetically have to be no vapour control layer in the wall, so I'll assume they never are .

I'm still a bit suprised about the temp mentioned being 16-17 degrees as I didnt think the point at which water condensed is fixed, thought it would depend on the insulation thickness and the exterior temperature.

Ive read the dew point is pushed to the exterior surface, but Im trying to establish for a range of external temperatures (or other criteria like RH) in any insulation scenario that this is absolutely certain, how much heat might have to be on to prevent the dew point occuring inside the wall.
This was one of the main reasons I decided I wouldnt proceed with a DIY internal insulation as I considered (I think it was after reading "breaking the mould" or some of the other articles) that internal insulation would not be a good idea unless it was worked out for all scenarios (ranges of external temperatures and moisture conditions, the later of which I think might prove more difficult to carry out?).

BryanF

google ' physometric chart' & separately 'external wall dew point calculator'