Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

The AECB accepts no responsibility or liability for any errors or omissions in the content of this site. Views given in posts are not necessarily the views of the AECB.



General: Cavity walls Why?

Bottom of Page

31 to 60 of 62

  1. <
  2. 1
  3. 2
  4. 3
  5. >
  1.  
    Thanks ciaranw. No problems with the tape. Not sure what its called but is design especially for the job, sticks lik s*** to a blanket!
  2.  
    Mike,

    what was the external finish make-up on top of the insulation?

    Thanks,
    Mark.
    • CommentAuthormarktime
    • CommentTimeNov 19th 2009 edited
     
    Mike, when you foam the joints, do you have an on-site mixer or is it straight out of a can?

    Interesting paper, Tom. Thanks.
  4.  
    Mark

    Outer leaf of concrete block, render finish

    Marktime.

    Straight out of the can. Imprtant to use gun grade foam with regulator
  5.  
    Posted By: Mike GeorgeMark

    Outer leaf of concrete block, render finish


    Ah, OK, so this was still a cavity wall insulation.

    Cheers,
    Mark.
    • CommentAuthorjamesingram
    • CommentTimeNov 19th 2009 edited
     
    And I thought I was the foam gun king .
    the tapes usely just called foil tape , stocked by most buildeers merchants etc., as Mike mentioned it normal sticks well, got to be dry and clean though.

    On a slightly different thought , yes cavity walls can be made airtight and work well with detailing and quality
    workmanship like Mikes, but I dont think its unfair to say 98%+ of builds wont be done like this
    Builders/ bricklayers just want to get stuff up quick and cheap, to a reasonable standard , building inspector are just looking to tick boxs , so no real quality controls from them.

    So Perhaps a build method that takes on board the reality of everday sites and average achievable standards
    would be the best route.
    Therefore would the solid wall EWI method potentially give better results ?

    cheers Jim
  7.  
    Like many of you I am not a fan of the cavity wall system. For my extension in Mid WAles my architect informed me that i HAD to have a cavity! Since gone with Durisol wall system which is a different matter.... However, a thought that I have not had answered is has anyone taken into accout the ammout of cooling that takes place when a wet brick outer wall is subjected to wind? (Latent heat of cooling if my school days serve me well?) I believe that in these conditions the outer wall will be cooled below the outside air temp with a subsequent negative impact on any wall insulation calculations - (place a wet cloth over a bottle of wine in the wind and the wine is cooled) Anyone come accross this being taken into account anywhere?
    • CommentAuthorMaria CEA
    • CommentTimeNov 20th 2009 edited
     
    "...................outer wall will be cooled below the outside air temp ................"

    How? I don't understand.

    Maria
    • CommentAuthorMaria CEA
    • CommentTimeNov 20th 2009
     
    Oh, I see. They used to use this effect for passive cooling in the Oman. They would hang porous jars of water in the window facing the shore and the onshore wind would blow past the jar evapourate the water on the outside to provide cooling and humidity.

    Anyway, ignore me, back to the menace of the cavity wall!

    Maria:smile:
  10.  
    Maria,

    Lick one hand then blow on it then blow on the dry hand .... you should sence the wet hand being cooler than the dry hand when you blow as the wet area will be cooled by the air passing over it (the wind)

    I think the correct term is latent heat of evaporation - I am sure someone out there can remember more from their physics lessons than me ..................????
    • CommentAuthorTerry
    • CommentTimeNov 20th 2009
     
    Just a comment on Mikes taping of the joints on his insulation. We did it with the same make of insulation with no problems, but when we tried it on a different manufacturers product the tape didnt stick. We did however find a different tape that did, so might be a good idea to check with the insulation manufacturer.
  12.  
    Posted By: jamesingramAnd I thought I was the foam gun king .


    I can do lessons for a small fee

    Posted By: jamesingram.

    On a slightly different thought , yes cavity walls can be made airtight and work well with detailing and quality
    workmanship like Mikes, but I dont think its unfair to say 98%+ of builds wont be done like this
    Builders/ bricklayers just want to get stuff up quick and cheap, to a reasonable standard , building inspector are just looking to tick boxs , so no real quality controls from them.


    Sadly, I have to agree

    Posted By: jamesingramSo Perhaps a build method that takes on board the reality of everday sites and average achievable standards
    would be the best route.
    Therefore would the solid wall EWI method potentially give better results ?


    Wouldn't the 98+% find a way to cut [different] corners?

    There are also some potential difficulties common with cavity walls

    Fixing boards flush to substrate
    Leaving gaps [between and behind boards]
    Taping joints

    The above mostly relating to walls cladded and having a ventilated cavity.

    But I guess you're mostly referring to rendered EWI which we discussed above. Suppose I have to accept that your practical experience of doing this carries more weight than my theoretical concerns. Not sure I have the confidence to undertake one though [yet]

    :bigsmile:
  13.  
    Posted By: AberborthinLike many of you I am not a fan of the cavity wall system. For my extension in Mid WAles my architect informed me that i HAD to have a cavity! Since gone with Durisol wall system which is a different matter.... However, a thought that I have not had answered is has anyone taken into accout the ammout of cooling that takes place when a wet brick outer wall is subjected to wind? (Latent heat of cooling if my school days serve me well?) I believe that in these conditions the outer wall will be cooled below the outside air temp with a subsequent negative impact on any wall insulation calculations - (place a wet cloth over a bottle of wine in the wind and the wine is cooled) Anyone come accross this being taken into account anywhere?


    Hi Aberporthin.

    Isn't this accounted for within a u-value's calculated method? Surface resistances Rsi [resistance of surface inside] and Rso [Resistance of surface outside]
    In any event it would apply to all wet surfaces not just outer leafs of cavity walls wouldn't it?
  14.  
    Mike,

    I'm not sure.... Brick walls will absorb water and the wind will then cool the bricks as the mosture is evaporated. A rendered or other wall that is "waterproof" will only have any moisture that has not run off the surface to evaporate and cool the wall - a much smaller amount than some bricks that will / can have the whole thickness saturated with moisture. If my school days memory is still working, it is the amout of moisture available for evaporation that provides the cooling effect.

    A simple test would be to place 2 bottles of wine / beer outside on a windy day - one covered with a wet cloth and one with a dry cloth - I believe that the wet covered bottle will become much colder especially if the cloth is kept wet.
    • CommentAuthortony
    • CommentTimeNov 22nd 2009
     
    Brian

    You are correct that this effect is not taken into account in thermal calculations. It ca lead to vicious circling where the wall cools and condenses water on the inside face which soaks in and evaporates from the outside where it cools the wall etc etc.

    Ideally the outside of the wall should be thermally isolated from the inside by insulation
  16.  
    Very interested in this tony

    When you say 'not taken into account in thermal calculations' do you mean it is not considered at all as part of a calculated u-value?

    Or that it is another aspect of heat loss the u-value does not predict accurately?
    • CommentAuthortony
    • CommentTimeNov 22nd 2009
     
    Both -- it is not taken into account in U valve calcs

    It is not allowed for in thermal calculation software -- the cooling effect depends on many things, rain direction porosity, wind speed, rain duration, humidity -- almost impossible to calculate.
  18.  
    So in this context a partially filled [correctly installed] cavity wall is actually a good thing as the outer leaf protects the insulated inner structure from this effect?
  19.  
    Mike and Tony,

    Reason I raised this issue is my belief that like many on this thread, the UKs insistance on cavity walls is flawed as is our love affair with bricks (dont get me wrong a well laid brick wall can be an attractive feature) However, in this day and age to build with such a labour intensive material that absorbs water and can actually have a cooling effect on a house would appear to be barking especially as the cooling effects are not taken into account! I am noticing many timber framed housed being built (from SIPs / factory manufactured panels) which are then brick clad - to me this is building a well insulated property and adding a cooling layed to the exterior.

    Regarding Tonys comments -

    - If the outer skin should be thermally insulated from inside then the 100mm brick wall should not not included in any wall U values??

    - Agree that software modeling the effect of latent heat of evapouration would be difficult but if one building method has such a negative impact on U values how can we ignore it? If I had some more time I would be tempted to build 2 small brick walls and paint one with waterproof paint, leave both to get wet and cooled by the prevailing wind and then measure the temp of the bricks.....

    Would it be worth starting a tread on the pros and cons of bricks as maybe someone has done work on this subject already???
    • CommentAuthorMike George
    • CommentTimeNov 22nd 2009 edited
     
    Aberporthin,

    I meant to respond to your earlier post but do you realise that rendering is not actually waterproof? The principle is that areas of high exposure are protected by up to three porous coats of render, which allow rainfall to be absorbed and then subsequently evaporated. This render can be lime or cement based or a combination of the two.

    Waterproof render is a very bad thing. It is too hard and too impermeable. When it cracks [and it always does] it allows rainfall in through the cracks, and this water becomes 'trapped' behind the mostly impermeable coating. This can lead to further deterioration of the fabric, particularly in older buildings where timber was routinely embedded in the masonry.

    So whether a wall is cavity construction or not, whether it is rendered or not, whether it is clad with porous clay or concrete tiles, or any other porous material - it seems to me all will be affected to a greater of lesser degree by the latent heat of evaporation.

    It seems to me also, that a partially filled cavity wall will isolate the insulation from such an effect. The fact that such a cavity may also be ventilated to a degree also matters not. It is the quality and integrity of the insulated inner leaf which is important, and a cavity will continue to ensure that the insulated part has longevity.
    • CommentAuthortony
    • CommentTimeNov 22nd 2009
     
    Further in a well insulated wall the effects of this evaporation process are very small probably negligibly small -- only in little insulated or uninsulated walls would the problem be of concern.
  22.  
    Posted By: Mike GeorgeWaterproof render is a very bad thing. It is too hard and too impermeable. When it cracks [and it always does] it allows rainfall in through the cracks, and this water becomes 'trapped' behind the mostly impermeable coating. This can lead to further deterioration of the fabric, particularly in older buildings where timber was routinely embedded in the masonry.


    Mike - is this true (in your experience) for silicone/acrylic renders? They are advertised as flexible and anti-crack for this very reason and I was hoping to use this on my build.
  23.  
    Hi mark,

    I have little experience of acrylic renders so I don't know sorry.
    I think James Ingram may be the man to offer more on acrylics?
    • CommentAuthorjamesingram
    • CommentTimeNov 23rd 2009 edited
     
    The acrylic based renders are suppose to be breatherable / vapour permeable
    most carry a 10 year manifactures guarantee and have been accelerated tested (whatever that is ?)
    to show they last 20+ years ( doesn't seem that long really ), how this compares with modern lime renders I'm unsure, which can also be used for thro-colour finishes or for EWI jobs
    Have a word with the technicial dept. of the system you intend to use.
  25.  
    What about the millions of homes that have a masonary paint finish?? Are these all doomed to cracks and damp??

    The limited experience I have of people living in homes with render and a paint finish do not seem to have any problems (both old and newer properties)

    If a cooled outer brick skin has no noticable effect on the insulation of a well constructed wall why bother with it. My understanding is that the outer brick layer does not carry structural loads, is expensive and time consuming to build and bricks require large amount of energy (heat) to make.....
    • CommentAuthorMike George
    • CommentTimeNov 23rd 2009 edited
     
    Posted By: AberborthinWhat about the millions of homes that have a masonary paint finish?? Are these all doomed to cracks and damp??


    Yes, to some degree or other. Where I live there are many, many sandstone frontages to houses - many painted - and many now being stripped and laboriously repaired due to the damage caused by painting.

    Posted By: Aberborthin

    If a cooled outer brick skin has no noticable effect on the insulation of a well constructed wall why bother with it. My understanding is that the outer brick layer does not carry structural loads, is expensive and time consuming to build and bricks require large amount of energy (heat) to make.....


    Sorry to disagree again but the outer leaf of a cavity wall does indeed contribute to the structural integrity of Buildings. Have a look at Part A of the buildings regs for requirements relating to height : wall thickness ratios
    • CommentAuthorMike George
    • CommentTimeNov 23rd 2009 edited
     
  28.  
    I don't think the case for EWI versus cavity wall is so clear cut.

    Although the inner leaf bears the floor & roof loads, the outer leaf plays an important role in providing bracing. Either you need two leaves of 100mm or one leaf of 180-215mm with external render. So its not really about structural efficiency or wall thickness, it's all about what finish you want, what insulation you choose & where you choose to put it.

    Putting the insulation on the outside puts all the thermal mass on the inside where it can do some good. However, the benefits of going above 100mm are limited & could probably be mimicked by using a denser 100mm block.

    EWI has the advantage that it can be inspected & filled prior to rendering. However, not everyone wants render and there is no reason why bricklayers can't be trained/supervised to build to the standard necessary for energy efficient cavity walls.

    For me the main considerations were that I wanted to minimise my use of plastic insulation, I wanted to use a flexible insulation that would adapt to the variations in the inner leaf and I wanted a brick finish. My target U value is 0.105 & wall thickness 502.5mm with full-fill DriTherm 32. Can this U value be achieved with EWI? What would the overall system thickness be?

    David
    • CommentAuthorBenj
    • CommentTimeNov 26th 2009
     
    Tony why are you seemingly anti cavity at the start of the thread. I thought you chose this method for your build.
  30.  
    Posted By: AberborthinBrick walls will absorb water and the wind will then cool the bricks as the mosture is evaporated. A rendered or other wall that is "waterproof" will only have any moisture that has not run off the surface to evaporate and cool the wall - a much smaller amount than some bricks that will / can have the whole thickness saturated with moisture.


    If we are taking this into account then shouldn't we also account for solar radiation?

    Most renders are light in colour, I guess this is to reduce damage caused by the sun. Bricks have a wide range of colours & the dark red ones on the south facing walls of my current house are noticeably above ambient air temperature when the sun is out.

    David

31 to 60 of 62

  1. <
  2. 1
  3. 2
  4. 3
  5. >
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press