Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Air Tightness....am i missing something?

Options
  • 16-08-2010 7:07pm
    #1
    Just Bob
    Closed Accounts Posts: 18 ✭


    just about to roof my block built house and something have some real confusion in terms of air tightness! Am i correct in saying that sand&cement plaster with skim coat is air tight? is skim coat airtight? if this is the case is it not just the case of sealing around the windows-skim reveals -carefully skim ceilings and walls top to bottom and make sure all pipes/electrics are sealed. Why would membraines be required?


Comments

  • Options
    #2
    MicktheMan
    Registered Users Posts: 2,823 ✭✭✭MicktheMan


    You are right to a point. Sand / cement on a blockwork wall is an airtight layer in itself so no membrane needed there. Windows & doors need to be taped because no matter who well the reveals are plastered, gaps & cracks will occur over time as there will be differential movement by the different materials. Also as the ceiling will not have a sand/cement finish it needs a membrane to act as the airtight layer. Remember all airtight layers (be in sand/cement, membrane or tape) need to be connected to each other to ensure a continuous layer (i.e. floors to walls to windows/doors to roofs etc)!


  • Options
    #3
    sydthebeat
    Subscribers Posts: 41,021 ✭✭✭✭sydthebeat


    completely agree with mick.... its the JUNCTIONS between elements which are vital.... not the actual plane of the element itself.

    Just because it may look like the ceiling skim is tightly connected to the wall, is no guarantee that there is not gaps there.

    some of the most common locations for air infiltration would include around window boards, around attic access, around vent grills, quality of doors and windows, pipes egress areas...


  • Options
    #4
    Just Bob
    Closed Accounts Posts: 18 ✭Just Bob


    ok thanks for clearing that up for me - but I have another question! On the underside of the hollowcore slabs on the first floor, i am proposing fixing battens to fix ceiling slabs to. If this is airtight in the void between hollowcore and ceiling is there a risk of rot/fungus growth?


  • Options
    #5
    sydthebeat
    Subscribers Posts: 41,021 ✭✭✭✭sydthebeat


    Just Bob wrote: »
    ok thanks for clearing that up for me - but I have another question! On the underside of the hollowcore slabs on the first floor, i am proposing fixing battens to fix ceiling slabs to. If this is airtight in the void between hollowcore and ceiling is there a risk of rot/fungus growth?

    firstly, battens are not a great idea as the slabs can be way off level and it is heart breaking shimming work to get battens level. If your budget can stretch a metal rail system is the proper job.

    secondly, no there is not a risk of fungus here are it is internal work.

    thirdly, sin order to make this junction airtight, ie between the slab and the wall, you need to wrap the ends of the slab in membrane and carry up and down inner face of inner leaf....


  • Options
    #6
    country home
    Closed Accounts Posts: 98 ✭✭country home


    IMO, airtightness is all new. . .

    living in a tank with HRV is very very very OTT. . . .

    would NASA laught at us, i wonder. .


  • Advertisement
  • Options
    #7
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    country home wrote: »
    IMO, airtightness is all new. . .

    living in a tank with HRV is very very very OTT. . . .

    would NASA laught at us, i wonder. .

    Not an uncommon sentiment - but airtightness is here to stay make no mistake . One can still rely on natural ventilation .


  • Options
    #8
    sydthebeat
    Subscribers Posts: 41,021 ✭✭✭✭sydthebeat


    country home wrote: »
    IMO, airtightness is all new. . .

    living in a tank with HRV is very very very OTT. . . .

    would NASA laught at us, i wonder. .

    no nasa wouldnt...

    it makes complete sense to me. consider:

    both natural and mechancial ventilation can change the whole air in a room 4 times in every hour.
    If the HRV system is working at 75% efficiency, that means the rooms radiator needs to heat the room only once every hour.
    In a naturally vented situation the rad needs to heat the air four times every hour... so therefore 300% more fuel is used to heat a naturally vented room , than a HRV room.

    hows is this considered to be over the top....??? you must understand that air tightness issues are a sign of bad designing and bad building... the fact that this bad building has become the normal standard is not a good enough reason for dismissing airtightness strategies.

    If you wear a thick wooly jumper on a cold day you will be warm... however if the wind builds up and blows through your jumper your cold again, so you put on a wind breaker..... same theory, same physics.... and nasa doesnt laugh at you....


  • Options
    #9
    imitation
    Registered Users Posts: 1,815 ✭✭✭imitation


    Just to jump on the bandwagon, HRV has been used in other countrys for a few decades now. As always our great nation is just playing catch up. Then again, when its -20C out, your going to have a more acute interest in your heating system and how to make savings.


  • Options
    #10
    The Barrier
    Registered Users Posts: 24 ✭The Barrier


    On the topic of ari tightness. I am putting stone in the front part of my new build. Would I need to plaster this section before I put on the stone?


  • Options
    #11
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    No - wet plaster internally . Remember we are looking to keep warm internal air - internal . So looking to create air tightness anywhere else is like bolting the stable door ....


  • Advertisement
  • Options
    #12
    The Barrier
    Registered Users Posts: 24 ✭The Barrier


    Thanks, but would you need to plaster the outside before you put on the stone to keep out moisture?


  • Options
    #13
    galwaytt
    Registered Users Posts: 12,761 ✭✭✭✭galwaytt


    Barrier, short answer is yes.

    I'd always scratch coat the blockwork behind the stone.

    If you have any issues after, otherwise, it's way too hard to fix, otherwise. Cost to scratch-coat is minimal.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



Advertisement