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Minimum level of Airtightness in tender

  • 13-10-2011 11:36am
    #1
    K3v
    Registered Users, Registered Users 2 Posts: 225 ✭✭


    My architect is drawing up a the builders tender for my house. I am including a MHRV system in it. Its not a passive house I am building but I would like a high level of airtightness. I know that the passive standard must achieve a q50 result of probably no more than 0.75 m3/(hr.m2). What would be a good level of airtightness to aim for and should I specify it in the tender?


Comments

  • #2
    sydthebeat
    Subscribers Posts: 42,171 ✭✭✭✭sydthebeat


    K3v wrote: »
    My architect is drawing up a the builders tender for my house. I am including a MHRV system in it. Its not a passive house I am building but I would like a high level of airtightness. I know that the passive standard must achieve a q50 result of probably no more than 0.75 m3/(hr.m2). What would be a good level of airtightness to aim for and should I specify it in the tender?

    you should specify a minimum performance rating... your BER assessor can crunch the numbers to show you what difference each air change rate will mean.
    Aim for best as possible by including a bonus clause ie maybe specify q50<= 4 as minimum, with a bonus for a q50<2.

    Remember that the quality of window, door, attic hatch etc being installed will have an effect on the q50, which may be outside the contractors responsibility.


  • #3
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    2011 regs are <7m3/hr/m2 at q50

    imo the min spec for MVHR is < 3m3/hr/m2 at q50

    but what about putting in a clause stating if < 1m3/hr/m2 at q50 is achieved there's a cash bonus/ incentive!:) (call it an 'energy saving performance bonus')


  • #4
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    snap


  • #5
    K3v
    Registered Users, Registered Users 2 Posts: 225 ✭✭K3v


    I knew the 2011 regs are <7m3/hr/m2 at q5, but it did seem a bit high and not suited for my build.Brian & Syd your idea of a cash bonus incentive is actually a good one. I will definately suggest it to my architect.


  • #6
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    K3v wrote: »
    I knew the 2011 regs are <7m3/hr/m2 at q5, but it did seem a bit high and not suited for my build.Brian & Syd your idea of a cash bonus incentive is actually a good one. I will definately suggest it to my architect.
    dont forget to ask your architect for details showing solutions of the major thermal bridges (as lighted by Syd) and how the air-tightness tapes/ plaster etc will be applied.. freak him right out:)


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  • #7
    K3v
    Registered Users, Registered Users 2 Posts: 225 ✭✭K3v


    BryanF wrote: »
    dont forget to ask your architect for details showing solutions of the major thermal bridges (as lighted by Syd) and how the air-tightness tapes/ plaster etc will be applied.. freak him right out:)


    I had mentioned to my architect about identifying cold bridges, but I only suggested including fiberglass wall ties in the spec. She will have her work cut out by the time the tender is fully drawn up!


  • #8
    MicktheMan
    Registered Users, Registered Users 2 Posts: 2,880 ✭✭✭MicktheMan


    sydthebeat wrote: »
    Aim for best as possible by including a bonus clause ie maybe specify q50<= 4 as minimum, with a bonus for a q50<2.
    BryanF wrote: »
    but what about putting in a clause stating if < 1m3/hr/m2 at q50 is achieved there's a cash bonus/ incentive!:) (call it an 'energy saving performance bonus')

    Why a bonus? Why not just specify the result to be achieved given the house design. The reason I say this is that if the air handling/heating and other mechanical systems are optimised for the specific build then by achieving an airtightness of 1 rather than 3 m3/hr/m2 will result in over spec'ed equipment being installed. This, of course, assumes that care is taken during the build on thermal bridging/insulation details etc.

    To the op: Depends on your house style/design. To achieve an airtightness of say 2m3/hr/m2 is relatively easily achieved by a competent builder on a simple design but can be a lot more difficult (more labour intensive) to achieve on a convoluted dormer style house.


  • #9
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    MicktheMan wrote: »
    Why a bonus? Why not just specify the result to be achieved given the house design. The reason I say this is that if the air handling/heating and other mechanical systems are optimised for the specific build then by achieving an airtightness of 1 rather than 3 m3/hr/m2 will result in over spec'ed equipment being installed. This, of course, assumes that care is taken during the build on thermal bridging/insulation details etc.

    To the op: Depends on your house style/design. To achieve an airtightness of say 2m3/hr/m2 is relatively easily achieved by a competent builder on a simple design but can be a lot more difficult (more labour intensive) to achieve on a convoluted dormer style house.

    you know your dead right re sizing of equipment (but the initial test would be done at first fix and so would allow for this adjustment then), but the point is, if a builder has an incentive he's more likely to do a good job and will take on the responsibility instead of blaming other trades for cutting holes etc and the client doesn't pay if the spec is not meet..


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