Air Tightness in a Masonry Build

rockabaloo

Hello all. I know that there are a lot of posts on air tightness already but I was wondering if I could get a list of what is necessary in a masonry build.

I would assume the following are essential:

1) Tapes around windows and doors.
2) Wrap around 1st floor hollowcore.
3) Service penetrations.

What else would be essential or strongly recommended? Do you need to use tapes or membranes where the walls meet the floors and ceilings or is the plaster sufficient? Anything else to think of?

Cheers.

esox28

I've installed 18mm osb3 on celings as air tight membrane have to tape all joints and tape junction between wall and board with a tape with plaster reinforcement edge, 50mm batton and counter batton will create a services cavity to inclose wiring and hrv ducting in the air tight envelope. This removes the problem of penetrations through membrane and insulating the hrv ducting.

rockabaloo

Interesting. Are you meaning a service cavity at the ceiling on the first floor (before the attic). That would work well if there were a lot of downlighters. Interesting indeed. How big is the cavity then? Do you have one on the ground floor ceiling as well? Did you build with extra height to allow for this?

esox28

Yea spot on to all questions, Down lighters and pendent lights you haven't to seal penatrations, im first fixing hrv ductwork at the moment, electric and heating next, but its not overly cheep to do at 17.50 euro a boards down at 1200 x 2400mm plus fitting and fixings plus tapes plus 50mm battons (service cavity is 100mm) then plaster board. On the plus side no wires in attic space and in my case no hrv ducting or hrv units. I also spaced out roofing rafters and ceiling ties at 600mm centres to aline with boards.

MicktheMan

rockabaloo wrote: »

Hello all. I know that there are a lot of posts on air tightness already but I was wondering if I could get a list of what is necessary in a masonry build.

I would assume the following are essential:

1) Tapes around windows and doors.
2) Wrap around 1st floor hollowcore.
3) Service penetrations.

What else would be essential or strongly recommended? Do you need to use tapes or membranes where the walls meet the floors and ceilings or is the plaster sufficient? Anything else to think of?

Cheers.

4) Wet plaster to internal leaf of external walls before 1st fix's

rockabaloo

MicktheMan wrote: »

4) Wet plaster to internal leaf of external walls before 1st fix's

Before 1st fix? What stage is plastering normally done? Is it more effective if it's done before 1st fix?

Rock12

For my airtight masonry build I am going to put a coat of wet plaster on all external walls just where the floor screed will meet the inner leaf. This will be done before any first fixings. I hope this plaster will seal any air gap that may occur at the point where the floor screed should meet the wall plaster and will make an airtight joint between the two. Hope this helps.

MicktheMan

rockabaloo wrote: »

Before 1st fix? What stage is plastering normally done? Is it more effective if it's done before 1st fix?

Best practise is to make the building airtight, carryout a prelim air test, find/fix all weaknesses and then let the trades in explaining to them the airtight strategy.
Sometimes ducts, piping, cabling ets are fitted at or too close to external walls during 1st fix. This then restricts the plasterer from either plastering the wall in this area or getting a good wall to floor seal resulting in air leakage. This is especially the case when multiple pipes/cables converge (e.g. utility/plant room). By right a plan is needed on how each penetration of the airtight barrier will be sealed.

rockabaloo

All good pointers. Thanks guys.

My builder has got really good results from blower door tests for buildings he has done in the past. This was just as a result of good workmanship and he didn't make any extra effort for air tightness.

I'm hoping with his good work and my additional efforts I should get a good air tight house.

rockabaloo

I've been thinking a bit more about this. While I like the sound of esox28's OSB board and service cavity ceiling I'm not sure I have enough ceiling height to do this cos the MVHR I have a quote for uses 125mm ducting.

If you were to just plasterboard and skim the ceiling (taping the junction between edges and walls and also any penetrations) would this be an adequate airtight barrier or would you need to use a membrane?