Air Tighness, Where to Start?

[Triassic]

So the timber frame is up and I need to start my air tighness regime. So where do you start? Is a simple as making sure the house wrap membrane is neatly fastened down and the internal vapour membrane is complete? Would you, for example, fill any obvious holes in the timber frame and cork any gaps before fixing the exterior membrane down? Here’s a few examples.

 

Edited February 25, 2019 by Triassic

[Jeremy Harris]

I went around our frame and sealed up every small external gap I could find with expanding foam.  The main areas where I found small gaps were along the eaves and verges, although I'm not sure that they were worth bothering to seal up, really, as the blown cellulose forms a pretty good airtightness barrier.  One thing I did add was additional external insulation along the verges, in the overhang ladder frames.  I did this to help reduce the natural geometric thermal bridge that is present at any angled junction.  Again, I'm not convinced it was worth the effort, but I had some cans of foam and offcuts of foam insulation, plus a week of spare time with nothing much else to do, so had nothing to lose.

 

Well worth stapling membrane over any exposed timber, though, if only to help prevent insects getting in.

[ProDave]

If your timber frame is wrapped in Tyvek or similar, and is going to be clad with blockwork, then go round and stick down EVERY joint.

 

At our last house we didn't, and there was obviously a loose flap of tyvek, and when the wind blows in a certain direction you can hear this loose end flapping. It sounds like the house is farting.

[ToughButterCup]

22 minutes ago, ProDave said:

[...]  It sounds like the house is farting.

 

Guess who gets the blame at our place..... Mmmmm, yes. Right first guess.

[Simplysimon]

1 hour ago, recoveringacademic said:

 

Guess who gets the blame at our place..... Mmmmm, yes. Right first guess.

my wife gets the blame as well

[TerryE]

5 hours ago, Triassic said:

So the timber frame is up and I need to start my air tightness regime.

 

Since you're an old forum hand, then I can afford a  bit of gentle sarcasm: well before you erect the frame -- oops too late.  ?

 

My underlying point is that your TF company and erectors should have integrated air tightness design features into the erection.  In our case the TF supplier wrapped the joist ends with airtightness membrane (see pic below before they brought the top layer back in-front of the next stage cassets); they used a special "green" OSB3 which has a high-spec airtight surface, and every joint was properly taped.  You can do the same in retrospect but it's a lot of work, especially around all fenestration and joist-ends.

 

[Thedreamer]

This is more a general point. If your panels are manufactured off site, do the team erecting the kit typically leave you a bit of membrane to those tiny areas? 

 

I had a fair bit of the roll left over which was handy for any small patches but it's quite handy to have the membrane for any future jobs.

[dpmiller]

Yes, I've rolls of clear poly ( wrapped around the floor cassettes per @TerryE above),  exterior sheathing, and roofing membrane all spare.

[Triassic]

8 hours ago, TerryE said:

 

Since you're an old forum hand, then I can afford a  bit of gentle sarcasm: well before you erect the frame -- oops too late.  ?

 

My underlying point is that your TF company and erectors should have integrated air tightness design features into the erection.  In our case the TF supplier wrapped the joist ends with airtightness membrane (see pic below before they brought the top layer back in-front of the next stage cassets); they used a special "green" OSB3 which has a high-spec airtight surface, and every joint was properly taped.  You can do the same in retrospect but it's a lot of work, especially around all fenestration and joist-ends.

  

Being an old hand, my floor cassette was installed correctly. It’s the expansion gaps in the OSB on the outside of each panel I’m pondering calking up, before fixing the flap of external membrane in place.

Edited February 26, 2019 by Triassic

[scottishjohn]

think its  as simple  as you suspect it is ,but are wanting someone to tell you it don,t matter  .LOL

bung up every gap you can see and wrap it all and seal or staple it all down  with decent overlaps

you will never get at these bits again 

 

Edited February 26, 2019 by scottishjohn

[Triassic]

19 minutes ago, scottishjohn said:

think its  as simple  as you suspect it is ,but are wanting someone to tell you it don,t matter  .LOL

bung up every gap you can see and wrap it all and seal or staple it all down  with decent overlaps

you will never get at these bits again 

 

It’s always worth checking !

 

The next question is what sort of sealer to use to fill gaps in wood?

[TerryE]

We did a lot a hammer stapling and tidying of our external tenting layer and made sure everything was correctly overlapped and fixed, but this was more to do with vapour control and had nothing to do with airtightness as this was achieved by the internal sealing layer.  We had a pumped cellulosic filler for insulation and this effectively eliminated the risk of any convention loops / paths within the cassette panels themselves.    We didn't bother trying to close any tiny airgaps in the external Panelvent layer.  I am really not sure what if anything doing this would achieve.

 

The one thing that we did do was to ban all of our trades attempting to put any services of fixings through the walls: where these were needed, then (as I've posted before) we installed the appropriate pipe openings front to back ourselves and sealed these.  These pipes were then foamed and sealed after the wires or whatever have been pulled through the pipe.  In the case of the out skin wall-ties, we marked the centre line of the framing on the outer tenting, and all ties had to be screwed in at the lines to ensure that they were screwed into the backing CLS, but this was more a structural requirement than an airtightness one.