Longevity of air tightness

[davidc]

Has anybody any evidence or inclination as to how well air tightness endures over periods of years say in a TF with taped up smartply on the interior with blown cellulose or woodfibre insulation (and less importantly medite vent boarding on the outer) ?

Edited May 23, 2019 by davidc

[Jeremy Harris]

I doubt airtightness would degrade for that build up, TBH, as the blown cellulose itself provides a great deal of the airtightness sealing. 

 

The question I'd ask is whether or not the vapour tightness will last for decades, as that's dependent on how well the tapes remain sealed.  I can see the tapes in our service room, as we didn't bother to board this area out, and after five years there's no indication at all that the Siga tape is degrading.  I still have a part-roll left over, and that still seems to be as good as it was when new, too.

[davidc]

I see, thanks - that is helpful to know. As well as possible tape degradation i wondered if any settlement or slight timber movement might become a factor - less likely in modern engineered frames i guess ?

Edited May 23, 2019 by davidc

[Jeremy Harris]

Timber movement isn't really going to have any effect with blown cellulose, as the stuff will flex with any slight movement and airtightness will be maintained. 

 

Movement is only very small, too.  The only places we can see any movement is around the window frames, where I'd guess there's been around 1mm of movement in places.  The tape can easily handle this sort of movement range I'm sure, as it's pretty tough stuff.

[lizzie]

A very interesting topic @davidc Its something I have wondered about myself.

 

I have a lot of movement and cracking internally.  The areas around my window frames need resealing too as shrinkage gaps and can feel cooler air.

 

My carpenter told me all TF structures move and he allowed for some frame shrinkage when he did the outside cladding.....he said he has seen them shrink by quite a bit over a few years as they dry out and settle,  its normal apparently even with the new TF constructions.  

 

I guess really no-one has the answer on longevity of air tightness only time will tell.

[joe90]

My recent airtest only about a year after building showed the biggest problem was shrinkage around windows (timber windows in brick built walls) which is why I wanted the plasterers to use a stop bead before the window so I could use a flexible caulk between the two, but he insisted it was not needed , guess what, he was wrong and I wished I had insisted on them being installed. Mine is fixable very easily but I don’t like the idea of membranes hidden from view that cannot be fixed or seen without lots of work (mess).

[Jeremy Harris]

1 hour ago, lizzie said:

 

I have a lot of movement and cracking internally.  The areas around my window frames need resealing too as shrinkage gaps and can feel cooler air.

 

 

Are there no tapes around the windows? 

 

The window tape is designed to take up a fair bit of movement and still maintain a seal all the way around, unlike some sealants that may pull away.

 

If there is air flowing through gaps around the window frames with a timber frame then something's seriously wrong, and needs fixing, and that won't be that easy, as it will mean removing the plasterboard around the reveals and looking to see what's gone awry.

[lizzie]

20 minutes ago, JSHarris said:

 

Are there no tapes around the windows? 

 

The window tape is designed to take up a fair bit of movement and still maintain a seal all the way around, unlike some sealants that may pull away.

 

If there is air flowing through gaps around the window frames with a timber frame then something's seriously wrong, and needs fixing, and that won't be that easy, as it will mean removing the plasterboard around the reveals and looking to see what's gone awry.

@JSHarris window fitting was  a shambles.  We filled gaps with foam and flexible silicone and put some sort of tape around the frames after window fitters had 'finished'. I bought the same one used on frame. I forget the name begins with a C but not Compriband. That tape was left stuck overlapping window frames and was showing on the frames after plastering and was a nightmare to get off - others on here have had similar with tape.  I am hoping if I caulk the gaps inside where plaster has shrunk away from walls it may fix it.  I don't even want to think about anything else.....yet!

[Jeremy Harris]

The window tape isn't the same as the airtightness tape used elsewhere, from what I saw of the stuff we used.  The tape used between the vapour tight boards etc was Siga, which is yellow, and the stuff used to seal the windows was white and had a very different look and feel to the airtightness tape used elsewhere.  It also had a split backing, so that it could be carefully lined up on the window frames (to avoid it being stuck on too far and end up showing) and stuck down neatly, then the larger backing could be peeled off and stuck to the reveal.

 

My concern if you have air blowing through gaps around the windows is that you may end up with condensation between the timber and window frame.  That's not at all good, and really needs sorting properly, IMHO.  The chances are that the silicone won't stay bonded well to the timber side, as silicone isn't really the right stuff to use for this application.  An MSP sealant might have been OK, but even then I think I'd be a bit concerned about movement.  The window sealing tapes are designed to seal and allow movement, when they are properly applied.

 

I have to say that I wasn't impressed with our window fitting either, but I chose to not have them seal the windows, and said I'd do it myself.  I spent a couple of days going around adjusting the fit of the frames and sealing up around them.  I'm glad I did, from what I've heard of the experience of others with some window fitters.

[dpmiller]

Our UPVC frames went in with cleats screwed to the TF, the gaps spray-foamed, and then SIGA window tape installed. It's pre-folded and comes off the roll with the narrow window side ready to adhere; the inner release paper can be pulled off once satisfied with positioning.

As we're in NI the blockwork forms a check reveal all round so all else that was needed was a strip of compriband-ish foam between the bottom of the frame and the concrete sill to allow for shrinkage.

[Oz07]

Is anyone ever happy with window fitters they're all rough as a badgers. 

Most firms seem to have all Muppets with one old boy who goes round fixing all their rubbish work. 

[dpmiller]

^raises hand.