Hello, I'm looking for advice from those with experience or are in similar situation where your aluminum framed single glaze windows have leaked and the wood wall membrane has gone rotten somewhat. I have attached photos. My issue is thus, when I removed the rotten wood membrane to then replace it I found the outer underside of the window frame to be sweating with condensation on the colder days which from what I could see could be why the wood membrane was rotten? Does this mean that the whole window frame could be 'sweating' and the wood frame holding the window frame is also rotten, from what I can see, the wood membrane around the window is exposed, I can't see any other rot. I'm now thinking it's because the window frame is now exposed to the air and it then sweats.
What are your thoughts? Before I replace the wood I'd like to know if I need to take the window out and line 'insulate' the wood from the aluminum window frame.
1. Air seals around penetrations in the cladding are the most important factor in preventing leaks. Effective continuous seals with no or minimal air leakage provide a positive pressure inside the house compared with the outside which constantly pushes against the outside air and any water travelling with it.
15mm is a bit big to seal continuously with expanding foam unless the installer has a good steady hand. Generally 7 - 12 mm works well but ensure you use a PEF backing rod so that the foam is only bonded on two sides between the joinery reveal and the trimming framing and that a width to depth ratio of around 2:1 is maintained. If in a Very High or Specific Design wind zone expanding foam may not hold up and a modified silicon sealant will work better. Just make sure whatever you use actually bonds to any wrap or tape at the perimeter of the opening. Do not use flashing tape all around the perimeter of openings, only to the four corners 150mm each way and also the entire sill - but anywhere else is simply unnecessary and expensive.
2. Replacing any wall framing affects NZBC clause B1 and therefore requires a building consent. There are valid arguments for exempting non structural framing such as nogs but studs, lintels, bottom and top plates or window trimmer replacement all push works into requiring a building consent.
3. Any works resulting from external moisture NZBC clause E2 will also require a building consent.
4. Asbestos used as wall cladding or ceiling coatings stopped being manufactured and installed in New Zealand in 1984.
My steak is ready so i'll shut up and go eat it. Hope it goes well.
An aspect to building consent - if required to do whatever Grahame intends - is that changes made may not be required to bring things up to present code, but must not perform worse than what is existing. Looking at the photos above, there's a cut off double stud under the window frame. Looks to me that perhaps it was the remains of a jamb on the side of an original window, and at some stage the window has been replaced with a larger one. Perhaps poor workmanship has caused the problems. There's also a decent crack in the foundation wall - which looks large enough to me to warrant a repair (epoxy injection). The single 90x45 "new timber ready to be installed" isn't adequate IMO - should be double stud full length to the lintel, as it's supporting weight above. That is restricted work (LBP only) even if not needing consent - not "DIY".
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