I want to improve the sealing around the windows in our house.
Basically, the horizontal cross-section of the connection between the frame and the wall looks as follows. The only thing missing is 3. Backing rod and 4. Sealant. Since everything is built and needs to be completed afterwards, I obviously want to demolish as little as possible. The easiest thing should be to loosen the trim board from the outside, remove the insulation (caulking), and somehow create the same function that a backing rod and sealant would have, i.e., a vapor-tight seal connecting the vapor barrier to the frame. You must then be able to insert this from the outside, which is why I'm considering either a sealant or a vapor-tight expanding tape. It's not just a few millimeters gap, rather 10 sometimes 20 mm.
Are you going to add soft sealant and backing rod at the top and bottom of the window as well? You will probably get a good result by opening up from the inside. It might be doable from the outside too, but tricky to get the sealing right.
Are you going to supplement with soft sealant and backing rod at the top and bottom edges of the window as well? You'll likely get a good result by opening up from the inside. It might be doable from the outside too, but it's tricky to get the sealing right.
I'm only after the function of sealing; the seal won't be visible if you do it from the outside.
I'm only interested in the functionality of sealing, the joint won't be visible if done from the outside.
Ok, but you are unlikely to achieve a 100% seal from the outside because it's hard to see the diffusion barrier from that side, and if you don't get it completely sealed, the idea falls apart.
If you want it sealed, you need to do it from the inside, even if it means a lot more work.
Personally, I would ignore the absence of soft sealant.
I understand that it's the density you are aiming for and think it's easiest to ensure from the inside. It might be possible to access from the outside with an extra long nozzle for the soft sealant.
