How to add insulation to the exterior wall inward?

[Vinterland]

I have an extension that is thinly insulated on the outer wall, and I want to add insulation to the outer wall as part of a window replacement. The wall currently consists of plastic foil and particleboard on the inside, which separates it from the existing insulation, and I'm wondering how to add insulation to this. Should I tear down the particleboard and plastic and insulate from there, or can I attach directly to the board and insulate on that?

The additional insulation can be a maximum of 45mm.

Thanks in advance

 

[bilarebob]

How much insulation is in the existing wall?

The plastic should be placed so that the dew point is "outside" the plastic film, which is determined by the ratio between your planned additional insulation and the existing insulation outside the plastic film.

If you have enough insulation on the outside, it is normally standard procedure to stud/insulate 45mm on the inside of the plastic film.

 

[Vinterland]

How much insulation is in the existing wall?

The plastic should be placed so that the dew point is "outside" the plastic film, which is determined by the relationship between your planned additional insulation and existing insulation outside the plastic film.

If you have enough insulation outside, it is normal practice to frame/insulate 45mm on the inside of the plastic film.

The insulation thickness is 150mm. So what I'm wondering is if I have to tear down the chipboard and possibly the plastic if it needs to be moved, which is inside the board - before I add 45mm, or if I can frame and insulate directly against the chipboard and simply build a "new" wall on top of the old one. What would be wise in this context?

 

[bilarebob]

There should probably be more insulation on the outside to ensure that the dew point ends up outside the plastic. For example, if it is -20°C outside and +20°C (perhaps not so often??) inside, the plastic layer can end up at 10°C (1/4 of total insulation), which risks creating condensation in the insulation.

Further uncertainty exists in how well the plastic is covered (are there many penetrations for electricity?). And how the implementation has been (are all the seams taped, etc.). Even if there is "real" age-resistant plastic that is there today (in my house built in the 70s, there is often thinner plastic that is not as dense as today’s).

My advice is probably to tear down the board and the plastic and install new plastic (closest to the inner wall) so that you know it will be effective.

 

[Rickard.]

Tearing down chipboard is not particularly difficult or time-consuming, and there are many advantages to doing so.

I would tear down the chipboard and plastic wrap to then install new airtight foil, mount 45x45 horizontally (so-called installation layer), and then gypsum or gypsum+osb/plywood/chipboard.

When the wall is open, you have all the opportunities to go through and adjust the old insulation and wind protection, which are just as important for achieving a well-insulated wall.

 

[Vinterland]

Removing chipboard is not particularly difficult or time-consuming and there are many advantages to doing it.

I would remove chipboard and plastic sheeting, then install new tight sheeting, mount 45x45 horizontally (so-called installation layer), and then gypsum or gypsum+plywood/chipboard.

When the wall is open, you have the opportunity to go through and adjust the old insulation and wind barrier, which are important to get a well-insulated wall.

Yes, that's what I'm thinking too. That will be the solution. But should the foil be on the outside of the new 45 rule, or should it be inside?

 

[Rickard.]

Yes, I think so too. That will be the solution. But should the foil be on the outside of the new 45 rule or should it be inside?

The general guideline for the vapor barrier is as warm as possible but a maximum of 1/3 of the insulation inside the vapor barrier. Yours is not even close to that limit and I think the advantages of having the vapor barrier protected outweigh the disadvantages (don't really know if there are any).