Effects of leaving the upper floor uninsulated to move in faster

[KnockOnWood]

"Passive house standard" for us is well-insulated and airtight, with FTX ventilation. So much insulation and low U-values that the house stays warm with the help of household electricity and body heat. However, we might not 100% follow the standards set by "someone" in Sweden for the house to be called a passive house by these purists. Anyway. Thus, perhaps that discussion can be left in favor of the topic's question...

Then we probably see it roughly the same when it comes to passivity

Well-insulated, good windows, simple sensible installations.

And sorry for going off-topic

Regarding the staircase, attic, and insulation, I/we have solved it in another way.
We don't need more living space than the ground floor's 108 m2 since we are only two with "moved-out" children.
But we have a good attic floor, it's about 70 m2 between the support beams because we must have at least a 38° roof pitch.
It is only used as storage and temporarily as a guest room.
So we have an external staircase on one gable. There are no air leaks from the living space to the attic.
And no one is bothered by this construction method out here in the boonies either

The day we sell, there's room to put a staircase inside the hall.
Space for it is prepared if desired.

The most important thing with your temporary attic/floor construction, I believe, is to make it airtight,
so that warm, humid air doesn't leak up to the cold attic.
And how this is solved depends on the material you choose for the ceiling.
Large panels - tight and good
Narrow boards - more leakage

If it is then "vapor-tight" probably doesn’t matter much.

Perhaps, after all, the simplest thing is to put plastic sheeting.
It doesn't do any harm when the attic is finished.

 

[ronolo]

We built just like that. The basement first, then with a boarded-up and insulated stairwell to the first floor. Lived like that for 2 years. Then another 2 years passed before we opened up to the second floor. In both cases, there are 220mm mineral wool-insulated intermediate floors without plastic sheeting. Now, we didn't lay the boarding on the intermediate floors until it was time to finish, so it was inspectable. There were no problems with this procedure.

We have mechanical exhaust that only extracted air from the areas we lived in.

 

[martinradbo]

We built just like that. Basement first, with a boarded-up and insulated stairwell to the first floor. Lived like that for 2 years. Then another 2 years before we opened up to the second floor. In both cases, it's 220mm mineral wool insulated floor structures without plastic sheeting. Now, we didn't install the floorboards on the floor structures before it was time to finish, so it was inspectable. There were no problems with this procedure.

We have mechanical exhaust ventilation that has only extracted air from the areas we've lived in.

I've thought more about this and am leaning towards the idea that it works without plastic in the floor structure.

Several arguments for this:

1. The unfinished upper floor has no plastic at all, just the wind barrier inside the air gap. The roof is also permeable (a breathable roof membrane). Any moisture should therefore escape.

2. With ordinary ceiling gypsum boards on the first floor, it can't be much moisture that practically makes its way up. The stairwell will anyway be closed to prevent construction dust from the upper floor from making its way down.

3. Good FTX-ventilation that can be run a bit more forcefully if needed.

4. Insulating and plastic wrapping of the upper floor begins almost immediately after moving in.

Point 4 might be the strongest argument...

But surely, for good measure, I could take some wind barrier and place it in the floor structure.