ᐅ Insulating a sloped roof with blown-in insulation and prior furring out?

Hi everyone,

My house from 1970 has 13 cm (5 inches) rafters in the roof without any insulation in the sloped ceiling, and 10 cm (4 inches) of polystyrene insulation on the floor of the upper floor, which is walkable. The upper floor is finished with a small slope starting at about hip height. The roof is covered with concrete tiles and two layers of roofing felt. The tiles rest on a simple battens system.

Now the question:

If I am considering blown-in insulation and want to achieve about 20-25 cm (8-10 inches) of insulation, is it feasible to renovate room by room over time, doubling the rafters during this process, and then insert bags into the sloped sections to manage moisture and fill them later? At the end, could something be placed on top of the polystyrene or have insulation blown in there as well?

Is this approach doable and sensible?

I aim for an iterative process.

Thanks!

I didn’t quite understand the part about the bags. However, under similar conditions, we doubled the insulation layers and then blew paper flakes between the joists. It worked great and created a lot of usable space. You could probably do this room by room, but it doesn’t seem very practical and would be more costly.

karl.jonas schrieb:

I didn’t quite understand the thing about the bags. But with similar conditions, we doubled the layer and then blew paper pieces between the joists. It worked really well and created a lot of usable space. You could probably do it room by room, but that seems less practical and more expensive to me.

So the idea was just to prepare the insulation step by step. In the end, everything will be blown in all at once.
Did you add an additional intermediate layer for the roof and roofing felt?

jrel1238 schrieb:

Did you add any intermediate layer between the roof and roofing felt?

In our case, the battens were placed directly on the joists, followed by the tiles. From the interior side, we attached small battens to the joists and then closed the gap to the tiles with some kind of boards, possibly wood fiberboards? I’m not entirely sure about that. On the joists towards the interior, there was a vapor barrier film installed, then another layer of boards, with shredded paper insulation in between. But that was about 15 years ago, so I wouldn’t bet on it.