Expanded attic: What to do with existing insulation?

Hello everyone,

a brief introduction: we have a terraced middle house (built in 1969) with an already converted attic (end of the 80s/beginning of the 90s). Since all other work is slowly being completed, the attic is now to be reactivated (children’s room for the older daughter + work corner for dad), preferably as budget-friendly as possible.

Already converted means that the attic was equipped at the time of purchase with wooden floorboards + internal insulation (aluminum foil-coated insulation wool) + ceiling cladding (wood profiles) (DIY by the previous owner). We have already replaced the old attic windows, completely removed + disposed of the wood profiles because we wanted to see how it looks underneath and at one point a garden dormouse (or someone else) had already gnawed through the insulation. Moisture does not seem to have been a problem so far, ceiling profiles + beams were all dry except for one leaky spot due to slipped tiles (now repaired).

Now a new cladding should go on (this time not wood but plasterboard) and the insulation should be done as optimally (and budget-friendly) as possible.

The question now is: what to do with the existing insulation?

It looks like this: insulation material = aluminum foil-coated insulation wool (exact material = ?). Behind the insulation or between the insulation and bricks there is apparently only one layer of roofing felt. Nothing else. The beams must be about 10 - 12 cm thick (near the attic windows rather 12, elsewhere 10 cm). Accordingly, the insulation is also about 10 cm thick. On top of that is the old battens, to which the wood profiles were attached.

An energy consultant and several craftsmen (drywall installers) said the old insulation would still be okay, therefore: tape existing holes with aluminum tape, then put a vapor barrier underneath and then put on the new cladding. Done.

From everything you read, however, I have doubts whether it is that simple. Above all: does putting a vapor barrier underneath the insulation (i.e. between old insulation and new ceiling cladding) even make sense? Because the aluminum-coated insulation practically works as a vapor barrier, so moisture could accumulate between the aluminum coating and the vapor barrier? Or it finds its way through the (undoubtedly existing) gaps between the old insulation and rafters etc. and possibly causes moisture damage there?

Would the combination "punch holes in the aluminum coating (spiked roller)" + additional vapor barrier therefore be useful? Or completely renew the old insulation? The main concern is that I do not make things worse and that the whole thing becomes habitable again with as little (or inexpensive) effort as possible.

Thanks in advance for tips and/or experiences. I am attaching photos (hope that works...)



Regards,
Stephan

Hello. I would patch the old insulation, that is, fill in any gaps. Then I would have created another insulation layer "underneath" (on the inside), at least 60mm thick. That way, I think you get the most out of it.

Question: Is the old insulation separated from the roofing felt by an air gap, or does it lie directly against it? If there is an air gap, can you determine whether effective airflow is possible there, i.e. are there appropriate intake and exhaust vents at the ridge and at the eaves?

If any of these questions are answered with no, in my opinion you must definitely install a vapor barrier on the room side, i.e. an aluminum foil, and seal it airtight everywhere. The reason for this is that the externally located roofing felt is quite diffusion-tight.

Hello.

I'm afraid there's probably no air gap here – except where the dormice were active. Therefore vapor barrier, because of very diffusion-tight construction? (So far it has probably always been dry up there and last summer also nicely warm, but it has not yet been used as a bedroom...)

That means, I would have to double the beams/rafters for the additional insulation (that's what it's called, if I'm not mistaken?), right?

And a vapor retarder would (whether with or without additional insulation) bring nothing at all, but would actually be counterproductive, because the moisture would then either
a) already get stuck between the vapor retarder and the old aluminum-coated insulation
b) accumulate on the roofing felt in case of deliberately pierced aluminum coating?

I wonder why the craftsmen who looked at it were all so keen on the vapor retarder...

Thanks again

Regards Stephan

If the vapor barrier is properly installed, no more moisture will enter the insulation.
Therefore, the structure behind the vapor barrier is "irrelevant."
Certainly, one should consider everything as a whole, and a vapor-open structure to the outside is always desirable.

I find 10cm of insulation no longer up to date for an attic. Please keep in mind that under the roof you almost only have "exterior walls."
In this situation, it would be advisable to add more insulation here, since everything is already open anyway.

It is recommended to include the rafters in the insulation layer. This means insulating between the rafters at rafter height and then adding another layer on top so that the rafters do not become thermal bridges.

Heat protection in summer...
Before the renovation, I had about 10cm of glass wool insulation installed. In summer, after two days, it would be 30°C in the rooms. Now, with about 180mm of roof insulation, it takes about a week or a bit longer.
However, the structure is crucial here. I would definitely not leave this unconsidered under the roof and include it in the planning.
However, one must also keep in mind that even the best insulation can no longer provide any heat protection if the air temperature does not drop below 25°C for weeks; eventually, it will always be warm under the roof.

By the way, I find it strange that the energy consultant just dismisses the whole thing, since 10cm of insulation is simply too little.
The drywallers may be right, but it is questionable from which perspective they said that.
That means, did they only consider the current situation or also think long-term energetically?

I would get a roofer/carpenter and ask for their advice.
Maybe also consult another energy consultant.
You can then explain what you intend to do and find a good solution together.
Perhaps it really makes sense not to do much on the inside and in x years, if the roof tiles need to be replaced, to work with roof insulation on top or to combine it with internal insulation.

There are always several possible solutions.

If the vapor barrier is properly installed, no moisture will get into the insulation.

I would, if possible, use a BARRIER so that it is really much more diffusion-tight on the inside than on the outside.

If the old insulation can still be used, in my opinion it makes no economic or ecological sense to replace it. Patch, yes, because of the thermal bridges. Add another layer to the inside of the rafters or battens perpendicular to the rafters, if room height allows. I also think that 10 cm is no longer up to date. Depending on the insulating material, the second layer also provides some sound insulation.

Thanks already for the tips.

I also think that we should have another energy consultant take a closer look. They can then go into the details and we will see what to do next.

Best regards
Stephan