How to insulate the attic? How do you proceed?

  • Erstellt am 2018-09-05 19:58:51

Maximo1975

2018-09-05 19:58:51
  • #1
Hello,
we are currently renovating an inherited house built in 1958.
The attic is initially intended to be used as storage and maybe later converted.
The electrical system is already being prepared for this.
In the attic, insulation will be installed between the rafters and a vapor barrier foil applied, but that’s not the issue now!
The main concern is the floor. As seen in the picture, it is filled with about 8 cm of rubble/ stones/ debris and lies on the wooden cladding (visible from the floor below) since the old ceiling with sauerkraut boards was removed everywhere.
What is the best way to insulate the floor here?? Lay out/ place/ screw wooden boards evenly on top, then vapor barrier foil, and then walkable insulation boards???
I would be happy if someone could help me :-)
 

dertill

2018-09-06 07:49:22
  • #2


If you want to convert the attic into living space, you don’t need to insulate the floor, at least not thermally, only soundproofing. If you want to save effort and everything is solid, you can leave the loose fill in place, lay OSB on top, and then laminate/parquet with good impact sound insulation in between. You don’t need a vapor barrier on the floor if there is also a living space underneath.

BUT: Are you sure you want to use it for residential purposes? It looks like 2.5m in width and 2.2-2.5m in height at the ridge in the photo. Plus the supports in the middle. I could only imagine this as an extension of a children’s room / sleeping nook.

The rafters look like 14cm and you don’t have an underlay membrane under the tiles, which also don’t look sealed — that is, sealed with mortar. Because of this, they are not resistant to driving rain/snow and you have occasional moisture ingress. This rules out sensible insulation between the rafters, as it would be damaged over time. You need to ensure ventilation behind the roof tiles and a waterproof layer under the tiles. This is difficult to do from the inside. There are options that reduce insulation thickness and you should opt for moisture-resistant insulation (e.g., sheep wool/jute) — this is more expensive and less efficient compared to mineral wool, for example.

Additionally, with 14cm rafters you will get an unfavorable U-value of about 0.3-0.4 W/m²K with low heat storage capacity. This will be a pretty warm sleeping nook in summer. Insulation under the rafters or adding thickness to the rafters inward is possible but again reduces living space. For both between-rafter and under-rafter insulation, don’t forget the vapor barrier on the INSIDE!

My advice: Unless the roof is being redone or a dormer is being added anyway, I would think carefully about the conversion and see if the space inside the house isn’t sufficient and keep the attic as a cold room, laying the floor with 20-24 cm mineral wool mats, vapor barrier underneath.

Oh yes: What about heating? That also has to be planned in advance.
 

Maximo1975

2018-09-06 19:44:16
  • #3
I think the idea of using OSB for the attic/storage is good and various items can be easily placed/stored there! The loose fill insulation will remain. Removing it is actually still very uncertain, as the room is really very small and the upcoming doubling of the rafters + vapor barrier from the current 12 cm to about 19 cm takes away a lot more space/room. So actually not an issue in the near future!

In the living area under the storage (3 rooms), which already has sloping ceilings, all the old fiberboard panels and drywall have been removed. The rafters were doubled and insulated from underneath with a vapor barrier and airtight sealed. There is still about 3 cm of air between the roof tiles and the insulation. The currently missing underlay membrane worries me a bit, as it is not yet precisely planned when exactly the roof will be re-covered. However, I have the impression that everything is very tight, even without the waterproof layer. At the start of gutting in spring, everything also seemed very, very dry in the rafter area... and in all other places as well. I am watching this very closely... but unfortunately I’m not a professional to assess it 100%. Maybe it’s because the roof is very steep and rainwater can flow off very quickly. All rafters and battens on the roof make a very good impression.

In the long term, though, it could certainly be fatal without a new underlay membrane, right??
 

dertill

2018-09-07 07:39:26
  • #4


The installation guidelines for clay tiles stipulate that for higher demands on roofs, especially buildings used for residential purposes, there must always be a second water-bearing layer installed, even if the attic is not developed. Especially so if insulation between the rafters has been installed.

That is the regulation; the practice is another matter. There are thousands of roof trusses without underlay and not all of them have flooded yet. If your roof is steep enough (the pictures look very steep) and everything is installed correctly and intact, the roof should be splash rainproof – snow tightness is another matter. Snow can also fly horizontally or upwards in the wind.

Insulation directly under the tiles can also work well; it just means there is no safety net if something does go wrong. One tile breaks / shifts and a serious rain shower comes, and you have a wet wall and insulation.

In the sloped living areas, that is how it is now. In the attic, I would then resort to floor insulation and put chipboard on top or, if not walkable, hydrophobized glass wool mats with a water-repellent fleece coating. If a few more snowflakes get through the tiles up there, it is at least not so bad because everything dries out again.

In the medium term, however, you should definitely equip the roof with an underlay.
 

Maximo1975

2018-09-07 19:46:02
  • #5
My parents-in-law still have a lot of rafter insulation wool + vapor barrier left over, which should be enough for an attic. The rafters are supposed to be doubled up like a floor below... well, it will be a lot of work! then it will be enough for the attic if OSB is laid... from what I gather, that actually should have been enough.
 

Knallkörper

2018-09-07 20:53:51
  • #6
Hello. I would have laid a 20 cm walkable insulation in the attic, e.g. made of wood fiber boards. If you only lay OSB, then the ceiling of the rooms below is not sufficiently insulated.

Have you laid the vapor barrier completely in the upper floor, i.e. from the knee wall over the sloping walls and over the ceiling?
 

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