Insulating a RC slab ceiling

[Chiron]

Hi all, I have a challenge...

 

The ceiling of my bedroom is a 500mm thick RC slab that forms the floor of the flat above. It also forms a projected balcony of for the flat above. The slab is bare concrete finished with textured paint on the ceiling. There is no insulation.

I've attached an image of the original engineering drawings of the block showing the red concrete slab/balcony.

 

In the summer the internal concrete of the balcony heats up and soaks heat into the room. Slab internal temperature is currently 25C and has been constant for about 3 weeks. In the winter the balcony gets cold and draws heat out, it also causes condensation unless managed. (thermally imaged to prove this)

 

I would like to insulate the ceiling with PIR or similar. I can get about 50mm max before hitting the curtain rails/wardrobes.

 

I think i have 2 options:

 

1) insulated plasterboard, glued with Dow insta-stik and mechanically screwed to the slab, skimmed, painted.

2) PIR boards, glued, foil taped and papered with a semi-textured paper, painted.

3) ??? ideas please!

 

Option 2 is considerably cheaper, less messy (dust) and can be DIY'd. Option 1 is expensive, messy and potentially problematic: The slab is 40 years old and has rebar about 25mm in. Drilling into it (even with high-impact SDS) is difficult and it is very easy to hit rebar melting the drill-bit. The slab also forms the floor/ceiling of other flats and impact noise travels everywhere so drill-time has to be coordinated with neighbours.

 

Any advice is greatly appreciated!

 

 

[markc]

Pir or insulated plasterboard could both be glued but if surface finish isn’t that important then I would go for extra insulation thickness. When hot the heat will still come through but will take longer.

[Mr Punter]

It looks like solid walls as well.  If you could do the whole block with external wall insulation and take it around the balcony it could work well with no loss of floor space, ceiling height or internal disruption.

[Chiron]

On 12/08/2022 at 11:29, Mr Punter said:

It looks like solid walls as well.  If you could do the whole block with external wall insulation and take it around the balcony it could work well with no loss of floor space, ceiling height or internal disruption.

I don't have access/own the rest of the block unfortunately. EWI on the balcony would be the obvious choice for a full retrofit though.