Internal wall insulation on 1990s insulated cavity

[embra]

Hi folks,

 

We're remodelling our ~1990s built two storey, end of terrace home, and I'd like to improve our current wall insulation, since at present it offers the least thermal resistance of the building fabric. I'm interested in recommendations on approach we can take to improve this.

 

Walls

 

Current: Brick / cavity / block walls with some questionable looking EPS boards in the cavity. Dot and dab plasterboard on the inner block.

 

Plan: Help! 😬. I've read a lot of conflicting information about whether internal insulation is suitable or will cause interstitial condensation. Also not sure of the most cost effective construction method (insulated plasterboard on dabs, insulated wet plaster etc...)

 

 

There would be roughly 34 linear metres of wall to insulate per floor, at 2.4 m ceiling height.

 

I’d like to focus on simple and practical solutions that we can relatively easily implement.

 

The underlying work for our builder is to reconfigure the layout involving some light structural changes, and construct a porch area (all on ground floor of property). We're having the heating system pipework upgraded to suit low flow temperatures and fitting an ASHP.

 

Any disruptive works (e.g. plasterboard off) would be constrained to ground floor initially, and could be extended to first floor as a phase 2 at a later date.

 

 

Construction materials are:

 

Ground Floor

Current: Uninsulated beam and block, battens, chipboard deck.

 

Plan: Lay DPM / PIR / floating floor deck on top of beam and block. 

 

First Floor

Current: Chipboard deck suspended on timber joists.

 

Plan: Nothing so far.

 

Roof

Current: Pitched roof / cold loft, around 100 mm wool insulation already laid.

 

Plan: Increase to ~300 mm wool insulation.

 

 

Happy to hear everyone's thoughts and advice 🙏

[IGP]

On the presumption that its free cavity, save the EPS presumably affixed to the internal leaf, I’d fill the rest with blown EPS beads.

Airtightness, check brickwork and penetrations like pipes, wires, windows , doors and seal up with FM330 and AT tape. 
 

Otherwise looks sensible so far to me. 

 

[embra]

@IGP thanks for the comments.

 

Based on a couple of borescope images (unfortunately I don't have a copy of these), we seem to have ~25 mm thick EPS foam boards in the cavity between outer brick and inner block it doesn't look particularly well secured, or evenly distributed.

 

Is it feasible to just top this up with blown EPS beads? I'd love to get more insulation in there, but not sure if we need to try and remove the existing stuff completely before considering anything else. Or whether to simply ignore the cavity and focus on internal insulation only...

Edited July 6, 2023 by embra

[Mr Punter]

No easy answer here.  With 25mm cavity boards there is presumably not much space left.  Blowing in EPS beads could cause moisture ingress especially as the outer leaf is brick and not rendered.  The internal insulation will lose a fair amount of floor space.  Because the cavity boards are not tightly fitted and are thin I don't think they will contribute to condensation risk.  They cannot practically be removed.

 

I would remove the dabbed plasterboard and the dabs, parge the external walls to stop air leakage, and install internal insulation.  There is no point in doing anything the the first floor floors as they are internal to the heated / insulated envelope.

 

Loft insulation is the easy win.  Make sure there is still airflow from outside into the loft.  You may need to add some extra ventilation via vent tiles.