Internal Insulation of filled cavity wall

[rwb]

Hi, I'm looking for some info on this subject which has to some extent been discussed before but I'd like some further clarification for my own situation.

The house is 1930's with a cavity wall which was filled 20 years ago.

There are some vents in the external walls but not sure if there is much passage of air.

My intention is not just about "U" values but very much about comfort given our age.

I would like to further insulate the external walls and also consider some internal walls too but not to the same extent.

External walls;
If I use foil backed PIR (50mm) can these be fixed directly to the filled cavity walls?
They would then be sealed all round and then plasterboarded and skimmed.
The walls are pretty good so would use dot'n'dab for PIR and PB supplemented by some mechanical fixings for fire safety.

Should the existing vents be extended to the new wall surface? Or might they already be redundant on the inside by the cavity fill?

I am also considering foil quilt which will be fitted according to instructions so no connection to wall surface so no issue there.

Any thoughts on PIR as opposed to multifoil type?

Purely in the interests of comfort I'm considering insulating some interior walls in a some rooms, ie lounges and bathroom. I would be interested in your thoughts on the benefits of this.

The floor and ceilings are already insulated (200mm wire wool) and i will do a bit more above the ceiling which I have access to.
I'm going to fit a foil overlay on the floor prior to 11mm underlay and decent thickness carpets.

So the main issue is the walls if anyone can help me I'd be very grateful.

Thanks, Bob.

 

[jeds]

PIR will be far more effective, take less space and simpler to install. If you have good plaster surface you could consider thermal laminate plasterboard fixed dot and dab. I would also advise using a high grab primer for the dabs - e.g. Febond Blue Grit.

 

[rwb]

Thanks Jeds. Pleased to hear that I can dot'n'dab straight on to the wall as the cavity is filled and wondered if that meant the wall should be considered as a "solid" wall and requiring battens for an air gap. I suppose the dot/dab will create a small air gap anyway.
Thanks again, Bob.

 

[rwb]

On 2 of the walls I'm insulating there will be 6mm cables behind the insulation. I'm not sure about retaining sufficient clearance for them with dot & dab or expanding foam adhesive and wondered if 10mm battens at 400mm centres would be ok. Extra work I don't mind doing but I don't want to end up with a skew whiff wall.

Also, the wall is a cavity wall (1930's) that was filled 25 years ago, would this be an issue?

 

[jeds]

Dot and dab is normally at least 12-15mm. Unless the cables are bigger than that I wouldn't worry. 2.5mm t&e cable is commonly covered with dot and dab, including capping.

 

[rwb]

Thanks Jeds.

 

[robinbanks]

Have you checked how applying the insulation affects the CCC of the cable? It sounds like they've gone from Method 1 to Method 4.. You may need to reduce the size of the MCB or fit a bigger cable depending on the demands of the load

 

[rwb]

Hi Robinbanks. I had already sent info to the electrician who is doing a full rewire about my intentions and he should be back to me today on this. Obviously I will take his advice into account.
Thanks.