Acoustic and thermal insulation

[Bogfrog]

The task ahead is to insulate two external brick walls from the inside plus the roof.

 

Im sorry if this comes over as being incredibly stupid but I’m not sure how to do this properly.

-Do you leave an air gap between the insulation and brick wall?

-Do you insulate thermally first then proceed to rock wool slabs (finishing with acoustic plasterboard).

-Is there a product which serves both types of insulation?

-Would the likes of a thinner type of insulation work best eg Actis T100 type?

-Do you need a vapour barrier in first? If so, does it go hard on to the brick wall or do you need an air gap?

-Is the flexible rock wool type better for the vaulted ceilings area?

How do you ensure an air gap? Do you make a frame of say, 1 inch depth then attach the ( thermal) insulation?

I have to do this work myself as my budget is very low and need to get it right. The wall to the left of the photo plus either side of the fireplace are the two main areas needing done.
 

Thank you in advance for any replies.

 

[Mr Punter]

I would insulate the walls with PIR like Celotex or Kingspan, 60mm thick.  Either tape the joins with aluminium foil of cover the lot in polythene.  Use 25mm x 50mm battens with 130mm screws and rawlplugs to hold it in place and create a service void.  Finish with 15mm plasterboard.

 

For the loft assuming you are having a ceiling you could use loft roll insulation 300mm, making sure there is decent airflow from the eaves.

[saveasteading]

What is the wall costruction? Looks like it might be solid, 1 brick thick ( 9 inch) in whuch case damp must be considered.

[Bogfrog]

Thank you both for your replies and yes, saveasteading, it is just that. Even worse, the entire lower floor is thick cement with no damp proofing underneath with concrete walls.

The roof had been very badly damaged so a lot of water ingress in this room. It has taken a few years to dry it out but I’m hoping to put a very small stove in. 
The window is the original 1935 single pane and will have to do for a while…I know this negates the whole sound proofing attempt but needs must and all that.

 

The debris in the fireplace is caused by nesting jackdaws in the chimney pot. Today’s task is clearing out the rubble and an attempt at sweeping the chimney.

[Mr Punter]

You may find that external wall insulation will be better in terms of damp, as the wall will be kept much warmer.

[Bogfrog]

I agree, Mr Punter. It never had any insulation at all, the fire had not been lit for over 60 years and it was freezing cold, not just this room but the entire upstairs.

If you see me on here today, please chase me away to shift that rubble!

[Nickfromwales]

The most important and most difficult to detail area is at the lower outer edge of the roof where it forms the eave / soffit.

On garage conversions where we typically have to retro insulate, just as you need to there, I found it SO much easier to get a sheet of 200mm rigid PIR ( kingspan / cellotex etc ) and make ~600mm x400mm blocks which I then cut in half diagonally ( to form wedges which match the pitch of the roof ) and to push fit them into those awkward spaces and foam for rigidity to keep the minimum 25mm air gap. Remember to cut them short, eg lose the thin tapered bit of the wedge by cutting it off, so they only project as far as the ventilated cavity. That ensures good airflow is still free flowing up the cavity and into the space above the soffit and up to the ventilated ( cold ) roof space. 
 

Worked a treat and completely mitigated against the risks of rock wool touching the roof / felt and causing condensation / bridging damp etc. A pig of an area to detail with wool.

 

I then fit 2-300mm of rock wool up tight to the PIR where it has a nice uniform edge to abut with. running horizontally across the ceiling to meet the same detail the other side. 

The PIR on the walls can be taped to the PIR at the eave junction also then, giving a very robust joint detail where the wall meets the ceiling  

Edited July 12, 2021 by Nickfromwales