Solid wall insulation - Options ?

[paulc]

Looking to insulate the walls of the upper half of my 1920s build semi - The ground floor walls are conventional cavity, whilst the upper half is double thickness solid brick and rendered externally with a cement rend & pebble-dash. Insulating the walls internally would be something I could do and avoid the cost of scaffolding. The stairwell is the largest single piece of wall that needs doing and has a step between the lower cavity wall and the upper solid brick. Loosing the step would be nice and would allow for approximately 3" of insulation.

With the recent drop in temperature, condensation has become a serious issue on this wall - My options for insulating are:

• Celotex/Kingspan PU foam with warm battens & vapour barrier
• 3" stud with fibreglass/rockwool batts and a vapour barrier
• Woodwool boards with a lime plaster finish and no vapour barrier
• Insulating lime plaster (either cork or hemp)

With a cement render externally, vapour permeability is going to be minimal, so I'm leaning towards the PU foam sheets. Is there anything else I could/should consider ?

 

[Roger H]

Good question. In a rendered house I would always go for external insulation. Might be worth also posting this on Green Building Forum.

 

[malcolm]

Where a wall is waterproof inside and outside any water that finds it's way into the wall won't be able to get out again. It only takes a few cracks in the render (like the ones that killed my timber frame), an imperfect vapour barrier, or an electrician making holes to allow the water in. Oddly, impermeable both sides seems to be the normal way to do things.

I am planning wood wool board without vapour barrier for internal insulation on my concrete rendered wall, but it is a temporary measure to get through building regs before I get around to knocking the wall down. My logic is if the whole wall becomes soaked I might see some evidence on the inside.

 

[paulc]

Good question. In a rendered house I would always go for external insulation.

There are a few properties in this area of a similar build that have had external wall insulation put on. To my eye, it looks damned ugly, especially around the windows, doors and any downpipes. The costs of scaffolding also puts it well out of budget - Insulating internally has the advantage that I can do a room at a time, and the only costs incurred are just for the materials.

 

[a twig]

From what I have heard from thems what has dunnit, the insulating mortar does not make a huge difference.

I am employing woodwool boards and lime plaster in places where internal insulation is required here. With my wife's ever changing decisions on where things should go on walls (light switches, doors, pictures, shelves) I avoid vapour barriers where possible as it will inevitably end up looking like (and being as effective as) swiss cheese.