Quick (and stupid) question - internal wall insulation - solid walls.

ChasingtheWelshdream

I know this is probably really obvious and but can I just check?

If we were to fit internal wall insulation (celotex/kingspan with battens and boarding over) to solid walls (brick), is it only on the external walls or should it also be on the internal partition walls (which are also solid brick). And it should presumably also be around chimney breasts (on the external wall side)?

 I know we need to pay attention to window reveals etc. but just costing things up if we were to take the plunge whilst decorating a room.

Thanks!

FreeBear

Just the external walls need doing.

Internal walls act as a thermal store and are not subject to heat loss unless the room the other side is freezing cold. If the chimney breast is above a fireplace (or stove) still in use, it will also act as a thermal store and radiate heat in to the room - I have a disused chimney breast in an upstairs bedroom, but there is a flue running up inside from the stove downstairs. When the fire is lit, this chimney breast  gets warm (25-30°C) and helps to heat the bedroom.

Bendy_House

What are your external walls made from, CTWD?

I wonder if there's a need to batten and stuff - can't you just D&D the insulated p'board straight on (with occasional metal fixings)?

ChasingtheWelshdream

Thanks both. 

The external walls are rendered solid brick. 

The room we are thinking about is on the third floor with two external walls and partially coombed ceiling. Easily the coldest room as it’s North facing. The chimney breast has a flue lining from the woodburner on the ground floor. I’ve not noticed it being particularly warm I must say.

The loft insulation above has been upgraded when the roof was re-tiled but there is currently none on the coombed part. So we are thinking of doing the walls at the same time. 

The second room - also North facing has very little external walls. Just a bay window and underneath two side windows so that is not expensive to do. And the chimney breast with the stove. Which would be awesome if there is no point insulating that it’s the only part I would need to remove and reinstate cornicing. 

Edited: We were thinking of using battens to provide studs in case anyone wants to put up shelves etc in the future.

FreeBear

Admittedly, I prefer the warm batten method of insulating a wall internally. It avoids any potential cold spots that you might get using mechanical fixings with insulated plasterboard. Gives you opportunity to run conduit/cables up behind any plasterboard. Having battens to fix shelving to is a nice idea in principle, but locating the battens once the room is decorated is next to impossible.

ChasingtheWelshdream

Thank you, much appreciated.

ComicGeek

You also need to consider whether the external render is permeable, how to deal with any risk of driven rain, how to deal with internal moisture, risk of interstitial condensation etc. How old the property is, quality and type of external render (is it original or added later?) are important questions. If it's a much older property, then worth looking at the historic England guidance https://historicengland.org.uk/images-books/publications/eehb-insulating-solid-walls/

It's not as easy as just sticking some insulation on the wall, moisture can cause a lot of unseen damage. A lot of schemes I'm working on have a ventilated void between the external wall and insulated studwork to deal with condensation, and use breathable insulation. 

Bendy_House

Good point, C-G, hence me asking what type of wall construction.

If it's a wall construction that is naturally allowed - requires - to breathe, then this type of insulation could cause issues.

There are alternatives, such as the fibreboard(?) types used on cob houses and stuff, but I have no idea what's best.

stuart45

The problem with stopping heat getting to the external walls is that occasionally the external brickwork spalls and timber lintels rot.
Even cavity wall insulation has been known to cause spalling.

ChasingtheWelshdream

I am sorry, I should have come back to reply earlier. But life.....

We have insulated our top landing and it has made a noticeable difference. It comprises a coombed bit and upright wall and we are satisfied there is sufficient air flow to stave off any condensation issues. The roof has breathable membrane and the upright bit has an air gap the other side where it adjoins another roof (hard to explain), but we are confident we will not trap any damp on the walls/rafters.

The other room we wish to do comprises a chimney breast with a flue lining inside, 2 upright outside walls and coombed areas above a dormer window. There has been no evidence of damp since we have been here, but we are wary of introducing any.

We have costed up and think it will be well worth doing in terms of comfort, but we need to be sure of how to proceed.

External render is not lime-based (we checked before painting last year). We are unsure if it is original - most of the houses in the street are the same. Walls are solid brick with lime mortar. There are large areas of sound original lime plaster inside, but also a few large patches of gypsum.

Any thoughts?