A domestic insulation project. Chapter 2 – dust, destruction and a lot more dust

Did I mention the dust? One of the reasons given in favour of external wall insulation (as opposed to internal wall insulation that I am doing here) is that it is much less disruptive to the residents. Whilst being out at work all day means the practical disruption to my life is pretty minimal, when I get home I get the strong impression that the wall construction is basically a dry slate wall, mostly rubble, with dust.

The ‘why I’m doing this’ post is here, and the prequel post from a couple of weeks ago is here.

The work undertaken since the last post has been almost entirely removal of the old plaster to expose the stone walls. As you can see from the photo below, the vast majority was lime plaster (the white dusty areas), with very localised cement plaster on anything that was more recent (the orange areas).

The downstairs room with the plaster removed from the walls. The corner wall was prone to mould patches, and whilst walls are dryer in the summer than in winter, the fact that the corner is bone dry might suggest that any mould had been due to a low wall surface temperature causing condensation of moisture from the indoor air, as opposed to any moisture penetrating the wall from the outside.

Quite a lot of old houses in the area have steel straps holding walls together. Seeing the corner of my walls it’s easy to see why. A combination of lack of large stones keying the two walls together, and the fact that the walls are designed to take a vertical load not a horizontal one means that if there’s any ground movement, or other horizontal force, the whole structure can be quite unstable.

In case you can’t read it, the tape measure went 3 inches into the wall at this point. This isn’t from the removal of a stone, it’s just lime/aggregate dust that came out. It’s possible that some of the localised damp spots in this corner were due to cold spots caused by some of these gaps, but unfortunately I didn’t measure exactly where these spots were before the plaster got hacked off.

Whilst the wall construction isn’t inspiring, the floor/ceiling joists are all oversized by today’s standards. Over 7 inches. Timber must have been cheap.

Whilst timber was cheap, bricks were expensive. Only used in key places like the chimney stacks and a couple of corner points. The gap in the wall above the basin was not where a stone has been removed, it was all dust.

Removing the surface decoration of the house can potentially expose some absolute horrors. I’ve been lucky, this is the only one so far. A completely bodged slate replacement (a glued half slate) led to a roof leak which has completely rotted away the joist. Not visible from the outside of the house at all, and not visible from inside before the plaster was removed. It must predate when I bought the house (2001), so it just shows how much water can pour into a dusty wall without any visible signs. A combination of a roofer replacing slates and some joist/batten replacement on the inside and this will all be fine to cover up again. The amusing/terrifying aspect of this part of the job is that to get to the base of the joist in order to investigate replacement, the slate wall needs removing to that level. It’s simply lifted off by hand, no force required; the stuff that looks like mortar in the photo is so old that it’s nothing more than dust. Luckily Steve who is doing the work doesn’t get stressed by stuff like this.
One of the disadvantages of internal wall insulation is said to be that you lose floor area. This picture shows the depth of floorboard that was covered with plaster; 50mm or so and then the skirting board. Quite why it was this deep I don’t know; it’s possible that successive occupants just added more skims of plaster to flatten walls or to hide cracks, but we didn’t see any evidence of that. Anyway, in this house, 50mm insulation is not going to make the room smaller, and we can go thicker than that if we decide to. It also brings into sharp focus how the approach of having ‘brushed plaster’ where the shape of the wall is still visible would have used drastically less material.

One of the advantages of doing such a deep retrofit is that you can get to the cause of problems rather than just address the symptoms. Window reveals are always problematic; cold surfaces, not much air circulation and thermal bridging around the frame can all contribute to damp/mould issues in these areas. In this reveal, we can see the use of two timber lintels, with an enormous gap in between (1.5 inches). There was a significant draught in this gap (tell tale cobwebs), which would make it very cold and liable to damp. This gap will get filled to improve the airtightness.

Ever since I moved into the house, there has been a suspicious draught from behind the bath panel. But I always chickened out at the idea of removing the bath and dealing with it. But now the culprit is revealed. This is where basin waste, bath waste and an overflow pipe all exit the house. The bathroom is being rearranged, so these pipes will all come out and the wall will get repointed. Not sure when the bathroom was last redone (70’s perhaps), but copper must have been cheap or plastic unavailable; several metres of 1.5 inch diameter copper used as waste pipe…

Geeks go to a lot of trouble to do computer modelling of joist ends and what happens if they’re insulated. I might write about this at some point, or I might eat my spleen. But, much as in the bathroom where gaps around service penetrations are not really pointed or airtight, every single joist in the house is probably as draughty as this. I’ve certainly had the impression of there being wind tunnels between the floors. Whilst timber does need to be ventilated, particularly where it’s cold, when it’s inside what is supposedly the thermal envelope, the risks are lower. We will do some vapour permeable insulation details around these joist ends (details TBC). The ground floor is also suspended timber, but we will leave that well alone, including the joist ends, as the moisture risks to the joist ends are much higher.

Environmental taxation is brilliant; this is clean rubble (so is relatively inert). If it was mixed waste, it would cost 4-5 times as much to dispose of because it would be so much trickier to recycle. Exactly the way it should be.

Project management and buiding work undertaken by Steve Cole, Addasu.

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