I live in a standard 1930s semi with walls of solid brick, with no cavity.
The area pictured under the stairs always suffered from condensation and mould. Upon discovering the mould had colonised multiple layers of old wallpaper and paint, I ripped it all back to brick for a fresh start.
I uncovered a dry wall in good condition, with a large air vent which had been blocked up at some point.
I’m interested in trying to plaster this wall with a lime-hemp based product to add some insulation while keeping the wall breathable.
However I don’t think the original plaster was lime, nor is the existing mortar as far as I can tell. Do you think that is a problem? Am I misguided in wanting to try lime-hemp or a similar solution for this area?
You have a very interesting understair area. Was it previously enclosed as a cupboard?
As it stands it is over endowed with ventilation, to put it mildly. Before considering the final wall finish you need to know what you want to do with this area. While thinking about the options all the voids need filling. The main ones I have marked in the photo below.
Is the gas meter staying or are you going all electric? I would never go back to gas. The void under the window could be filled with aerated concrete blocks.
Do you need to keep the window? If not, more blocks and remove the cill.
Is the airbrick needed? This depends on its intended purpose. If the area has always been open then it was intended as part of the whole house ventilation and may need keeping but bear in mind that our living habits are different from when the house was built. For a start, I very much hope you aren’t heating by burning coal!
If the area was enclosed, it may have been intended only to ventilate the cupboard. An enclosed area with a gas meter might have warranted its own ventilation.
Is this work part of an airtightness master plan? If so use airtightness tape at all junctions or paint the area with Blowerproof, including overlapping all edges. Other brands exist.
You are now ready to plaster the wall, which should be done to millimetres from the floor boards, not inches as it probably was before you stripped it. A gap is still needed for expansion and contraction.
Given that this is a relatively small area your choice of plaster won’t make a big difference to the house as a whole but as you have reported damp issues probably caused by condensation a moisture active layer would probably be best. This is where lime and insulation come in. The insulation would keep the inside surface warmer, thus helping to reduce relative humidity and condensation whilst a lime finish would absorb and release remaining moisture harmlessly.
Lime hemp I believe has slight insulating properties and is definitely hygroscopic so would work but I have no real knowledge of its characteristics .
Diathonite would function as both insulation and lime and would be my choice. Other brands now claim to do the same but I cannot comment on them.
Once the wall coating has dried, use a sealant along the mm gap between wall and floor and decorate with a breathable finish.
Thank you for the welcome and for the detailed response Tim. It’s taken me a while to reply while managing and a poorly one-year-old.
We’ve begun the process of getting off gas by switching induction cooking and having the old supply to the kitchen capped. I would really like to replace the boiler with an air source heat pump but this feels a way off at the moment.
It’s a curious feature isn’t it? I think in the original layout of the house this area was designed to be a pantry, with a door into the original galley kitchen (right). The inset formed a niche with a marble slab sill for keeping food cold. In any case, yes, it’s probably worth blocking this up so at least we have a full thickness of wall. That would make the plastering more straightforward too.
I don’t know why there were two missing bricks behind the skirting board, but while I’m doing the blockwork I’ll fill those in with bricks and mortar (which appears to be sand and cement )
Preferably, yes.
Great question. I intend to leave this area open, possibly separated by a curtain at most. We keep our Brompton bikes folded away on the left, and we’ll need the space for our daughter’s bike in a few years. I would also like to install a desk and use the space by the window as a “working at home hotdesk” space as my wife and I both WFH and often need separate workspaces.
Not as such, at least not yet. I’m continually inspired by the work of my friend @paulf who is in the process of air-tightening his own house to within an inch of its life. My house however seems about as airtight as a colander. I suppose this project is a good place to begin this effort.
To that end, around the window I plan to fill the voids in the brickwork with Ilbruck FM330 foam, then tape over the joint all round with their ME508 membrane. This should probably include blocking and capping over the useless trickle vent.
I would like eventually to have a whole-house ventilation solution but it’s such a daunting prospect I need to get some expert advice on how to get there.
Hooray! I did some research on Ty-Mawr and it looks as though Ecocork Insulating Plaster might fit the bill, with a finish coat of fine hemp-lime and some sort of breathable paint. I’m hoping to talk to their sales advisors to make sure that would be suitable and play well with the airtightness tape. I’ll also look into Diathonite as per your suggestion.
Sick family, particularly babies, always take priority. I understand. My youngest is now 7.
I’m pleased to see that you have a friend that is taking the same journey. Having friends or family following the same path is really helpful.
Regarding the trickle vent, I nearly suggested blocking it but experience tells me that such a message is generally not well received.
I would knock off the protruding grill, fill as much of the top section with insulating foam as practical and use white tape to seal it.
If you plan to have a desk in the area you don’t want the airbrick, unless you like cold draughts on your legs. You might need a fan instead to dry residual dampness from the bikes. If the house is like a colander you have a long way to go before having to worry about adequate ventilation. A word of caution though, enough ventilation to breathe is potentially less than the house needs to avoid damp and mould. Not burning gas for cooking will help. Half the emissions from burning gas are water vapour, the rest being carbon dioxide.
The life expectancy of a boiler is 12-15 years. You could plan your migration to heat pump around that. I changed when mine was 17 years old but it had only ever been run at low temperature, with associated low corrosion.
As you have whole house ventilation in mind you can allow for it in your staged retrofit plans. One of the factors against fitting MVHR is that there is nowhere for the ducts. You are in a position to avoid that.
You may not need a wall finish. Untreated Eco-cork is quite pleasant and Diathonite has through coloured options, so even future chips won’t show. That saves future work and expense.
Please keep us updated on choices and progress. It helps you justify your decisions to yourself and inspires others.
