What to do about an uninsulated stairwell (that we do not have space to actually insulate)?

[Garald]

There's one weakness in our insulation plan, which is otherwise going well: a small stairwell going from the first floor to the attic.

 

(This is an old plan; now we are also insulating the kitchen's long wall, and also filled in the gap above the pantry/closet on the top end of the corridor.)

 

We simply do not have the space to insulate that corner without destroying the staircase, or so the architect says. Unfortunately, that means that the heat loss from that staircase alone is about 650W, that is, well over 10% of the total heat loss in the house. (It may be more like 10%: the first meter or so of the stairwell's long wall benefits from being adjacent to a building next door. (The rest doesn't, if my memories of checking it with an infrared thermometer have a year ago are accurate.)

 

One obvious measure is to insulate the door leading to it (seen in the plan above) as well as possible. The architect says we can't really close the top off easily - hopefully convection will work its charm and just let cold air accumulate down the bottom part of the stairs. I imagine I should *not* put a radiator there.

 

Are there other small measures we should take to reduce heat loss through that corner?

[Adsibob]

How about adding EWI? You mention part of the outside is covered by an adjoining building, but what about the other part? Can you annotate the pan to show which part of the wall is attached to the neighbouring building and which part is detached?

Edited December 12, 2022 by Adsibob

[Garald]

 

3 minutes ago, Adsibob said:

You mention part of the outside is covered by an adjoining building, but what about the other part?

 

I'm actually not sure whether their first story is just particularly low in that corner, or whether they have some sort of peculiar machine that cools that corner (and sends the heat off to feed reptiloids or what have you). I'd imagine it's the first one. At any rate, the thermal thermometer showed that a spot was particularly cold.

 

3 minutes ago, Adsibob said:

How about adding EWI? You mention part of the outside is covered by an adjoining building, but what about the other part?

My architect once talked about it, but in the end felt it would not be cost-effective for such a small bit of wall. We would need to ask permission from the owners of the neighboring building (I have no idea who they are), get the workers to install scaffolding... And of course we are already in the middle of things, and would like to be done in a couple of months. In summary, it's an option that we have kept for when and if I decide to raise the roof/add an extra story to the building (whenever that would be; certainly not in the immediate future).

 

And of course the short wall in the stairwell would remain uninsulated (unless we were to apply insulation to my entire courtyard side on the outside; sounds a bit daft, given that we are already insulating it from the inside). Again, we could rethink the staircase if a story is ever added, but...

[Adsibob]

The floor plans suggest you are in France or Canada. If the former, I wouldn’t worry about it too much. You are unlikely to have long hard winters, and this is a corner of your house that doesn’t appear to contain any living space, just staircase.

 

 If you are in Canada, that’s a different story, but even then not terrible.

[Garald]

I am in France (Paris area, in fact), but, as I said, this tiny corner accounts for more than 10% of heat loss. It's not nothing, in that it's the difference between "I feel comfortable with a 7kW heat-pump (which is really 6kW in the rare occasions when it gets to -7C)" and "maybe I should think about that a bit more". (10kW would be very oversized, but that's the next step up in Saunier-Duval aka Vaillant.)

 

[Adsibob]

If you insulated that door, I think all that will happen is that stairwell will be a degree or two colder than the rest of the house. If everything else is well insulated, then overall you will be okay. If you are really worried, see if another manufacturer makes an 8kw heat pump.

 If the window in that stairwell is 2G, could you upgrade it to 3G?

Edited December 12, 2022 by Adsibob

[Garald]

29 minutes ago, Adsibob said:

If you insulated that door, I think all that will happen is that stairwell will be a degree or two colder than the rest of the house.

 

Or three or four. That's fine; the space under the stairwell will be used either for books we don't use that often, or for board games, or for the cat toilet. It won't be a space to live in.

 

29 minutes ago, Adsibob said:

If everything else is well insulated, then overall you will be okay. If you are really worried, see if another manufacturer makes an 8kw heat pump.

 

Right, there's Mitsubishi Zubadan Silence, which is considerably more expensive, though one of the installers strongly suggested that it was better quality than Saunier-Duval/Vaillant (whether that's true or motivated by salesmanship or just his honest but subjective opinion, I don't know). The external unit is also 1cm too tall for the least expensive model in the line of sound boxes I've been looking at (but then I am sure there are alternatives.)

 

 

29 minutes ago, Adsibob said:

 If the window in that stairwell is 2G, could you upgrade it to 3G?

 

Significant cost for not that much of a difference, given that the wall is cold, no? That's more of a change that would be imperative if we eventually insulated on the outside.

 

Here's a picture, by the way: 

 

 

Edited December 12, 2022 by Garald

[Garald]

Ah wait, did the workers just manage to insulate the short side with a bit of reflective material and just did not tell me? Nice!

[Garald]

A quick review of their technical specifications, however, reveals that the Zubadan Silence 8kW and the Saunier-Duval 7kW don't really differ much in terms of power when shove comes to push. Zubadan Silence gives 8kW nominally (whatever that means) and 9.51 maximally (presumably with some supplementary electrical heating it includes) when it's 7C outside, with water flowing at 35C. In the same circumstances, Saunier-Duval gives 5.8 nominally and 9.8 maximally. Of course that's not the sort of situation where I need 6kW, so let's look at lower temperatures. At -7C (rare in Paris, but it happens once every couple of years; -2C is much more common, and it's around what I've taken as the modelling temperature), with water at 35 C, Zubadan offers 6.3kW and Saunier-Duval offers 6.7kW (how can this be, given that it promises less when it's 7C, I don't know). More relevantly, given that I'll work with 45C, Saunier-Duval offers 5.9kW for -7C/45C... and the technical specifications for Mitsubish Zubadan don't say anything.

 

https://www.saunierduval.fr/france/download/genia-air-1/geniaset-split/saunier-duval-geniaset-split-brochure-gp-202103-2041667.pdf

https://files.izi-by-edf-renov.fr/files/catalogue/produits/fiche-technique-ecodan-hydrobox-duo-silence-zubadan-mitsubishi.pdf

 

So maximal power is not really a reason for choosing between the two.

 

[ProDave]

I can see why yo can't do much above the stairs, but there is no reason you can't insulate the wall below the stairs, that will be about half of it insulated.

 

And a thick pair of curtains over that suicide door / window.

[Garald]

3 hours ago, ProDave said:

And a thick pair of curtains over that suicide door / window.

 

Do curtians really help substantially?

 

OTOH, they might keep.one from realizing that the window is open...

 

(Btw, that window locks, with a key.)

[Radian]

The problem having one space colder than the rest of the house is that it will attract condensation as the air in the warmer spaces will host a greater amount of water vapour. This will degrade the fabric and anything you store in the space, therefore I would ensure that there was a mains outlet under the stairs and invest in a desiccant style de-humidifier with a drain hose for unattended operation (with a drain exit from the space). Desiccant because they are effective in unheated spaces (unlike refrigerated types of dehumidifier) and the small amount of electrical power used to recharge the desiccant provides a tiny bit of warmth.

[DamonHD]

2 hours ago, Garald said:

 

Do curtians really help substantially?

 

About the same as an extra pane of glass.

 

And if that window gets direct sun in summer, have reflective liners to minimise the risk of overheating then also.

 

Rgds

 

Damon

[Garald]

53 minutes ago, DamonHD said:

About the same as an extra pane of glass.

 

 

Ah, nice. I had been looking forward to getting some William Morris curtains, or blinds, partly as to annoy my girlfriend. I suppose Roman blinds are just as good as curtains for insulation? (They are easier to keep relatively free of dust, no?)

 

 

53 minutes ago, DamonHD said:

 

And if that window gets direct sun in summer, have reflective liners to minimise the risk of overheating then also.

 

It faces NWN. But what is this about reflective liners? (I'm already getting retractable awnings, outside shutters, etc., on the south-facing windows, but one can always learn more.)

[Garald]

2 hours ago, Radian said:

The problem having one space colder than the rest of the house is that it will attract condensation as the air in the warmer spaces will host a greater amount of water vapour. This will degrade the fabric and anything you store in the space, therefore I would ensure that there was a mains outlet under the stairs and invest in a desiccant style de-humidifier with a drain hose for unattended operation (with a drain exit from the space).

 

a) Would this also help with hygiene and odors if this corner does end up hosting the litter box?

b) What size of dehumidifier are we talking about? They seem to vary greatly in scale and price.

[Garald]

6 hours ago, ProDave said:

And a thick pair of curtains over that suicide door / window.

 

Does the fact that the curtains would go in the inside mean I would be getting just as much solar gain in the afternoon as if they weren't there?

[Garald]

2 hours ago, Radian said:

The problem having one space colder than the rest of the house is that it will attract condensation as the air in the warmer spaces will host a greater amount of water vapour. This will degrade the fabric and anything you store in the space, therefore I would ensure that there was a mains outlet under the stairs and invest in a desiccant style de-humidifier with a drain hose for unattended operation (with a drain exit from the space).

 

Since I'll have PIV, isn't there an easier solution?

[Jilly]

Have you come across Aerogel?

[Garald]

9 minutes ago, Jilly said:

Have you come across Aerogel?

Yes - you mean for outside insulation (that Swiss plaster) or inside insulation?

[Jilly]

It’s very thin super NASA type insulation, for various applications, including iwi for narrow spaces such as yours. As others have said, be mindful of interstitial condensation. 
 

I used it on some steels to try to reduce cold spots. 

Edited December 12, 2022 by Jilly

[Garald]

6 minutes ago, Jilly said:

It’s very thin super NASA type insulation, for various applications, including iwi for narrow spaces such as yours. As others have said, be mindful of interstitial condensation. 

 

I know - it's just that my architect is a bit skeptical of things that have been proved to work in the lab but haven't been certified yet. She found a Swiss aerogel-based product - its R was a bit disappointing, but it could be very useful for outside insulation.

 

The thing would be to get something that is certified to have a substantially higher R/cm than reflective materials (notice how the workmen managed to make reflective material fit on the short wall). We really have just 1-1.5cm (if that) to play with in the (long-wall) space above the staircase. We are talking about the diagonally ascending area painted black here (before it becomes horizontal) and the white space above it: 

 

It's not a large space - once one gets to the upper landing, there's already a bit of wall insulation installed by the previous owners (or the antepenultimate ones).

[DamonHD]

I have used aerogel to good effect in my own home, in several varieties:

 

https://www.earth.org.uk/note-on-Spacetherm-aerogel-thermal-insulation.html

 

Blinds are unlikely IMHO to be air-tight enough to be much good to retain heat.  To keep sun/heat out:

 

https://www.earth.org.uk/towards-a-LZC-home.html#reflblinds

 

Rgds

 

Damon

Edited December 12, 2022 by DamonHD

[Adsibob]

Look at aerogel. Your architect is mistaken if he/she thinks it only works in a NASA lab.

[saveasteading]

3 hours ago, Garald said:

Does the fact that the curtains would go in the inside mean I would be getting just as much solar gain in the afternoon as if they weren't there?

In theory yes, as the sun and energy has entered the room. In practice it can help a lot if it fills or covers the window opening. I haven't seen it discussed, but I think simply containing the heat allows a proportion to conduct back through the glass. Plus, a light colour will reflect some light back outside...if you can see it from outside, that is reflected energy.

[Radian]

You need to perform a condensation risk on that wall. As a poorly insulated surface amongst better insulated surfaces and other warmed spaces, it will be a surface that acts like an unintentional dehumidifier in you home.