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A bit of background: I've bought a house built in the 1960s which has been retrofitted with "bolt-on" insulation. On the inside, which was done first, there is a layer of plasterboard with insulation bolted to the brick and plaster walls - in places this was very shoddily done.

On the outside, there is cladding that has been bolted to the outside and rendered with some kind of spray-on roughcast - this was done much more professionally.

Having recently discovered the internal insulation (by trying and failing to fit a shelf) I'm considering removing the internal insulation to both increase space and allow me to more easily fix shelves etc to the walls.

Is this advisable given the external insulation, and does anyone have any data comparing heat loss with internal vs external vs none vs both?

Edit with more info:

Thanks for the answers so far, I will consider carefully before deciding whether to remove or not.

I'm in a wet & windy climate, between 1 and 15 degrees C year-round. Wall construction is brick & plaster (I believe there is a cavity), then 3" thick polystyrene insulation on the outside.

According to another answer I read on here, internal insulation can have the effect of keeping the brick walls "cold" by reflecting the heat back into the room. This has the effect of stopping heat leaking out, but when the heating is off, it gets cold very quickly - this has been my experience so far. Considering I have external insulation, I could remove the internal, and lose a bit of heat to the walls but warm them up, helping to keep the rooms warmer for longer rather than warm / cold immediately. The external insulation will stop this heat loss being extreme.

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  • If you're living space is not retaining (or quickly losing) heat you need to find out why. As HenryJackson mentioned noting the total R-value of the wall insulation will give you a baseline. Seeing that you reside in a cold climate it would be wise to not remove , but add more insulating material.
    – ojait
    Nov 2, 2015 at 15:32
  • You should also look at your roof and how it is constructed. An extremely large percentage of heat is transferred through the roof (in both directions). Adding insulation there is also advisable.
    – ojait
    Nov 2, 2015 at 15:32
  • Lastly, most homes inevitably have minute openings to the outside. I've read that the totals of these openings can sometimes equal that of an open window! Drafts equal heat loss. Plugging openings will help keep the heat inside. I believe that if you seal any drafts, make sure you have enough insulation in the walls and ceiling your home will maintain a comfortable temperature (for a reasonable duration) no matter what your walls are constructed from.
    – ojait
    Nov 2, 2015 at 15:32
  • @ojait thanks for the advice - the roof is insulated with the same insulated plasterboard but I'm not sure about the ceiling of the ground floor, where the rooms are coldest. I'll see if I can find out what's in there, it may be that a roll of glass wool would help.
    – jammypeach
    Nov 2, 2015 at 16:13

2 Answers 2

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It sounds like you are willing to spend money to remove something that that is designed to help save money. If your houses walls are made entirely of brick and mortar the two layers of (rigid) insulation is the only material slowing the heat from conducting through the walls. I think you will find most, if not all, information and scientific data states the more (thicker) insulation in a conditioned space the less energy will be loss from heat conductance. If I can suggest that a better question posed here might be how to hang a shelf on a insulated brick wall. It could save you an un-needed financial burden.

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  • you're quite right about removing something designed to be beneficial - I've edited my question to better reflect my reasons for thinking this. It's not a large cost for me to remove the walls, as the walls underneath are finished (and the original wallpaper and skirting boards are still in place!) it's just a case of time & manpower. thanks for your thoughts
    – jammypeach
    Nov 2, 2015 at 11:08
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There is not any difference between "internal" and "external" insulation. The only thing that matters is what the insulation layers are made of and how thick they are. If you want to know what the insulation value ("R-value") of the wall is, you will need to know the thickness and material of the insulation. If you have multiple layers of insulation (like you do), you can just add together the R values.

This website has a table of many types of insulation (note that some of them are listed as "per inch" where you need to know the thickness, and some of them are a total value for the item, like a 4" concrete block). Also, you can see from a table that most structural materials (wood, brick) have practically insignificant insulation values.

Removing insulation is obviously going to raise your heating and/or cooling costs, but there's not enough information in your question to estimate the magnitude of the effect. What climate are you in? What is the type & thickness of the insulation?

In the USA, the federal government has recommended levels of insulation depending on climate: http://www.applegateinsulation.com/Product-Info/Technical-Pages/249732.aspx

You really need to know what you're working with, though. I have to assume that if insulation was added to your house then someone decided that it was worth it so I would not remove it without a little bit of thought.

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  • Thanks for the link, I'll calculate the R values with & without and compare them before deciding. I've also edited the question to contain more detail, including climate details. My thought is that the internal insulation was added first as a cheap means of keeping it warm, then the external added later to double down - it used to be local authority owned and these things were done cheaply & rapidly, en-masse and weren't always the best course of action, hence my doubts.
    – jammypeach
    Nov 2, 2015 at 11:04
  • This answer is misleading: there's a huge difference in internal and external insulation, when it comes to vapor barriers (and thus moisture, mold and rot).
    – Bryce
    Jan 4, 2016 at 9:46
  • @Bryce: true, if there is a vapor barrier (sounds like probably not based on the question information), the location of the insulation relative to the barrier matters. But that's a whole separate issue. Insulation has the same effect no matter where it's placed in the wall assembly.
    – Hank
    Jan 5, 2016 at 20:35
  • update months later - I removed the insulation and it turned out the be the best move. There was square metres of black mold under the insulation, because the inside insulation was preventing moisture escaping the wall on the inside, and the outer insulation was preventing it escaping the other way. serious problem as it was a bedroom. Wall is now dry, mold gone.
    – jammypeach
    Feb 24, 2016 at 15:55

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