internal wall insulation

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Hello,

i'd like to fit internal wall insulation to one of the bedrooms in my victorian semi. I plan to install it throughout the house as i do up each room. A builder did two rooms already (as part of a wall/chimney removal) and he did it with metal studwork, kingspan and plaster board. He didn't tape the kingspan joints to maintain the vapor barrier and left a large gap between the brickwork and the kingspan circa 75mm.

The room I am doing is fairly straightforward 1 flat plastered external wall , 1 centrally located sash window , and I was going to do the kingspan tight to the plastered wall, tape the joints , seal the perimeter with expanding foam and then plasterboard... I'll probably use metal studding to support the plasterboard but make sure it doesn't contact the external wall... i.e. 50mm studding , 80mm kingspan

My question is about the detail around the floor boards / joists. The joists run parallel to the wall and my plan was to cut back the floor boards where they overhang and fill the gap between the wall and the joist with insulataion/ and or expanding foam... however I've realised there is a flat roofed bay window in the room below which means that there is a wooden beam in the wall (below the floorboards) which is supporting the external wall that I am talking about doing. If I insulated between the last joist and this beam it will leave this wooden beam on the cold side embedded in the wall. Am I better off accepting that I cant do a full job on a period property like this and just do the area of the wall above the floorboards?

p.s. any other advice on fitting IWI is much appreciated!! If the joists ran the other way into the wall what is the best approach/ current thinking?
 
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What is on the other side of the beam, is it exposed, or behind lead flashing or the bay window structure?

Generally insulating where you propose wouldn't create any extra risk of condensation. But it will mean slightly less heat loss through the beam, and so slightly less of a drying effect if there is any current wetting through moisture penetration or condensation.


He didn't tape the kingspan joints to maintain the vapor barrier and left a large gap between the brickwork and the kingspan circa 75mm.

Wut?

why didn't he tape these joints (oh wait, I know, it's cus his a builder).

There is a small risk of condensation forming on the brickwork with insufficient vapour checks, un-taped joints might not be an issue.

Not sure what you mean by a 75mm gap, where is this and why does it exist?
 
I think on the other side of the beam will be the cavity that's under the lead flashing and whatever board that supports it..

The 75mm gap is the gap between the plaster and the rear face of the insulation. I guess it's there to ensure there are no damp problems behind the insulation. I don't want to repeat this if I don't have to.
 
I think on the other side of the beam will be the cavity that's under the lead flashing and whatever board that supports it..

I would leave it be then. It would probably be OK to insulate, but unless you can be certain of the build-up, I wouldn't alter it.

The 75mm gap is the gap between the plaster and the rear face of the insulation. I guess it's there to ensure there are no damp problems behind the insulation. I don't want to repeat this if I don't have to.

Nope, I'm not getting it?

Is that 75mm used for services, otherwise it's just a waste of 75mm.

This is a good guide https://www.english-heritage.org.uk/publications/eehb-insulating-solid-walls/
 
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Thanks for the help so far. I think the builder was used to doing cellars and has used the same approach . I.e keep away from the wall and allow air to circulate behind the insulation. Inan upstairs room it didn't seem appropriate. Any way I didn't want to spend time complaining about him.in all other respects he was great and I'd use him again. But not for IWI!. No services just a gap which does seem a waste and doesn't appear to give me a benefit.

So in the rooms he's done so far he hasn't addressed the cold bridges at the floors but in these old houses it's a lot harder than it looks as there is fair bit of wood in the walls already and the construction isn't straightforward as I've found with this room. I'm inclined to just insulate the wall and leave the floor and joists alone. What might be useful is to maybe "seal" the floor with hard board and seal to the skirting all the way round. That way the floor will have a basic vapour barrier so I shouldn't get any occupancy generated moisture condensing in the floor spaces? Ie a halfway house. The alternative seems to be using vapour permeable insulation and lime plasters etc but even then I wouldn't feel comfortable as if it does get damp it would likely make things worse... I wonder what a professional IWI firm would do in my case?
 
I.e keep away from the wall and allow air to circulate behind the insulation. Inan upstairs room it didn't seem appropriate. Any way I didn't want to spend time complaining about him.in all other respects he was great and I'd use him again. But not for IWI!. No services just a gap which does seem a waste and doesn't appear to give me a benefit.

It makes less sense in a cellar, but nevermind.

FYI it is what it is, you can't necessarily fill that space with insulation as too much insulation can be bad for the brick wall (or at least some say this). Going forward why not just use insulated plasterboard, or otherwise just lose that space.

So in the rooms he's done so far he hasn't addressed the cold bridges at the floors but in these old houses it's a lot harder than it looks as there is fair bit of wood in the walls already and the construction isn't straightforward as I've found with this room. I'm inclined to just insulate the wall and leave the floor and joists alone. What might be useful is to maybe "seal" the floor with hard board and seal to the skirting all the way round. That way the floor will have a basic vapour barrier so I shouldn't get any occupancy generated moisture condensing in the floor spaces? Ie a halfway house. The alternative seems to be using vapour permeable insulation and lime plasters etc but even then I wouldn't feel comfortable as if it does get damp it would likely make things worse... I wonder what a professional IWI firm would do in my case?

The general rule of thumb is to use more vapour impermeable materials on the warm side, so VCL and sealing as you suggest, or to use materials of similar breathability all the way through the wall (what some people call 'breathing walls', though I have heard that used to describe a few methods).

The latter needs to be done carefully when dealing with very high levels of insulation.
 
Fix thermal insulated plasterboard direct to the walls. (no gaps behind) These can be fixed with adhesive or mechanically and are the safest method to avoid condensation issues. This method also provides the least thickness at reasonable cost and is fairly easy to install. When costing boards be aware that there are different grades of insulation so make sure you compare like for like. Go for the thickest board of the highest grade that your budget allows.

e.g. http://www.kingspaninsulation.co.uk...cd6/Kooltherm-K17-Insulated-Plasterboard.aspx
 
I know that this an old thread but it raises an issue that is misunderstood and as a consequence manufacturers of materials to remedy these problems have a field day. Numbers are quoted re U values etc but I would question the accuracy of many. I have dealt with issues such as underfloor insulation and used 100mm Cellotex in an old Edwardian House I renovated. I have now issues in a modern (late 50's) bungalow. It also has a suspended floor as its on a hillside. One end of the bungalow retains heat better, and receives more sun/daylight. The greatest issue and surprise is that internal walls are really cold in places. These are walls not only external to the building but internal ones. I am surprised about the internal ones in the middle of the building. My take on it is that the void underneath is cold and the concrete block walls are subjected at the base to this cold. So I have done a few 'tests' and having become frustrated paying silly money for Cellotex played about with some polystyrene. The benefits is that its cheap because its unfashionable. However its benefits are obvious...it is warm to the touch and does not transmit cold-retains heat etc. I stuck a section to my wall and took temperature readings. It was 1.5 degrees cent. warmer than the wall, and that was without adding plasterboard (as yet). So I shall buy large sheets from Wickes for a fraction of the price of cellotex and build a stud frame (25mm as per the boards). Plasterboard on top-joint and plaster. One day job. Cost approx: £100. One aspect of Cellotx/Kingspan etc is the foil in their products in themselves create issues of condensation in certain circumstances. This is not the case with polystyrene.. I know its a bit off topic but relevant all the same...
 
25mm of insulation does not seem worth effort to me.

Forget the monetary cost, the main 'cost' in your example is your time spent doing the job.

Why spend days doing a job to add only 25mm.

I personally would add 50mm direct to the wall between 'studs', 25mm over that (so as to reduce cold bridging through the studs), then plasterboard over it.

Also looks like 50mm and 25mm sheets have a cheaper combined price than 75mm sheets on the wicks website.

polystyrene.

It is not as good for the same thickness, but this is no secret.

Polystyrene is fine if you don't care about the extra space it takes up, or if you are trying to upgrade insulation but not necessarly botherd about achieving the 'best' u-value for X thickness.

One aspect of Cellotx/Kingspan etc is the foil in their products in themselves create issues of condensation in certain circumstances.

Err, no.

But a plastic sheet or VCL will do the job, foil is just a lazy method when used with tape on the joints (and I don't trust that the tape will last).
 

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