Insulating interior walls, is it worth the hassle?

Mark A

Mark A

Mark A

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I'm looking into getting hold of some 25mm foil backed cellotec insulation board to try and make my downstairs loo warmer, as it is the coldest room in the house despite having a radiator in there.

Its a small room and 2 of the walls are external walls on the corner of the house. I was thinking of dropping the ceiling by a few inches so that the 2400mm board will be high enough and then gluing the 25mm insulation to the walls then gluing the plasterboard to that. Also bang some mechanical fixings in as well to make sure.

My question is; is it worth doing this? I have read that anything less than 50mm isn't worth bothering, but surely if they sell it in 25mm it must do something?

The 'Combined R-Value (m²K/W)' is 1.25. I have no idea what this means, but would this help to insulate the room so that it doesn't get so cold? The sheets cost about £14 each from ebay, so i'd only need 3 to do what I need, then the plasterboard and plaster on top.

TIA
 
If you're not going to do the floor I wouldn't bother if you're only using 25mm

We put 140mm of kingspan kooltherm k3 in new builds, 25mm without at least 75mm in the floor won't touch the sides
 
maccapacca said:
If you're not going to do the floor I wouldn't bother if you're only using 25mm

We put 140mm of kingspan kooltherm k3 in new builds, 25mm without at least 75mm in the floor won't touch the sides
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Its an ex council house and we moved in about 18 years ago. The floor in there and the kitchen is concrete, but I'm not sure when it was done and if they would have used insulation. When I took off the skirting boards I could see the blue dpm, so it must have been done fairly recently as the house is about 70 years old.

One thing worth mentioning is that when I replaced the windows I looked into the cavity wall and could see that the bottom of the cavity was full of rubble. Could this be bridging the cold through to the concrete floor?

ANDARIAL said:
You can get plasterboard with insulation bonded to the back you know
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Yeah and its £48 a sheet ;p
 
Would you not be far cheaper getting a small oil heater? You can get them for about £35 and they are pretty efficient when run on a timer.
 
Yeah i'd much rather try and sort the problem than add extra heating. There is a 600mm x 500mm double radiator in there and its only a small room. I can't get my head around why its so cold in there. I even installed an A rated PVC window and it's still as cold as when there was a single glazed window.

I might get the breaker out and see if there is insulation under the concrete floor :D
 
Mark A said:
The 'Combined R-Value (m²K/W)' is 1.25. I have no idea what this means, but would this help to insulate the room so that it doesn't get so cold? The sheets cost about £14 each from ebay, so i'd only need 3 to do what I need, then the plasterboard and plaster on top.
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The R-Value is the Resistance. Which is Thickness (m) / Thermal Conductivity (W/m K) = Resistance (m²K/W). The U-Value (W/m²K) = 1 / Total Resistance. This would give you a calculation of the total heat-loss through that particular fabric. But you need to include all materials that make up that wall/partition/floor etc.

I doubt you'd see much benefit, as you're loosing heat from your external wall. In which case you're better off insulating that, if it's not already insulated. We had ours done not long ago, and it was for free. It seems the government is trying to get us all to better insulate our homes. You should be able to get yours done as well for free.
 
We had a guy round from British gas to evaluate whether or not we could have cavity wall insulation and he said we couldn't. It's random stone on the outside, with a cavity and then brick on the inside with metal wall ties. Not exactly sure why it wasn't possible as I wasn't in when he came. Maybe something to do with the cavity not being a uniform size with it being random stone...
 
I did a house with 50mm fibreglass batts to the inside of the external walls, it made a noticeable difference and the rooms heated faster. The equivalent would be 25mm Cellotec which should do the same job, if you can do the exterior wall with 50mm then even better. The concrete floor should have been insulated, but if it isn't then the underlay boards used for laminate might make a small difference.

With that radiator and insulated as above then it should be pretty toasty, but check the door for draughts too.
 
bitslice said:
With that radiator and insulated as above then it should be pretty toasty, but check the door for draughts too.
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Also the windows. It's common to see weak spots where different materials join together i.e. upvc & brick wall, timber frame/door & brick wall etc. etc.

Mark A said:
We had a guy round from British gas to evaluate whether or not we could have cavity wall insulation and he said we couldn't. It's random stone on the outside, with a cavity and then brick on the inside with metal wall ties. Not exactly sure why it wasn't possible as I wasn't in when he came. Maybe something to do with the cavity not being a uniform size with it being random stone...
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Oh, I see. In that case you could use a 'Roughcast Lime Render' on the outside of your whole house. It's very common with older buildings, and buildings made of stone. Because lime is a breathable material, it allows moisture to leave the building, as well as help retaining heat in thermal mass of the external walls. The trouble with using concrete and/or plastic paints is you'll end up with really bad condensation in the building.

Perhaps consider insulating the roof, and/or partition walls (i.e. in-between the joists). You can also get insulating plasterboard for the floors or rubbercrete. Not sure how the later performs, but specs are meant to be pretty good.

Check out the Building Regulations: http://www.planningportal.gov.uk/buildingregulations/approveddocuments/
They are free to download, and have some pretty detailed information.
 
Thanks I'll look into the floor insulation you mentioned, if I don't find any under the concrete.

The windows are decent, they are A-rated according to the Spectus website. Also the glass is low E and argon filled etc. I was fully expecting replacing the single glazed window with these would have cured the problem.

The roof design in this house is a real weak spot for insulation. The roof rafters actually form part of the ceiling inside. So there is an angled plasterboard going around the outside edge of the room. There is no insulation in there, so its basically slates, an empty space and then the plasterboard. The rest of the loft I have insulated with 270mm of rockwool insulation. I was considering cutting some of the 25mm insulation board up and then sliding that between the rafters to give some insulation to the uninsulated area. But not sure if that would be equally pointless...
 
Bit of an update, I took some bricks out and the cavity was filled with rubble about 2" higher than the floor level. Could this have been bridging cold from the outside stone wall, to the inside brick and then the concrete floor?

Also I broke some of the concrete floor and it appears that they haven't insulated it :mad:. I don't know what to do now. Its only a small room so I guess it wouldn't be too hard to remove all the concrete and dig it out a bit more to put some insulation under the floor. But is it actually going to make a big enough difference for all the effort?

DSC_4332.jpg
DSC_4338.jpg

As you can see its about 50mm of concrete with no insulation in sight.
 
Because I want to find out if its going to be worth me ripping my house apart and spending a fair bit of money on concrete, insulation, plasterboard, batons etc etc. Hence how I titled it ;).

Meh, I'll just do it then. Like you say it can only help if anything.
 
We dry lined our entire house with 50mm celotex internally then replastered, made a massive difference
 
Mark A said:
Because I want to find out if its going to be worth me ripping my house apart and spending a fair bit of money on concrete, insulation, plasterboard, batons etc etc. Hence how I titled it ;).

Meh, I'll just do it then. Like you say it can only help if anything.
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dont worry, insulation does what it says, insulate..

its defiantly worth doing. once the room is upto temp, it will stay upto temp a lot longer and it will also hold its heat, so will be able to get very warm, unlike an un insulated room which loses its heat so fast, that it is very hard to warm up.

some rooms are so bad that people cant get it above 20c, that ive come across.
 
The rear wall of my house has no cavity so all walls over time have been drylined with 30mm k board.
In the bathroom and kitchen condensation used to be an issue but no longer as walls feel warm.
 
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