What thickness of insulation?

DonnyDave

I'm in a 1920's house which has a two layers of 4½" bricks upstairs with no cavity inbetween. I intend to line the inside of the outer walls with Celotex/Kingspan insulation. What thickness do you reckon? 2 or 3 inches maybe.

SailorSam

With insulation i'd always say the more the merrier. But lining inside walls you always have to remember it's making your room smaller and this could cause all sorts of problems especially arond doors & windows if you need to alter them, or even where electrics and pipes are.
Have you thought about putting the insulation on the outside ?

DonnyDave

No, I haven't thought about putting the insulation on the outside, but I've sussed the things you mention. A new radiator will be fitted in one room and in both the pipes will need bringing inwards a few inches.

The insulation will only be fitted to two upstairs rooms, which are to be redecorated.

The door to one of the rooms is up to the outside wall so I'll stop the insulation short so that the door will still open. I need to find new, deeper, window sills, the current being about 20cm.

A.Penny.Saved

There are rules and regulations regarding fitting insulation. If you do more 25% of your walls, I believe it to be, then you have to meet strict building regulations and meet certain standards. That means you have to fit a certain thickness of insulation and only if it takes up 5% of your floor space can you fail to meet the required standard.

External insulation is always best because it should not cause timber rot if you get the insulation wrong.

DonnyDave

A.Penny.Saved wrote: »

There are rules and regulations regarding fitting insulation. If you do more 25% of your walls, I believe it to be, then you have to meet strict building regulations and meet certain standards. That means you have to fit a certain thickness of insulation and only if it takes up 5% of your floor space can you fail to meet the required standard.

External insulation is always best because it should not cause timber rot if you get the insulation wrong.

The dimensions of the rooms to be insulated are: front room: 4m x 2.7m; back room: 3m x 2m. Both rooms are on the detached end of the house, so each has two outside walls and two inside walls.

With 75mm insulation the outside walls will be brought in around 90mm to 100mm (once plastered). This is much less than 5% of the floor space in both rooms.

Perhaps you can expand on your comment about timber rot. Where could this happen and what could be the reasons?


[Is it not silly nonsense that one can "fail" if too little insulation is installed but no insulation is perfectly acceptable? What is the sound logical engineering reason for it being this way? I fully agree that new-build properties should have to meet a required standard.]

muckybutt

Have you thought about using Actis superfoil insulation ?

Damned good stuff we used it on a loft conversion years ago, damp and rot proof for sarters, thin - only 25mm but the equivalent kingspan thickness was something like 150mm dont quote me on that though!

A.Penny.Saved

DonnyDave wrote: »

The dimensions of the rooms to be insulated are: front room: 4m x 2.7m; back room: 3m x 2m. Both rooms are on the detached end of the house, so each has two outside walls and two inside walls.

With 75mm insulation the outside walls will be brought in around 90mm to 100mm (once plastered). This is much less than 5% of the floor space in both rooms.

Perhaps you can expand on your comment about timber rot. Where could this happen and what could be the reasons?


[Is it not silly nonsense that one can "fail" if too little insulation is installed but no insulation is perfectly acceptable? What is the sound logical engineering reason for it being this way? I fully agree that new-build properties should have to meet a required standard.]

I am certainly no expert on this, but I was considering doing a similar thing to my (semi)solid walled (no fines concrete) home. Fitting insulation can cause damp to build up behind the insulation which can cause timbers to rot over a long period of time. The direction that joists run can affect things. My home has cross joists from the party walls either side of my home, a terraced house, which are also supported by internal brick/concrete block walls. However for the upstairs the ceiling joists run in the opposite direction running from the front and back walls which are the walls which would require insulation. That puts those joists at risk from damp and rot. It can be very risky doing internal insulation so I would urge you to investigate this before beginning and do not under any circumstances accept a "it's okay, don't worry about it" - it will be someone else's problem kind of thing. External insulation is the preferred method and grants etc are available. I got mine done by an Energy company under ECO.

DonnyDave

A.Penny.Saved wrote: »

I am certainly no expert on this, but I was considering doing a similar thing to my (semi)solid walled (no fines concrete) home. Fitting insulation can cause damp to build up behind the insulation which can cause timbers to rot over a long period of time. The direction that joists run can affect things. My home has cross joists from the party walls either side of my home, a terraced house, which are also supported by internal brick/concrete block walls. However for the upstairs the ceiling joists run in the opposite direction running from the front and back walls which are the walls which would require insulation. That puts those joists at risk from damp and rot. It can be very risky doing internal insulation so I would urge you to investigate this before beginning and do not under any circumstances accept a "it's okay, don't worry about it" - it will be someone else's problem kind of thing. External insulation is the preferred method and grants etc are available. I got mine done by an Energy company under ECO.

Thanks. This sort of thing has crossed my mind: that I'm putting this stuff against the wall which will therefore not have air circulating and the question of whether damp could ensue. It's always advisable to leave a gap between the wall and back of furniture on outside walls and I'd be lying if I said I've never seen or felt the walls I'd like to insulate to be wet with condensation.

How does this external insulation work? What does it consist of and how is it applied?

I should explain that there is an empty cavity which runs up to below the upstairs window sills. Above that the two rows of bricks have no cavity.

Having removed the window sill I can see into the cavity. I will spray some foam into it to stop any drafts and help insulate that.

On the outside where there is no cavity there is pebbledash. Below that, where there is a cavity, there is bare brick.

DonnyDave

muckybutt wrote: »

Have you thought about using Actis superfoil insulation ?

Damned good stuff we used it on a loft conversion years ago, damp and rot proof for sarters, thin - only 25mm but the equivalent kingspan thickness was something like 150mm dont quote me on that though!

No, never heard of it, but I'll look into it.

I wonder if it could be put on the wall (on top of the existing plaster) and covered with plasterboard which is then plastered over. Are there any potential issues with damp that could arise with this solution?

Furts

muckybutt wrote: »

Have you thought about using Actis superfoil insulation ?

Damned good stuff we used it on a loft conversion years ago, damp and rot proof for sarters, thin - only 25mm but the equivalent kingspan thickness was something like 150mm dont quote me on that though!

This type of insulation was introduced into UK around ten years ago. It was claimed to be the best thing since sliced bread. Spool on a couple of years and the sales pitch was rumbled. The NHBC banned such products from being used to build new homes. The sales people fought back - their commissions and profits were at stake. The result was it can now be used provided the manufacturers recommendations are followed in every detail. If not, then it will fail making the claims about super insulation BS.

cyclonebri1

Just a couple of things to add, without offending anyone I really would not involve building control with this 1. I think that's taking thing 2 far. IMHO of course.

There will be no issue with condensation, that only happens on the hot side of a cold wall/ceiling. All you need do is seal around the edge of every sheet, I'd go 50 celotex or similar, and seal each sheet to each other and to the roof and floor. All just to ensure no warm air reaches any voids left behind.