Insulating new house with solid walls

[DeeDeeRmoan]

Hi all, 

 

Just purchased a 1920s ex-police house at auction which has solid wall construction. 

I'm wanting to insulate the outer walls so it's not so difficult to keep warm but having read various threads now am thinking this isn't going to be anywhere as easy as a cavity wall property. 

 

I have a couple of issues to consider, the first being the rooms inside are very small so the less space taken away the better and the external has barely any roof overhang for an external insulation system.  

 

Is anyone aware of internal insulation that takes up the least room possible? 

 

There's a hundred other things to consider once we start renovations but I'm quite worried about getting the house warmer before the cold winter weather starts again. 

 

Any advice greatly appreciated. 

 

Dee

 

[joe90]

The first inch of insulation gives the greatest return and gives a better chance to make draught proof. (It’s called diminishing returns). Eaves can be extended if you want to EWI.

[DeeDeeRmoan]

40 minutes ago, joe90 said:

The first inch of insulation gives the greatest return and gives a better chance to make draught proof. (It’s called diminishing returns). Eaves can be extended if you want to EWI.

You're a star Joe90! 

So basically anything that's still breathable but at least an inch thick will make a big difference to how warm the house feels? 

[joe90]

6 minutes ago, DeeDeeRmoan said:

So basically anything that's still breathable but at least an inch thick will make a big difference to how warm the house feels? 

Not specifically, the reference to the “first inch” is that the first inch gives X amount of benefit, 2 inches will not give 2 x X benefit (diminishing returns). There’s some on here that built and insulated a 300mm cavity, I compromised and full filled a 200mm cavity (near Cornwall is quite mild). With regard breathability there are others here who know more about interstitial condensation when insulating and where to put airtight layers and will be along shortly….once insulation is up to a “good“ standard droughts become more of an issue to keeping a house warm.

[Redbeard]

Welcome. 25mm of (breathable) wood-fibre could give you a U value (heat lost in Watts per sq m of building fabric per degree C.) of around 0.85W/m2K - around half of the heat loss (1.7W/m2K) for the uninsulated wall. Better than a poke in the eye with a sharp stick but the Bldg Regs target of 0.3(or as close as you can get without seriously risking interstitial condensation (condensation within the slices of the insulated 'sandwich') ) is a lot better. 100mm would give you about 0.35.

[SteamyTea]

If you can only install internal wall insulation, then you will probably want to install a vapour control layer on the room side.

This VCL stops the water vapour condensing as it hits the colder structure if the house.

 

"Insulation" or to use the proper term, thermal conductivity has 3 measures.

 

The intrinsic material properties, the k-Value. This is measured in W.m^-1.K^-1.

When the thickness is taken to to account, it becomes resistivity, thickness (length) in meters divided by the k-Value. 

R-Value = length / k-Value.  The size nits become m².K.W^-1.

 

To get to the more useful U-Value, W.m^-2.K^-1, the reciprocal of R-Value is used.

U-Value = 1/R-Value.

 

It is generally easy enough to get the k-Valueb of a material, but realistically you need to be looking a foamed phenolic sheet.

 

There is no reason why you cannot mix and match insulation types, as long as moisture transmission is thought about and catered for.

So you can put IWI (internal) on the front, and EWI (external) on parts that the public don't see.

The biggest problem with EWI is size of roof overhangs and around window and door openings.

[JoeBano]

In my 1930’s house I used 50mm phenolic insulation on the outside walls. It has better U-value than pir board so you can reduce the thickness but it’s very expensive. You can get phenolic insulated plasterboard with a vapour barrier.