Interval vs external house insulation - which is best?

dudmis · 27-09-2012 08:23PM #1

(Not sure if this is the correct forum, mods please move if required)

Does anybody have any views which is the most effective building insulator: internal or external insulation?

I understand that external is preferable if you dont want the hassle of redoing the inside of the house, but if this wasn't an issue, which would be the best? what are the pros and cons?

thanks in advance.

murphaph · 27-09-2012 09:05PM

External is better all round if you can do it.

With external, the entire mass of the masonry (assuming block built) house is insulated and so when you heat up the house, the walls will heat up as well and radiate energy back into the living space, even after the heating is switched off.

With internal you also have many cold bridges where you physically can't slap the insulation onto the external wall (think internal walls and floors) so the heat can "escape" more easily to the cold outside wall. Related to this is the issue of dampness due to the walls being colder than before (the heat from the rooms can't as easily heat the walls up) and so moisture in the air can more easily condense on the colder walls and cause damp/mould. To mitigate against this, internal insulation needs to be very well fitted with vapour barriers and so on. There's simply more to go wrong and you won't see it's gone wrong as the mould will develop out of sight behind the new insulation.

You might consider injecting your walls, IF you have a proper cavity. 9" block walls are not suitable, despite what some people say (way too many cold bridges to make any difference IMO).

The only time they do internal here in Germany is when the property is listed and the facade can't be touched, otherwise it'll be external.

Milk & Honey · 28-09-2012 12:58PM

I think external house insulation is horrible. i have neighbours who have done it.

1. It is very expensive.
2 It requires the window sills to be moved out and distorts the appearance of the house.
3. The houses are unbearable hot in Summer.
4. It is easily damaged. The plaster skin can be easily broken. A wheelbarrow hitting off it will break it.
5. It is a relatively new process and it is not known what adverse effects may manifest themselves long term.

I think that insulation has become a fetish. If some insulation is a good thing then more must be better. Like food this is not necessarily the case.

Outkast_IRE · 28-09-2012 01:04PM

Milk & Honey wrote: »

I think external house insulation is horrible. i have neighbours who have done it.

1. It is very expensive.
2 It requires the window sills to be moved out and distorts the appearance of the house.
3. The houses are unbearable hot in Summer.
4. It is easily damaged. The plaster skin can be easily broken. A wheelbarrow hitting off it will break it.
5. It is a relatively new process and it is not known what adverse effects may manifest themselves long term.

I think that insulation has become a fetish. If some insulation is a good thing then more must be better. Like food this is not necessarily the case.

Insulation isnt a fetish , its a way to reduce energy costs, granted i will agress with you that sometimes the work done isnt "perfect" but there are many different options .

Also externally insulated houses arent unbearable in the summer, the insulation will help keep the heat gains from the sun out. The only major gains you will get is from large south facing windows and thats a whole other story.

Penny Dreadful · 28-09-2012 01:11PM

Outkast_IRE wrote: »

Insulation isnt a fetish , its a way to reduce energy costs, granted i will agress with you that sometimes the work done isnt "perfect" but there are many different options .

Also externally insulated houses arent unbearable in the summer, the insulation will help keep the heat gains from the sun out. The only major gains you will get is from large south facing windows and thats a whole other story.

Totally agree.

My parents got the external insulation done on their house a couple of years ago (the summer period between the two bad winters we had back to back) and it has made such a big difference I can hardly believe it.
The house looks different on the outside yes but this as a price for a much warmer more comfortable home in which to live is well worth paying.
They have dramatically reduced their oil bills and have never once regretted getting the work done.

dory · 28-09-2012 01:25PM

I think it's generally accepted that external is better, but it wasn't an option for my house for many reasons. Against some people's wishes I went with internal and it has completely changed my home. I only got it done a year ago so can't talk about long term effects, and to be honest in the long term I plan to knock the house and rebuild. But for now, it was a cheaper and easier option. My house is way warmer than before.

murphaph · 28-09-2012 02:38PM

dory wrote: »

I think it's generally accepted that external is better, but it wasn't an option for my house for many reasons. Against some people's wishes I went with internal and it has completely changed my home. I only got it done a year ago so can't talk about long term effects, and to be honest in the long term I plan to knock the house and rebuild. But for now, it was a cheaper and easier option. My house is way warmer than before.

If done properly with all the precautions against mould taken then it will certainly improve the energy efficiency of the property. Glad it has worked for you!

One option to internally insulate onto block walls (at least here in Germany) is to use Autoclaved aerated concrete blocks (perhaps 4 inches thick) which are stuck on to the inside of the walls with special adhesive and skimmed over.

The advantage is that the blocks (which are made of normal portland cement which has been manufactured in such a way as it contains 80% air by volume) function as the insulating material, but at the same time can absorb moisture from the air (in a bedroom at night for example) and release it back steadily during the following day.

You are effectively incresing the mass of masonry in the walls but at the same time adding an insulant. This material is used to build entire houses here and they require little to no extra insulation once built.

Not sure if this material is even available in Ireland. Brand names would include Ytong.

dudmis · 28-09-2012 07:49PM

thanks for all the replys.

i didn't realise that most people believe external to be best. i've seen it on a couple of houses and really didn't like hte look or feel of it. it was just like painted polystyrene - is this always the case, or can you plaster over it to give a nicer finish?

murphaph · 28-09-2012 08:20PM

dudmis wrote: »

thanks for all the replys.

i didn't realise that most people believe external to be best. i've seen it on a couple of houses and really didn't like hte look or feel of it. it was just like painted polystyrene - is this always the case, or can you plaster over it to give a nicer finish?

It should always be rendered/plastered to give it a weatherproof finish ready for painting. I've never seen anyone not do this. They stick the polystyrene panels onto the wall with adhesive/mushrooms and then render, including a mesh which gets embedded into the render to give it more integrity.

You know a house has been "done" alright and to some people it may look "weird" but to me I immediately think $$$ saved on energy and a more comfortable home all year round.

maddragon · 28-09-2012 08:31PM

I have seen houses where the external insulation and finish improved the appearance of the house immeasurably. As murphaph said, external is always better where practical because it eliminates cold bridging and of course if you are living in the house there will be no disruption to your life. Also it is easy to add 120-150mm externally whereas internally you would lose alot of space in the rooms if you added that much insulation.

dudmis · 28-09-2012 08:39PM

thanks.

i think i'll have to take a visit around the town to see other examples - obviously the ones i've seen weren't the best!

ynotonavillus · 29-09-2012 11:13PM

External is without doubt the best.

The existing concrete acts as a thermal store and the insulation keeps the cold away from it.

I had a place in France built in this manner, 400 watts of electric heater kept the place cosy in minus 10C., took two days to get the concrete warm, whenever we arrived at Christmas but then toasty warm once minimal heating was left on.

germack3 · 30-09-2012 07:16PM

my personal opinion is why let the heat out to the external before heating the house dry line with insulated plaster board keep the heat in and get it instantly, I live in a timber frame house and my wife would never live in a block house.

GreeBo · 30-09-2012 07:24PM

germack3 wrote: »

my personal opinion is why let the heat out to the external before heating the house dry line with insulated plaster board keep the heat in and get it instantly, I live in a timber frame house and my wife would never live in a block house.

If you are keeping the heat from the concrete heat store then as soon as someone opens an external door the heat is instantly lost as all you have is hot air.
If you externally insulate then you have hot air and after a couple of days a house that acts like a storage heater, meaning it takes far less time and energy to reheat the air. Also the thermal bridging issue with internal only is massive.

Bigcheeze · 30-09-2012 08:21PM

How much does external cost on say a 2000sq ft detached house?

does it look weird on semis or terraced houses where the insulated house will be jutting out an extra foot?

germack3 · 01-10-2012 08:26AM

my preference when I turn on the heat I get heat, not wait to heat up a block wall first to allow it to radiate back, I keep an eye on my heat oil bill. last fill, which was not because the tank was empty, was 760 last top up was 14 months previously. There is arguments to and for, and each argument could be valid for the person putting the argument forward. I spent 17 years in U.S. large majority of their houses are timber frame, 80% of a country can’t be wrong…..

murphaph · 01-10-2012 08:12PM

germack3 wrote: »

my preference when I turn on the heat I get heat, not wait to heat up a block wall first to allow it to radiate back, I keep an eye on my heat oil bill. last fill, which was not because the tank was empty, was 760 last top up was 14 months previously. There is arguments to and for, and each argument could be valid for the person putting the argument forward. I spent 17 years in U.S. large majority of their houses are timber frame, 80% of a country can’t be wrong…..

80% of that country?

Seriously though, you're right, there are pros and cons for almost everything. I wouldn't look at the US and assume that because they primarily build timber frame, that it means it's "better". It's traditional there to build timber frame, like block is in Ireland, so the skills are there so they keep building that way.

Most americans I know here however consider american houses to be, well, sh!t, compared to the homes they live in here

I certainly wouldn't take a house from southern California and plonk it in the midlands and expect it to last beyond a couple of decades without heavy maintenance. The climate is just too damp.

Nermal · 01-10-2012 08:17PM

If you may get external some years in the future, should you purposely AVOID doing internal now?

flintash · 01-10-2012 09:41PM

germack3 wrote: »

my preference when I turn on the heat I get heat, not wait to heat up a block wall first to allow it to radiate back, I keep an eye on my heat oil bill. last fill, which was not because the tank was empty, was 760 last top up was 14 months previously. There is arguments to and for, and each argument could be valid for the person putting the argument forward. I spent 17 years in U.S. large majority of their houses are timber frame, 80% of a country can’t be wrong…..

Though I keep an eye on temperature and humidity. My familys health is most important.
I def go for external insulation. Never seen advantage of internal- well apart from cheapo part.

murphaph · 01-10-2012 10:44PM

Nermal wrote: »

If you may get external some years in the future, should you purposely AVOID doing internal now?

If it's in the not too distant future then there's no benefit and I'd avoid.

Internal is very disruptive remember-you have to completely redecorate and you lose living space to boot. With external, you don't!

ted1 · 01-10-2012 10:49PM

germack3 wrote: »

. I spent 17 years in U.S. large majority of their houses are timber frame, 80% of a country can’t be wrong…..

My kids know the story of the 3 little piggies and would never stay in a wooden house, they get blown down.

If I didn't turn on my heating I'd have a low bill too. Unless everybody is heating there home to the same temperature and the house is the same size, you can't make comparasions

Interval vs external house insulation - which is best?

Comments