Exterior V's Interior Insulating

TimeonmyHands

I've received approval for the grant scheme to insulate my house. The current insultation in my cavity wall is yellow fiber glass insulation and have been advised that further insulating the cavity wall will be of no benefit.

My question is which is more benefical for reducing the cost of heating fuel usage. I've been advised by friends that to insulate the interior walls as opposed to the exterior walls is the most cost efficient as no heating fuel will be lost to heating the interior cement brick. I've queried this with contractors but have not received a plausable reply.

At the end of the day, I obviously want the BER Certificate which will give me the highest rating.

Any advice would be greatly appreciated.

zuroph

wrong forum, try the construction forums, theres even a BER specific forum.

http://boards.ie/vbulletin/forumdisplay.php?f=1162

TimeonmyHands

Thanks Zuroph...A mod may be able to move it to the correct forum for me?

Builderfromhell

Briefly and simply, externally insulating a cavity wall is a wste of money for reasons others on the construction forum can explain. Externally insulating a solid wall is a great idea.
Internally insulating, unless done properly, can lead to mould growth behind the new interior insulation. This system, although grant approved in Ireland, is outlawed in most of Europe for health reasons.
There are many threads on this subject on ; http://www.boards.ie/vbulletin/forumdisplay.php?f=876

TimeonmyHands

"Internally insulating, unless done properly, can lead to mould growth behind the new interior insulation"

Builderfromhell can you suggest anyone who would do a proper job on "internally insulating"?

billy the squid

Moved from Limerick City

Please read the charter for the BER forum before posting, as it may have different rules to the Limerick City forum

d'Oracle

First up, I think ruling out internal insulation based on such little information isn't a great idea.

It can cause mould growth, but this is not always the case and is dependant more on external factors. There are horror stories associated with poor EWI too.
If other European countries jumped off a cliff, would that make it a good idea?

To address your friends comment about heating the walls, while its not nonsense, it demonstrates a lack of understanding of the issue.

An externally insulated wall with the cavity closed will be of "high thermal mass". Which is fancy term to say it absorbs a lot of heat. Because it is insulated on the outside, this heat will radiate back into your house. It means that your house will take longer to heat from cold, but will also stay warm for longer.

The Internal insulation however will lower the "thermal mass" of the wall.
This means that the room will warm quicker, but also cool quicker.

The rule of thumb would be if you spend a lot of time in the house (say kids and parent at home all day) higher T.M. is ideal.
If the house spends a lot of time empty, (e.g. Working couple with long commute) lower T.M. may be beneficial.

In terms of fuel usage the grant terms stipulate roughly equal performance.

GreenTech

While all of the above points are valid I think your best bet is to have somebody run a 'condensation risk analysis'. This basically tells you if there is a risk of condensation by insulating internally and with what products. The risk of condensation and ultimately mould growth is definitely real and shoul not be taken lightly. WUFI software is one of the packages used to generate this information. Good luck with it and hope it turns out well for you!

dunie001

Some good reasons to avoid Internal insulation:

1.you have to remove and refit everything on the internal face of external walls (radiators, kitchens,skirting boards,paint,tiles etc). make sure that this cost is included in any quotes from builders.

2. reduces thermal mass considerably. meaning that your house will lose heat a lot faster.

3. you will reduce the size of the rooms of the house by up to 150mm (2 x 75mm) if two walls of a room are external.

4. mould may not be an issue with cavity walls as there will be no rising damp of penetrating damp in the wall anyway. mould is usually only an issue if the wall is solid.

5. serious distruption to the inside of your house will be inevitable.


Reasons to go for external insulation:

1. no distruption whatsoever to the inside of the house.
2. does not reduce size of rooms.
3. thermal mass is not affected.
4. far more insulation can be applied (drylining is typically 75mm if lucky when battons and plasterboard is used, external can be as much as twice that)

GreenTech

Dunie,

Although I totally agree with extrenally insulating a building I don't think that your reasons for not drylining are entirely accurate. Points 1., 3., and 5. are very valid points as the disruption caused by external insulation are minimal.
You may just have misworded point 2. in your reasons to avoid drylining. I dont think by adding insulation it could possibly mean the house loses heat quicker! The house loses heat at a slower rate due to being insulated of course, but the fabric of the building does not allow the temperature to be maintained for long periods due to the low thermal mass. High thermal mass means your structure retains heat and releases it slowly but it also means that the repsonse time for your heating is slower as you must raise the fabric temeprature of the building as well as the air temperature. For instance if you go away on holidays your house may be unheated for 2-3 weeks and would take much longer to reheat if it has high thermal mass. Both have their pros and cons.

Mould growth is more often caused by interstitial condensation rather than rising damp. This can occur when you insulate internally due to the fact that the dew point within the wall moves to the inner face of the structural wall as you are cooling the wall. Another issue is that solid walls allow a certain amount of moisture into the stucture. Heat pasing throught the wall from inside to outside allows the wall to dry to the outside. Dry lining slows the drying out process and the walls can become saturated to the point that the water actually reaches the inner face of the structure. (This drying out is also a reason not to replace lime render on a solid wall with sand cement render, as lime based renders are breathable and allow mositure to escape from a structure. Sand cement render is not breathable - another days story ... maybe! )

Don't forget to consider the planning implications when rendering externally - if it is deemed a material change of you may require planning permission

dunie001 wrote: »

Some good reasons to avoid Internal insulation:

1.you have to remove and refit everything on the internal face of external walls (radiators, kitchens,skirting boards,paint,tiles etc). make sure that this cost is included in any quotes from builders.

2. reduces thermal mass considerably. meaning that your house will lose heat a lot faster.

3. you will reduce the size of the rooms of the house by up to 150mm (2 x 75mm) if two walls of a room are external.

4. mould may not be an issue with cavity walls as there will be no rising damp of penetrating damp in the wall anyway. mould is usually only an issue if the wall is solid.

5. serious distruption to the inside of your house will be inevitable.


Reasons to go for external insulation:

1. no distruption whatsoever to the inside of the house.
2. does not reduce size of rooms.
3. thermal mass is not affected.
4. far more insulation can be applied (drylining is typically 75mm if lucky when battons and plasterboard is used, external can be as much as twice that)

d'Oracle

dunie001 wrote: »

Some good reasons to avoid Internal insulation:

1.you have to remove and refit everything on the internal face of external walls (radiators, kitchens,skirting boards,paint,tiles etc). make sure that this cost is included in any quotes from builders.

2. reduces thermal mass considerably. meaning that your house will lose heat a lot faster.

3. you will reduce the size of the rooms of the house by up to 150mm (2 x 75mm) if two walls of a room are external.

4. mould may not be an issue with cavity walls as there will be no rising damp of penetrating damp in the wall anyway. mould is usually only an issue if the wall is solid.

5. serious distruption to the inside of your house will be inevitable.


Reasons to go for external insulation:

1. no distruption whatsoever to the inside of the house.
2. does not reduce size of rooms.
3. thermal mass is not affected.
4. far more insulation can be applied (drylining is typically 75mm if lucky when battons and plasterboard is used, external can be as much as twice that)

Point 2 is wrong.

Low thermal mass does not mean the house looses heat more quickly.
It means that the walls store less heat. This is not the same as loosing heat. In a dwelling which is intermittently occupied it is far preferable to have lower thermal mass walls as walls with high thermal mass take longer heat to a desired set point.

Incidentally Externally insulating does have an effect on the thermal mass of a wall. It has the effect of increasing the thermal mass of a wall, being that the wall the becomes a layer of material which is insulated on the outside, meaning the whole wall is counted towards the thermal mass.

Also the thickness of the insulant is largely irrelevant here, as internal insulation is usually a higher performance insulant such as Polyiso board (xtratherm, kingspan) where as with external uses thicker a layer of less effective material. As such it is possible (and indeed demanded by the terms of the grant) to achieve identical results with 60-75mm of internal as 100mm of external.

Edit: or what Green tech said.:)

Lantus

A few people are off the mark with regards to comments re thermal mass.

Basically internally insulating while an option isn't ideal. Like a previous poster stated you will make your house smaller and every socket, switch and fitting will have to moved. Windows will become more recessed slightly decreasing natural light. There can be issues with condensation subject to the contruction method and the existing house build. This occurs because there would now be a cooler temperature where the 'old' internal wall was and so a greater risk that water vapour occurs before it hits the vapour barrier. A spcialist should check this.

However, given the huge drawbacks to making your house much smaller it wouldn't really be a viable option in nearly all cases, unless you enjoy pain and suffering, decreased property value and wasting money.

Externally insulating is on the other hand fairly quick and painless. Solid board insulating panels are fixed and then rendered over.

The figures I have seen would indiacte that internal insulating can be as much as double the cost of external. Good luck either way.

magicbastarder

sorry for digging up an old thread, but my father was advised that exterior insulation was little use on house built from cavity block - the reason being that you lose the benefit of the thermal mass, as the warmth convects up through the cavity blocks themselves and is lost. was this accurate advice?

BryanF

magicbastarder wrote: »

sorry for digging up an old thread, but my father was advised that exterior insulation was little use on house built from cavity block - the reason being that you lose the benefit of the thermal mass, as the warmth convects up through the cavity blocks themselves and is lost. was this accurate advice?

Close top of blocks and continue insulation to overlap roof. Who was offering this advice?

Linto

We too are considering internal insulation on a hollow block wall for 2 main reasons: 1 cost of doing IWI is far less the External and 2) we are doing extensive renovations anyway so disruption is not a concern.

My question is, our builder is planning on dabbing the existing walls and putting the insulation board 75mm + 12mm plasterboard directly on the wall without a damp proof layer or battons. Is this okay?

goz83

Linto wrote: »

We too are considering internal insulation on a hollow block wall for 2 main reasons: 1 cost of doing IWI is far less the External and 2) we are doing extensive renovations anyway so disruption is not a concern.

My question is, our builder is planning on dabbing the existing walls and putting the insulation board 75mm + 12mm plasterboard directly on the wall without a damp proof layer or battons. Is this okay?

I'm not sure batons are necessary. They would also take away a significant amount of space, making it impossible to meet the regulations in some houses when it comes to stairway width, which must be 800mm minimum afaik.

My father in law did our IWI and put the foam boards right onto the walls, no battons, no damp proof layer that I know of and the difference during the winter was very noticeable. He also used the big plastic bolt things, rather than metal, because the metal ones can create cold spots on the wall.

Linto

goz83 wrote: »

I'm not sure batons are necessary. They would also take away a significant amount of space, making it impossible to meet the regulations in some houses when it comes to stairway width, which must be 800mm minimum afaik.

My father in law did our IWI and put the foam boards right onto the walls, no battons, no damp proof layer that I know of and the difference during the winter was very noticeable. He also used the big plastic bolt things, rather than metal, because the metal ones can create cold spots on the wall.

I certainly like the sound of that! Thanks for advice. Hope it works out.