# Internal Insulation - Very limited space!



## CBGB (23 Dec 2009)

Hi

I have a house cavity block walls and zero insulation and I want to get them up to a reasonable U-value. The usual options for internally insulating that I hear about is attaching studs and insulate between with fibre glass and plasterboard outside.However our floor space is TINY. So, I have to internally insulate (cant do external) but have no space. Is there a product out there that can be used in this sort of structure that has such a good k-value that it will only need minimum thickness to get good results? 
Does anyone have any recommended products for this option? I have heard of some aerospace insulations but not sure of their application. 
Any help would be appreciated.


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## buyingabroad (23 Dec 2009)

[broken link removed]

Very expensive though


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## onq (23 Dec 2009)

CBGB said:


> Hi
> 
> I have a house cavity block walls and zero insulation and I want to get them up to a reasonable U-value. The usual options for internally insulating that I hear about is attaching studs and insulate between with fibre glass and plasterboard outside.However our floor space is TINY. So, I have to internally insulate (cant do external) but have no space. Is there a product out there that can be used in this sort of structure that has such a good k-value that it will only need minimum thickness to get good results?
> Does anyone have any recommended products for this option? I have heard of some aerospace insulations but not sure of their application.
> Any help would be appreciated.



Haven't done hi-tech insulation myself and happy to stand corrected.

This makes no sense on first reading - where's your imperative - tiny spaces cost the least to heat.
Also I fail to understand why can't you do external - and of course party walls don't need to be insulated.

Hi-tech internal solutions can end up "freezing" the wall behind them and you can get condensation forming on the inner face of the outer wall of the building.
You may have to adopt a hi-tech sealing solution with vapour check to minimise water vapour reaching the cold wall.
You may also need an MVHR system to lower the RH/level water vapour within the space.

At least, that's the impression I get from reading problem pages.
Ictis [sp?] is one of the materials I have heard about but I also heard there may have bene certification issues in England.
I certainly don't advise basing your choice in thermal performance alone as this can be a two-edged sword if you fail to consider vapour checking and ventilation as well.

ONQ.

[broken link removed]


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## 3CC (23 Dec 2009)

Hi ONQ,

I have seen some of your posts before and you seem to know a bit about this area.

Given that both internal and external insulation have their drawbacks,have you any comments on the idea of mounting internal insulation on battens with a 25mm ventilated cavity between the wall and the insulation.

Of course every effort should also be made to vapour check as well and there is a loss of performance due the fact that you would have to ignore the existing wall in terms of insulation.

Would be interesed in your thoughts.

Thanks 

3CC


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## onq (24 Dec 2009)

3CC said:


> Hi ONQ,
> 
> I have seen some of your posts before and you seem to know a bit about this area.
> 
> ...



Hi 3CC,

<bows>

Thank you for your vote of confidence.

Don't take any one person's word for it - including mine - check different opinions.

That having been said, lets review some options first.

Yes you can do this, the problem is the venting.

Use of vented cavities:

 Vented cavities are best located on the cold side [outside] of the insulation.
This is the basis for the timber frame cavity detail.

 A one way breather paper allows water vapour to pass through.
 Moisture condensing on the outer face cannot pass back in.

 The cavity is vented to aid evaporation and carry it away.
It is vented top and bottom to encourage ventilation.
The cavity runs from below Gd Floor DPM to Eaves.

All ope and penetration passing through it are firesealed.

In relation to what I understand your suggestion to be:

You cannot ventilate an internal cavity between the masonry wall and the insulation unless you; -

A) vent it back into the room which defeats the purpose.
[Venting like this removes any vapour checking action but see Note: 1 below.]

B) vent it with supply air naturally
[if cold, this will reduce the effectiveness of ordinary quilted insulation]

C vent it with MVHR supply air
[pointless exercise as venting the room would be better]

Note: 1

I've seen Option A) used to deal with dry rot in older buildings - by preventing a build up of humidity within the structure.
That is a special case and the insulation may be located differently, i.e. there may be none, just plaster board on battens

A variation exists for new construction where variable vapour membranes can allow interstitial moisture that's built up back into the room to be vented away in certain conditions. Joseph Little Archtiects has written about this on Construct Ireland.

I don'trecommend internal cavities as you describe - they can become routes for cold smoke and gases to reach a sleeping occupancy and such require to be carefully sealed at floors, ceilings, penetrations and around opes [doors, windows, room vents] etc.

Battening out and filling with fibreglass doesn't help - filling with Rockwool may add to the fire resistance of a stud, but it still has to be sealed as noted above.

This can be achieved using timber stud members or continuous dabs of plasterboard in the locations noted, but the junction of the ceiling and wall needs special attention regardless.
Seal that properly [and any ceiling penetrations] and smoke will find it hard find its way up to the bedrooms.
In an ordinary house it will still get out the room door, but that will pass by and activate the fire alarm.
The important thing is that people don't die in their sleep from toxic fumes and smoke before this.

Kingspan do a reasonably simple mechanical fixed warmboard with integral vapour check - flat to the wall, no cavity.
The danger with the warmboard is that there are no frame members or plaster dabs-
This means that the junction between block and ceiling plaster must be carefully sealed.

In all proposed solutions You have to think through the detail in section - floor, walls, roof.
 This will identify any discontinunity in the vapour check, insulation or vented cavity.
It will help identify any lack of fire sealing at walls, floor ceilings and penetrations.

A note on condensation also; -

Thermal and humidity gradients across internal spaces and external envelope are what gives rise to condensation.
Warm air absorbs moisture in the kitchen [say] and wanders through the house until it finds a surface that is RELATIVELY cold enough for that heavily laden air to deposit its moisture on.

Consider this if not using your extractor fans in the bathroom, kitchen or utility.

It is also useful whatever detail you use to ensure low level heat is maintained even in bedrooms during the day.
This will help avoid condensation on walls but also on the cold [outer] face of the insulation if internal insulation is used.
This hidden condensation on the inner face of outer walls behind the internal insulation may dissipate but heat helps this process.

So <takes deep breath> you can see that insulation, ventilation and protection of occupants from fire are all interlinked, even in relatively simple buildings like traditional houses.

Its why I keep telling people to talk to professionals.



ONQ.

[broken link removed]


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## 3CC (26 Dec 2009)

Hi ONQ,

Thanks for a detailed and thorough reply.

To clarify, my suggestion is to use Kingspan type rigid board insulation for internal insulation on a hollow block semi detatched house. The insulation would be 100mm thick attached to 25mm thick treated battens. I accept that great care needs to be taken to prevent vapour getting past the joints at the board/board interfaces and the board/joist interfaces (more difficult). As a belt and braces approach, I wondered at the sense in having the 25mm cavity ventilated with external cold air. This would be done at first floor level by opening the cavity into the attic space at the top and by using 50mm holes through the hollow block at the bottom. The vent holes to be sleeved with PVC tubes, sloped outwards and incorporate fly screens etc.

Similar ventilation of the cavity at ground floor level could be achieved with vents at the top and opening the cavity to below the suspended ground floor at the bottom.

The reason for the query is that I think internal insulation is often knocked on the basis of the potential for interstitial condensation. It would be nice if there was a relatively practical way of reducing this risk to an acceptable level.

Thanks,

3CC


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## onq (26 Dec 2009)

3CC said:


> Hi ONQ,
> 
> Thanks for a detailed and thorough reply.
> 
> ...



Hi 3CC

I think you're going to create a cold, damp cavity inside the house.
I think you'll compromise the insulation with convection currents.
Damp air will end upcoming in contact with plaster and timber.
I think it will be difficult to seal this cavity from the house.
I think it will tend to create expensive fire-break details.
This is just my common sense reaction to this detail
I have no empirical studies done to back this up.

ONQ.

[broken link removed]


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## 3CC (27 Dec 2009)

Fair enough ONQ. I appreciate your opinion. Your points are very valid.

The reason for my trying to make internal insulation work is that I have seen Ext Ins done by what I would regard as one of the more reputable insulation contractors and it seems to have a lot of drawbacks, such as:

- Difficult to get a good continuity of insulation at the eaves and still maintain ventilation path to the attic.
- Difficult to close the cold bridge at ground level without excessive cost of removing footpaths etc.
- In a semi-d, no real solution to the cold bridge at the party wall.
- In the example I saw of EI, the soil and rain water pipes were buried in the insulation. This reduced or removed the insulation locally depending on the pipe diameter. ( I really thought this was poor detailing.)
- In hollow block, I presume the voids in the blocks tend to form a vertical uninterrupted corridor when laid in stretcher bond. If there is any gaps at the wall plate or in the joints below floor level, this can set up a convection current inside the insulation which is bad. Same result as thermal looping for poorly fitted cavity insulation.
- Personally, for a house that is not oriented for solar gain, I imagine that low thermal mass is preferable (quicker heat up time).

I have to admit that I am not expert on all of this but this is the opinion I have come to. Would you agree with any of the above?

Thanks,

3CC.


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## onq (27 Dec 2009)

3CC,

You have obviously considered some of the drawbacks of external insulation.
There are some problems e.g. downpipes, which I agree can be awkward.
Other issues can include; -

restricting opening window action when insulating reveals
extending sills to thrown off water [75mm overhang]
extending steps at thresholds
You have already mentioned the difficulty of avoiding cold bridges at the eaves.

However...

I'm assuming this is not modern house construction we're talking about here.
If so, the object of the exercise is to minimise heat loss in an overall sense.

As the insulation is applied outside a relatively massive construction this will tend to fudge local heat losses - there should be few real cold "spots".
Where a risk exists - such as at downpipes a relatively small amount of hi-tech foil insulation behind the pipes might resolve it.

There are several firms offering in-house solutions to the eaves problem.
Its basically similar to any eaves vent with insulation and an air gap.

There are also firms offering solutions to the window sill detail.

Can I point you towards http://www.ecofix.ie/ for a minute.

I'm not affiliated to them, nor have I direct experience of them, but they answered all my questions at Plan Expo 2009 in November.

The main bugbears were windows and the ground floor.
We agreed that externally insulating at the same time as replacing the windows would be useful.
With the ground floor extending the insulation to ground level was the best compromise.

Regardless of the location of the wall insulation, you may have to consider insulating the ground floor itself.
This could best be done as part of a package when putting in after-market underfloor heating.
This will reduce ceiling levels, raise your floor levels and require all the ground floor doors and steps to be adjusted to suit.
As a perfectionist you also need to consider your last step on your stairs.
This is difficult to resolve and may involve a chat with your local building control officer.

In a semi- D the party wall used to be assumed to be insulated because its an internal wall, unless the adjoining house is vacant.
If it is, or you're a perfectionist, you could consider using HD insulation board with a plaster finish mech-fixed [no cavity - again ] on the room faces, with Rockwool at first floor level.

When its cold;
Internal insulation with low thermal mass does lead to quicker warm up times.
This is only a concern with a house which gets cold every so often and your new insulation should mitigate against this and make it affordable to maintain a low level of heat on constantly.
Under floor heating works most efficiently leaving it on at low level all the time.
Condensation around the house is avoided with some low level of heat in the bedrooms and hall all the time.

After this the house will be so well insulated, relatively speaking, that your main problems will be draughts from window glass and poor sealing.
This opens the whole question of sealing, BER assessment and blower tests.
Again at Plan Expo 2009, some surprisingly good figures for wall sealing were discovered in 1950-1960s houses with wet plaster internal wall finishes [not boards.
Assuming replacement windows were properly fitted, the blower test may surprise you.

Except for the wall vents and chimney, which then raises the question of whether to go for the MVHR system or not.
Over to you but avoid breaching the 1st floor FR30 fire resistance.
Also avoid short circuiting the supply and vent air flows.

That just leaves the appearance any planning issues.
Some may consider this minor and some planners may not.
This partly depends on the design of the house and existing finish.
Again you need to talk to the local authority - this time with the planner.

HTH

ONQ

[broken link removed]


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## CBGB (12 Aug 2010)

So should I take it from this that the number of contractors out there that can do internal insulation correctly is not as great as the number of fliers and advertisements I see floating about.  Have to say that its very scary to hear the level of detail needed when you get every person who can hang some plasterboard telling you they can do a great job of drylining. 

For the amount of risks associated with both internal and external would I be better off upgrading windows and doors (20 - 30% heat loss) the ceiling insulations (20 -30%) and other areas (chimney etc) and see if this works before risking the structure of the building with either internal or external?


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