Possibly a bonkers idea - cavity wall insulation

[Joeboy]

I like option 3 done to the max and wonder if there are any financial sourcing shuffling can be done to reduce the final chimney sum?

I take it an aerogel solution doesn't get it done either?

I looked at aerogel as it was suggest to me by Smegal.

When we did the sums on it it didn't work out to be good enough on the U-value score to be thin enough for IWI and the costs were eye watering per m2.

I think there are a few areas that I can look at to reduce the cost, such as the skips .... going for a grab lorry instead. Materials are about as cheap as I can get but I might be able to push the builders merchant for a discount given that I have already spent a ton of money with them.

Labour is as cheap as I think I am going to get it .... which only really leaves the scaffolding which I am not sure how to get cheaper .... but will keep digging.

Thanks for the thoughts

Fair enough. The external insulation and render is where I personally would go after digging into it for longevity. Anyone local who has installed for decades, maybe see some of their older works for wear?

[Joeboy]

You can't combine option 1 & 2 to save dimension? Too dear?

All 3 options allow wall to breathe?

[cojmh]

To be fair, I was expecting the main objection to my option 3 (rebuild the wall) to be how can I consider taking down the outer wall on a cavity wall that is 2 stories high plus roof. Would this be a structurally sound thing to do to a house.

I guess it might not be as bonkers as I initially thought as to be honest that was the bit that worried me the most!

Personally I feel.thats a question for the architect. Why is it your going to these extremes. What's the endgame?

I ask as it must be quite something? I'm sorry to hear that you are being forced by the local council to these extremes.

Architect is didn't seem to bat an eyelid but I suspect this is more for the structural engineer (whom I am trying to get hold of)

The thing is that we are happy in our house and I have spent 10 years improving the house to the point that we have most of what we want (and we own the house next door which we rent out - my builder is my tenant too!) and we are in the catchment area for one of the best schools (grammar school) in Birmingham so the children are sorted ..... so don't really want to move.

We have needed to create a ground floor bedroom and wet room for my mother-in-law who has lived with us for nearly 10 years since having a very serious stroke and is now getting to the point mobility is an issue - our current facilities are not ideal (they never were but we used to be able to make it work). This is the reason that internal space is so critical if she ends up in a wheel chair permanently, so we need to ensure we have as much space as possible - hence IWI becomes an issue if it is too thick. We have gone to lots of lengths to remove fixtures from the smaller rooms (like radiators and switch to under floor heating) simply because they get rid of obstacles. Doors slide in to walls,

The second phase of the work is to open up the rest of the living area to make it open plan and again wheel chair friendly (plus I like more open plan spaces anyway) - which also includes a modest extension.

So as a result of needing to rebuild part of the front the house (the garage protruded at the front of the house) and the small extension at the back we come under new build/extension rules and hence the strict U-value.

However all that being said both the architect and building control are aware of why we are doing what we are doing and have bent over backwards to assist and advise where possible - but they have to stick to the overall rules set by the government for building regulations.

So that is where we are at and also the why .....

Hopefully it makes sense

[cojmh]

You can't combine option 1 & 2 to save dimension? Too dear?

All 3 options allow wall to breathe?

The problem with trying to combine options is that you end up with a more insulation everywhere - I cannot get my head around it fully and I know Nora said that insulation effect is on a logarithmic scale .... but by having brick in the middle the numbers seem to change and you end up needing more overall.

For example when I asked the question of the architect about combining options this was the results:

With a 70mm cavity you could fill it with 60mm PIR insulation and then 40mm insulation +12.5mm plasterboard on the inner side of the blockwork. This would achieve a U-value of 0.17 W/m2K, as per the calculations of Celotex.

But to fill the wall with PIR (with a 10mm air gap) I would have to remove the outer bricks anyway .... so why not just make it bigger and stick all the insulation in the cavity.

There do not seem to be any calculators that I have found that allow you to model EWI, cavity and IWI as a complete system. So I think some of my problems lie here.

With respect to the breathing - my understanding is that PIR does not allow air to permeate it so the outer course of bricks would breath out to the environment and the inner bricks would have to breath inwards to the house.... but again I could be wrong.

[cojmh]

Another, maybe daft suggestion at first glance, but can you not use that multi multi layer foil stuff used in roof constructions, but on a vertical stud frame? Am most certainly no expert on building regs nor insulation, but if good enough for roofs, maybe it may be possible to use 'the other way up' as such - even in duplicate layers?

I'll get my coat

unfortunately not .... I think it is only considered acceptable in parts of the house that are not inhabited hence why it is mainly used in lofts (I have used it in my loft too)

[Joeboy]

To be fair, I was expecting the main objection to my option 3 (rebuild the wall) to be how can I consider taking down the outer wall on a cavity wall that is 2 stories high plus roof. Would this be a structurally sound thing to do to a house.

I guess it might not be as bonkers as I initially thought as to be honest that was the bit that worried me the most!

Personally I feel.thats a question for the architect. Why is it your going to these extremes. What's the endgame?

I ask as it must be quite something? I'm sorry to hear that you are being forced by the local council to these extremes.

Architect is didn't seem to bat an eyelid but I suspect this is more for the structural engineer (whom I am trying to get hold of)

The thing is that we are happy in our house and I have spent 10 years improving the house to the point that we have most of what we want (and we own the house next door which we rent out - my builder is my tenant too!) and we are in the catchment area for one of the best schools (grammar school) in Birmingham so the children are sorted ..... so don't really want to move.

We have needed to create a ground floor bedroom and wet room for my mother-in-law who has lived with us for nearly 10 years since having a very serious stroke and is now getting to the point mobility is an issue - our current facilities are not ideal (they never were but we used to be able to make it work). This is the reason that internal space is so critical if she ends up in a wheel chair permanently, so we need to ensure we have as much space as possible - hence IWI becomes an issue if it is too thick. We have gone to lots of lengths to remove fixtures from the smaller rooms (like radiators and switch to under floor heating) simply because they get rid of obstacles. Doors slide in to walls,

The second phase of the work is to open up the rest of the living area to make it open plan and again wheel chair friendly (plus I like more open plan spaces anyway) - which also includes a modest extension.

So as a result of needing to rebuild part of the front the house (the garage protruded at the front of the house) and the small extension at the back we come under new build/extension rules and hence the strict U-value.

However all that being said both the architect and building control are aware of why we are doing what we are doing and have bent over backwards to assist and advise where possible - but they have to stick to the overall rules set by the government for building regulations.

So that is where we are at and also the why .....

Hopefully it makes sense

It does indeed make sense. It would be option 2 for me I think. I had a quick look on Google and there are companies out there who have been installing for 35+ years.

That would give me some confidence in the external systems?


https://acwhyte.co.uk/services/external ... nsulation/

You're a good man doing all that for your MIL.

[spread-tee]

It's not so hard to achieve .18 U value and I wouldn't fear the building control fellows, as long as you have a build up plan for the wall with its calculated value, and s/he can see you have built it according to the plan they will sign it off whoever does it.

PP is your problem if they do insist on brick slips but have you queried whether PP may be granted with a rendered finish, sometimes the duty PP dept officer will drop pretty big hints. Also as it would not be a material change of plan you could apply for a rendered finish and if they do object submit an amendment, your architect should be able to advise also..

It's an interesting one.

ATB

Desp

[cojmh]

It does indeed make sense. It would be option 2 for me I think. I had a quick look on Google and there are companies out there who have been installing for 35+ years.

That would give me some confidence in the external systems?


https://acwhyte.co.uk/services/external ... nsulation/

You're a good man doing all that for your MIL.

Thank you for your kind words,

I do have some confidence in the external wall insulation systems .... where my confidence falters a little is the application and installation by someone I don't know even if they are qualified. Who knows in 30 years I might still have the house and don't want to do it again!

My line of thought is yes it is more (by about 15%) but I know the people doing the building work and I can see if it is done properly more easily and once it is done it is done. If they do change the rules it will affect both installations.

I need to do a bit more digging (to see the current foundations) and wait on the structural engineer to give me a yes/no it is safe to do.

I will keep the thread updated if people are interested

[cojmh]

It's not so hard to achieve .18 U value and I wouldn't fear the building control fellows, as long as you have a build up plan for the wall with its calculated value, and s/he can see you have built it according to the plan they will sign it off whoever does it.

PP is your problem if they do insist on brick slips but have you queried whether PP may be granted with a rendered finish, sometimes the duty PP dept officer will drop pretty big hints. Also as it would not be a material change of plan you could apply for a rendered finish and if they do object submit an amendment, your architect should be able to advise also..

It's an interesting one.

ATB

Desp

That is true - despite everything I am on really good terms with the building control inspector.

Planning is a different ball game at the moment. Unfortunately due to the financial circumstances of Birmingham it is harder to get hold of people and the only route is email (that I can find). I have enquired by email and the response I got was:

Thank you for your email

I have contacted a Planning Officer for advice

The advice is that planning permission is required if it involves changing the external material of the building

I hope this is of assistance to you


I have double checked and although it is a grey area whether they mean actual material or the look of the material but the upshot is the same - I have to go brick slip as opposed to render unless I get planning permission.

In my planning application I spoke at length with the planning officer about what they would allow and not allow (as they were refusing one particular area despite other houses on my street having what I wanted) and the upshot was that the houses look relatively uniform in certain characteristics one was the brick work and the other was an area of vertical tile cladding on the front of the house. They would not allow anything that would significantly alter either of these points. The reason they would not allow me to have what the other two houses had was one was done 30 years ago and the planning scheme had changed since. The other house was done without planning so whilst they get to keep it (older than 7 years) - I am not allowed.

One house on the street has gone with render - but they have done so without planning permission and I have a nasty feeling if I start pushing the point they will taken to task (as it was only done 4 years ago).

So I have come to the conclusion that brick slip is the EWI approach I can take, most other routes seem to be deadends.

Hope that makes sense and thanks for your thoughts.

[resybaby]

Echo Joeboys comments about going through all this for the MIL, mine would have to put up with a cabin in the garden at best !

Very interesting thread (ex-Silhillian myself) and all adds to the grey cell exercises