Insulation Quandary!!!

[bighouseproblems]

So there are some people on here which have spent much longer than I have working out these things and would like your opinions.

This is the time old question which has been gone over a thousand times.......... However I want to throw in a dynamic variable into the equation.

 

So I have a solid wall property. Sandstone front-Solid Brick rear.

 

Insulation mockup is

 

1. Wood fibre board and lime plaster with airtightness tapes as best as possible.

2. Mineral Wool and Plasterboard with Cavity.

3. Mineral Wool and Plasterboard without Cavity.

4. Mineral Wool and Plasterboard with Cavity and vapour barrier.

5. Mineral Wool and Plasterboard without cavity and vapour barrier.

 

So the dynamic variable is as follows - I have just installed a wood burner and it is clear that since then the walls are dramatically dryer. on one side of the property. It is our intentions to install a rayburn on the other side thus having to forms of heat on both side walls. This may also increase to another burner in a third room downstairs. 

 

The point of this post is to establish whether this would mitigate the risk of interstitial condensation behind the insulation to the point of not requiring a vapour barrier which makes the process of insulation more complicated combined with fixings and punctures etc.

 

I am off to the googles to try and find some info on this but I was hopeful some clever people on here had been through this scenario and worked out some physics already.

 

****Wood Fibre and Lime would be my preference given a money no object approach however i have to balance the risk against cost if i can *****

[Temp]

Perhaps have a look at some of the options here..

 

https://www.greenspec.co.uk/building-design/internal-insulation/

 

 

 

 

[larry]

23 minutes ago, bighouseproblems said:

So there are some people on here which have spent much longer than I have working out these things and would like your opinions.

This is the time old question which has been gone over a thousand times.......... However I want to throw in a dynamic variable into the equation.

 

So I have a solid wall property. Sandstone front-Solid Brick rear.

 

Insulation mockup is

 

1. Wood fibre board and lime plaster with airtightness tapes as best as possible.

2. Mineral Wool and Plasterboard with Cavity.

3. Mineral Wool and Plasterboard without Cavity.

4. Mineral Wool and Plasterboard with Cavity and vapour barrier.

5. Mineral Wool and Plasterboard without cavity and vapour barrier.

 

So the dynamic variable is as follows - I have just installed a wood burner and it is clear that since then the walls are dramatically dryer. on one side of the property. It is our intentions to install a rayburn on the other side thus having to forms of heat on both side walls. This may also increase to another burner in a third room downstairs. 

 

The point of this post is to establish whether this would mitigate the risk of interstitial condensation behind the insulation to the point of not requiring a vapour barrier which makes the process of insulation more complicated combined with fixings and punctures etc.

 

I am off to the googles to try and find some info on this but I was hopeful some clever people on here had been through this scenario and worked out some physics already.

 

****Wood Fibre and Lime would be my preference given a money no object approach however i have to balance the risk against cost if i can *****

 

Two questions as I don't think these are your only variables:

 

Are your walls rendered or just solid brick/block?  And how thick - 9"? 

 

When you say 'dynamically dryer' since putting in the wood burner, what do you mean and how do you know? Was there evidence of a damp problem before? What's the venilation like in the house and are you likely to produce less/average/more than typical humidity (e.g. showers, drying clothes etc). 

[bighouseproblems]

7 minutes ago, Temp said:

Perhaps have a look at some of the options here..

 

https://www.greenspec.co.uk/building-design/internal-insulation/

 

 

 

 

Hi Temp,

 

Thanks for the link however I am aware of all the different buildup types. 

 

What I have not come across in my research is how a heat source directly warming the wall will play a part of the effects of condensation etc.

 

Regards

[Nickfromwales]

1 minute ago, bighouseproblems said:

Hi Temp,

 

Thanks for the link however I am aware of all the different buildup types. 

 

What I have not come across in my research is how a heat source directly warming the wall will play a part of the effects of condensation etc.

 

Regards

You should t find the two ever correlating, as you’d have to;

a) model with burner cold 24/7

or

b) model with burner lot 24/7. 
 

Design for the house to be u heated, accepting the heat sources as a bonus. You can’t media out interstitial condensation with internal heating as a variable 👎

[bighouseproblems]

1 minute ago, larry said:

 

Two questions as I don't think these are your only variables:

 

Are your walls rendered or just solid brick/block?  And how thick - 9"? 

 

When you say 'dynamically dryer' since putting in the wood burner, what do you mean and how do you know? Was there evidence of a damp problem before? What's the venilation like in the house and are you likely to produce less/average/more than typical humidity (e.g. showers, drying clothes etc). 

Solid Sandstone - Painted which will be removed

Solid Brick Rear - Painted which will be removed

 

Somewhere around 9Inch without measuring.

 

On the front wall the sandstone is wet through the winter months and dries out through summer. There is a missing section of paint which i look at everyday to see what it is doing. The wood burner has been running for 3-4 days now and it is almost bone dry. 

 

Ventilation is minimal but we open the back door around 30 times a day. We have hygrometers in every room and since installing triple glazing the humidity has dropped to around 40%, 50% at worst.

[larry]

4 minutes ago, larry said:

 

Two questions as I don't think these are your only variables:

 

Are your walls rendered or just solid brick/block?  And how thick - 9"? 

 

When you say 'dynamically dryer' since putting in the wood burner, what do you mean and how do you know? Was there evidence of a damp problem before? What's the venilation like in the house and are you likely to produce less/average/more than typical humidity (e.g. showers, drying clothes etc). 

Oh, and if you go without a vapour barrier, what do you plan to cover the plasterboard with? i.e. do you plan to simply tape and fill or are you covering the plasterboard face with.... gypsum? lime? something else? And paint?? I suspect the surface above the plasterboard could make a big difference to vapour permeability. 

[bighouseproblems]

1 minute ago, larry said:

Oh, and if you go without a vapour barrier, what do you plan to cover the plasterboard with? i.e. do you plan to simply tape and fill or are you covering the plasterboard face with.... gypsum? lime? something else? And paint?? I suspect the surface above the plasterboard could make a big difference to vapour permeability. 

The walls and ceilings would be plastered with gypsum thus creating an airtight barrier. 

 

Just to clarify i am not trying to reinvent the wheel or avoid using the correct products on a period property. 

as it stands woodfibre and lime plaster is the default.

I am simply playing devils advocate in my mind and exploring the potential drying of a heat source and would it mitigate the risks etc.

[larry]

3 minutes ago, bighouseproblems said:

Solid Sandstone - Painted which will be removed

Solid Brick Rear - Painted which will be removed

 

Somewhere around 9Inch without measuring.

 

On the front wall the sandstone is wet through the winter months and dries out through summer. There is a missing section of paint which i look at everyday to see what it is doing. The wood burner has been running for 3-4 days now and it is almost bone dry. 

 

Ventilation is minimal but we open the back door around 30 times a day. We have hygrometers in every room and since installing triple glazing the humidity has dropped to around 40%, 50% at worst.

 

How do you tell it is wet? By looking? Or do you have a damp meter? And presumably you mean from outside?  I'm just trying to differntiate between the walls getting damp outside from rain and the risk of interstital condensation depending on whether or not you have a vapour barrier. 

 

I have to say I don't think I can help your specific question about the specific impact of a burner, but it seems to me you've already at least half answered it if the wall is drying out...?

 

[nod]

If cost is a consideration lime plaster isn’t for you I buy and use a lot of lime plaster Clay works at £60 plus vat per bag soon Racks up 

[larry]

5 minutes ago, bighouseproblems said:

The walls and ceilings would be plastered with gypsum thus creating an airtight barrier. 

 

Just to clarify i am not trying to reinvent the wheel or avoid using the correct products on a period property. 

as it stands woodfibre and lime plaster is the default.

I am simply playing devils advocate in my mind and exploring the potential drying of a heat source and would it mitigate the risks etc.

 

Fair enough - nod has mentioned cost which is a consideration.

We have done wood fibre and lime plaster (and one room wood fibre flexi between battens with plasterboard) but the price has really rocketed up and I am also wondering about Rockwool between battens for the next room. It is breathable although of course doesn't buffer moisture in the way that wood fibre does. 

I worry most about the top surface though - seems to me you have to be quite careful if you are trying to keep things breathable, both with  the paint you use, and if you are using plasterboard, to avoid using PVA first. In my internal mental model you might as well be covering the wall with cling film. 

[Roger440]

I think you need to consider what you are doing here.

 

You have a sandstone wall, presumably with no DPC.

 

Your list of options includes both vapour premeable and non permeable. Given your wall build up, why are you considering a non permeable build up?

 

 

 

[bighouseproblems]

4 minutes ago, nod said:

If cost is a consideration lime plaster isn’t for you I buy and use a lot of lime plaster Clay works at £60 plus vat per bag soon Racks up 

Hi Nod,

 

If needs must then it will be Lime Plaster in all 8 rooms potentially on 16 external walls. I have estimated the cost will around £26K. 

If I can mitigate the risk then this cost will be significantly reduced of course. 

One issue I have with Vapour barrier is ensuring the work is done to the highest standard.

I would love to do the work myself but as it stands im not sure if i will have the time.

[bighouseproblems]

4 minutes ago, Roger440 said:

I think you need to consider what you are doing here.

 

You have a sandstone wall, presumably with no DPC.

 

Your list of options includes both vapour premeable and non permeable. Given your wall build up, why are you considering a non permeable build up?

 

 

 

Hi Roger,

 

As i said i know the right option, Just amusing my mind and wondering what research has been done into a good heat source in a wall and the impacts of them. 

[Roger440]

1 minute ago, bighouseproblems said:

Hi Roger,

 

As i said i know the right option, Just amusing my mind and wondering what research has been done into a good heat source in a wall and the impacts of them. 

Are you sure.?in your previous posts you talk about vapour barriers.................................

[jayc89]

AFAIK, wood fibre covered with lime plaster doesn't need a VCL as the wood fibre itself is hygroscopic. Of course you need to consider the finer details, around junctions etc.

 

Surely heat can only reduce the risk of condensation and indeed damp showing on the external face, if that heat is allowed to pass through the wall, negating the purpose of insulation?

 

Damp walls are generally a symptom of a problem, the root cause needs addressing (reducing ground levels, fixing gutters, removing that external paint (assuming it's non-permeable)) etc.

[bighouseproblems]

Just now, Roger440 said:

Are you sure.?in your previous posts you talk about vapour barriers.................................

Vapour Open buildup is obviously the right way to go.

 

I was merely offering the list of buildups commonly debated by people with solid walls. I did not imply any of the vapour barrier systems were correct. 

 

I find debating a subject and stressing it's validity constructive. I like solving problems...... So even if I fully intend to go down the route of wood fibre and lime plaster i like the idea of testing the theory against the other solutions.

 

I can throw 30K at my walls no problems but others may be less fortunate and need a more cost effective solution. 

I have seen many posts with people who have a great deal of experience in these matters such as yourself steamytea, Jayc89 and others.

 

[Iceverge]

With that budget I'd consider EWI. 

 

Then all the interstitial problems go away. 

 

Also it is important that you have a proper ventilation strategy. Suckling out or blowing in continuously at a small volume. It'll really help control moisture in the house.