Condensation Conundrum

[saxonborg]

I have a low line Buerstner T660 Nexxo, this is an overcab shelf which is boarded in with three panels which fit between shelf and the GRP pod. Last year I decided to add some recycled plastic wool insulation behind these panels because I thought it would be a good idea for sound deadening and heat retention. In the last week or so I needed to remove these panels to add some wiring, whilst poking about I noticed the insulation was very damp at the point where the GRP pod is fastened to the cab metalwork. I have now removed all the insulation and it has dried out completely. So is this something I shouldn’t have done, or maybe insulated it differently. I would add that the GRP pod has a lining stuck to it which extends part way down behind the removable panels but then there is a bare section of GRP where it is attached to the cab frame over the windscreen.

 

[SimonM]

I’d like a picture or two of what you’ve found as I also have a Nexxo T660 on a Ducato.

 

[cliveandann]

I have a low line Buerstner T660 Nexxo, this is an overcab shelf which is boarded in with three panels which fit between shelf and the GRP pod. Last year I decided to add some recycled plastic wool insulation behind these panels because I thought it would be a good idea for sound deadening and heat retention. In the last week or so I needed to remove these panels to add some wiring, whilst poking about I noticed the insulation was very damp at the point where the GRP pod is fastened to the cab metalwork. I have now removed all the insulation and it has dried out completely. So is this something I shouldn’t have done, or maybe insulated it differently. I would add that the GRP pod has a lining stuck to it which extends part way down behind the removable panels but then there is a bare section of GRP where it is attached to the cab frame over the windscreen.

It helps to understand the physics of what is happening. The amount of water vapour in the air is measured by the relative humidity so 0% means there is no water vapour in the air and 100% means the air is saturated and cannot contain any more water than it does already. When the relative humidity reaches 100% then dew forms. This is referred to as the dew point and is the temperature at which air reaches saturation by water molecules.

Warmer air can hold more water molecules. As warm air cools the dew point falls and it loses water vapour in the form of condensation. The air itself is saturated once the dew point matches the air temperature. The dew point can never exceed air temperature.

When warm air comes in contact with a cold surface such as the exterior surface of the van the temperature of the air touching the cold surface will drop. If the air has a high humidity such as it may do if you have been cooking or boiling a kettle then the dew point will drop close to the cold surface and there will be condensation.

To prevent condensation you need to keep the dew point below the air temperature. In your situation there are several methods to achieve this.
1 Improve ventilation. This will bring air with a lower dew point into the affected area. This is what you did when you removed the insulation.
2 Reduce the relative humidity. This means making sure you don’t create extra water vapour inside your van. Not easy as just breathing will have an effect.
3 Reduce the risk of humid air meeting cold surfaces to form condensation. You can do this by insulating potentially cold surfaces with closed cell insulation. You can find this from conversion suppliers and on ebay. Use at least 10mm thick self adhesive rolls. The closed cell prevents the humid air seeping through the insulation which is what happened with your insulation wool.
4 Reduce the access of humid air to cold surfaces. You can improve the risk of condensation in 3 above by covering the joins in the insulation with sticky tape and then covering it all with plastic sheet to form a vapour barrier similarly taped up to prevent the access of damp air.
5 Insulation reduces the rate of the flow of heat through the material compared to other materials such as metal. If the vehicle is left unheated the inside will eventually reach the same temperature as outside however much insulation there is. The more insulation the slower this process. So if you get into a cold vehicle, put on the heating and create a lot of water vapour there may even be condensation on insulation. Ventilation will help this as long as the relative humidity of the air being drawn in from outside is lower than that in the van. However if the outside is very damp, ventilation won’t help although insulating the cold panels will significantly limit any condensation that forms from getting onto areas which may corrode.

 

[Okta]

If the moist air can get between the insulalation and the cold surface it will condense on the cold surface. Non contact insulation can worsen the situation because it insulates the cold surface from the internal warmth and reduces air circulation. Unfortunately it does not completely prevent the moist air getting through. A form of insulation such as Thinsulate (which comes in rolls for the motor industry) which can be glued to the cold surface should help with noise and condensation.

 

[saxonborg]

It helps to understand the physics of what is happening. The amount of water vapour in the air is measured by the relative humidity so 0% means there is no water vapour in the air and 100% means the air is saturated and cannot contain any more water than it does already. When the relative humidity reaches 100% then dew forms. This is referred to as the dew point and is the temperature at which air reaches saturation by water molecules.

Warmer air can hold more water molecules. As warm air cools the dew point falls and it loses water vapour in the form of condensation. The air itself is saturated once the dew point matches the air temperature. The dew point can never exceed air temperature.

When warm air comes in contact with a cold surface such as the exterior surface of the van the temperature of the air touching the cold surface will drop. If the air has a high humidity such as it may do if you have been cooking or boiling a kettle then the dew point will drop close to the cold surface and there will be condensation.

To prevent condensation you need to keep the dew point below the air temperature. In your situation there are several methods to achieve this.
1 Improve ventilation. This will bring air with a lower dew point into the affected area. This is what you did when you removed the insulation.
2 Reduce the relative humidity. This means making sure you don’t create extra water vapour inside your van. Not easy as just breathing will have an effect.
3 Reduce the risk of humid air meeting cold surfaces to form condensation. You can do this by insulating potentially cold surfaces with closed cell insulation. You can find this from conversion suppliers and on ebay. Use at least 10mm thick self adhesive rolls. The closed cell prevents the humid air seeping through the insulation which is what happened with your insulation wool.
4 Reduce the access of humid air to cold surfaces. You can improve the risk of condensation in 3 above by covering the joins in the insulation with sticky tape and then covering it all with plastic sheet to form a vapour barrier similarly taped up to prevent the access of damp air.
5 Insulation reduces the rate of the flow of heat through the material compared to other materials such as metal. If the vehicle is left unheated the inside will eventually reach the same temperature as outside however much insulation there is. The more insulation the slower this process. So if you get into a cold vehicle, put on the heating and create a lot of water vapour there may even be condensation on insulation. Ventilation will help this as long as the relative humidity of the air being drawn in from outside is lower than that in the van. However if the outside is very damp, ventilation won’t help although insulating the cold panels will significantly limit any condensation that forms from getting onto areas which may corrode.

Thank you for going to the trouble of putting together this comprehensive reply, it all makes complete sense so I will have another go at it taking your advice into consideration.

 

[saxonborg]

If the moist air can get between the insulalation and the cold surface it will condense on the cold surface. Non contact insulation can worsen the situation because it insulates the cold surface from the internal warmth and reduces air circulation. Unfortunately it does not completely prevent the moist air getting through. A form of insulation such as Thinsulate (which comes in rolls for the motor industry) which can be glued to the cold surface should help with noise and condensation.

Thanks for this tip, I have seen rolls of aluminium backed self adhesive closed cell foam which I presume would do the job adequately.

 

[saxonborg]

I’d like a picture or two of what you’ve found as I also have a Nexxo T660 on a Ducato.

Here are some pictures of the area I was trying to insulate, also pictures showing the panels that I had removed just placed to show where they fit.

 

[SimonM]

Ooh, I don’t think mine looks at all like yours. I’ll have to pop outside and take a shufti when I get a chance.

 

[saxonborg]

View attachment 42467Saxonborg...I took some images in my 2009 Nexxo T 620 G this morning....they are identical to yours but I come to a different reason for the damp!
On my MH the channel at the bottom of the fibre glass moulding was full of water....sufficient to soak a large bath towel!
After heavy rain last night one of the two (one at each end) of the channel held water.
On close inspection I conclude that the endcaps are both damaged, there has obviously been a previous repair, and water is gaining entry there.
I will not comment anymore publicly as I am discussing details with the dealer after my very recent purchase.

PS. Will happily discuss via PM if there is one here.

View attachment 42465

Just been out to mine to check for damp again given that we have just had a wild and wet night, pleased to say that it is dry. Before I purchased my Nexxo the chap selling it discovered a few drips inside the front top locker behind rhe driver, fortunately he had it repaired before parting with it, so it could have been the endplate or the seam that runs along the front pod and the roof. Hope you get your’s fixed without hassle.