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Cold bridging - how to prevent it?


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I'm doing some refitting work on our boat which includes replacing the 25mm polystyrene insulation with 25mm Kingspan. I'm concerned about possible cold bridging and condensation issues - at the moment exposed steel is covered by by strips of polystyrene 'wallpaper' and there are some signs of surface rust on the steel presumably caused by condensation.

The roof battens are set into inch U-section channeling, the steel edges being exposed; there's more horizontal U-section at the top of the cabin sides where the electric ducting runs and the hull sides have two inch L section steel with insulation behind so there's plenty of exposed steel there.

So - what's best to cover the exposed steel? Poly wallpaper again; the stuff you put behind radiators or something else?

       should I put some sort of vapour barrier immediately behind the linings? If so, doesn't condensation just run down the barrier?

       should I get the Kingspan flush against the hull sides with any airspace in front or the other way round?

 

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I would glue thicker sheets of Kingspan leaving u section recessed by half an inch or so, this can then be filled with aerosol foam, trim flush when hard. Blocking any steel from air will prevent condensation. 

 

Beauty of Kingspan is the ability to easily achieve a uniform thickness, with sprayfoam having to apply it too thick then trimming back is a tedious job. After a well known company spray foamed our boat it took me two weeks to finally track down and fill small cavities and holes with aerosol foam, even then I missed one pinhole which made itself known after a couple of winters. 

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5 minutes ago, koukouvagia said:

Another way is to use the high density Rockwool slab insulation.  You can cut this slightly oversize and stuff it in all the nooks and crannies.  It's designed to be a friction fit.  

 

As this stuff doesn't exclude air from steel what thickness would it need to be to prevent condensation on steel surfaces in sub zero weather and 30° C temp inside? 

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You could use strips of camping mats to cover the exposed steel, stuck on with PU sealant or Stixall. B&M Stores or HomeBargains may well have the mats at this time of year. 

My preference would be to stick the Kingspan to the shell with aerosol foam, preferably gun-grade B1 fire-rated, and leave the air gap on the liner side. 

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1 hour ago, nb Innisfree said:

As this stuff doesn't exclude air from steel what thickness would it need to be to prevent condensation on steel surfaces in sub zero weather and 30° C temp inside? 

These two pictures show what I mean. (Not very good pictures, I'm afraid).  The channel at gunwale level is filled with rockwool to a depth of about 3" and then covered with a vapour barrier. Absolutely no condensation.

1795460993_InteriorOwlpartinsulation.JPG.8a617a49baa7e68801c23d58c154805e.JPG

 

884551430_Owlliningoutmaincabin33-99.jpg.e6ea7861ed0cb5857d731bd9f77929e8.jpg

 

 

51 minutes ago, koukouvagia said:

 

 

Edited by koukouvagia
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1 hour ago, Alan de Enfield said:

Just a thought, but whilst its stripped out, why not do a 'proper job' and spray foam it ?

Did think about it but I'm only stripping out a couple of areas and those I would have had to strip out even more. 

Edited by starman
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cut the Kingspan to a tight fit and stick to hull with a few dabs of silicone then cover all joints with silver tape leaving a small air gap to the lining, I used silicone between the battens and steel side stiffeners to avoid a cold bridge and seems to work well.

 

Neil

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  • 2 weeks later...
On ‎17‎/‎07‎/‎2018 at 12:06, starman said:

I'm doing some refitting work on our boat which includes replacing the 25mm polystyrene insulation with 25mm Kingspan. I'm concerned about possible cold bridging and condensation issues - at the moment exposed steel is covered by by strips of polystyrene 'wallpaper' and there are some signs of surface rust on the steel presumably caused by condensation.

The roof battens are set into inch U-section channeling, the steel edges being exposed; there's more horizontal U-section at the top of the cabin sides where the electric ducting runs and the hull sides have two inch L section steel with insulation behind so there's plenty of exposed steel there.

So - what's best to cover the exposed steel? Poly wallpaper again; the stuff you put behind radiators or something else?

       should I put some sort of vapour barrier immediately behind the linings? If so, doesn't condensation just run down the barrier?

       should I get the Kingspan flush against the hull sides with any airspace in front or the other way round?

 

Bit late to this discussion but I'm not sure that anyone actually answered the question.

 

The point raised by the OP is that if any steel (or wooden batten) is left exposed then this will form a thermal bridge to the outside - whether condensation forms on the cold bridge is a related but slightly different question.

 

The way that the vast majority of boats are insulated between the battens leaves a multitude of uninsulated cold bridges along the length and breath of the boat and it seems astonishing to me that some people go to so much trouble and expense to make sure their insulation is as thick as possible while not even bothering to think about all the thermal bridges that render even the thickest insulation much less effective than it should be.

 

If you google the insulation properties of common building materials you will find that a wooden batten doesn't make for a very good insulation material, and as for a smear of silicone... well it might help to reduce or even prevent condensation forming, but its insulation value will be negligible.

 

I'm afraid that the only way to eliminate thermal bridges is to insulate over them, and who does that? Nobody. It's a flaw in boat building/fitting in my opinion.

   

Edited by blackrose
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24 minutes ago, blackrose said:

The way that the vast majority of boats are insulated between the battens leaves a multitude of uninsulated cold bridges along thelength and breath of the boat.

But aren't these battens usually wooden?  In which case there won't be any cold bridges because the wood is a perfectly adequate insulator.

 

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54 minutes ago, blackrose said:

If you google the insulation properties of common building materials you will find that a wooden batten doesn't make for a very good insulation material,

 

26 minutes ago, koukouvagia said:

But aren't these battens usually wooden?  In which case there won't be any cold bridges because the wood is a perfectly adequate insulator.

One of you is wrong...

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7 minutes ago, WotEver said:

 

One of you is wrong...

Wood is a natural insulator due to air pockets within its cellular structure, which means that it is 15 times better than masonry, 400 times better than steel, and 1,770 times better than aluminum. In addition, lightweight wood framing methods allow easy installation of additional fibre or foil insulation.

As a result of this improved thermal performance, buildings produced using timber, particularly engineered timber such as Cross Laminated Timber (CLT), Glulam and Laminated Veneer Lumber (LVL) require less energy to heat and cool, resulting in reduced energy bills.

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5 hours ago, blackrose said:

Bit late to this discussion but I'm not sure that anyone actually answered the question.

 

The point raised by the OP is that if any steel (or wooden batten) is left exposed then this will form a thermal bridge to the outside - whether condensation forms on the cold bridge is a related but slightly different question.

 

The way that the vast majority of boats are insulated between the battens leaves a multitude of uninsulated cold bridges along the length and breath of the boat and it seems astonishing to me that some people go to so much trouble and expense to make sure their insulation is as thick as possible while not even bothering to think about all the thermal bridges that render even the thickest insulation much less effective than it should be.

 

If you google the insulation properties of common building materials you will find that a wooden batten doesn't make for a very good insulation material, and as for a smear of silicone... well it might help to reduce or even prevent condensation forming, but its insulation value will be negligible.

 

I'm afraid that the only way to eliminate thermal bridges is to insulate over them, and who does that? Nobody. It's a flaw in boat building/fitting in my opinion.

   

I did

1146126_654405454597990_382436001_o.jpg

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1 hour ago, linnit said:

I did

1146126_654405454597990_382436001_o.jpg

That's rather the way I was planning to do it. Good to see a proper engine too - I'd post a pic of our DM2 but the whole area looks like a bombsite of dismantled bits: I envy your pristine workspace

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