How thick...

[Doodlebug]

Hi all,

 

I am getting ready to insulate the top half of our boat with another inch of insulation.

 

There are two ways I can do this, I can either take down the plywood walls and put the insulation over the current insulation, then put the board back on but the only way to get the walls of is to take the ceiling down which involved dismantling the bathroom.

 

Or I can put the insulation over the internal walls and then put up another layer of new plywood on top. Question is how thick? I would have thought it needs to be quite thick to hold up picture frames and curtains so would have said about 6mm but I get the feeling from the way the walls bend when pushed that its more like 3.

 

Any thoughts on what thickness is considered normal?

 

Thanks

 

Doodlebug

[Ex- Member]

What insulation ?????

[Doodlebug]

I think i'm going to use another 25mm of polystyrene.

 

I am slightly put off using celotex bearing in mind its so much more expensive then celotex and although celotex is better it doesn't justify the price.

 

In fact if anyone has any better ideas on how I can insulate better I would be grateful. The main problem is the struts on the walls are right behind the ply, so we get strips of condensation and then mildew.

 

Cheers

[DeanS]

walls...9mm ply....should be ok then to hold up some shelf type weight. If you dont plan on the walls having any load on it, then 6mm would do....but the price of 9mm and 6mm isnt much difference.

[RLWP]

What's happening here? Doodlebug is sweating the details of insulating walls, roof and windows - yet boat dwellers with solid fuel stoves say they have to open windows because they are much too hot in winter

 

Richard

[Ex- Member]

I think i'm going to use another 25mm of polystyrene.

 

I am slightly put off using celotex bearing in mind its so much more expensive then celotex and although celotex is better it doesn't justify the price.

 

In fact if anyone has any better ideas on how I can insulate better I would be grateful. The main problem is the struts on the walls are right behind the ply, so we get strips of condensation and then mildew.

 

Cheers

 

Well then it really needs the paneling to come off and insulated properly. Doing what you're suggesting is basically a bodge and would most likely lead to further problems. Just slapping insulation over an already problematic area will probably be a total waste of money and time.

 

If you need to sort this really cheaply, try tins of hand held spray foam and inject this in to your existing cavities where condensation problems currently exist. There are clearly air gaps behind the paneling that's allowing this to happen.

 

Failing that just do the job properly but try to do smaller sections at a time.

[nb Innisfree]

New ply wouldn't need to be very thick as you would be screwing through two spaced sheets of ply which would result in the screw being supported at two points, much better from an engineering angle. So another 3mm would, together with the original 3mm, make for a rigid structure. Also less than 25mm of insulation would suffice I guess, 12mm or even less maybe?

[DeanS]

If you need to sort this really cheaply, try tins of hand held spray foam and inject this in to your existing cavities where condensation problems currently exist. There are clearly air gaps behind the paneling that's allowing this to happen.

 

Yes, I agree. I have a brand new boat...sprayfoamed. In places where I took foam off...last winter the condensation formed in those places...and not on the bits that were still foam covered. Reminds me to buy some spray foam myself and touch up a few spots

New ply wouldn't need to be very thick as you would be screwing through two spaced sheets of ply which would result in the screw being supported at two points, much better from an engineering angle. So another 3mm would, together with the original 3mm, make for a rigid structure. Also less than 25mm of insulation would suffice I guess, 12mm or even less maybe?

 

Yes....this makes sense..so ignore my 9mm comment ;-)

[nb Innisfree]

 

Well then it really needs the paneling to come off and insulated properly. Doing what you're suggesting is basically a bodge and would most likely lead to further problems. Just slapping insulation over an already problematic area will probably be a total waste of money and time.

 

If you need to sort this really cheaply, try tins of hand held spray foam and inject this in to your existing cavities where condensation problems currently exist. There are clearly air gaps behind the paneling that's allowing this to happen.

 

Failing that just do the job properly but try to do smaller sections at a time.

Prob with injecting foam is it wont help with the strut prob as that is probably down to insufficient insulation between ply and strut. I can't see any prob with a second layer of foam and ply, in fact, if done well it would result in a wall made of two sheets of ply sandwiching a layer of foam.

[Doodlebug]

What's happening here? Doodlebug is sweating the details of insulating walls, roof and windows - yet boat dwellers with solid fuel stoves say they have to open windows because they are much too hot in winter

 

Richard

 

A number of reasons, firstly even with the stove going you get damp patches in the corners of the room and cupboards, and we get condensation in strips on the walls as mentioned.

 

Second being such small boat if we have a window open because its too hot you get very cold areas and very hot areas, the heat doesn't mix too well. Although I am installing a system that will suck hot air from above the stove and blow it into the corners of the room.

 

Lastly because I hate spending money on fuel that is going straight out the window.

 

 

I have just found a place to get a look at the thickness and it is indeed 3mm thick.

The proper way to do it would be to rip everything out the boat and get it spray foamed but we just aren't in a position to do that so insulating areas one at a time is the best alternative.

[Phil Ambrose]

Be wary of spray foam, I have heard of cases where the foam has pushed ply off when it has expanded, don't have first hand knowledge of thid though.

Phil

[The Bagdad Boatman (waits)]

We have 4 inches of polystyrean on the outside of our park home as we are now trailer trash after 25 years on the cut. Kingspan is highly efficiant but expencive your shelves and pictures can be supported by battons instead of expensive ply. Condensation is blocked by a vapor proof skin on some insulation padding. which is more flexible than kingspan and you fill in the gaps with spray foam.

[nb Innisfree]

if you can get the foam sheet to adhere well to the existing ply and another sheet adhered well on top of that you will finish up with quite a solid wall.

 

I would key the existing ply, probably by just rough sanding and preferably use polyurethane foam such as celotex as it will adhere very well if you use polyurethane adhesive plus it has better insulating properties than polystyrene foam. 12mm polyfoam sounds just the business I think.

[Ex- Member]

Prob with injecting foam is it wont help with the strut prob as that is probably down to insufficient insulation between ply and strut. I can't see any prob with a second layer of foam and ply, in fact, if done well it would result in a wall made of two sheets of ply sandwiching a layer of foam.

 

And risk the continuing production of condensation behind. Certainly wouldn't risk that on my boat.

 

Ive seen the spray foam solution work really well in many situations including stopping condensation through struts. It's likely the boat is insulated with poly and doesn't insulate the struts. Injecting spray foam around the struts will insulate them, and as a result produce much less condensation, at can also press the poly tight to the boat sides again removing air gaps and reducing condensation. A litre tin of this stuff can be bought for around a fiver and it goes a surprisingly long way. You used to be able to buy a 6 pack and free gun for around £30 from screwfix. Just 1 decent sheet of ply and a sheet of poly would cost as much.

 

I know what I would be trying first.

Be wary of spray foam, I have heard of cases where the foam has pushed ply off when it has expanded, don't have first hand knowledge of thid though.

Phil

 

If paneling is pushed off by spray foam then it can't be fixed properly. If doing this then you should also drill holes periodically so you know how far the foam is going and also offering an escape route for pressure.

[nb Innisfree]

 

And risk the continuing production of condensation behind. Certainly wouldn't risk that on my boat.

 

Ive seen the spray foam solution work really well in many situations including stopping condensation through struts. It's likely the boat is insulated with poly and doesn't insulate the struts. Injecting spray foam around the struts will insulate them, and as a result produce much less condensation, at can also press the poly tight to the boat sides again removing air gaps and reducing condensation. A litre tin of this stuff can be bought for around a fiver and it goes a surprisingly long way. You used to be able to buy a 6 pack and free gun for around £30 from screwfix. Just 1 decent sheet of ply and a sheet of poly would cost as much.

 

I know what I would be trying first.

 

I agree, I was suggestingd injecting foam alone would be unlikely to cure strut condensation, I would do as you say and try it first followed by my method.

 

Ideally though, all, or at least some existing ply needs removing first to investigate what's behind.

[BlueStringPudding]

When I T&G'd the walls inside my boat, I put it over the top of the ply already there. It made a noticeable difference to how quickly the boat warmed up and how warm it stayed on very cold days and nights.

 

I think your ply and insulation idea will do the job quite well.

[smileypete]

What's happening here? Doodlebug is sweating the details of insulating walls, roof and windows - yet boat dwellers with solid fuel stoves say they have to open windows because they are much too hot in winter

 

Richard

 

Probably 'cuz said boat dwellers have oversized and/or poorly regulated stoves.

 

Bit puzzled as to why Doodlebug can't remove the wall panelling, some pics would help.

 

BTW you could always reword your sig a bit more politely, I'm sure Dan spends a lot of time keeping the forum running and has quite a few other things on too.

 

cheers, Pete.

~smpt~

[blackrose]

 

 

If paneling is pushed off by spray foam then it can't be fixed properly. If doing this then you should also drill holes periodically so you know how far the foam is going and also offering an escape route for pressure.

 

That's not true. Too much expanding sprayfoam could easily pull even the most well fixed boat paneling off a wall. The expansion is very powerful.

 

I've injected sprayfoam into cavities on 2 boats - once with a big kit and once with handheld cans. Either way you need to pump small amounts of of foam into holes spaced about 6" apart (starting at the bottom and working your way up). Contrary to what one may think, the foam wants to expand spherically and does not travel well along a linear path such as along a cavity. If the cavity was brick then this isn't an issue because the foam is forced to travel, but ply lining fixed at 18" centres will bulge and may be pulled off the wall.

 

A number of reasons, firstly even with the stove going you get damp patches in the corners of the room and cupboards, and we get condensation in strips on the walls as mentioned.

 

Second being such small boat if we have a window open because its too hot you get very cold areas and very hot areas, the heat doesn't mix too well. Although I am installing a system that will suck hot air from above the stove and blow it into the corners of the room.

 

Lastly because I hate spending money on fuel that is going straight out the window.

 

 

I have just found a place to get a look at the thickness and it is indeed 3mm thick.

The proper way to do it would be to rip everything out the boat and get it spray foamed but we just aren't in a position to do that so insulating areas one at a time is the best alternative.

 

I think you could stick 12mm or 20mm thick celotex to the wall and then use thin ply or T&G over the top. It's not a proper job but it would solve the problem.

 

http://www.insulationshop.co/12mm_celotex_tb4000_pir_insulation.html

 

The only caveat to that is that the extra weight might pull your existing panelling off the wall depending on how well it's fixed, but you could try one section first to find out.

Edited September 8, 2013 by blackrose

[Ex- Member]

 

That's not true. Too much expanding sprayfoam could easily pull even the most well fixed boat paneling off a wall. The expansion is very powerful.

 

I've injected sprayfoam into cavities on 2 boats - once with a big kit and once with handheld cans. If you do this you need to pump small amounts of of foam into holes spaced about 6" apart (starting at the bottom and working your way up). Contrary to what one may think, the foam wants to expand spherically and does not travel well along a linear path such as along a cavity. If the cavity was brick then this isn't an issue because the foam is forced to tavel, but thin ply lining will bulge and may be pulled off the wall.

 

I think you could stick 12mm or 20mm thick celotex to the wall and then use thin ply or T&G over the top. It's not a proper job but it would solve the problem.

 

http://www.insulationshop.co/12mm_celotex_tb4000_pir_insulation.html

 

The only caveat to that is that the extra weight might pull your existing panelling off the wall depending on how well it's fixed, but you could try one section first to find out.

 

Oh well, I've done this numerous times myself with aerosol on a few boats now, and seen it done several times with the full spray foam kit., I haven't seen paneling lifted yet, you're obviously over filling LOL or not drilling big enough holes LOL

 

Again trying to solve the problem by covering it with insulation and board is nothing more than a bodge, it might even look pretty, but it's still a bodge up. Akin to studding a damp wall in a house.

 

The underlying problem will remain and within months, some on here will probably suggest more insulation and boarding. I would think after a couple of years you would have about 4 f't internal width left LOL

[blackrose]

The main problem is the struts on the walls are right behind the ply, so we get strips of condensation and then mildew.

 

Cheers

 

If by "struts" you mean the wooden battons that the ply is fixed to, then that's the same on most boats - although it shouldn't cause the problems you're experiencing. However, people who insist on ridiculously thick applications of sprayfoam or other insulation between the battons somehow seem to forget that they have 2" wide thermal bridges running all over their boats.

 

If you do end up using cellotex over the existing ply you will emiminate these thermal bridges. Use cellotex, not polystyrene - go on, you know you want to!

[Ex- Member]

 

If by "struts" you mean the wooden battons that the ply is fixed to, then that's the same on most boats - although it shouldn't cause the problems you're experiencing. However, people who insist on ridiculously thick applications of sprayfoam or other insulation between the battons somehow seem to forget that they have 2" wide thermal bridges running all over their boats.

 

If you do end up using cellotex over the existing ply you will emiminate these thermal bridges. Use cellotex, not polystyrene - go on, you know you want to!

 

Nonsense, if condensation is already being produced in a cavity, covering it with insulation will not solve the problem. The condensation will remain as long as air still exists in that cavity.

 

You have a point with thermal bridging, but battened and insulated ribbing still has some level of insulation so in most boats does not cause the ingress of moisture.

 

The boat clearly has a severe lack of insulation which needs to be sorted prior to bodging up with Celotex & board.

Edited September 8, 2013 by Julynian

[blackrose]

 

Oh well, I've done this numerous times myself with aerosol on a few boats now, and seen it done several times with the full spray foam kit., I haven't seen paneling lifted yet, you're obviously over filling LOL or not drilling big enough holes LOL

 

Again trying to solve the problem by covering it with insulation and board is nothing more than a bodge, it might even look pretty, but it's still a bodge up. Akin to studding a damp wall in a house.

 

The underlying problem will remain and within months, some on here will probably suggest more insulation and boarding. I would think after a couple of years you would have about 4 f't internal width left LOL

 

That's right. Phil was originally talking about the hazards of over-filling. You said panels couldn't be ripped off the walls unless the panels weren't properly fixed and on that point you're wrong. I'm not ashamed to admit that I overfilled behind some panels on my first boat. They bulged badly. Also it's not really about hole size, it's more about hole frequency and filling with smaller amounts of foam in each hole to get an even fill all over the cavity. Your post seemed to suggest that you just pump foam into a few holes and the foam will even itself out as long as you provide some holes for the foam to escape. That's not the case at all.

 

If insulating over a problem wall is such a bodge then how come people have had long-term success doing it? I know people who've done it and never had a problem since. All you're trying to do is prevent warm air in the boat reaching a cold badly insulated surface. It's called adding insulation. Whether you do that by ripping the ply off and putting more insulation in, or insulate over the top of the ply doesn't make that much difference. Also Doodlebug said the problem is happening over his struts (battons). If he rips off the lining and just puts more insulation between the battons he will still be left with the same issue. If he insulates over the battons he will not.

 

Nonsense, if condensation is already being produced in a cavity, covering it with insulation will not solve the problem. The condensation will remain as long as air still exists in that cavity.

 

You have a point with thermal bridging, but battened and insulated ribbing still has some level of insulation so in most boats does not cause the ingress of moisture.

 

The boat clearly has a severe lack of insulation which needs to be sorted prior to bodging up with Celotex & board.

 

Nonsense. Condensation will not form in the cavity if you prevent warm air getting in there in the first place.

 

You have a very basic misunderstanding of thermal dynamics.

 

On most boats the battons are not actually insulated on their contact faces, and although most boats don't suffer from problems the OP's does have problems and that's the point!

 

If Blue String Pudding is happy with her job of putting T&G over the ply on her boat and says the boat is now warmer, how is that any less of a botch (not bodge) than putting some cellotex in there as well? Surely that would be a better job? Are you saying that Blue String Pudding's job was a botch too?

 

It's fine for you to say it's a botch, but I'm making a suggestion to try to help the OP who for various reasons can't rip out the existing lining. I've seen it done on other boats and contrary to what you say it has worked long-term.

Edited September 8, 2013 by blackrose

[Ex- Member]

So where's the condensation coming from LOL

 

Am I getting condensation mixed with damp LOL Apologies, I was under the impression damp was coming through the linings where ribbing occurs, that suggests that moisture is accumulation behind the panels, If I've got that wrong then apologies.

Edited September 8, 2013 by Julynian

[smileypete]

Sounds like it's thin panelling fixed directly to steel (maybe T stud) instead of via a wooden batten.

 

Maybe one of those multi tools will cut round the edges of the panelling OK and allow it to be removed more easily, hopefully it's not glued down with no nails type stuff.

 

cheers, Pete.

~smpt~

[Doodlebug]

Thanks for all the replies. To clear up some confusion i'll explain how it is set up at the moment.

 

About 2 inches to the side of each window frame we have a 1 inch thick strip of mildew. Every time we clean it and repaint it it comes back after a few months. When its cold outside the strips are soaking wet and dripping with condensation on the walls.

 

Our insulation at the moment is 25mm polystyrene under 3.6mm ply. I drilled a hole in the wall to have a look.

 

The problem is that because there is no insulation on top of the metal 'struts' that strengthen the boat, we get damp patches on the walls.

 

What I am going to do is screw some batons to the wall around each window frame and at intervals. I will put 25mm insulation in each of the gaps and then cover it with 3.6mm ply. The reasoning being that the walls have been fine for holding up picture frames up until now so there seems no need to put extra thick stuff on top.

 

By doing this it will create a thermal barrier on the entire wall and should prevent any more condensation.

 

I wouldn't say that it is a bodge. It is commonly done in houses with solid brick walls.

 

Btw, there are no air gaps behind the internal walls that would need filling.

 

As to polystyrene v celotex. I have found out for deffo that celotex is 50% better than polystyrene. Bearing in mind that 25mm celotex would be the same as 37.5mm polystyrene I don't think the difference will be that noticeable. I am only after a solution to the condensation with the added benefit of a warmer boat. And if I can do the whole boat for £30 instead of £90 that makes sense.

 

And the other factor is that heat loss through the windows and doors is greater than the walls, so using celotex to achieve perfection when there is more to be done elsewhere is less of a priority. I can then put the money saved towards double glazed glass.

 

Cheers

 

Ps The thinnest insulation I have available is 25mm