Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    Hi forum members -

    I hope I'm posting in the right section and my question makes sense.

    I'm working on a boat project (liveaboard) and the roof insulation set-up is, literally, giving me sleepless nights as I try to think of how to eliminate cold bridging through the timber rafters forming the 'flat' roof.

    I'm familiar with the principals of 'cold' and 'warm' roof designs but unlike a double-skinned brick structure or similar, the timber rafters will, at the end of the day, be attached to the steel hull of the boat. This, in turn, will directly let the outside cold travel through to the rafters.

    I would much prefer to go down the route of a warm roof but my poor brain cannot see past just insulating everything (roof and walls) from the inside like a a kind of separate 'innertube' of insulation.

    I'm sure more details are required but hopefully there's enough here to get the ball rolling and let me get some sleep at night!


    • CommentTimeAug 3rd 2016
    Are you familiar with a 'Larson truss'.
    It is basically external insulation added onto the outside of a timber frame building while all the structural elements are within the thermal envelope.
    Failing that, is there any way you can but a thermal break between the hull and the super-structure.

    Or ditch the timber and go for a GRP Foam GRP sandwich.
    • CommentAuthorgyrogear
    • CommentTimeAug 3rd 2016
    Posted By: discotrollthe timber rafters will, at the end of the day, be attached to the steel hull of the boat.

    Could you not first bolt a timber stringer to the hull, isolating it with "floating" rubber pads (like vehicle engine mounts) then attach the rafters to the stringer ? The gap between the stringer and the steel is filled with squidgy foam. This ought to limit the amount of thermal bridging.

    • CommentAuthorSilky
    • CommentTimeAug 4th 2016 edited
    could you isolate using compacfoam ( edit: or Puren )? It's meant to be a material that has similar bearing properties to wood but insulation value is higher, material is expensive, but maybe you only need a small ammount. i.e. could you could cut squares, or strips to support rafters and fill the rest with with EPS/XPS or something?

    clever video here for windows where they only use a small ammount and then infill with EPS

    • CommentTimeAug 4th 2016
    Posted By: discotrollI'm sure more details are required

    How will the hull be insulated?

    Is there no deck?

    A picture would help, I think.
    • CommentTimeAug 4th 2016
    What is your worry with thermal bridging?
    • CommentTimeAug 4th 2016
    Posted By: Silkyclever video here for windows where they only use a small ammount and then infill with EPS
    Can't see our window fitters working to that quality every day, all they need is a can of foam and some silicone sealant. :devil:
    Right - just got in from work -

    WOW! So many thoughts and suggestions - thanks to all who've posted! :bigsmile:

    Now, where to start...

    I'm taking a good look at the Larsen Truss info - lots of reading there (!) - thanks Steamy Tea.

    To give a better idea of project, this is a steel barge so basically the roof rafters will bridge across the original open section of the vessel (where the goods would have been loaded), connected (for want of a better term) to the steel structure (so no actual 'deck' area). The rest of the barge will be insulated with solid 'Celotex' type insulation between the outer steel structure and internal wood framing (so a good thermal insulated barrier between outside and inside).

    Going on from the suggestions by Gyrogear and Silky I remember from when I worked in the steel industry that we had to specify Farrat thermal breaks for things like balconies so the cold wouldn't travel from the outside structures through to the internal building frame (very similar to the Compacfoam) - this type of solution also fits in well with how I would like the rafters to sit into the opening.

    I'm off to do some reading and roof designing....

    Thanks again for the input!

    • CommentTimeAug 4th 2016
    Where is this hull?
    • CommentTimeAug 4th 2016
    Posted By: discotrollThe rest of the barge will be insulated with solid 'Celotex' type insulation between the outer steel structure and internal wood framing

    Not an expert, but I thought that people used sprayed on insulation, especially with steel hulls, to eliminate condensation forming on the hull and collecting in the gap between other forms of insulation and the hull?

    I'd be surprised if you didn't want to still be able to walk over the top of whatever roof you build, effectively creating a deck.

    Perhaps there might be a way to suspend the rafters (or whatever supports the insulation and deck) from above (i.e. the cold side) rather than from the ends.
    • CommentAuthorgyrogear
    • CommentTimeAug 4th 2016
    a mate of mine lived on a houseboat at Paris, it was the center section of a fuel lighter.
    Basically a beautiful luxury 5-room appartment. He cut off the front and the stern (with the engine) and sold them for more than he paid for the boat !

    You basically need a double hull, I'd guess - personally I'd build a wooden "shed" inside the hull and suspend it from the steel...

    (but it's your project) :devil:
    • CommentAuthordiscotroll
    • CommentTimeAug 5th 2016 edited
    Posted By: gyrogear

    (but it's your project)

    Hahaha - read that as 'Your *problem*'! :shocked:

    Yep - a double-hull with wooden inner shell is the basis of what I'm hoping to do...

    I'd like to avoid spray foam insulation just because it becomes such a pain if you need welding work undertaken in the future (though the potential condensation issues to the inside of the hull needs to be properly adressed).
    • CommentTimeAug 5th 2016
    If there's a 'double hull' with a separate inner structure, then the roof doesn't need support from the outer hull since it can be supported by the inner hull. All that's needed is some low-strength connection to support the watertightness and insulation layers and it is easy to make low-strength insulating connections.
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press