Author Topic: Cabin layered roof  (Read 210 times)

Offline larspa

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Cabin layered roof
« on: March 03, 2021, 10:43:49 AM »

I need some input on the jumbo roof.  I’m doing a layered roof with the original plan being to use ¼” foam for the middle layer.  But when we get serious about the details and ready to lay it up, we’re looking at the blocking apparently required.  There’s enough blocking that the part that’s foam begins to look like small patches and strips.  That is, much less foam that I original imagined.

So I’m looking for information about how blocking was handled vs. foam, etc. Another way to say it is that if we’re getting down to coverage half or less foam, am I to the point where I may as well just give up and forget the foam insulation?

Thanks a bunch.   TE
Jumbo 24' in progress.

Offline Kobuk

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Re: Cabin layered roof
« Reply #1 on: March 03, 2021, 02:18:26 PM »
Why so much blocking?
22' Widebody
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020

Offline pfithian

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Re: Cabin layered roof
« Reply #2 on: March 03, 2021, 03:08:15 PM »
Here's what I did, it is almost all XPS foam.  You want wood on all surrounding edges to elminate shear on the foam.
Made It Jumbo 25
Skiffkits No. 7025 1/2009
Build Start:  3/2009
Hull Flipped: 1/31/2010
Maiden Voyage:  9/16/2011

Offline larspa

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Re: Cabin layered roof
« Reply #3 on: March 03, 2021, 06:34:27 PM »
Kobuk,

We are treating the perimeter wood as blocking rather than putting it on top of the top layer as Renn has us do.  Probably should put it on the top layer and use a small piece to cover the edge or front the insulation, but we still need something for the grab rails on the edge of the roof.  Then there's the longitudinal beams which while anchored on each end, should also tie into the roof some how -- blocking for that.  The RADAR mount needs a piece...18" square(?), to include the nav light, and a small piece for the GPS puck.  So 8+" for each edge - 16"; 2 @ 4" for the interior beams / grab rails - 8"  We're looking at ~40" split three ways for three strips of ~14".   In the end, we just didn't see how two layers of door skin and one of ¼" foam would be enough to support grab rails screws, etc. in lieu of blocking.  We were thinking about just swapping out the top door skin for a ¼" layer, wondering if that would provide enough purchase for the screws.  In the end we  decided to see if there was some elegant solution that one or another of our forum friends might have come up with.
Jumbo 24' in progress.

Offline Kobuk

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Re: Cabin layered roof
« Reply #4 on: March 03, 2021, 08:56:39 PM »
Hmmm, I'll refrain from offering advice; I'd feel really bad if I did and it didn't work out.  The only sandwich roof I built was for my cuddy. I used 3/4 foam sandwiched between two 4mm sheets.  It's very strong.  It may not have been necessary, but for added measure I ran a couple stainless screws through the sandwich from the inside into the bottom of each grab rail to supplement the epoxy bond. (I used screws with ~5/8" dia. pan heads). The grab rails are extremely strong.  I've been thinking about what I'd do differently if I was to build another skiff and I think I would build the entire cuddy/pilothouse topside structure, walls and all, with the same 4m sandwich I used for the cuddy roof.  I think it would be at least as strong or stronger (likely stronger) than the 8 mm I used for this build. I don't think I'd feel the need for any blocking at all, unless maybe the item to be mounted was really, really heavy and/or was able to exert a whole lot of leverage.
« Last Edit: March 03, 2021, 09:07:41 PM by Kobuk »
22' Widebody
Started: 3/2019
Flipped: 6/2019
Floated: 6/2020