Roof insulation

Gents this is a question for the old salts out there

Cabin top insulation against the sun, how important is this,
when you are out there in the middle of nowhere and the sun is beating down
even if you have reasonable ventilation, wouldn't it be better to have say 50mm = 2 inches of polystyrene sandwiched between two layers of ply and glass

So how good or bad would just a single skin of 9mm (3/8") plywood with a layer of glass over it painted a light colour be.

The Beneteau i sailed on was old and the roof lining **** and loose, so i couldn't really tell. Just worried that my micro becomes an oven inside on a bright sunny day.

 

Wear sunglasses, a hat and long sleeved white shirt, paint the roof white (do not even consider a light gray) and does not need to be 50mm I would guess at as little as 10mm or less would be effective, but better still some cloth sheet that could be supported by the stays on those windless days in conjunction with some carefully placed hatches to admit the breezes when desired...

 

Hi Manie,

I am planning some PV panels to provide shade. Distance will be around 30 to 40 mm to have a sufficient airflow underneath.
Should lower the inside temp by min. 10°C.

edit:
on top of insulated roof, of course.

Regards
Richard

 

Most of my small boat design incorporate a foam cored roof panel. It makes a big difference in both warm (my climate) or cold areas. A 6 mm plywood skin over 25 mm of foam with a 6 mm plywood inner skin, makes a strong roof, with little need for hanging beams to smack your head on., It's also lighter then plank over beam and is made water tight with the sheathing.

 

Thanks PAR

this is exactly what i had in mind
just very nice to know that i am not re-inventing the wheel
and that it comes from experience

 

Would this have internal beams? How big an area would this span and how much load would it support? Have you ever tried this for cabin walls?

 

You can span as big an area as you'll find on most small yacht roofs. You can use internal beams if you like, depending on crown size and distances involved, etc. I generally "edge" the perimeter with milled 2 by stock and any opening to offer a finished edge and something to drive a fastener into, but no internal beams per say unless the crown is slight. No, I haven't used this for cabin walls, as it's more effort then necessary, when a piece of plywood or solid limber will do just fine. I don't like to make things any more complicated then necessary, though if I was doing a severe service craft, where I could justify the extra bother, cabin walls could be made this way. Of course sheathings in this type of craft would be just as important as the cored wall.

 

I was thinking of it for walls of a house boat. It's like the insulated structural panels used in timber frame houses. When that was a new idea for enclosing timber frames there weren't many manufacturers of the panels and one writer tells of the local lumberyard making them. A sheet of ply was rolled with glue, a piece of foam layed on that and rolled with glue and another sheet of ply then layed on the foam. Then another set of ply/foam/ply etc. until the pile got too high to easily work on. A layer of cement blocks was then put on and that pile was left to set up and another pile started. This was done by high school kids after school.

The structural panels in timber framing have evolved over the years to being a structure in itself, with no need of any frame to support them, and large structures can be assembled in a day that usually take weeks.

In some situations it might be less bother to assemble a large panel on a work surface and then put it in place instead of assembling it in place piece by piece. In the ply/foam/ply roof panels you've made, what kind of foam and what kind of "glue" did you use, and did you use any clamps or pressure? Thanks.

 

Blue Foam

Blue Foam for house construction can be used.

You could use construction glue , but epoxy would be much better.
The 40 mm panels , when sandwiched between plywood , gives a much stiffer panel than the 20 mm on the same camber.



STYROFOAM™ LB

STYROFOAM™ IB Insulation improves the thermal performance of existing walls without affecting the appearance of the building. The insulation is lightweight and easy to cut, making it suitable for use around existing details. STYROFOAM LB Insulation can be adhered to or mechanically fixed to the existing walls. 　 Board Size(length x width, mm) 2500 x 600, 2500 x 1200 Thickness (mm) 20, 40, 60, 80, 100, 120 Edge Treatment Butt edge Surface Planed

Don`t use polystyrene.

 

In the ply/foam/ply roof panels you've made, what kind of foam and what kind of "glue" did you use, and did you use any clamps or pressure? Thanks.

 

SamSam, the structural panels that are used in land based roof systems and timber framing now are pretty highly engineered products, which also requires a "system" of attachment and stabilization. You'd be well advised to hire the loading out to a designer, which would be a small portion of the total build effort.

My panels use epoxy and 4 pound polyurethane foam and have perimeter solid wood elements as well as carlins for all openings. If the carlins are load bearing, then they are tied to the perimeter elements with stringers. It's the exact same engineering rules, used in the structural panels employed in land based systems. Don't kid yourself about how much engineering goes into these seemly simple panels.

 

I bought a infrared thermometer and measured three parts of hull all next to each other in direct sunlight, black, grey and white. Huge difference. Put a piece of astroturf on top, even bigger difference. So paint it white and put something over it, tarp, rug or some canvas.

 

Separation is what you need, which is one reason the foam panel is what I employ in my designs. Thermal isolation is what you need and this construction method works quite well at it.

 

Actually PAR , in the 18 plus years I have spent in the building industry , I have yet to see a panel system that is regularly used that is highly engineered for high loading.

The industry is a rather conservative bunch and don`t take to change too readily.

Speed of construction has improved significantly , but , at least in the domestic sector that I work in ,all systems now commonly used still rely on the conventional premise that paneling is fixed to , or hung off skeletal
framing or sub - framing.Just as it has been for decades , in fact more than a century.

Here in Australia and in Europe ,the framework spacing supporting the panels is standardized , usually in 300 mm increments so spans are usually in sums of 300 , 600 ( studs ), 900 , 1200 etc mm centres. Small spans that are well understood , and hence - not a lot of engineering required. Ditto for roofing. Flooring often 450 mm centres.

More attention is directed at the loadings of the supporting structures , i.e. framework , and the method of fixing the panels.After the horrendous Darwin cyclone on christmas day in 1974 the codes were re - written and changes were made to anchoring systems , particularly upper and lower wall plates,and associated perimeter tie - downs. Not the panels.

All wall panels used here today are regarded as cyclone safe but not all the methods of fixing .If best practice is followed , it is sufficient for walls on house boat construction.Once again it is the framing and / or sub framing that carries the loads on a house boats ,as they are built here , roofing align with wall framing ( studs ) etc....again 300mm c , floors are engineered to resist excessive torque etc. engineering will be required there , and while panels help with bracing by their nature, panels for house boat construction , at least here , is nothing special.

 

I agree that most industries are slow to adopt new methods, techniques and materials, with construction well known to it's slowness of evolution.

Just because the current use of land based SIP's has yet to take advantage of higher levels of engineering possible with the method, doesn't mean it's not occurring. It just means as you've pointed out that they're slow on the up take. This is the usual course. It took nearly a half a century for plywood and other sheet goods to fully catch on.

SIP's used over framing is a safe way to introduce folks to the idea of something new. It doesn't use the panels to full effect, but does get them on site and change building patterns.

On the other hand, I've seen modular buildings go fully seal up in 3 days, using a fully integrated SIP's based system. The walls are built off site, under climate control conditions, with everything in place. A crane spends a day or two erecting panels, then the finished doors and windows are slapped in, sealing the building. I watched a friends 2,000 sq. ft. two story garage go up in 2 days this way. On the third day the roof was skinned with shingles and the siding went on. The whole project, from start to finish was a week, paint, plumbing and flower boxes. So, it's actually being done, just not as much as hanging them on conventional frame works.

With some modest engineering (http://www.sips.org/elements/uploads/fckeditor/file/SIP Engineered Design Guide.pdf) you can save about 30% in dimensional lumber. With the curved roof panels I designed and was discussing in this thread, the solid lumber savings is more on the order of 60%, of course these are more highly engineered structures.

You can take this to the next logical step, which eliminates most of the dimensional lumber requirements, but now you have to get the industry to bite into goo's and monocoque structures, which is more then pulling teeth to say the least. Maybe by then, we'll have moved into the era of high modulus polyesters and resins that remove the need for wooden sheet goods all together. Wooden platform frame construction will be considered "quaint" and inefficient, with the wife complaining about the stairs creaking as she walks up them. You and I will be long dead, but it's coming.