Solar heat gain reduction for roof using a cover deck?

[ourmefa]

I am curious about those who may have a deck installed over their bus or know of those who do have one. How much does having a deck provide solar gain reduction on the roof of the bus?

I would like to make our bus as efficient as possible and it seems that most of the comments I see about skoolies being hot, revolves around the bus not being parked in the shade.

It makes sense to me that a deck over the entire top of the roof would provide a huge thermal break from direct sun. Additionally, it would provide the ability to mount various items like solar panels or a condenser unit from a split system, without having to make any holes in the roof.

I would be interested in thoughts about this. Are there any downsides to adding a roof deck to a bus?

[superdave]

it would probably affect the mpg a little. it would help some being shaded but you would have to shade the whole bus. light hitting the sides/windows is also just as bad. I'm in fl in direct sun now just testing my foam job. I'm very happy with my bus, in hot and cold weather. the side the sun hits is hot, I'm going to have another set of shades made. trying to figure out a little outside canopy I can clip on to shade the windows.

[Tango]

The "second roof" idea works and can make quite a difference. All the old safari Land Rovers employed a standoff roof just above the factory one to allow air flow in between. Basically, you are carrying your own "shade" everywhere you go. And I have had a number of bus converter friends who have gone the roof deck path over the years and they all saw a big difference in what it took to cool their rigs. I am going that route myself.

[dalez]

I'm seriously looking into building a shade of solar panels over my next bus's roof, with airgap, and extra solar panels that fold/slide out over the sides of the bus for both more power and more shade

[ourmefa]

Originally Posted by Tango

The "second roof" idea works and can make quite a difference. All the old safari Land Rovers employed a standoff roof just above the factory one to allow air flow in between. Basically, you are carrying your own "shade" everywhere you go. And I have had a number of bus converter friends who have gone the roof deck path over the years and they all saw a big difference in what it took to cool their rigs. I am going that route myself.

I did not know that about land rovers! That is very cool! Sounds like I am on the right track!!

This is the currently my favorite of the attachment methods. It is light, minimal wind resistance and the design would allow me to attach other things to the vertical supports, such as additional foldable pipe along the edges that we can install a full length window canopy.

I happened to have 40' x 4' of painters drop cloth (much heavier than we would use) and I rolled the full length of it up attached end to end and the roll was less than 12' in diameter. This is more than enough material to create a nice angled canopy down from the roof line, above the windows and it wont take up a ton of storage space. We will have a small porch coming off of the back door and I will create a small storage unit under that to house it.

Composite decking seems to be the most common thing that I see in roof racks and makes sense. I am just wondering about the difference in weight compared to regular wood. I did find some open cell decking (think corplast) that looked interesting, but it is going to be EXPENSIVE!

I will likely not use wood for the cross members, but instead, another piece of pipe and then use U-bolts to attach to the pipe.

Link to full conversion photo thread - April 2 - SeanF


Click for large view - Uploaded with Skitch

[ourmefa]

One thing that I think I will have to address though, with this design, is how to insert a thermal break between the mounting brackets and the bus. I think I can probably just sandwich some thick felt between the bracket and bus and this should provide some form of thermal break so that heat gain from the deck and the pipe is not transferred to the bus body. Granted, this solar gain would be minimal, but easy enough to try and avoid.

[Iceni John]

I first repainted my entire roof down to the gutters with gloss white Rustoleum enamel with Thermacels insulation powder added - it made a slight difference to ceiling temperature. I then built a walkway between my two roof hatches to which are hinged the eight big grid-tie solar panels. When the panels are stowed down against the roof for travel there is still several inches of airgap under them, more than enough to allow air to circulate under them. This makes a noticeable difference to ceiling and interior temperatures, and will also help the panels from getting too hot. So far, so good.

In the 1970s (I think) MCI built some of their MC5 buses for Aramco in Saudi Arabia, and they have a double roof. It appears to be only an inch or two above the roof itself, but apparently it does help in hot weather. There is someone who advocates making double roofs over existing roofs of bus conversions - I forgot his name, but he has a webpage talking about it.

Didn't that old Series 1 Land Rover ("The Anti Christ") in The Gods Must Be Crazy have a tropical roof? It's been quite a while since I've seen that film, so who knows?

John

[jimburke77502]

Anyone ever look into self adhesive TPO vinyl roofing??? Wide enough to cover well over the edges, no seams, and in its regular application is energy star rated. In putting a deck on the roof, check out the Denali bus build on you tube, episode 7 I think. This is how I will be doing my deck. Reason being, no direct mounting to the roof itself and no potential for roof leaks. Also designing an arched solar panel canopy that goes up and down. Up for the shaded part of the deck and to get the solar panel heat build up as far away from the roof as possible, and down for travel.

[Robin97396]

Originally Posted by ourmefa

I think I can probably just sandwich some thick felt between the bracket and bus and this should provide some form of thermal break so that heat gain from the deck and the pipe is not transferred to the bus body.

If you can get some scraps of an old rubber conveyor belt it would work well, but felt would be better than nothing.

[Robin97396]

Iceni John, thanks for the TPO info. That actually sounds like it has high potential.

Excerts taken from; https://www.roofingcalc.com/tpo-roofing-pros-and-cons/

Quote;
For most residential applications, TPO membranes come in two thicknesses options: 45 mils (.045″) or 60 mils (.060″). Commercial grade TPO membranes may have a thicknesses of up to 80 mils (.080″) and may come in up to 12 feet-wide rolls.
The width and length of the membrane can vary depending on the manufacturer, with a typical TPO membrane roll being 6 to 6.5 ft wide and 100 ft long. Other membrane thicknesses and widths are also available depending on the manufacturer, including a 3 feet-wide rolls for the edges of the roof. Commercial grade TPO membranes may have a thicknesses of up to 80 mils (.080″) and may come in up to 12 feet-wide rolls.
They are available in white, light gray, and black colors. White TPO roofs offer the best heat reflective properties are are consequently the most popular choice due to their energy-saving potential.
Hot-air welded seams are very strong, with seam strengths being as much as 3-4 times greater than EPDM adhesive and tape seams.
A TPO membrane is considered to be a cool roof and is Energy Star rated. Not all TPO membranes are created equal, and some perform a lot better than others.
Endquote;

This stuff sounds pretty good especially for a bus with challenged roof seams (a leaker). A walkway down the center line of the roof would probably be a good idea to avoid walking directly on the TPO. At the same time this material doesn't make much sense if someone has a deck. It was priced at $5 to $7 per square foot installed residentially, so the self installed price should be significantly lower.

Personally I'd rather have a deck over the roof if I were making a choice in this bus.

[Scott Marcano]

I painted the whole thing, well almost not quite done yet but the front has two coats and plan to paint the whole bus with a lesser expensive gloss white,..

[Scott Marcano]

and plan in the next year or so to add some large solar panels, raised a tad to intervene with the Sun heating.

[joeblack5]

Tango Thanks, The wife and me just got the movie after you mentioned over here. That was a hell of funny movie.
"The gods must be crazy"
People in buses need a simpler life.... Going bushman seem to trump it all.

Later J

[BlueBirdman]

A lot of my recent professional experience is in spray foam insulation, energy efficient construction methods, wood stoves and off-grid solar. Here are my thoughts:

1) Think of your bus as a system made up of sub-systems. The summer comfort system includes insulation, shading, ventilation and (perhaps) mechanical cooling.

2) Close cell spray foam is the best insulation, bar none.

3) Shading is critical. If your bus is out in the sun, it will absorb a tremendous amount of heat and it will take hours to cool it off before you can sleep comfortably. Conversely, if your bus is well shaded it will never get much warmer inside than ambient temperature. (There will be some interior heat gain from your fridge, cooking, bathing and people's warm bodies being in there. That's nothing compared to the heat gain from the sun hitting an un-shaded bus!)

4) After shading comes ventilation. I like Fantastic Fans!

5) If you'll be in a hot zone most of the time, do a roof raise even if you don't otherwise want one. Before air conditioning, homes were built with high ceilings so the hottest air could rise ABOVE where your head will be. You'd be astonished how much difference that makes!

Then, install your Fantastic Fan(s) in the ceiling to get that hottest interior air out of there!

6) There's enough room on the roof to install a large PV system. That not only provides shade - it provides enough power to run a small air conditioner for a few hours a day if needed!

Some other observations:

I don't like Trex decking in general, and specifically not for vehicle decks. It's heavy as hell (bad for your cg) and it absorbs (and hence radiates) a lot of heat. It can easily get too hot to walk on!

I wouldn't worry about a thermal break between the bus body and the mounting legs of the deck. That's a small area, it's highly unlikely you'd ever notice the trivial amount of heat or cold conducted into the body. (You are insulating on the inside, right? That's all the thermal break you need!) Much more important to get a strong mount!

On that note, I don't like the pipe mount in the pictures. There is not adequate side-to-side or front-to-back rigidity in that design. If you drive much, that deck is eventually coming off the bus, and not in an orderly fashion.

My awning idea is to use 80% shade cloth to make awnings that will shade the entire bus. It's relatively cheap, not terribly heavy and made for UV resistance/high winds. I've used this stuff in greenhouses and over part of an outdoor garden, and like it.

I think it would be a great idea to build a canopy out of this stuff that would be large enough to shade an entire bus while working on the conversion!

Hope this helps everyone!

[BlueBirdman]

LOL. Haven't watched "The Gods Must Be Crazy" in years. Gonna have to find a DVD of that for my library!

[EastCoastCB]

Originally Posted by BlueBirdman

LOL. Haven't watched "The Gods Must Be Crazy" in years. Gonna have to find a DVD of that for my library!

I remember watching that with my papa when I was little.

[PNW_Steve]

Originally Posted by EastCoastCB

I remember watching that with my papa when I was little.

Go to your room!

You are making some of us feel old......