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Old 02-20-2011, 12:26 PM   #1
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Adding R14 under-floor without losing interior space...

So this week, I had an idea on how to gain some extra insulation under my bus without losing any interior space. I spent a lot of time thinking it through and doing some research and measuring, and decided to document the idea in case it might work for someone else. I plan to implement this idea in my own bus.

Now this will work specifically for Thomas busses for sure. Other brands may do their floors differently. On all 3 of the Thomas busses in my yard, the flooring is done identically.

Basically, on a Thomas bus, the floor consists of C channels laid crosswise on top of the frame rail, and attached to each other somehow. They are 9.5" on center on unleashed, but I haven't measured any of the others yet as it is cold out there. In unleashed, the space "inside" the C channel is approximately 2" of vertical space by 9.25" of horizontal space. This space extends all the way across the bus, and is repeated many times from front to back.



Now, my idea is to somehow seal this volume and then fill it with slow expand cavity fill foam. Tiger Foam has some that is reasonably priced, and R7 per inch. This is a closed cell foam that stops air flow, moisture, and sound in addition to being great in a fire and better than RMax insulation value. It does need to be protected from UV though.





After installing a small insert into the opening of the channel, I will caulk it down, using the caulk to both adhere the insert and prevent moisture from getting up between the insert and the channel.





Once it is enclosed, simply drill a small hole from above, and fill with foam.



My plan is to use a thin (but not too thin) gauge of galvanized steel. I will figure out the size I need, and the number, and order it precut. I will order some extra, as I have some obstacles. I figure I can cut pieces down and overlap them and caulk them in order to get past obstacles.

In my floor, the only thing within the volume of the channels is the protrusions from above (nails holding the flooring) and the clamps that attach every so often to hold the whole floor/body to the frame rails.

This is not a replacement for insulating the floor inside. The abutting pieces are still made of steel, and will conduct heat quite nicely. It is just like a stud in a wall transferring heat from one side to the other. But if you combine this with an inch or two on the inside of your floor, you can get R21 to R28 with only 1 to 2 inches of height loss inside for insulation.

In my application, I plan to put at least 2 more inches on the inside of my floor, then put minimum 3/4" plywood on top of the insulation.

I'm also considering getting a rhino-liner type coating to put on the bottom after the galvanized insert and foam in place to help protect everything better. I figure it won't hurt anything.

I hope this idea helps others,
jim

[edit: removed the incorrect fire rating information]
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Old 02-20-2011, 12:29 PM   #2
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Re: Adding R14 under-floor without losing interior space...

i wonder.. could you just get the floor spray foamed? would it stay?
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Old 02-20-2011, 01:09 PM   #3
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Re: Adding R14 under-floor without losing interior space...

I plan to do the fast expand spray-on foam for the top of my floor. I'll use the slow stuff to fill the void.

I imagine a fast type sprayed on from beneath would work, but you'd have to at least paint it to protect it from UV. You also want to be very careful where it all goes as you install it. Having your air brake connections covered in foam would suck for example.

On my pusher, there's about 3' or so of crawl space beneath. I have 2 battery boxes, a large storage box, and a spare tire box to work around, not to mention all the chassis related things. I didn't want to be laying on my back under the bus spraying up and having all that stuff splattering back at me.

I think any foam sprayed up would stay as long as the surface was cleaned and dried first.

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Old 02-20-2011, 01:11 PM   #4
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Re: Adding R14 under-floor without losing interior space...

You need to use more than one hole. The canned expanding foam seems to need AIR and lots of it. I filled the square tubing on the Eagle with Great Foam brand canned foam. I had read about doing it on the coach conversion forums. I thought it was a great idea. I drilled a hole at the bottom, half way up and a hole at the top of a vertical section of square tubing about 30" long. I shoved the tube as far up into the tubing as I could get it and filled the tube while slowly drawing the tube out. I have previously "practiced" a line to see how fast/slow I needed to go and how long it took to expand... in open air. I did this on about half of the bus. Drilled three hole (one on each end and one in the middle) Filled the tube from all three holes. Foam expanded out the holes, Looked good. A few days later, David decided he needed to cut out a piece of the tubing (I forget why) and it was one that I have "filled". It was far from filled. The foam expanded only right at the holes, where the foam could get air. I was POed. All that work, all those pricey cans of foam that I had used. We figured that the foam need the air to cure and expand. I plan on using the same method to fill the bus doors with foam BUT I will place a small air pump that we use to fill the air mattresses to where it will blow air into the door cavity thru a little hole and HOPEFULLY that will work (front door has LOTS of little screw holes). I know that the two part foam (the "pour in" stuff) instructions have always showed the stuff being poured into a cavity with a large opening in the top. I also have run across videos where the foams seems to expand faster in the "open air" areas as opposed to the "closed in" nooks and crannies.

Our BlueBird floor is similar to yours. Except for the front section where the engine is and all the tanks/filters are, we have access to the bottom of the floor. We can't reach the front 2 ft or so of the front living space (behind the drivers seat) but we can pressure wash the dirt and dust from the bottom then, once completely dry, use canned foam to spray the cavities in between all the hoses and tanks. We would have to cover the tanks/hoses with thin plastic (like plastic painters drop cloths) because the foam acts like a "glue" and would make replacing a filter/hose difficult. the rest of the floor will have PEX for the hydronic heat attached and then (a layer of Reflectix and foamboard sheathing insulation, cut to fit, stacked under that, with canned foam filling any voids around the edges. Except in the tankage areas that we will need to have heated. Those areas will be in insulated boxes because we will be using the heat from the hydronic system to heat the tanks (and have ducts from the forced air system). Foam board exposed to the road will be sheathed with aluminum flashing or other metal sheets. It depends on price and availability of materials.

Part of the reason spray foamed insulation has a higher R-value is because it expands and fills all voids. It seals up against everything and eliminates the tiny air leaks that using sheet foam or insulation batts leaves.

Every metal screw/rivet you use to tap into the metal structure, that is exposed to the outside, will act as a "heat sink". It will allow the transfer of heat/cold unless you have a thermal break. Building thermal breaks in to your construction can be achieved in many ways... most of which take up precious space that most of us do not have.
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Old 02-20-2011, 01:46 PM   #5
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Re: Adding R14 under-floor without losing interior space...

Lorna, those are good comments.

I'm not planning to use those spray-paint sized cans of foam. Instead, I will be using Tiger Foam.

They have a fast rise fire rated surface foam, and a slow rise foam specifically designed to fill cavities. They specifically mention filling walls in old homes, tanks, pontoons, and other such large volume small opening cavities.

While rechecking things, it seems the slow rise has this fire rating: ?DIN ?4102?1 ?B2? (basically, the same as timber or other ordinary construction materials). The fast rise has this fire rating: ASTM E-84 Flame Spread: 20, Smoke Developed: 400. These seem to be quite good numbers for a foam insulation.

I should hopefully know how the cavity will fill before the end of May. I will definitely report my progress.
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Old 02-20-2011, 02:45 PM   #6
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Re: Adding R14 under-floor without losing interior space...

Quote:
Originally Posted by baadpuppy
... I should hopefully know how the cavity will fill before the end of May. I will definitely report my progress.
Please do. I wish I had known about how the spray cans would turn out before I did the Eagle. I posted my experience on a coach forum. But others who had attempted it and were dissatisfied with results, didn't post anything until AFTER I had posted my dissatisfaction with the procedure. If they had posted BEFORE, I could have saved time and money! Neither of which I had lots of at the time (still don't have the money ). That is why I will often post about something that I have tried and didn't work, to prevent others from doing the same using the same product. I KNOW the canned Great Foam did not work as hoped for. My postings are not always to address the specific post but to lend a little experience in an alternative that may come up later down the road by someone else. I also like to read where someone tried something and then post how it turned out both immediately after and a little time later. I also like to know if it DIDN'T work. I also like to know if there is an additional step that may need to be added to the procedure to prevent a problem later down the road.

A personal web page may disappear over time but the forums (usually) last much longer. And they are searchable. I have "lost" so much info that were on personal web pages that have disappeared over the years. I have a copy of an article that used to be at several places on the internet on my personal website,. It tells how to make a "One Piece Eagle Door". Last time I looked ( a couple months ago) it was no place else (I also tell what book it is now in and the recommendation to buy the book... you should buy the book... lots of good info, lots of what if's and some not so good in his books.. do not use cabinet slides to make a slide out... just don't). I keep it up for two reasons... it shows how much work is involved in turning a two piece door into a one piece door... not every one would want to do that work... and we used that article as a basis for turning the two piece hinged BlueBird door into a one piece door... without having to repair rust (hey, it's a BlueBird not an Eagle). Also I will post a link to something I am not interested in (like the marine wood stoves... I no longer split wood) yet others may want to or need to use a link like that.
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