Insulation under the floor

[vanster]

I am about to build a new belly pan on my shell off project and I need to add insulation, or I think I do under the parts of the floor that are not covered by tanks or a tire well.
If I buy 2in closed cell insulation, how does it adhere to the bottom of the floor?

[Belegedhel]

Try some spray adhesive backed up with some appropriate length deck screws with a plastic fender washer.


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[Bauxter]

I used construction adhesive and screws/home-made washers, similar to above. I had a lot of scrap aluminum, so I just cut 1x1 aluminum squares and drilled holes in them, and used as washers.

I am a cheap B@S*@%D

It worked for me.

[aquinob]

If you are talking about the rigid foam board insulation, that would be fine. I used decking screws and metal fender washers. I wouldn't bother with any sort of adhesive since the screws should hold it up fine and you may someday need to drop it down to look at the underside of the plywood subfloor.

[thesignlady]

For the shell on floor insulation...

Cut the rigid foam insulation to approximately fit each of the cavities in the framing.

Then cut the leftover scraps into about 1.5" strips, put double sided tape onto both faces of the strips

Tape the scrap bits roughly 1 inch in from the perimeter to the underside of the floors, tape some more strips in the middle of bigger cavities. The tape is not structural it is just to hold it in place well you work.

Once the strips are in place peel the backing off the double sided tape and position the large panels that you cut first into position

Then drill stainless steel screws with an added washer that are long enough to get through the two combined pieces of foam board and in to the sub floor about half an inch. I say stainless because I can tell you the factory not stainless ones that were used in the perimeter of my trailer all rotted away

Now comes the messy sticky part, Buy a couple cans of CLOSED CELL spray foam insulation, closed cell does not absorb water.... open cell is like a sponge. Place a tarp under the work area, wear protective eye wear and a tight fitting hat or a shower cap and spray into all the perimeter gaps. Some of the spray foam will fall down, work at an angle and don't let it get you. I dragged my ponytail through some that hit the tarp, it was part of me for months... and the plus side though, after it dries it pulls right off the tarp, not so much for hair...

On my trailer I did not spray the outer edge until just as I was wrapping the sides over the belly pan area.

Be advised that the foam board really stinks, I brought mine home in my car and it made my eyes water, I hosed it off and left it outside a few days before using then I left the belly pan open a month before wrapping her back up. It just gives it more time to off gas before trapping the smell in your trailer.

This method gives a closed air gap that will keep your trailer a wee bit warmer on the feet and you happier in the long run.

[vanster]

Great information, thank you. What thickness did you use. Somehow 2" seems to stick in my mind. Not thick enough? What was the brand as well?
The only area that I am going to insulate is the back where the bed will be as the tanks are in the middle section, either side of the axle and a small area forward then I have the spare tire well.

[thesignlady]

I used 1.5 inch but you could use 2 if that is available to you. Do your best to insulate every area to the best of your ability, any gap will just let the cold (or hot) air flood right in and take away from what you are trying to accomplish.

[vanster]

Thank you very much
I will take pics once we have completed it
v