Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 08-24-2019, 07:06 PM   #1
3 Rivet Member
 
1976 27' Overlander
Milwaukie , Oregon
Join Date: Oct 2018
Posts: 119
Using foam board insulation under subfloor

Hey guys. I saw a thread on here where one of the airstreamers used foam board insulation screwed into the underside of the subfloor. I like this idea, and plan to do something like this myself. What I don't want to do is trap water against the subfloor in the event water makes it's way between the wood and the foam board. Would it be wise to use some sort of standoff to create an air gap between the wood and the foam? Would I want to create a way to ventilate said air gap or do I want to seal things as good as possible to maintain the best insulation?

Thanks for any pointers!

(PS - Using 3/4 ACX subfloors with West Systems marine epoxy to cover the entire tops of subfloors, outer edges, and about 10" of the underside edges of the wood, leaving the central underside non-epoxied to allow the wood to breath and dry in event of a leak.)
JoleneAS is offline   Reply With Quote
Old 08-24-2019, 07:59 PM   #2
3 Rivet Member
 
SandKSmith's Avatar
 
2006 25' Safari FB SE
Phoenix , Arizona
Join Date: Oct 2018
Posts: 154
Hi, I’m doing that now on my Safari. We had a vent not closed tight when it was shipped to us last January. We didn’t realize the subfloor was soaked until 2 weeks ago. Anyway, we pulled down what Airstream calls insulation to let it dry.

I had the same concerns about putting the insulation against the subfloor. We made “hat” sections to space the insulation board 1/2” from the floor. I made them out of 20 ga stainless steel- because that’s what I had (we own a sheet metal shop) and screwed them to the underside of the floor. I put some rivnuts on the flat section so I could screw the foam board to to them. I was worried that sheet metal screws would come loose over time. Screws will have a drop of Loctite on them.

Key is going to sealing around the gap between the floor and the insulation otherwise the insulation won’t be effective. My plan, although I didn’t have time to try it today, is to use expanding foam around the parameter of the panel and put it in position before it cures. It should make a form fitting gasket against the subfloor. I hope.

In the photo, you can see the headless screws that will punch through the insulation board when dry fitting it so I can locate where the screws go. That part works great.

I’m traveling all week so it will be next weekend before I get this done. I’ll let you know how it goes.

Steve
Attached Thumbnails
Click image for larger version

Name:	CD7542EA-32E5-416E-BBDD-9474E7134219.jpg
Views:	195
Size:	288.8 KB
ID:	350393  
SandKSmith is offline   Reply With Quote
Old 08-24-2019, 08:07 PM   #3
Rivet Master

 
1966 22' Safari
1955 22' Flying Cloud
Fredericksburg , Texas
Join Date: May 2015
Posts: 2,931
Steve, great idea using headless screws. Can’t go wrong doing that to line up perfectly.
Bubba L is offline   Reply With Quote
Old 08-25-2019, 11:05 PM   #4
3 Rivet Member
 
1976 27' Overlander
Milwaukie , Oregon
Join Date: Oct 2018
Posts: 119
Steve, looking forward to seeing what you end up doing! That looks like a great idea.
JoleneAS is offline   Reply With Quote
Old 08-26-2019, 10:59 AM   #5
3 Rivet Member
 
Rltports's Avatar
 
2015 25' Flying Cloud
Bettendorf , Iowa
Join Date: Mar 2019
Posts: 130
Following
Rltports is offline   Reply With Quote
Old 08-26-2019, 12:39 PM   #6
PEN
2 Rivet Member
 
2019 27' Globetrotter
Bryant , Arkansas
Join Date: Aug 2015
Posts: 92
Blog Entries: 1
Following
__________________
Paul & Deb
PEN is offline   Reply With Quote
Old 08-26-2019, 12:42 PM   #7
Rivet Master
 
1981 31' Excella II
New Market , Alabama
Join Date: Sep 2011
Posts: 6,145
Just make sure you have a path for water to get out and put some sort of spacers between the foam and floor. I chose to leave most of my floor uninsulated.



Perry
perryg114 is offline   Reply With Quote
Old 08-26-2019, 01:11 PM   #8
Rivet Master
 
waninae39's Avatar
 
2022 25' Flying Cloud
NCR , Ontario
Join Date: Feb 2017
Posts: 3,077
foam board, fiberglass, or spray insulation can all be used.
the issue is that the metal beams are a thermal break and will provide cold spots in cool conditions as they will transmit the heat through
waninae39 is offline   Reply With Quote
Old 08-27-2019, 03:01 PM   #9
2 Rivet Member
 
1974 25' Tradewind
Lexington , Kentucky
Join Date: Nov 2015
Posts: 76
No floor insulation

Tough subject that's hard to prove / verify BUT..... what we did was to not insulate under the floor or reinstall a belly pan thinking how much temperature difference can it be without them and is it worth the trouble ?!
We replaced 1/3 of the frame and floor (primed & painted frame with Rust Oleum, plywood sealed) and then sprayed the under floor wood with undercoating & truck bed sealant. The insulation is going to get wet and hold moisture and rot the frame again. Sure the wood & frame gets wet BUT it dries within a day or so.
Anyway...insulation: we camp only when the night temperature stays roughly above 30* and I very much like the idea of spending a little more $ for heat or A/C than letting the smell of wet underfloor insulation (that will hardly ever dry out) permeate the living area.
The Twinkie is offline   Reply With Quote
Old 08-28-2019, 06:50 AM   #10
Rivet Master
 
1981 31' Excella II
New Market , Alabama
Join Date: Sep 2011
Posts: 6,145
I have to agree. Insulation is going to cause problems if you have leaks. I ended up putting drains in the C-channel to funnel water out of that area above the floor and run it to the belly pan where it will run out. If it is a 3 season trailer, then it is not worth the trouble. I also have not covered my floor so I can find and deal with leaks that might occur.



You loose way more heat to the ribs around the shell since there is no thermal break between them and the outside shell.



Perry



Quote:
Originally Posted by The Twinkie View Post
Tough subject that's hard to prove / verify BUT..... what we did was to not insulate under the floor or reinstall a belly pan thinking how much temperature difference can it be without them and is it worth the trouble ?!
We replaced 1/3 of the frame and floor (primed & painted frame with Rust Oleum, plywood sealed) and then sprayed the under floor wood with undercoating & truck bed sealant. The insulation is going to get wet and hold moisture and rot the frame again. Sure the wood & frame gets wet BUT it dries within a day or so.
Anyway...insulation: we camp only when the night temperature stays roughly above 30* and I very much like the idea of spending a little more $ for heat or A/C than letting the smell of wet underfloor insulation (that will hardly ever dry out) permeate the living area.
perryg114 is offline   Reply With Quote
Old 08-28-2019, 12:15 PM   #11
3 Rivet Member
 
1976 27' Overlander
Milwaukie , Oregon
Join Date: Oct 2018
Posts: 119
I can definitely see the argument to insulate vs not insulate. I’m in favor of insulating personally. While I agree that there are areas that reduce the efficacy of insulation (such as thermal transfer via the ribs), I’m of the philosophy that something is probably better than nothing, assuming it can be applied in such a way to not promote rotting of the subfloor. I definitely don’t plan on dealing anything entirely though and want my solution to be able to breath when water inevitably makes it in.
JoleneAS is offline   Reply With Quote
Old 08-31-2019, 08:33 PM   #12
3 Rivet Member
 
SandKSmith's Avatar
 
2006 25' Safari FB SE
Phoenix , Arizona
Join Date: Oct 2018
Posts: 154
I finished the insulation under the floor in the rear of our 25’ FB. The hat sections I made are approximately the same height as the frame substructure so I could run the panel the full width of the airstream rails. I was going to seal with insulating foam but later decided to use aluminum tape to seal the big gaps. Most of the edges are up against the frame structure but not sealed tight. If water does get between the floor and insulation, there is a way to seep out.

I was able to get nearly the full width between the frames by scoring / breaking the panel to form a shallow V to get it in position then pressing it flat. My panel has foil on both sides so one side acted as a hinge when I scored/broke the panel.

I’m happy with how it all turned out. The top side is sealed with a penetrating epoxy so I’m not too worried about water getting through the floor to the insulation.
Attached Thumbnails
Click image for larger version

Name:	E5644038-D3B7-4BF0-A2CF-A85AF6A261FB.jpg
Views:	124
Size:	246.7 KB
ID:	350989   Click image for larger version

Name:	E2EA2474-AFC4-40FE-9A58-6C895956A85C.jpg
Views:	126
Size:	235.0 KB
ID:	350990  

SandKSmith is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Rigid foam board insulation in belly..XPS or EPS? Jeremy9107 Repairing/Replacing Floor &/or Frame 4 02-19-2018 10:57 PM
Insulation- Prodex or Foam Insulation Board? Danny Z General Interior Topics 7 08-26-2015 08:21 PM
Foam board thehandyman General Repair Forum 2 08-20-2013 07:20 AM
expanding foam insulation DinubaDave Exterior Restoration Forum 8 06-30-2005 08:19 AM
Foam Insulation? Aluminum? Loose Curtain Rails? Revamp Goucho? 74Argosy24MH General Interior Topics 4 02-03-2005 08:39 PM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 01:29 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.