Six Easy Steps for Installing Rigid Insulation

With each tiny house we build (or re-build) we have the opportunity to try a new type of building material.  Sometimes, changing things up is intentional, and sometimes it is not.

For My Tiny Wine Wagon, due to a major miscommunication regarding the ceiling joists, I ended up with non-vented 2x4's. Certainly this is not ideal but because the roof pitch is 12/2 or steeper, at least it isn't a safety issue.

However, this means I really only have one insulation option that will provide adequate R value while also minimizing (and hopefully eliminating) moisture issues; rigid foam.

In a nutshell, I am using 2" thick (6.5 R value) and 1-1/2" thick (4.5 R value) pieces to fill the 3-1/2" deep spaces between the joists. As such, fiberglass insulation would have been R13 and the rigid insulation is only R11.  But, since we also do not have any venting in the ceiling cavities we'll need an insulation that will fully eliminate air circulation or warm air accumulation.

Lesson Learned:

"Normal" home builders commonly don't understand the challenges of tiny houses. 

Yes, I realize all of this is less than ideal and the builder who did this really screwed up; but alternatively I would have to completely tear apart the roof and rebuild it.  I'll take less-than-ideal over the timeline and monetary impact of fully correcting it.

Next I needed to figure out how to install it.

The process isn't too tough, but worthy of a few quick pics so here goes....

Step One: Measure the space between the ceilings joists.  Do not assume that the space is always the same.

Step 2: Mark the width on the insulation.

Step 3: Using a straight metal edge, mark the cutting line.

Step 4: Cut the foam with a blade or saw.  

For our install, the foam was 8 feet long so we would cut the width first then cut the few inches off the end as needed.

This is a VERY messy process that creates and aerates a LOT of foam particles and at first I was worried about it and researched various blades and methods to reduce the dust.  In the end I decided to use a utility saw and then vacuum up after the mess.

Step 5: Press the pieces between the ceiling joists.  

If you have cut them to the correct width, no adhesive is needed. If you choose to use an adhesive to hold up the pieces that don't fit tight (you can see a bit of sag in the middle here) use a type of construction adhesive with a very fast set up time so you won't be standing there holding it up for long.

I decided not to use adhesive since the ceiling panels will easily hold up the insulation in the few spots where it sage.

Step 6: Admire, vacuum, and get ready for ceiling panel installation!