There are similar post to what I'm asking but not an exact one. I have a sunroom extending out the back of my house - inside environment. It is supported by wood post, beams and 2x10 joists - sitting on an existing deck. When the original owner built it, he placed R-19 (Central Maryland) fiberglass roll insulation with the paper facing down and enclosed the joists under the room with plywood on the bottom and joist blockers between the joists, beam and floor. There is one duct running between the joist to the outmost wall of the sunroom.

I am totally replacing the insulation because the floor is cold in the winter and because water, wasps, ants, etc. have worked their way into the enclosed space and made a mess of the existing insulation. I assume I can solve the water issue but don't know about some of the other things. I think I want R-30 roll insulation although I'm open to suggestions. Other questions:

Shouldn't the paper be facing the floor instead of the bottom?

Should I totally enclose the space between the joists and the floor?

If I keep rain out do I still have to worry about moisture?

Would a piece of rigid insulation directly under the floor and above the fiberglass keep me warmer or would that create a moisture problem?

Sorry if this is long - I wanted to give a complete picture.

Thanks in advance on any help or suggestions --John

I would recommend a closed cell sprayed on foam. It will seal it tight and you get more R-value per inch.

If you use roll insulation, the vapor retarder should be UP against the subfloor, in a cold climate. If you use R-30, or even R-38 in the floor, I don't think a rigid insulation layer would be necessary.

You can use inexpensive vented vinyl soffit material to close the bottom, which will keep out most ionsects and allow your insulation to ventilate.

The water problem probably had to do with two factors: the insulation was in upside-down, and the space between the joists was enclosed and unable to ventilate. Putting the insulation in the correct way and allowing the space to ventilate should solve that problem.

Thank you both for your suggestions.

Can the closed cell foam be successfully applied to an upside down horizontal surface?

Richard - what do you think about the close cell foam? This is a relatively small area (~100 sq ft) so cost isn't as important a factor as it would be for a whole house application.

Also - regarding the water. It was due to leakage from rain. The rest of the are was nice and dry - just full of various vermin nests. I'm pretty certain I can protect the space from the rain. If so, is there any problem with totally enclosing an area such as this?
Thanks again. John

Do I understand you correctly? You're asking about totally enclosing the underside of the joists, with the insulation inside? If that's your question, I prefer that the insulation be allowed to vent. That's why I suggested the inexpensive vented vinyl soffit material.

Personally, I do not care for foams, and I only rarely use them. We don't yet know, despite manufacturers' claims, all the things they do chemically to the air we breathe, and most are quite flammable and must be protected by gypsum board or the like. And if they do burn, the gases produced are quite toxic.

Yes - you do understand me correctly. I just don't want those bugs in there. But I guess with the vented soffit material you mention(and I could screen that even more) there will be minimal bug invasions.

Thanks for the feedback on the foam too. I share some of your concerns but I do like its sealing capabilities.

If I can ever help you with a photography question - just let me know. At least I know something about that. Thanks.

My friend, the point is, help the next person who asks for help. It doesn't have to be me. That is the best way to thank someone. One particluar person elsewhere on this forum needs to learn that.

JJS,

I have used closed cell foam in exact instances such as yours with very successful results. In fact your post prompted me to call the guy who I did it for 2 years ago and see how it was holding up and he said he couldn't be happier. If you have something there that needs to be vented, then insects can get in too, thus defeating the purpose of what you are trying to do.

It sometimes takes more than two years for cancer to develop. We don't know what foams do and do not do to affect the air we breathe, and I don't want my clients finding out the hard way. That's why I avoid them whenever possible. Call me conservative, but at the same time, call my clients healthy.

The holes in a vented soffit are little more than perforations, and are no bigger than the openings in screens.

Is the floor tile covered? That may be the cause of it"feeling" cold. Or it may be cold because air gets in through the same openings that the bugs get in through.The bugs may not crawl in through the intentional soffit perforations, They will go around the edge.
I suggest that the space NOT be vented but rather sealed tight on the bottom with plywood. My understanding is that the previous owner enclosed the bottom of the joists with plywood.If the space is invaded by vermin, then it is not enclosed very well so you still have prep work to do before placing insulation. I would then rip sheets of DOW board (any thickness you choose,2"x4'x8'cost me $28.29)+ tax) to fit between the joists and then seal the joist to dow connection with expanding foam or if it fits tight just use caulk. It will cost a significant amount for a foamer just to show up to do 100 sq. ft. Do it yourself!